fix: smart turn-completion detection — eliminates 600s delay for clean turns

.claude/skills/multi-agent-orchestration/SKILL.md

@@ -338,6 +338,7 @@ When modifying orchestration, verify:
 - [ ] **INV-O7**: Worker timeouts use 10-minute default (600s for resumed sessions)
 - [ ] **INV-O8**: Cancellation tokens propagated to all async operations
 - [ ] **INV-O15**: IDLE-DEFER flushes CurrentResponse before breaking (content preservation)
+- [ ] **INV-O17**: IDLE-DEFER-REARM re-arms IsProcessing when idle arrives with backgroundTasks but IsProcessing is already false (PR #472)
 
 ---
 
@@ -763,6 +764,59 @@ These layers remain as fallbacks for edge cases where IDLE-DEFER doesn't fire:
 | `RecoverFromPrematureIdleIfNeededAsync` | Poll signal + events.jsonl freshness | Collect full response after partial TCS |
 | `IsEventsFileActive` | events.jsonl mtime < 15s | Detect ongoing CLI activity |
 
+### IDLE-DEFER-REARM (PR #472)
+
+When multiple `session.idle` events arrive for a session with active `backgroundTasks`,
+the first IDLE-DEFER correctly defers completion. But if `CompleteResponse` runs between
+the first and second idle (e.g., triggered by a watchdog or another code path), then
+`IsProcessing` is already `false` when the second idle arrives. Without re-arming,
+background agents would finish their work but no completion event would fire — the
+classic "zero-idle" symptom where the session appears stuck.
+
+**IDLE-DEFER-REARM** detects this scenario and re-arms processing:
+
+```csharp
+case SessionIdleEvent idle:
+    CancelTurnEndFallback(state);
+
+    if (HasActiveBackgroundTasks(idle))
+    {
+        // ... existing IDLE-DEFER logic (flush, break) ...
+
+        // REARM: If IsProcessing is already false, re-arm it so the
+        // next idle (without background tasks) triggers CompleteResponse.
+        if (!state.Info.IsProcessing)
+        {
+            state.Info.IsProcessing = true;
+            state.Info.HasUsedToolsThisTurn = true; // 600s tool timeout
+            RestartProcessingWatchdog(state);
+            Debug($"[IDLE-DEFER-REARM] ...");
+        }
+        break;
+    }
+
+    CompleteResponse(state, idleGeneration);
+```
+
+**What the re-arm sets:**
+- `IsProcessing = true` — so the next non-deferred idle fires `CompleteResponse`
+- `HasUsedToolsThisTurn = true` — enables the 600s tool timeout instead of 120s,
+  since background agents may run for several minutes
+- Restarts the processing watchdog — provides a safety net if no further idle arrives
+- Logs `[IDLE-DEFER-REARM]` to `event-diagnostics.log`
+
+### `session.idle` Is Ephemeral — Never Persisted
+
+> **⚠️ `session.idle` is NEVER written to `events.jsonl` by design.** It is a
+> transient signal from the CLI, not a persisted event. Any restore or recovery
+> logic that depends on reading `session.idle` from disk is fundamentally flawed.
+> The poller in `PollEventsAndResumeWhenIdleAsync` watches for `session.shutdown`
+> instead, which IS persisted.
+
+This matters for IDLE-DEFER because after an app restart, there will be no
+`session.idle` replay — the watchdog and resume logic handle completion detection
+for interrupted sessions, not idle event replay.
+
 ---
 
 ## "Fix with Copilot" — Multi-Agent Awareness
@@ -959,6 +1013,7 @@ Reflect mode runs multiple iterations. Expect this pattern:
 | Orchestration hangs on reconnect | Check for missing TrySetCanceled | TCS not canceled; see INV-O9 |
 | Many IDLE-DEFER entries | `grep "IDLE-DEFER" diagnostics.log` | Normal — worker has active sub-agents; wait for completion |
 | IDLE-DEFER but worker never completes | Check if background tasks are leaking | Sub-agent/shell not terminating; check CLI logs |
+| IDLE-DEFER-REARM entries | `grep "IDLE-DEFER-REARM" diagnostics.log` | Normal — IsProcessing was false when deferred idle arrived; re-armed for next completion |
 | Worker stuck 30+ min, events.jsonl fresh | Check file size across watchdog cycles | Dead connection — file-size-growth check should catch in ~360s (INV-O16) |
 
 ---

.github/copilot-instructions.md

@@ -254,6 +254,8 @@ For multi-agent sessions, Case B also checks **file-size-growth**: if events.jso
 
 Note: `session.idle` is an ephemeral event (`ephemeral: true` in the SDK schema) — it is delivered over the live event stream but intentionally NOT written to `events.jsonl`. When `session.idle` includes active `backgroundTasks` (sub-agents, shells), the IDLE-DEFER logic defers completion until a subsequent idle arrives with empty/null backgroundTasks. In rare cases where `IsProcessing` was already cleared (by watchdog timeout or reconnect) before the deferred idle arrives, the session may appear stuck until the watchdog fires again — see issue #403.
 
