feat(subagent): default continuable delegation to background

examples/acp-agent/tests/snapshots/advanced-toolchain/session.jsonl

@@ -31,12 +31,12 @@
 {"type":"step/end","seq":29,"time":1785730458520,"data":{"turn":1,"step":2}}
 {"type":"step/start","seq":30,"time":1785730458527,"data":{"turn":1,"step":3}}
 {"type":"assistant/chunk","seq":31,"time":1783950000029,"data":{"turn":1,"step":3,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":32,"time":1783950000030,"data":{"turn":1,"step":3,"chunk":{"type":"tool-call-delta","index":0,"id":"advanced-direct-child","name":"subagent","argumentsDelta":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}}
-{"type":"assistant/chunk","seq":33,"time":1785036891179,"data":{"turn":1,"step":3,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}}}
+{"type":"assistant/chunk","seq":32,"time":1783950000030,"data":{"turn":1,"step":3,"chunk":{"type":"tool-call-delta","index":0,"id":"advanced-direct-child","name":"subagent","argumentsDelta":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":33,"time":1785036891179,"data":{"turn":1,"step":3,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":34,"time":1785498801872,"data":{"turn":1,"step":3,"chunk":{"type":"usage","usage":{"inputTokens":3,"outputTokens":3}}}}
 {"type":"assistant/chunk","seq":35,"time":1785730458531,"data":{"turn":1,"step":3,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":36,"time":1785730458531,"data":{"turn":1,"step":3,"message":{"role":"assistant","content":[{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"51fe1d59-eebc-457b-a072-fe217546ff04"},"usage":{"inputTokens":3,"outputTokens":3}},"sourceEventSeqs":[31,32,33,34,35],"surfaceOp":"append"}
-{"type":"tool/call","seq":37,"time":1785730458531,"data":{"turn":1,"step":3,"callId":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}
+{"type":"assistant/message","seq":36,"time":1785730458531,"data":{"turn":1,"step":3,"message":{"role":"assistant","content":[{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"51fe1d59-eebc-457b-a072-fe217546ff04"},"usage":{"inputTokens":3,"outputTokens":3}},"sourceEventSeqs":[31,32,33,34,35],"surfaceOp":"append"}
+{"type":"tool/call","seq":37,"time":1785730458531,"data":{"turn":1,"step":3,"callId":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}
 {"type":"tool/result","seq":38,"time":1785730458562,"data":{"turn":1,"step":3,"message":{"source":{"kind":"tool","callId":"advanced-direct-child"},"content":[{"type":"tool-result","toolCallId":"advanced-direct-child","content":[{"type":"text","text":"DIRECT_CHILD_OK"}],"isError":false}],"role":"user","id":"09028579-5ae5-4d57-955e-02504f4dfc2a"}},"sourceEventSeqs":[37],"surfaceOp":"append"}
 {"type":"step/end","seq":39,"time":1785730458563,"data":{"turn":1,"step":3}}
 {"type":"step/start","seq":40,"time":1785730458572,"data":{"turn":1,"step":4}}

examples/acp-agent/tests/snapshots/advanced-toolchain/system-prompt.expected.md

@@ -21,6 +21,8 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 ## Writing code for run_code
 
 Pass `run_code` the body of an async TypeScript function (erasable syntax only — no `enum` or namespaces; type annotations are advisory, the code runs type-stripped). Inside the program:
@@ -132,16 +134,16 @@ interface ToolArgsMap {
     /** The exact skill name from the available skills list. */
     name: string;
   } & Record<string, JsonValue>;
-  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work. */
+  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action. */
   subagent: {
     /** A short (3-5 word) description of the delegated task, for display. */
     description: string;
     /** The complete, self-contained task for the subagent. It does not share this conversation's context, so include everything it needs. */
     prompt: string;
-    /** Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message. */
+    /** Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result. */
     run_in_background?: boolean;
   } & Record<string, JsonValue>;
-  /** Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps. */
+  /** Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result. */
   subagent_fork: {
     /** A short (3-5 word) description of the delegated task, for display. */
     description: string;

examples/acp-agent/tests/snapshots/advanced-toolchain/tool-schemas.expected.json

@@ -309,7 +309,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -323,7 +323,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -334,7 +334,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/both-mode-turn/tool-schemas.expected.json

@@ -252,7 +252,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -266,7 +266,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -277,7 +277,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/code-mode-turn/system-prompt.expected.md

@@ -21,6 +21,8 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 ## Writing code for run_code
 
 Pass `run_code` the body of an async TypeScript function (erasable syntax only — no `enum` or namespaces; type annotations are advisory, the code runs type-stripped). Inside the program:
@@ -115,16 +117,16 @@ interface ToolArgsMap {
     /** The exact skill name from the available skills list. */
     name: string;
   } & Record<string, JsonValue>;
-  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work. */
+  /** Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action. */
   subagent: {
     /** A short (3-5 word) description of the delegated task, for display. */
     description: string;
     /** The complete, self-contained task for the subagent. It does not share this conversation's context, so include everything it needs. */
     prompt: string;
-    /** Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message. */
+    /** Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result. */
     run_in_background?: boolean;
   } & Record<string, JsonValue>;
-  /** Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps. */
+  /** Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result. */
   subagent_fork: {
     /** A short (3-5 word) description of the delegated task, for display. */
     description: string;

examples/acp-agent/tests/snapshots/lsp-definition/system-prompt.expected.md

@@ -22,3 +22,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/lsp-definition/tool-schemas.expected.json

@@ -268,7 +268,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -282,7 +282,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -293,7 +293,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/product-subagent-both/tool-schemas.expected.json

@@ -231,7 +231,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -245,7 +245,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -256,7 +256,7 @@
     },
     {
       "name": "subagent_claude_code",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -277,7 +277,7 @@
     },
     {
       "name": "subagent_codex",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -298,7 +298,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/product-subagent-codex/system-prompt.expected.md

@@ -20,3 +20,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/product-subagent-codex/tool-schemas.expected.json

@@ -231,7 +231,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -245,7 +245,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -256,7 +256,7 @@
     },
     {
       "name": "subagent_codex",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -277,7 +277,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/pty-tools/system-prompt.expected.md

@@ -22,3 +22,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/pty-tools/tool-schemas.expected.json

@@ -231,7 +231,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -245,7 +245,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -256,7 +256,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/read-image/tool-schemas.expected.json

@@ -247,7 +247,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -261,7 +261,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/session-query-spill/system-prompt.expected.md

@@ -22,3 +22,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/session-query-spill/tool-schemas.expected.json

@@ -435,7 +435,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -449,7 +449,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -460,7 +460,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-child-question-rejection/session.jsonl

@@ -9,13 +9,13 @@
 {"type":"request/header","seq":7,"time":1786173701218,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":8,"time":1786173701219,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":9,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_question_child","name":"subagent","argumentsDelta":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\"}"}}}
-{"type":"assistant/chunk","seq":11,"time":1786173701233,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\"}"}}}}
+{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_question_child","name":"subagent","argumentsDelta":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\", \"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":11,"time":1786173701233,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\", \"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":12,"time":1786173701233,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":13,"time":1786173701233,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":14,"time":1786173701233,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"f8909de9-23ae-4dbe-a8c1-eaf1e8f2aba5"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
-{"type":"tool/call","seq":15,"time":1786173701234,"data":{"turn":1,"step":1,"callId":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\"}"}}
-{"type":"tool/result","seq":16,"time":1786173701316,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_question_child"},"content":[{"type":"tool-result","toolCallId":"call_question_child","content":[{"type":"text","text":"UNRESOLVED: Should deployment use the CUDA fallback?"}],"isError":false}],"role":"user","id":"fdc5b075-574b-48c6-bdda-1b6442edfbef"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
+{"type":"assistant/message","seq":14,"time":1786173701233,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\", \"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"f8909de9-23ae-4dbe-a8c1-eaf1e8f2aba5"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
+{"type":"tool/call","seq":15,"time":1786173701234,"data":{"turn":1,"step":1,"callId":"call_question_child","name":"subagent","arguments":"{\"description\":\"Check deployment question\",\"prompt\":\"Call ask_user_question once to ask whether deployment should use the CUDA fallback. If the tool returns an error, include the unresolved question verbatim in your final result.\", \"run_in_background\":false}"}}
+{"type":"tool/result","seq":16,"time":1786173701316,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_question_child"},"content":[{"type":"tool-result","toolCallId":"call_question_child","content":[{"type":"text","text":"UNRESOLVED: Should deployment use the CUDA fallback?"}],"isError":false}],"role":"user","id":"1f6384c7-3d6b-4472-968f-2a4a4e3aba79"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
 {"type":"step/end","seq":17,"time":1786173701317,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":18,"time":1786173701334,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":19,"time":1786173701339,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}

examples/acp-agent/tests/snapshots/subagent-child-question-rejection/tool-schemas.expected.json

