fix(llm): classify empty model completions as retryable EMPTY_RESPONSE

A well-formed provider stream that ends with finish_reason stop and zero
content blocks previously became a successful empty assistant message: the
turn completed silently, and drivers like goal-session counted the no-op
round. Both adapters now map that degenerate completion to a finish
{kind:'error'} with the new canonical EMPTY_RESPONSE code from dsh-llm, and
dsh-llm-retry adds the code to its default retryable set, so the existing
closed-step recovery path retries it and fails loud once the budget is
exhausted.

Covered by adapter unit tests, an llm-retry default-policy test, and a new
authored keyless ACP snapshot (empty-response-retry) with a deterministic
1 ms zero-jitter retry overlay.

examples/acp-agent/retry.cordis.snapshot.yml

@@ -0,0 +1,41 @@
+# Keyless replay for the retry overlay: disable the key-requiring DeepSeek
+# adapter, insert `llm-replay`, and restate the app config with the same
+# deterministic 1 ms zero-jitter retry policy as the live sibling. A config
+# patch replaces the whole app config, so the base fields are restated
+# verbatim (raw JSONL persistence so the harness can harvest the log).
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: llm-deepseek
+        name: '@deepseek-ai/dsh-llm-deepseek'
+        disabled: true
+      - id: acp-agent
+        name: '@deepseek-ai/dsh-acp-demo'
+        config:
+          provider: deepseek
+          model: deepseek-v4-flash
+          persistenceRoot: !!js process.env.DSH_SNAPSHOT_SESSIONS_ROOT ?? './.sessions'
+          persistenceCompression: none
+          workspaceContext:
+            maxBytes: 65536
+          llmRetry:
+            maxTransientRetries: 2
+            initialDelayMs: 1
+            maxDelayMs: 1
+            jitterRatio: 0
+          persona: |
+            You are a coding assistant powered by the {{model}} model. Your working directory is {{cwd}}. Your bash tool runs under a file sandbox — a `[sandbox: file access denied …]` result is policy, not a command bug.
+
+            Verify your work by running the code or tests. Keep answers brief and factual.
+      - insert:
+          - id: llm-replay
+            name: '@deepseek-ai/dsh-llm-replay'
+            config:
+              providers:
+                - id: deepseek
+                  name: DeepSeek
+                  models:
+                    - id: deepseek-v4-flash
+                    - id: deepseek-v4-pro

examples/acp-agent/retry.cordis.yml

@@ -0,0 +1,30 @@
+# Retry-scenario overlay: pin the bounded transient retry policy to a
+# deterministic 1 ms zero-jitter delay so the durable `llm/retry` event
+# (`delayMs`) and replay wall time stay reproducible. The overlay changes no
+# tool or prompt composition, so its scenarios share the default header class.
+# A config patch replaces the whole app config, so the base fields are restated
+# verbatim; the model is re-pinned to `deepseek-v4-flash` like the other
+# snapshot overlays because the recorded corpus was captured on flash.
+- id: base
+  name: '@cordisjs/plugin-include'
+  config:
+    path: ./cordis.yml
+    patches:
+      - id: acp-agent
+        name: '@deepseek-ai/dsh-acp-demo'
+        config:
+          provider: deepseek
+          model: deepseek-v4-flash
+          persistenceRoot: !!js process.env.DSH_SNAPSHOT_SESSIONS_ROOT ?? './.sessions'
+          persistenceCompression: !!js "process.env.DSH_SNAPSHOT === undefined ? 'zstd' : 'none'"
+          workspaceContext:
+            maxBytes: 65536
+          llmRetry:
+            maxTransientRetries: 2
+            initialDelayMs: 1
+            maxDelayMs: 1
+            jitterRatio: 0
+          persona: |
+            You are a coding assistant powered by the {{model}} model. Your working directory is {{cwd}}. Your bash tool runs under a file sandbox — a `[sandbox: file access denied …]` result is policy, not a command bug.
+
+            Verify your work by running the code or tests. Keep answers brief and factual.

