fix: address codex review round 1

- listChildren() takes an optional AbortSignal and rechecks it after every
  un-signalled session-query await (the cold-resume cooperative-cancellation
  boundary); list_agents forwards exec.signal so the registry's drain of
  started tool bodies cannot block on a slow or large catalog.
- The list_agents description now presents running/complete as a stored-record
  snapshot and defers deliverability to send_message, matching the ownership-
  conflict semantics the service tests pin.

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

@@ -94,7 +94,7 @@ interface ToolArgsMap {
   } & Record<string, JsonValue>;
   /** Read the current same-session goal, including its exact id/revision, objective, phase, completed continuation rounds, round limit, blocker reason when present, and whether another continuation is armed. Call this before updating a goal. */
   get_goal: Record<string, JsonValue>;
-  /** List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped. */
+  /** List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped. */
   list_agents: Record<string, JsonValue>;
   /** Run a foreground fresh-agent Ralph loop toward one immutable objective. Use only when the direct human explicitly asks for Ralph or fresh-agent iteration. Each round opens a new child with no parent conversation or prior child session; the shared workspace is long-term memory, and only a bounded structured report crosses rounds. The call returns when a worker reports completion or a concrete blocker, or at the round limit. Ordinary long-running same-session work belongs to goal tools. */
   ralph: {

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

@@ -174,7 +174,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -77,7 +77,7 @@ interface ToolArgsMap {
   } & Record<string, JsonValue>;
   /** Read the current same-session goal, including its exact id/revision, objective, phase, completed continuation rounds, round limit, blocker reason when present, and whether another continuation is armed. Call this before updating a goal. */
   get_goal: Record<string, JsonValue>;
-  /** List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped. */
+  /** List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped. */
   list_agents: Record<string, JsonValue>;
   /** Run a foreground fresh-agent Ralph loop toward one immutable objective. Use only when the direct human explicitly asks for Ralph or fresh-agent iteration. Each round opens a new child with no parent conversation or prior child session; the shared workspace is long-term memory, and only a bounded structured report crosses rounds. The call returns when a worker reports completion or a concrete blocker, or at the round limit. Ordinary long-running same-session work belongs to goal tools. */
   ralph: {

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}

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

@@ -117,7 +117,7 @@
     },
     {
       "name": "list_agents",
-      "description": "List your background subagents: every subagent you started that can receive `send_message`, whether it is still working (running) or has finished its current turn (complete — a follow-up message starts a new turn on the same conversation). Children that could not be read are reported as diagnostics instead of being silently dropped.",
+      "description": "List your background subagents by durable id and label. Status is a snapshot of the stored record: running means the subagent session is currently live in this process, complete means it exists only in storage and a `send_message` starts a new turn on the same conversation. The snapshot is not a delivery promise — `send_message` performs the authoritative check and may still fail. Children that could not be read are reported as diagnostics instead of being silently dropped.",
       "parameters": {
         "type": "object",
         "properties": {}