@@ -294,7 +294,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -308,7 +308,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -319,7 +319,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-continuable-inheritance/system-prompt.1.expected.md

@@ -21,4 +21,6 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 Deliver your result with the report tool before you finish: call it once with a self-contained answer. The agent that started you shares your workspace but does not automatically receive your transcript, tool output, or reasoning, so a closing remark such as "done" leaves it nothing it can use. Report earlier as well whenever a partial finding changes what that agent should do next; reporting never ends your turn.

examples/acp-agent/tests/snapshots/subagent-continuable-inheritance/tool-schemas.1.expected.json

@@ -247,7 +247,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -261,7 +261,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-continuable/system-prompt.1.expected.md

@@ -21,4 +21,6 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 Deliver your result with the report tool before you finish: call it once with a self-contained answer. The agent that started you shares your workspace but does not automatically receive your transcript, tool output, or reasoning, so a closing remark such as "done" leaves it nothing it can use. Report earlier as well whenever a partial finding changes what that agent should do next; reporting never ends your turn.

examples/acp-agent/tests/snapshots/subagent-continuable/tool-schemas.1.expected.json

@@ -247,7 +247,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -261,7 +261,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/replay.override.json

@@ -3,8 +3,8 @@
     "kind": "chunks",
     "chunks": [
       { "type": "block-start", "index": 0, "blockType": "tool-call" },
-      { "type": "tool-call-delta", "index": 0, "id": "call_root_child", "name": "subagent", "argumentsDelta": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}" },
-      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "call_root_child", "name": "subagent", "arguments": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}" } },
+      { "type": "tool-call-delta", "index": 0, "id": "call_root_child", "name": "subagent", "argumentsDelta": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}" },
+      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "call_root_child", "name": "subagent", "arguments": "{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}" } },
       { "type": "usage", "usage": { "inputTokens": 10, "outputTokens": 5 } },
       { "type": "finish", "reason": { "kind": "tool-calls" } }
     ]

examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.1.jsonl

@@ -6,17 +6,17 @@
 {"type":"subagent/descriptor","seq":4,"time":1786357533600,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Start depth one"}}
 {"type":"step/start","seq":5,"time":1786357533602,"data":{"turn":1,"step":1}}
 {"type":"user/message","seq":6,"time":1785730456014,"data":{"content":[{"type":"text","text":"Call subagent once. Ask that child to attempt one further subagent call, then report the result."}],"source":{"kind":"user"},"role":"user","id":"a8129357-1bde-4cbd-90b4-6b8ad51d52e1"},"surfaceOp":"append"}
-{"type":"user/message","seq":7,"time":1786357533602,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"d8d6b5bf-db7b-484f-8095-e35915b94274"},"surfaceOp":"append"}
+{"type":"user/message","seq":7,"time":1786357533602,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"212db1ef-823c-46f6-8a3b-ccc4f5e92bc5"},"surfaceOp":"append"}
 {"type":"session/title","seq":8,"time":1786357533602,"data":{"title":"Call subagent once. Ask that","messageSeqs":[6],"source":{"kind":"fallback"}}}
 {"type":"request/header","seq":9,"time":1785730456014,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":10,"time":1785730456014,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":11,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_one_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}}
-{"type":"assistant/chunk","seq":13,"time":1785498798883,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}}}
+{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_one_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\",\"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":13,"time":1785498798883,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\",\"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":14,"time":1785730456018,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":15,"time":1785730456018,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":16,"time":1785730456018,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"21044d12-2e0e-40e3-b47e-4920e21c3e83"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[11,12,13,14,15],"surfaceOp":"append"}
-{"type":"tool/call","seq":17,"time":1785730456019,"data":{"turn":1,"step":1,"callId":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\"}"}}
+{"type":"assistant/message","seq":16,"time":1785730456018,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"21044d12-2e0e-40e3-b47e-4920e21c3e83"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[11,12,13,14,15],"surfaceOp":"append"}
+{"type":"tool/call","seq":17,"time":1785730456019,"data":{"turn":1,"step":1,"callId":"call_depth_one_child","name":"subagent","arguments":"{\"description\":\"Start depth two\",\"prompt\":\"Attempt one subagent call beyond the configured cap, then report the rejection.\",\"run_in_background\":false}"}}
 {"type":"tool/result","seq":18,"time":1785730456072,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_depth_one_child"},"content":[{"type":"tool-result","toolCallId":"call_depth_one_child","content":[{"type":"text","text":"DEPTH_REJECTED"}],"isError":false}],"role":"user","id":"aa5451a8-812b-4a51-a52c-dbc5c84f16d0"}},"sourceEventSeqs":[17],"surfaceOp":"append"}
 {"type":"step/end","seq":19,"time":1785730456072,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":20,"time":1785730456082,"data":{"turn":1,"step":2}}

examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.2.jsonl

@@ -6,17 +6,17 @@
 {"type":"subagent/descriptor","seq":4,"time":1786357533628,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Start depth two"}}
 {"type":"step/start","seq":5,"time":1786357533630,"data":{"turn":1,"step":1}}
 {"type":"user/message","seq":6,"time":1785730456041,"data":{"content":[{"type":"text","text":"Attempt one subagent call beyond the configured cap, then report the rejection."}],"source":{"kind":"user"},"role":"user","id":"d4dc5a16-e542-4dd9-8e82-e6b7829cfc4b"},"surfaceOp":"append"}
-{"type":"user/message","seq":7,"time":1786357533630,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"e9907a11-3d7c-4796-a459-16afd4afde32"},"surfaceOp":"append"}
+{"type":"user/message","seq":7,"time":1786357533630,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"db7bb37e-3447-4ac8-82cd-2566300acea1"},"surfaceOp":"append"}
 {"type":"session/title","seq":8,"time":1786357533630,"data":{"title":"Attempt one subagent call beyond","messageSeqs":[6],"source":{"kind":"fallback"}}}
 {"type":"request/header","seq":9,"time":1785730456041,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":10,"time":1785730456042,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":11,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_three_rejected","name":"subagent","argumentsDelta":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}}
-{"type":"assistant/chunk","seq":13,"time":1785498798916,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}}}
+{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_depth_three_rejected","name":"subagent","argumentsDelta":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\",\"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":13,"time":1785498798916,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\",\"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":14,"time":1785730456047,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":15,"time":1785730456047,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":16,"time":1785730456047,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"467433db-5dbf-42ee-94c0-25c011ce711b"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[11,12,13,14,15],"surfaceOp":"append"}
-{"type":"tool/call","seq":17,"time":1785730456048,"data":{"turn":1,"step":1,"callId":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\"}"}}
+{"type":"assistant/message","seq":16,"time":1785730456047,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"467433db-5dbf-42ee-94c0-25c011ce711b"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[11,12,13,14,15],"surfaceOp":"append"}
+{"type":"tool/call","seq":17,"time":1785730456048,"data":{"turn":1,"step":1,"callId":"call_depth_three_rejected","name":"subagent","arguments":"{\"description\":\"Exceed depth cap\",\"prompt\":\"This child must never start.\",\"run_in_background\":false}"}}
 {"type":"tool/result","seq":18,"time":1785730456056,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_depth_three_rejected"},"content":[{"type":"tool-result","toolCallId":"call_depth_three_rejected","content":[{"type":"text","text":"Error: subagent depth 3 exceeds maxDepth 2"}],"isError":true}],"role":"user","id":"9a3d59f3-542a-4400-a62c-be28dcea3bd1"}},"sourceEventSeqs":[17],"surfaceOp":"append"}
 {"type":"step/end","seq":19,"time":1785730456056,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":20,"time":1785730456066,"data":{"turn":1,"step":2}}