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

@@ -38,6 +38,7 @@ const PTY_CONFIG = fileURLToPath(new URL('../pty.cordis.yml', import.meta.url))
 const DEPTH_TWO_CONFIG = fileURLToPath(new URL('../depth-two.cordis.yml', import.meta.url))
 const PACKED_CHUNKS_CONFIG = fileURLToPath(new URL('../packed-chunks.cordis.yml', import.meta.url))
 const SESSION_SANDBOX_ROOT_CONFIG = fileURLToPath(new URL('../session-sandbox-root.cordis.yml', import.meta.url))
+const RETRY_CONFIG = fileURLToPath(new URL('../retry.cordis.yml', import.meta.url))
 const LSP_CONFIG = fileURLToPath(new URL('./lsp.cordis.yml', import.meta.url))
 const SNAPSHOTS_DIR = join(dirname(fileURLToPath(import.meta.url)), 'snapshots')
 const PACKED_CHUNKS_SOURCE = 'hook-cc-pretool-deny'
@@ -137,6 +138,14 @@ const SCENARIOS: Scenario[] = [
     headerClass: 'model-switching',
   },
   { name: 'error-finish', hasModelTurn: true, recorded: false, overridden: true },
+  // Keyless, authored (like error-finish): a live provider cannot be coaxed
+  // into a degenerate empty completion, so the fixture scripts the adapters'
+  // EMPTY_RESPONSE error finish (step 1) followed by the recovered reply
+  // (step 2), proving the default retry policy end to end: the durable
+  // llm/retry event, the ACP discarded-attempt marker, and a clean completed
+  // turn. Its overlay only pins a deterministic 1 ms zero-jitter delay, so it
+  // shares the default header class.
+  { name: 'empty-response-retry', hasModelTurn: true, recorded: false, configPath: RETRY_CONFIG },
   // Keyless, authored (like error-finish/cancel): deterministically forcing a
   // LIVE model to repeat one call three times is not a stable recording, so
   // the fixture scripts five identical todo_write calls and pins BOTH reminder

examples/acp-agent/tests/snapshots/empty-response-retry/input.json

@@ -0,0 +1,7 @@
+{
+  "steps": [
+    { "op": "initialize" },
+    { "op": "newSession" },
+    { "op": "prompt", "text": "This prompt first receives an empty completion, then a retried reply." }
+  ]
+}