examples/acp-agent/tests/snapshots/subagent-depth-two-rejection/session.jsonl

@@ -9,12 +9,12 @@
 {"type":"request/header","seq":7,"time":1785498798841,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":8,"time":1785730455981,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":9,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":10,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_root_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}}
-{"type":"assistant/chunk","seq":11,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}}}
+{"type":"assistant/chunk","seq":10,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_root_child","name":"subagent","argumentsDelta":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":11,"time":1784540790309,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":12,"time":1785498798850,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":13,"time":1785730455990,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":14,"time":1785730455990,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"f0284ec5-b83d-4eca-8f10-d3e4e09d0a39"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
-{"type":"tool/call","seq":15,"time":1785730455990,"data":{"turn":1,"step":1,"callId":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\"}"}}
+{"type":"assistant/message","seq":14,"time":1785730455990,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"4683ea2f-13fc-42d8-9794-cf5f714fb001"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
+{"type":"tool/call","seq":15,"time":1785730455990,"data":{"turn":1,"step":1,"callId":"call_root_child","name":"subagent","arguments":"{\"description\":\"Start depth one\",\"prompt\":\"Call subagent once. Ask that child to attempt one further subagent call, then report the result.\",\"run_in_background\":false}"}}
 {"type":"tool/result","seq":16,"time":1785730456087,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_root_child"},"content":[{"type":"tool-result","toolCallId":"call_root_child","content":[{"type":"text","text":"DEPTH_ONE_DONE"}],"isError":false}],"role":"user","id":"6e5d6cdb-d9da-47a0-826a-50f7022b544d"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
 {"type":"step/end","seq":17,"time":1785730456087,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":18,"time":1785730456097,"data":{"turn":1,"step":2}}

examples/acp-agent/tests/snapshots/subagent-list-agents/system-prompt.1.expected.md

@@ -21,4 +21,6 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 Deliver your result with the report tool before you finish: call it once with a self-contained answer. The agent that started you shares your workspace but does not automatically receive your transcript, tool output, or reasoning, so a closing remark such as "done" leaves it nothing it can use. Report earlier as well whenever a partial finding changes what that agent should do next; reporting never ends your turn.

examples/acp-agent/tests/snapshots/subagent-list-agents/tool-schemas.1.expected.json

@@ -247,7 +247,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -261,7 +261,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-max-tokens-partial/session.jsonl

@@ -9,12 +9,12 @@
 {"type":"request/header","seq":7,"time":1786348800115,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":8,"time":1786348800115,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":9,"time":1786348800120,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":10,"time":1786348800120,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\"}"}}}}
+{"type":"assistant/chunk","seq":10,"time":1786348800120,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\", \"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":11,"time":1786348800120,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":12,"time":1786348800120,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":13,"time":1786348800120,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"f4269cd2-9132-4b68-8f9b-ff3a40321bc9"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12],"surfaceOp":"append"}
-{"type":"tool/call","seq":14,"time":1786348800121,"data":{"turn":1,"step":1,"callId":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\"}"}}
-{"type":"tool/result","seq":15,"time":1786348800163,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parent_1"},"content":[{"type":"tool-result","toolCallId":"call_parent_1","content":[{"type":"text","text":"Error: subagent run hit its token limit before finishing\nPartial output before the run ended:\npartial one"}],"isError":true}],"role":"user","id":"5dd34050-a533-4f1b-99ee-5fc62c6a4502"}},"sourceEventSeqs":[14],"surfaceOp":"append"}
+{"type":"assistant/message","seq":13,"time":1786348800120,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\", \"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"f4269cd2-9132-4b68-8f9b-ff3a40321bc9"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12],"surfaceOp":"append"}
+{"type":"tool/call","seq":14,"time":1786348800121,"data":{"turn":1,"step":1,"callId":"call_parent_1","name":"subagent","arguments":"{\"description\": \"Truncated child\", \"prompt\": \"Write the words 'partial one', call todo_write once, then keep going until you are cut off.\", \"run_in_background\":false}"}}
+{"type":"tool/result","seq":15,"time":1786348800163,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parent_1"},"content":[{"type":"tool-result","toolCallId":"call_parent_1","content":[{"type":"text","text":"Error: subagent run hit its token limit before finishing\nPartial output before the run ended:\npartial one"}],"isError":true}],"role":"user","id":"84e0d207-3fad-40bd-b68d-2dfefb0e181c"}},"sourceEventSeqs":[14],"surfaceOp":"append"}
 {"type":"step/end","seq":16,"time":1786348800163,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":17,"time":1786348800169,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":18,"time":1786348800173,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}

examples/acp-agent/tests/snapshots/subagent-mixed/session.1.jsonl

@@ -1,23 +1,23 @@
 {"type":"session","version":0,"id":"e4aafa18-b9e3-48d0-8aae-6c9b25dcae80","createdAt":1783352145223,"cwd":"{{cwd}}","parentSession":"959ffdf5-03e2-465e-9482-009b704632dc","origin":"subagent","delegationDepth":1}
-{"type":"approval/policy","seq":0,"time":1786357524735,"data":{"policy":"never","source":"delegation"}}
-{"type":"agent/inbox/spliced","seq":1,"time":1786357524735,"data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"73ce401a-faaf-408a-879e-7485380d537d"}]}}
-{"type":"turn/start","seq":2,"time":1786357524735,"data":{"turn":1}}
+{"type":"approval/policy","seq":0,"time":1786443013973,"data":{"policy":"never","source":"delegation"}}
+{"type":"agent/inbox/spliced","seq":1,"time":1786443013973,"data":{"target":"next-turn","start":0,"inserted":[{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"73ce401a-faaf-408a-879e-7485380d537d"}]}}
+{"type":"turn/start","seq":2,"time":1786443013974,"data":{"turn":1}}
 {"type":"agent/inbox/spliced","seq":3,"time":1786357524735,"data":{"target":"next-turn","start":0,"removedCount":1,"inserted":[]}}
-{"type":"subagent/descriptor","seq":4,"time":1786357524752,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Reply ALPHA only"}}
-{"type":"step/start","seq":5,"time":1786357524755,"data":{"turn":1,"step":1}}
-{"type":"user/message","seq":6,"time":1785730450187,"data":{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"73ce401a-faaf-408a-879e-7485380d537d"},"surfaceOp":"append"}
-{"type":"user/message","seq":7,"time":1786357524755,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"cb073ca7-b412-4509-99ef-4e1351e7e74d"},"surfaceOp":"append"}
+{"type":"subagent/descriptor","seq":4,"time":1786443013990,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Reply ALPHA only"}}
+{"type":"step/start","seq":5,"time":1786443013993,"data":{"turn":1,"step":1}}
+{"type":"user/message","seq":6,"time":1786443013993,"data":{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"73ce401a-faaf-408a-879e-7485380d537d"},"surfaceOp":"append"}
+{"type":"user/message","seq":7,"time":1786357524755,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"64e0fe5e-a3a5-44f1-bf43-b7dc74fad046"},"surfaceOp":"append"}
 {"type":"session/title","seq":8,"time":1786357524755,"data":{"title":"Reply with exactly the word","messageSeqs":[6],"source":{"kind":"fallback"}}}
-{"type":"request/header","seq":9,"time":1785730450187,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
-{"type":"request/context","seq":10,"time":1785730450188,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
-{"type":"assistant/chunk","seq":11,"time":1783352146014,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
-{"type":"reasoning-chunks","seq0":12,"time0":1783352146042,"data":{"turn":1,"step":1,"index":0,"dt":[1,0,0,0,28,0,0,0,0,0,29,0,0,0,0,29,0,0],"texts":["The"," user"," asked"," me"," to"," reply"," with"," exactly"," the"," word"," \"","AL","P","HA","\""," and"," nothing"," else","."]}}
+{"type":"request/header","seq":9,"time":1786443013994,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"request/context","seq":10,"time":1786443013994,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
+{"type":"assistant/chunk","seq":11,"time":1786443013998,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
+{"type":"reasoning-chunks","seq0":12,"time0":1785730450188,"data":{"turn":1,"step":1,"index":0,"dt":[-2378304174,28,1,0,0,0,28,0,0,0,0,0,29,0,0,0,0,29],"texts":["The"," user"," asked"," me"," to"," reply"," with"," exactly"," the"," word"," \"","AL","P","HA","\""," and"," nothing"," else","."]}}
 {"type":"assistant/chunk","seq":31,"time":1783352146129,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":1,"blockType":"text"}}}
 {"type":"text-chunks","seq0":32,"time0":1783352146129,"data":{"turn":1,"step":1,"index":1,"dt":[0,0],"texts":["AL","P","HA"]}}
 {"type":"assistant/chunk","seq":35,"time":1783352146129,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The user asked me to reply with exactly the word \"ALPHA\" and nothing else."}}}}
-{"type":"assistant/chunk","seq":36,"time":1785498797444,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"text","text":"ALPHA"}}}}
-{"type":"assistant/chunk","seq":37,"time":1785730450194,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":48,"outputTokens":23,"cacheReadTokens":2816,"reasoningTokens":19}}}}
-{"type":"assistant/chunk","seq":38,"time":1785730450194,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
-{"type":"assistant/message","seq":39,"time":1785730450194,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user asked me to reply with exactly the word \"ALPHA\" and nothing else."},{"type":"text","text":"ALPHA"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"cfff210d-8dd3-4acc-bbc3-fa860baf88cf"},"usage":{"inputTokens":48,"outputTokens":23,"cacheReadTokens":2816,"reasoningTokens":19}},"sourceEventSeqs":[11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38],"surfaceOp":"append"}
-{"type":"step/end","seq":40,"time":1785730450194,"data":{"turn":1,"step":1}}
-{"type":"turn/end","seq":41,"time":1785730450195,"data":{"turn":1,"reason":{"kind":"completed"}}}
+{"type":"assistant/chunk","seq":36,"time":1783352146129,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"text","text":"ALPHA"}}}}
+{"type":"assistant/chunk","seq":37,"time":1783352146129,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":48,"outputTokens":23,"cacheReadTokens":2816,"reasoningTokens":19}}}}
+{"type":"assistant/chunk","seq":38,"time":1785498797444,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":39,"time":1786443013999,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user asked me to reply with exactly the word \"ALPHA\" and nothing else."},{"type":"text","text":"ALPHA"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"cfff210d-8dd3-4acc-bbc3-fa860baf88cf"},"usage":{"inputTokens":48,"outputTokens":23,"cacheReadTokens":2816,"reasoningTokens":19}},"sourceEventSeqs":[11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38],"surfaceOp":"append"}
+{"type":"step/end","seq":40,"time":1786443013999,"data":{"turn":1,"step":1}}
+{"type":"turn/end","seq":41,"time":1786443013999,"data":{"turn":1,"reason":{"kind":"completed"}}}

examples/acp-agent/tests/snapshots/subagent-mixed/session.2.jsonl

@@ -27,7 +27,7 @@
 {"type":"subagent/descriptor","seq":41,"time":1786357524800,"data":{"version":2,"mode":"one-shot","provider":"fork","label":"Recall project codeword"}}
 {"type":"step/start","seq":42,"time":1786357524803,"data":{"turn":2,"step":1}}
 {"type":"user/message","seq":43,"time":1786357524803,"data":{"content":[{"type":"text","text":"What is the project codeword mentioned earlier in this conversation? Reply with exactly that one word and nothing else."}],"source":{"kind":"user"},"role":"user","id":"86e9f144-764f-460d-b72b-262cffe43d77"},"surfaceOp":"append"}
-{"type":"user/message","seq":44,"time":1786358036899,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"d5ebfdfe-de5f-4f3d-9772-7d6179fe8c3d"},"surfaceOp":"append"}
+{"type":"user/message","seq":44,"time":1786358036899,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"822cdf7d-2a4d-4e51-9a7b-212db77f8b94"},"surfaceOp":"append"}
 {"type":"request/header","seq":45,"time":1786358036900,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"resume"}}
 {"type":"assistant/chunk","seq":46,"time":1783352148077,"data":{"turn":2,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
 {"type":"reasoning-chunks","seq0":47,"time0":1783352148077,"data":{"turn":2,"step":1,"index":0,"dt":[0,0,29,0,0,0,35,0,0,0,0,26,29,31,0,30,0,0,27,1,27,0,1,0,0,31,1,0,0,1790157964],"texts":["The"," user"," is"," asking"," me"," to"," recall"," the"," project"," cod","ew","ord"," that"," was"," mentioned"," earlier"," in"," the"," conversation","."," I"," was"," told"," to"," remember"," it",":"," SA","FF","RON","."]}}