examples/acp-agent/tests/snapshots/empty-response-retry/session.jsonl

@@ -0,0 +1,19 @@
+{"type":"session","version":0,"id":"{{sessionId}}","createdAt":0,"cwd":"{{cwd}}","delegationDepth":0}
+{"type":"turn/start","seq":0,"time":0,"data":{"turn":1,"trigger":{"kind":"message","source":{"kind":"user"}}}}
+{"type":"user/message","seq":1,"time":0,"data":{"content":[{"type":"text","text":"This prompt first receives an empty completion, then a retried reply."}],"source":{"kind":"user"}},"surfaceOp":"append"}
+{"type":"session/title","seq":2,"time":0,"data":{"title":"This prompt first receives an","messageSeqs":[1],"source":{"kind":"fallback"}}}
+{"type":"step/start","seq":3,"time":0,"data":{"turn":1,"step":1}}
+{"type":"request/header","seq":4,"time":0,"data":{"header":{"config":{"provider":"deepseek","model":"deepseek-v4-flash"},"system":"{{system}}","tools":"{{tools}}"},"reason":"initial"}}
+{"type":"assistant/chunk","seq":5,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"usage","usage":{"inputTokens":0,"outputTokens":0}}}}
+{"type":"assistant/chunk","seq":6,"time":0,"data":{"turn":1,"step":1,"chunk":{"type":"finish","reason":{"kind":"error","failure":{"message":"model returned a completed response with no content","code":"EMPTY_RESPONSE"}}}}}
+{"type":"step/end","seq":7,"time":0,"data":{"turn":1,"step":1}}
+{"type":"llm/retry","seq":8,"time":0,"data":{"turn":1,"step":1,"retry":1,"maxRetries":2,"delayMs":1,"failure":{"message":"model returned a completed response with no content","code":"EMPTY_RESPONSE"}}}
+{"type":"step/start","seq":9,"time":0,"data":{"turn":1,"step":2}}
+{"type":"assistant/chunk","seq":10,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"block-start","index":0,"blockType":"text"}}}
+{"type":"assistant/chunk","seq":11,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"text-delta","index":0,"text":"Recovered."}}}
+{"type":"assistant/chunk","seq":12,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"block-end","index":0,"block":{"type":"text","text":"Recovered."}}}}
+{"type":"assistant/chunk","seq":13,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"usage","usage":{"inputTokens":12,"outputTokens":3}}}}
+{"type":"assistant/chunk","seq":14,"time":0,"data":{"turn":1,"step":2,"chunk":{"type":"finish","reason":{"kind":"stop"}}}}
+{"type":"assistant/message","seq":15,"time":0,"data":{"turn":1,"step":2,"content":[{"type":"text","text":"Recovered."}],"provenance":{"provider":"deepseek","model":"deepseek-v4-flash"},"usage":{"inputTokens":12,"outputTokens":3}},"sourceEventSeqs":[10,11,12,13,14],"surfaceOp":"append"}
+{"type":"step/end","seq":16,"time":0,"data":{"turn":1,"step":2}}
+{"type":"turn/end","seq":17,"time":0,"data":{"turn":1,"reason":{"kind":"completed"}}}

examples/acp-agent/tests/snapshots/empty-response-retry/stdout.expected.jsonl

@@ -0,0 +1,7 @@
+{"jsonrpc":"2.0","id":1,"result":{"protocolVersion":1,"agentInfo":{"name":"deepseek-harness-acp","version":"0.0.1"},"agentCapabilities":{"loadSession":true,"sessionCapabilities":{"list":{}},"promptCapabilities":{"image":false,"audio":false,"embeddedContext":false}},"authMethods":[]}}
+{"jsonrpc":"2.0","id":2,"result":{"sessionId":"{{sessionId}}","modes":{"availableModes":[{"id":"default","name":"default"},{"id":"plan","name":"plan"}],"currentModeId":"default"},"configOptions":[{"id":"model","name":"Model","description":"Sets this session's provider and model.","category":"model","type":"select","currentValue":"[\"deepseek\",\"deepseek-v4-flash\"]","options":[{"value":"[\"deepseek\",\"deepseek-v4-flash\"]","name":"deepseek-v4-flash"},{"value":"[\"deepseek\",\"deepseek-v4-pro\"]","name":"deepseek-v4-pro"}]},{"id":"permission","name":"Permissions","description":"The session permission preset: each choice bundles a sandbox mode and an approval policy.","category":"mode","type":"select","currentValue":"danger-full-access","options":[{"value":"workspace-write","name":"workspace-write","description":"Write inside the workspace and permitted temporary directories; wider retries require approval."},{"value":"danger-full-access","name":"danger-full-access","description":"Full file access without approval prompts."}]}]}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"available_commands_update","availableCommands":[{"name":"goal","description":"set or view the goal for a long-running task","input":{"hint":"[<objective>|clear|edit <objective>|pause|resume]"}},{"name":"plan","description":"Enter or leave plan mode","input":{"hint":"[off|message]"}}]}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"session_info_update","title":"This prompt first receives an","updatedAt":"{{updatedAt}}"}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"\n\n[Previous model attempt discarded; retrying 1/2 in 1ms: model returned a completed response with no content]\n\n"}}}}
+{"jsonrpc":"2.0","method":"session/update","params":{"sessionId":"{{sessionId}}","update":{"sessionUpdate":"agent_message_chunk","content":{"type":"text","text":"Recovered."}}}}
+{"jsonrpc":"2.0","id":3,"result":{"stopReason":"end_turn"}}