examples/acp-agent/tests/snapshots/subagent-mixed/session.jsonl

@@ -27,14 +27,14 @@
 {"type":"assistant/chunk","seq":41,"time":1783352144533,"data":{"turn":2,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
 {"type":"reasoning-chunks","seq0":42,"time0":1783352144562,"data":{"turn":2,"step":1,"index":0,"dt":[1,0,0,28,1,0,0,29,29,0,0,28,1,0,0,0,0,28,1,29,1,0,0,27,29,0,1,0,0,29,68,0,39,1],"texts":["Let"," me"," do"," these"," two"," deleg","ations"," one"," at"," a"," time"," as"," requested",".\n\n","First",","," I","'ll"," use"," the"," sub","agent"," tool"," (","fresh"," child",")"," to"," reply"," with"," \"","AL","P","HA","\"."]}}
 {"type":"assistant/chunk","seq":77,"time":1783352144932,"data":{"turn":2,"step":1,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}}}
-{"type":"tool-call-chunks","seq0":78,"time0":1783352145000,"data":{"turn":2,"step":1,"index":1,"dt":[1,0,0,0,11,1,0,0,34,0,26,1,0,0,30,0,1,0,0,0,26,0,0,0,0,0,29,1,0,60,0,0,0],"id":"call_00_YvHr2bGomk5HhpgDTvE81896","name":"subagent","args":["","{","\"","description","\"",": ","\"","Reply"," AL","P","HA"," only","\"",", ","\"","prom","pt","\"",": ","\"","Reply"," with"," exactly"," the"," word"," AL","P","HA"," and"," nothing"," else",".","\"","}"]}}
+{"type":"tool-call-chunks","seq0":78,"time0":1783352145000,"data":{"turn":2,"step":1,"index":1,"dt":[1,0,0,0,11,1,0,0,34,0,26,1,0,0,30,0,1,0,0,0,26,0,0,0,0,0,29,1,0,60,0,0,0],"id":"call_00_YvHr2bGomk5HhpgDTvE81896","name":"subagent","args":["","{","\"","description","\"",": ","\"","Reply"," AL","P","HA"," only","\"",", ","\"","prom","pt","\"",": ","\"","Reply"," with"," exactly"," the"," word"," AL","P","HA"," and"," nothing"," else",".","\"",", \"run_in_background\":false}"]}}
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@@ -47,17 +47,17 @@
 {"type":"assistant/chunk","seq":211,"time":1785730450219,"data":{"turn":2,"step":2,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
 {"type":"assistant/message","seq":212,"time":1785730450219,"data":{"turn":2,"step":2,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The first subagent returned \"ALPHA\". Now I need to use the subagent_fork tool (forked child that inherits this conversation) to ask about the project codeword."},{"type":"tool-call","id":"call_00_JSr5rhREq23wSmwSkCP77184","name":"subagent_fork","arguments":"{\"description\": \"Recall project codeword\", \"prompt\": \"What is the project codeword mentioned earlier in this conversation? Reply with exactly that one word and nothing else.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"7790a2a8-64b3-4d98-8d85-6b2667f3adbc"},"usage":{"inputTokens":54,"outputTokens":128,"cacheReadTokens":3072,"reasoningTokens":40}},"sourceEventSeqs":[121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211],"surfaceOp":"append"}
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-{"type":"tool/result","seq":214,"time":1785730450254,"data":{"turn":2,"step":2,"message":{"source":{"kind":"tool","callId":"call_00_JSr5rhREq23wSmwSkCP77184"},"content":[{"type":"tool-result","toolCallId":"call_00_JSr5rhREq23wSmwSkCP77184","content":[{"type":"text","text":"SAFFRON"}],"isError":false}],"role":"user","id":"4e5624d0-b633-4df7-ad19-db764e298422"}},"sourceEventSeqs":[213],"surfaceOp":"append"}
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-{"type":"step/start","seq":216,"time":1785730450263,"data":{"turn":2,"step":3}}
-{"type":"assistant/chunk","seq":217,"time":1783352149217,"data":{"turn":2,"step":3,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
-{"type":"reasoning-chunks","seq0":218,"time0":1783352149246,"data":{"turn":2,"step":3,"index":0,"dt":[0,0,0,0,27,1,31,1,24,1,0,0,0,0,28,0,1,0,0,28,0,0,28,1,0,28,0,29,29,0,33,0,23,29,31,31,0,0,0,27,0,0,0,0,0,29,0,0,1,27,1,0,0,0,27,1,0,28,1,0,0,0,0],"texts":["Both"," sub","agents"," returned",":\n","1","."," First"," (","fresh"," child","):"," \"","AL","P","HA","\"\n","2","."," Second"," (","fork","ed"," child","):"," \"","SA","FF","RON","\""," -"," correctly"," inherited"," the"," conversation"," context"," where"," I"," was"," asked"," to"," remember"," the"," cod","ew","ord"," \"","SA","FF","RON","\".\n\n","Now"," I"," reply"," with"," \"","PAR","ENT","_D","ONE","\""," as"," instructed","."]}}
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+{"type":"step/start","seq":216,"time":1786443014055,"data":{"turn":2,"step":3}}
+{"type":"assistant/chunk","seq":217,"time":1786443014060,"data":{"turn":2,"step":3,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
+{"type":"reasoning-chunks","seq0":218,"time0":1786437123085,"data":{"turn":2,"step":3,"index":0,"dt":[1,-3084973840,0,0,27,1,31,1,24,1,0,0,0,0,28,0,1,0,0,28,0,0,28,1,0,28,0,29,29,0,33,0,23,29,31,31,0,0,0,27,0,0,0,0,0,29,0,0,1,27,1,0,0,0,27,1,0,28,1,0,0,0,0],"texts":["Both"," sub","agents"," returned",":\n","1","."," First"," (","fresh"," child","):"," \"","AL","P","HA","\"\n","2","."," Second"," (","fork","ed"," child","):"," \"","SA","FF","RON","\""," -"," correctly"," inherited"," the"," conversation"," context"," where"," I"," was"," asked"," to"," remember"," the"," cod","ew","ord"," \"","SA","FF","RON","\".\n\n","Now"," I"," reply"," with"," \"","PAR","ENT","_D","ONE","\""," as"," instructed","."]}}
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-{"type":"assistant/message","seq":291,"time":1785730450270,"data":{"turn":2,"step":3,"message":{"role":"assistant","content":[{"type":"reasoning","text":"Both subagents returned:\n1. First (fresh child): \"ALPHA\"\n2. Second (forked child): \"SAFFRON\" - correctly inherited the conversation context where I was asked to remember the codeword \"SAFFRON\".\n\nNow I reply with \"PARENT_DONE\" as instructed."},{"type":"text","text":"PARENT_DONE"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"256c985a-449a-4176-9233-7d29cf47ba5e"},"usage":{"inputTokens":69,"outputTokens":69,"cacheReadTokens":3200,"reasoningTokens":64}},"sourceEventSeqs":[217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290],"surfaceOp":"append"}
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-{"type":"turn/end","seq":293,"time":1785730450270,"data":{"turn":2,"reason":{"kind":"completed"}}}
+{"type":"assistant/message","seq":291,"time":1786443014062,"data":{"turn":2,"step":3,"message":{"role":"assistant","content":[{"type":"reasoning","text":"Both subagents returned:\n1. First (fresh child): \"ALPHA\"\n2. Second (forked child): \"SAFFRON\" - correctly inherited the conversation context where I was asked to remember the codeword \"SAFFRON\".\n\nNow I reply with \"PARENT_DONE\" as instructed."},{"type":"text","text":"PARENT_DONE"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"256c985a-449a-4176-9233-7d29cf47ba5e"},"usage":{"inputTokens":69,"outputTokens":69,"cacheReadTokens":3200,"reasoningTokens":64}},"sourceEventSeqs":[217,218,219,220,221,222,223,224,225,226,227,228,229,230,231,232,233,234,235,236,237,238,239,240,241,242,243,244,245,246,247,248,249,250,251,252,253,254,255,256,257,258,259,260,261,262,263,264,265,266,267,268,269,270,271,272,273,274,275,276,277,278,279,280,281,282,283,284,285,286,287,288,289,290],"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/subagent-multi/session.1.jsonl

@@ -6,7 +6,7 @@
 {"type":"subagent/descriptor","seq":4,"time":1786357521754,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Return ALPHA only"}}
 {"type":"step/start","seq":5,"time":1786357521756,"data":{"turn":1,"step":1}}
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-{"type":"user/message","seq":7,"time":1786357521756,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"6f423049-484c-48d6-9cdd-db504d79f892"},"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/subagent-multi/session.2.jsonl

@@ -6,7 +6,7 @@
 {"type":"subagent/descriptor","seq":4,"time":1786357521799,"data":{"version":2,"mode":"one-shot","provider":"spawn","label":"Return BETA only"}}
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 {"type":"user/message","seq":6,"time":1785730447881,"data":{"content":[{"type":"text","text":"Reply with exactly the word BETA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"53f6419d-8ddc-4eee-8803-5b68411336f9"},"surfaceOp":"append"}
-{"type":"user/message","seq":7,"time":1786357521802,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"5832009f-12a3-4f6e-85e5-257c06f4c716"},"surfaceOp":"append"}
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examples/acp-agent/tests/snapshots/subagent-multi/session.jsonl

@@ -11,27 +11,27 @@
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examples/acp-agent/tests/snapshots/subagent-parallel/session.1.jsonl

@@ -1,18 +1,18 @@
 {"type":"session","version":0,"id":"bbbbbbbb-0000-4000-8000-000000000002","createdAt":1783352127000,"cwd":"{{cwd}}","parentSession":"aaaaaaaa-0000-4000-8000-000000000001","origin":"subagent","delegationDepth":1}
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examples/acp-agent/tests/snapshots/subagent-parallel/session.2.jsonl

@@ -1,18 +1,18 @@
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-{"type":"user/message","seq":7,"time":1786373947174,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"670f5fc4-3eb6-4430-959a-08e8adf25036"},"surfaceOp":"append"}
+{"type":"user/message","seq":6,"time":1786338530749,"data":{"content":[{"type":"text","text":"Reply with exactly the word ALPHA and nothing else."}],"source":{"kind":"user"},"role":"user","id":"61226d6c-a359-4cdd-9eab-734557314ce9"},"surfaceOp":"append"}
+{"type":"user/message","seq":7,"time":1786373947174,"data":{"content":[{"type":"text","text":"Current runtime context. This snapshot supersedes earlier runtime-context snapshots.\n\nCurrent DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations.\n\nApproval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`).\n\nYou are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}],"source":{"kind":"plugin","plugin":"@deepseek-ai/dsh-system-prompt","form":"snapshot","sections":[{"name":"sandbox:policy","text":"Current DSH file policy: danger-full-access. The DSH file sandbox does not restrict file modifications by available operations."},{"name":"approval:policy","text":"Approval prompts are disabled in this session: actions that require approval are rejected automatically — do not request sandbox escalation (do not set `sandbox_permissions`)."},{"name":"subagent:delegation","text":"You are a delegated subagent: your permission scope was fixed when you were started and cannot be widened from inside this session — operations that require approval are rejected automatically. When the task needs access beyond that scope, do not retry the denied operation; state the limitation in your reply so the delegating agent can handle it."}]},"role":"user","id":"cf708e7a-d3c3-477a-91ed-f25605439130"},"surfaceOp":"append"}
 {"type":"session/title","seq":8,"time":1786373947174,"data":{"title":"Reply with exactly the word","messageSeqs":[6],"source":{"kind":"fallback"}}}
 {"type":"request/header","seq":9,"time":1786338530749,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":10,"time":1786338530749,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":11,"time":1786338530759,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
 {"type":"assistant/chunk","seq":12,"time":1786338530759,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"ALPHA"}}}}
 {"type":"assistant/chunk","seq":13,"time":1786338530759,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
-{"type":"assistant/message","seq":14,"time":1786338530759,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"text","text":"ALPHA"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"ac2dc91f-7dfa-45f6-88e0-21a2e762c3dd"}},"sourceEventSeqs":[11,12,13],"surfaceOp":"append"}
+{"type":"assistant/message","seq":14,"time":1786338530759,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"text","text":"ALPHA"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"ed8a19d2-6095-44db-990c-9f1f9309c824"}},"sourceEventSeqs":[11,12,13],"surfaceOp":"append"}
 {"type":"step/end","seq":15,"time":1786338530760,"data":{"turn":1,"step":1}}
 {"type":"turn/end","seq":16,"time":1786338530760,"data":{"turn":1,"reason":{"kind":"completed"}}}

examples/acp-agent/tests/snapshots/subagent-parallel/session.jsonl

@@ -9,15 +9,15 @@
 {"type":"request/header","seq":7,"time":1786338530717,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":8,"time":1786338530717,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":9,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":10,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"}}}}
+{"type":"assistant/chunk","seq":10,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":11,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":12,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"}}}}
+{"type":"assistant/chunk","seq":12,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":13,"time":1786338530722,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":14,"time":1786338530723,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"},{"type":"tool-call","id":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"6ff33634-55af-4c37-a491-dd5b8673923f"}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
-{"type":"tool/call","seq":15,"time":1786338530723,"data":{"turn":1,"step":1,"callId":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"}}
-{"type":"tool/call","seq":16,"time":1786338530723,"data":{"turn":1,"step":1,"callId":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\"}"}}
-{"type":"tool/result","seq":17,"time":1786338530770,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parallel_alpha_1"},"content":[{"type":"tool-result","toolCallId":"call_parallel_alpha_1","content":[{"type":"text","text":"ALPHA"}],"isError":false}],"role":"user","id":"9fa4fa59-7326-4bc8-8ea2-120b37d91ea3"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
-{"type":"tool/result","seq":18,"time":1786338530770,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parallel_alpha_2"},"content":[{"type":"tool-result","toolCallId":"call_parallel_alpha_2","content":[{"type":"text","text":"ALPHA"}],"isError":false}],"role":"user","id":"895bb620-534e-4857-9743-68273126eccf"}},"sourceEventSeqs":[16],"surfaceOp":"append"}
+{"type":"assistant/message","seq":14,"time":1786338530723,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"},{"type":"tool-call","id":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"6ff33634-55af-4c37-a491-dd5b8673923f"}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
+{"type":"tool/call","seq":15,"time":1786338530723,"data":{"turn":1,"step":1,"callId":"call_parallel_alpha_1","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"}}
+{"type":"tool/call","seq":16,"time":1786338530723,"data":{"turn":1,"step":1,"callId":"call_parallel_alpha_2","name":"subagent","arguments":"{\"description\": \"Say the word ALPHA\", \"prompt\": \"Reply with exactly the word ALPHA and nothing else.\", \"run_in_background\":false}"}}
+{"type":"tool/result","seq":17,"time":1786338530770,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parallel_alpha_1"},"content":[{"type":"tool-result","toolCallId":"call_parallel_alpha_1","content":[{"type":"text","text":"ALPHA"}],"isError":false}],"role":"user","id":"caa3552f-81bf-415c-852f-1c88ca1b29b3"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
+{"type":"tool/result","seq":18,"time":1786338530770,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_parallel_alpha_2"},"content":[{"type":"tool-result","toolCallId":"call_parallel_alpha_2","content":[{"type":"text","text":"ALPHA"}],"isError":false}],"role":"user","id":"ef6b5f6f-94bb-4719-a914-87bc0366660a"}},"sourceEventSeqs":[16],"surfaceOp":"append"}
 {"type":"step/end","seq":19,"time":1786338530770,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":20,"time":1786338530778,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":21,"time":1786338530782,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}

examples/acp-agent/tests/snapshots/subagent-published-run-failure/replay.override.json

@@ -3,8 +3,8 @@
     "kind": "chunks",
     "chunks": [
       { "type": "block-start", "index": 0, "blockType": "tool-call" },
-      { "type": "tool-call-delta", "index": 0, "id": "call_published_failure", "name": "subagent", "argumentsDelta": "{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}" },
-      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "call_published_failure", "name": "subagent", "arguments": "{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}" } },
+      { "type": "tool-call-delta", "index": 0, "id": "call_published_failure", "name": "subagent", "argumentsDelta": "{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}" },
+      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "call_published_failure", "name": "subagent", "arguments": "{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}" } },
       { "type": "usage", "usage": { "inputTokens": 10, "outputTokens": 5 } },
       { "type": "finish", "reason": { "kind": "tool-calls" } }
     ]

examples/acp-agent/tests/snapshots/subagent-published-run-failure/session.1.jsonl

@@ -1,2 +1,2 @@
 {"type":"session","version":0,"id":"eb69342c-62b6-4320-a78b-961745f89333","createdAt":1786358409171,"cwd":"{{cwd}}","parentSession":"11111111-1111-4111-8111-111111111111","origin":"subagent","delegationDepth":1}
-{"type":"approval/policy","seq":0,"time":1786358409171,"data":{"policy":"never","source":"delegation"}}
+{"type":"approval/policy","seq":0,"time":1786443070419,"data":{"policy":"never","source":"delegation"}}

examples/acp-agent/tests/snapshots/subagent-published-run-failure/session.jsonl

@@ -9,13 +9,13 @@
 {"type":"request/header","seq":7,"time":1785730452506,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
 {"type":"request/context","seq":8,"time":1785730452506,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}
 {"type":"assistant/chunk","seq":9,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}
-{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_published_failure","name":"subagent","argumentsDelta":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}"}}}
-{"type":"assistant/chunk","seq":11,"time":1785537317619,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}"}}}}
+{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"call_published_failure","name":"subagent","argumentsDelta":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}"}}}
+{"type":"assistant/chunk","seq":11,"time":1785537317619,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":12,"time":1785537317619,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}
 {"type":"assistant/chunk","seq":13,"time":1785730452515,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":14,"time":1785730452515,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"6af49587-fae3-4027-922d-bdc7b833e6d2"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
-{"type":"tool/call","seq":15,"time":1785730452515,"data":{"turn":1,"step":1,"callId":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\"}"}}
-{"type":"tool/result","seq":16,"time":1785730452525,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_published_failure"},"content":[{"type":"tool-result","toolCallId":"call_published_failure","content":[{"type":"text","text":"Error: subagent run failed: Error: snapshot published run failed; dispose failed: Error: snapshot published handle disposal failed"}],"isError":true}],"role":"user","id":"9a913910-4a99-4a22-825f-2cf9d51e665a"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
+{"type":"assistant/message","seq":14,"time":1785730452515,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"bcc7161a-d563-47ed-a854-1ccf563992cb"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[9,10,11,12,13],"surfaceOp":"append"}
+{"type":"tool/call","seq":15,"time":1785730452515,"data":{"turn":1,"step":1,"callId":"call_published_failure","name":"subagent","arguments":"{\"description\":\"Fail published run\",\"prompt\":\"This child prompt must never run.\",\"run_in_background\":false}"}}
+{"type":"tool/result","seq":16,"time":1785730452525,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_published_failure"},"content":[{"type":"tool-result","toolCallId":"call_published_failure","content":[{"type":"text","text":"Error: subagent run failed: Error: snapshot published run failed; dispose failed: Error: snapshot published handle disposal failed"}],"isError":true}],"role":"user","id":"280647fb-2acf-45e4-9b20-cbdad027fbfa"}},"sourceEventSeqs":[15],"surfaceOp":"append"}
 {"type":"step/end","seq":17,"time":1785730452525,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":18,"time":1785730452536,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":19,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}

examples/acp-agent/tests/snapshots/subagent-report/system-prompt.1.expected.md

@@ -21,4 +21,6 @@ Use the workflow tool ONLY when the user explicitly asks for a workflow or for l
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
 
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.
+
 Deliver your result with the report tool before you finish: call it once with a self-contained answer. The agent that started you shares your workspace but does not automatically receive your transcript, tool output, or reasoning, so a closing remark such as "done" leaves it nothing it can use. Report earlier as well whenever a partial finding changes what that agent should do next; reporting never ends your turn.

examples/acp-agent/tests/snapshots/subagent-report/tool-schemas.1.expected.json

@@ -247,7 +247,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -261,7 +261,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -272,7 +272,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/subagent-spawn/session.jsonl

@@ -11,14 +11,14 @@
 {"type":"assistant/chunk","seq":9,"time":1783352120053,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}
 {"type":"reasoning-chunks","seq0":10,"time0":1783352120080,"data":{"turn":1,"step":1,"index":0,"dt":[1,0,30,1,0,0,1,23,1,0,0,0,0,27,0,28,0,29,0,0,0,0,1,26,0,1,0,0,0,28,0,0,1,0,27,0,0,1,0,0,28,0,0,0,0,0,27,1,0,32,1,0,1,0,1,0,24,0,28,1,0,0,0,26,56,0],"texts":["The"," user"," wants"," me"," to",":\n","1","."," Use"," the"," sub","agent"," tool"," exactly"," once"," to"," delegate"," the"," task",":"," \"","Reply"," with"," exactly"," the"," word"," CH","ILD","_OK"," and"," nothing"," else",".\"\n","2","."," After"," the"," sub","agent"," returns",","," reply"," with"," the"," single"," word"," PAR","ENT","_D","ONE"," and"," stop",".\n","3","."," Do"," not"," use"," the"," bash"," tool",".\n\n","Let"," me"," do"," this","."]}}
 {"type":"assistant/chunk","seq":77,"time":1783352120559,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":1,"blockType":"tool-call"}}}
-{"type":"tool-call-chunks","seq0":78,"time0":1783352120560,"data":{"turn":1,"step":1,"index":1,"dt":[0,28,0,0,0,29,1,0,0,25,28,0,0,1,0,28,2,0,1,25,1,0,0,0,0,36,0,1,0,0,18,67,0],"id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","args":["","{","\"","description","\"",": ","\"","Reply"," with"," CH","ILD","_OK","\"",", ","\"","prom","pt","\"",": ","\"","Reply"," with"," exactly"," the"," word"," CH","ILD","_OK"," and"," nothing"," else",".","\"","}"]}}
+{"type":"tool-call-chunks","seq0":78,"time0":1783352120560,"data":{"turn":1,"step":1,"index":1,"dt":[0,28,0,0,0,29,1,0,0,25,28,0,0,1,0,28,2,0,1,25,1,0,0,0,0,36,0,1,0,0,18,67,0],"id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","args":["","{","\"","description","\"",": ","\"","Reply"," with"," CH","ILD","_OK","\"",", ","\"","prom","pt","\"",": ","\"","Reply"," with"," exactly"," the"," word"," CH","ILD","_OK"," and"," nothing"," else",".","\"",", \"run_in_background\":false}"]}}
 {"type":"assistant/chunk","seq":112,"time":1783352120852,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"reasoning","text":"The user wants me to:\n1. Use the subagent tool exactly once to delegate the task: \"Reply with exactly the word CHILD_OK and nothing else.\"\n2. After the subagent returns, reply with the single word PARENT_DONE and stop.\n3. Do not use the bash tool.\n\nLet me do this."}}}}
-{"type":"assistant/chunk","seq":113,"time":1783352120852,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\"}"}}}}
+{"type":"assistant/chunk","seq":113,"time":1783352120852,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":1,"block":{"type":"tool-call","id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\", \"run_in_background\":false}"}}}}
 {"type":"assistant/chunk","seq":114,"time":1785498793638,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":2907,"outputTokens":142,"cacheReadTokens":0,"reasoningTokens":67}}}}
 {"type":"assistant/chunk","seq":115,"time":1785730446696,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}
-{"type":"assistant/message","seq":116,"time":1785730446697,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to:\n1. Use the subagent tool exactly once to delegate the task: \"Reply with exactly the word CHILD_OK and nothing else.\"\n2. After the subagent returns, reply with the single word PARENT_DONE and stop.\n3. Do not use the bash tool.\n\nLet me do this."},{"type":"tool-call","id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"4da5cf2f-f9bd-4f1b-9c60-c9a56a7dae75"},"usage":{"inputTokens":2907,"outputTokens":142,"cacheReadTokens":0,"reasoningTokens":67}},"sourceEventSeqs":[9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115],"surfaceOp":"append"}
-{"type":"tool/call","seq":117,"time":1785730446697,"data":{"turn":1,"step":1,"callId":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\"}"}}
-{"type":"tool/result","seq":118,"time":1785730446730,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_gVbLWC12Qu8JheZpVRRz8749"},"content":[{"type":"tool-result","toolCallId":"call_00_gVbLWC12Qu8JheZpVRRz8749","content":[{"type":"text","text":"CHILD_OK"}],"isError":false}],"role":"user","id":"8afba8c6-ad6a-4389-851b-77fc8f1fe5c9"}},"sourceEventSeqs":[117],"surfaceOp":"append"}
+{"type":"assistant/message","seq":116,"time":1785730446697,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"reasoning","text":"The user wants me to:\n1. Use the subagent tool exactly once to delegate the task: \"Reply with exactly the word CHILD_OK and nothing else.\"\n2. After the subagent returns, reply with the single word PARENT_DONE and stop.\n3. Do not use the bash tool.\n\nLet me do this."},{"type":"tool-call","id":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\", \"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"4da5cf2f-f9bd-4f1b-9c60-c9a56a7dae75"},"usage":{"inputTokens":2907,"outputTokens":142,"cacheReadTokens":0,"reasoningTokens":67}},"sourceEventSeqs":[9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115],"surfaceOp":"append"}
+{"type":"tool/call","seq":117,"time":1785730446697,"data":{"turn":1,"step":1,"callId":"call_00_gVbLWC12Qu8JheZpVRRz8749","name":"subagent","arguments":"{\"description\": \"Reply with CHILD_OK\", \"prompt\": \"Reply with exactly the word CHILD_OK and nothing else.\", \"run_in_background\":false}"}}
+{"type":"tool/result","seq":118,"time":1785730446730,"data":{"turn":1,"step":1,"message":{"source":{"kind":"tool","callId":"call_00_gVbLWC12Qu8JheZpVRRz8749"},"content":[{"type":"tool-result","toolCallId":"call_00_gVbLWC12Qu8JheZpVRRz8749","content":[{"type":"text","text":"CHILD_OK"}],"isError":false}],"role":"user","id":"2f4bb919-c9c3-4011-98d2-65c904dddcef"}},"sourceEventSeqs":[117],"surfaceOp":"append"}
 {"type":"step/end","seq":119,"time":1785730446730,"data":{"turn":1,"step":1}}
 {"type":"step/start","seq":120,"time":1785730446739,"data":{"turn":1,"step":2}}
 {"type":"assistant/chunk","seq":121,"time":1783352122524,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"reasoning"}}}

examples/acp-agent/tests/snapshots/text-turn/system-prompt.expected.md

@@ -20,3 +20,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/text-turn/tool-schemas.expected.json

@@ -231,7 +231,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -245,7 +245,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -256,7 +256,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/web-fetch/system-prompt.expected.md

@@ -22,3 +22,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/acp-agent/tests/snapshots/web-fetch/tool-schemas.expected.json

@@ -231,7 +231,7 @@
     },
     {
       "name": "subagent",
-      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) and return its final result. Use this to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent runs to completion and you receive only its final answer, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. Set `run_in_background: true` to start a background subagent that keeps its conversation: this call returns only its subagent id, and the subagent works on its own from there. You are told when it finishes, so never poll or wait on it; `send_message` sends it more work.",
+      "description": "Delegate a self-contained task to a subagent (a separate agent that works in its own context) to offload focused, independent work — research, a scoped implementation, an analysis — so it does not consume this conversation's context. The subagent returns its result, not its intermediate steps. Give it a complete, standalone prompt: it does not see this conversation. This tool uses its continuable background route by default and immediately returns a durable subagent id. When that run settles, the runtime sends the parent a notice containing its outcome and any final assistant message; `send_message` starts a later turn in the same child conversation. Set `run_in_background: false` to use a foreground run only when you must receive its result before taking your next action.",
       "parameters": {
         "type": "object",
         "properties": {
@@ -245,7 +245,7 @@
           },
           "run_in_background": {
             "type": "boolean",
-            "description": "Run as a background subagent that keeps its conversation and return only its subagent id. This call does not wait for it; you are told when it finishes. Send it more work with send_message."
+            "description": "Whether to use the continuable background route. Defaults to true. Set false to run in the foreground and wait only when your next action depends on its result."
           }
         },
         "required": [
@@ -256,7 +256,7 @@
     },
     {
       "name": "subagent_fork",
-      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn), returning only its final result. Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive only its final answer, not its intermediate steps.",
+      "description": "Delegate a task to a subagent that inherits this conversation: a child agent seeded with all completed turns so far (it does not see the current in-flight turn). Use this when the subtask builds on this conversation's context — a follow-up analysis, a review, a continuation — without consuming this conversation's context for the work itself. You receive its result, not its intermediate steps. This call waits for the subagent and returns its result.",
       "parameters": {
         "type": "object",
         "properties": {

examples/acp-agent/tests/snapshots/workspace-context/system-prompt.expected.md

@@ -20,3 +20,5 @@ Use goal tools for one long-running completion objective in the current session.
 Use the workflow tool ONLY when the user explicitly asks for a workflow or for large multi-agent orchestration: you write a JavaScript script (the tool description documents the exact format) that fans work out across many subagents with phases and structured results. For one or two delegations, prefer plain subagent calls.
 
 Use the ralph tool ONLY when the direct human explicitly asks for a Ralph loop or fresh-agent iterative execution. Each Ralph round starts a fresh child with no conversation seed and uses the shared workspace as durable memory. Completion and blockers are worker reports, not independent evaluation. Use same-session goal tools for ordinary long-running objectives, and plain subagents or workflows for bounded delegation and fan-out.
+
+Use subagent's continuable background route by default. Start independent delegations together in one assistant message and continue useful work while they run. Set `run_in_background: false` only when you cannot take your next action without that subagent's result. When a background run settles, the runtime sends you a notice containing its outcome and any final assistant message.

examples/headless-agent/tests/headless.snapshot.ts

@@ -816,7 +816,7 @@ describe('headless stream-json snapshots', () => {
         expect(calls.map(record => (record.data as JsonObject | undefined)?.name)).toEqual(['subagent'])
         const callArguments = (calls[0]?.data as JsonObject | undefined)?.arguments
         if (typeof callArguments !== 'string') throw new Error('subagent call did not persist its arguments')
-        expect(JSON.parse(callArguments)).toMatchObject({ run_in_background: true })
+        expect(JSON.parse(callArguments)).not.toHaveProperty('run_in_background')
 
         const notices = parentRecords.flatMap((record) => {
           if (record.type !== 'agent/inbox/spliced') return []

examples/headless-agent/tests/snapshots/advanced-toolchain/stream-json.expected.jsonl

@@ -29,12 +29,12 @@
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"step/end","seq":28,"time":0,"data":{"turn":1,"step":2}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"step/start","seq":29,"time":0,"data":{"turn":1,"step":3}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":30,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":31,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"tool-call-delta","index":0,"id":"advanced-direct-child","name":"subagent","argumentsDelta":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":32,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}}}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":31,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"tool-call-delta","index":0,"id":"advanced-direct-child","name":"subagent","argumentsDelta":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":32,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":33,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"usage","usage":{"inputTokens":3,"outputTokens":3}}}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":34,"time":0,"data":{"turn":1,"step":3,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/message","seq":35,"time":0,"data":{"turn":1,"step":3,"message":{"role":"assistant","content":[{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"{{sessionId}}"},"usage":{"inputTokens":3,"outputTokens":3}},"sourceEventSeqs":[30,31,32,33,34],"surfaceOp":"append"}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"tool/call","seq":36,"time":0,"data":{"turn":1,"step":3,"callId":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\"}"}}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/message","seq":35,"time":0,"data":{"turn":1,"step":3,"message":{"role":"assistant","content":[{"type":"tool-call","id":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"{{sessionId}}"},"usage":{"inputTokens":3,"outputTokens":3}},"sourceEventSeqs":[30,31,32,33,34],"surfaceOp":"append"}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"tool/call","seq":36,"time":0,"data":{"turn":1,"step":3,"callId":"advanced-direct-child","name":"subagent","arguments":"{\"description\":\"Check direct child\",\"prompt\":\"Reply with exactly DIRECT_CHILD_OK and nothing else.\",\"run_in_background\":false}"}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"tool/result","seq":37,"time":0,"data":{"turn":1,"step":3,"message":{"source":{"kind":"tool","callId":"advanced-direct-child"},"content":[{"type":"tool-result","toolCallId":"advanced-direct-child","content":[{"type":"text","text":"DIRECT_CHILD_OK"}],"isError":false}],"role":"user","id":"{{sessionId}}"}},"sourceEventSeqs":[36],"surfaceOp":"append"}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"step/end","seq":38,"time":0,"data":{"turn":1,"step":3}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"step/start","seq":39,"time":0,"data":{"turn":1,"step":4}}}

examples/headless-agent/tests/snapshots/subagent-settlement/parent.override.json

@@ -3,8 +3,8 @@
     "kind": "chunks",
     "chunks": [
       { "type": "block-start", "index": 0, "blockType": "tool-call" },
-      { "type": "tool-call-delta", "index": 0, "id": "start-child", "name": "subagent", "argumentsDelta": "{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}" },
-      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "start-child", "name": "subagent", "arguments": "{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}" } },
+      { "type": "tool-call-delta", "index": 0, "id": "start-child", "name": "subagent", "argumentsDelta": "{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\"}" },
+      { "type": "block-end", "index": 0, "block": { "type": "tool-call", "id": "start-child", "name": "subagent", "arguments": "{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\"}" } },
       { "type": "usage", "usage": { "inputTokens": 10, "outputTokens": 5 } },
       { "type": "finish", "reason": { "kind": "tool-calls" } }
     ]

examples/headless-agent/tests/snapshots/subagent-settlement/stream-json.expected.jsonl

@@ -7,12 +7,12 @@
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"request/header","seq":6,"time":0,"data":{"header":{"config":{"provider":"deepseek-official","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"request/context","seq":7,"time":0,"data":{"provider":"deepseek-official","model":"deepseek-v4-flash"}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":8,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-start","index":0,"blockType":"tool-call"}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":9,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"start-child","name":"subagent","argumentsDelta":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}"}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"start-child","name":"subagent","arguments":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}"}}}}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":9,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"tool-call-delta","index":0,"id":"start-child","name":"subagent","argumentsDelta":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\"}"}}}}
+{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"block-end","index":0,"block":{"type":"tool-call","id":"start-child","name":"subagent","arguments":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\"}"}}}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":11,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":10,"outputTokens":5}}}}}
 {"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"tool-calls"}}}}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"assistant/message","seq":13,"time":0,"data":{"turn":1,"step":1,"message":{"role":"assistant","content":[{"type":"tool-call","id":"start-child","name":"subagent","arguments":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}"}],"source":{"kind":"model","provider":"deepseek-official","model":"deepseek-v4-flash"},"id":"{{sessionId}}"},"usage":{"inputTokens":10,"outputTokens":5}},"sourceEventSeqs":[8,9,10,11,12],"surfaceOp":"append"}}
-{"type":"session_event","sessionId":"{{sessionId}}","event":{"type":"tool/call","seq":14,"time":0,"data":{"turn":1,"step":1,"callId":"start-child","name":"subagent","arguments":"{\"description\":\"Return child result\",\"prompt\":\"Reply with exactly CHILD_RESULT and nothing else. Do not call report.\",\"run_in_background\":true}"}}}
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