+When `session.idle` with active `backgroundTasks` arrives but `IsProcessing` is already `false`, the handler re-arms: sets `IsProcessing = true`, `HasUsedToolsThisTurn = true` (600s timeout), restarts watchdog, logs `[IDLE-DEFER-REARM]`. This prevents zero-idle symptoms where IDLE-DEFER fires once but subsequent idles are no-ops.
+
 When the watchdog fires, it marshals state mutations to the UI thread via `InvokeOnUI()` and adds a system warning message.
 
 ### Diagnostic Log Tags
@@ -262,6 +264,7 @@ The event diagnostics log (`~/.polypilot/event-diagnostics.log`) uses these tags
 - `[EVT]` — SDK event received (only SessionIdleEvent, AssistantTurnEndEvent, SessionErrorEvent)
 - `[IDLE]` — SessionIdleEvent dispatched to CompleteResponse
 - `[IDLE-DEFER]` — SessionIdleEvent deferred due to active background tasks (agents/shells)
+- `[IDLE-DEFER-REARM]` — SessionIdleEvent re-armed IsProcessing after it was already cleared
 - `[COMPLETE]` — CompleteResponse executed or skipped
 - `[RECONNECT]` — session replaced after disconnect
 - `[ERROR]` — SessionErrorEvent or SendAsync/reconnect failure cleared IsProcessing
@@ -288,6 +291,8 @@ When a user changes the model via the UI dropdown:
 - The SDK continues using the original model from session creation
 - To truly switch models, the session must be destroyed and recreated
 
+`GetSessionModel` prioritizes: (1) user's explicit choice (`session.Model`), (2) backend-reported model from usage info, (3) `DefaultModel` fallback. `ShouldAcceptObservedModel()` in `ModelHelper.cs` prevents `SessionUsageInfoEvent` and `AssistantUsageEvent` from overwriting an explicit user model selection — the observed model is only accepted if no explicit choice was made or if the observed model matches the explicit choice.
+
 ### SDK Data Types
 - `AssistantUsageData` properties (`InputTokens`, `OutputTokens`, etc.) are `Double?` not `int?`
 - Use `Convert.ToInt32(value)` for conversion, not `value as int?`
@@ -302,6 +307,9 @@ Avoid `@bind:event="oninput"` — causes round-trip lag per keystroke. Use plain
 
 For detailed stuck-session debugging knowledge (8 invariants from 7 PRs of fix cycles), see `.claude/skills/processing-state-safety/SKILL.md`.
 
+### Smart Completion Scan
+**Smart completion scan:** `assistant.turn_end` and `assistant.message` are not unconditionally terminal — they appear between every tool round. `IsSessionStillProcessing` uses `IsCleanNoToolSubturn()` to scan backward from the last event within the current sub-turn (bounded by `assistant.turn_start`/`session.resume`/`session.start`). If any `tool.execution_*` event is found in the current sub-turn, the session is considered still processing. Clean no-tool turns are detected immediately, eliminating the 600s watchdog delay for simple conversations.
+
 ### Session Persistence
 - Active sessions: `~/.polypilot/active-sessions.json` (includes `LastPrompt` — last user message if session was processing during save)
 - Session state: `~/.copilot/session-state/<guid>/events.jsonl` (SDK-managed, stays in ~/.copilot)

PolyPilot.Tests/StuckSessionRecoveryTests.cs

@@ -303,8 +303,6 @@ public void StalenessThreshold_UsesWatchdogToolExecutionTimeout()
     [InlineData("assistant.reasoning")]
     [InlineData("assistant.reasoning_delta")]
     [InlineData("assistant.intent")]
-    [InlineData("assistant.turn_end")]       // between tool rounds — still processing
-    [InlineData("assistant.message")]        // mid-turn text — still processing
     [InlineData("tool.execution_end")]       // tool just completed — still processing
     public void IsSessionStillProcessing_AllActiveEventTypes_ReturnTrue(string eventType)
     {
@@ -331,7 +329,7 @@ public void IsSessionStillProcessing_AllActiveEventTypes_ReturnTrue(string event
     [InlineData("session.idle")]
     [InlineData("session.error")]
     [InlineData("session.shutdown")]
-    [InlineData("session.start")]     // created but never used — not actively processing
+    [InlineData("session.start")]         // created but never used — not actively processing
     public void IsSessionStillProcessing_TerminalEventTypes_ReturnFalse(string eventType)
     {
         var svc = CreateService();
@@ -353,6 +351,133 @@ public void IsSessionStillProcessing_TerminalEventTypes_ReturnFalse(string event
         }
     }
 
+    // --- Smart completion: assistant.turn_end/message without pending tools ---
+
+    [Fact]
+    public void IsSessionStillProcessing_TurnEndWithoutPendingTools_ReturnsFalse()
+    {
+        // Turn completed cleanly — no tool.execution_start after the last turn_end.
+        var svc = CreateService();
+        var tmpDir = Path.Combine(Path.GetTempPath(), "polypilot-test-" + Guid.NewGuid().ToString("N"));
+        var sessionId = Guid.NewGuid().ToString();
+        var sessionDir = Path.Combine(tmpDir, sessionId);
+        Directory.CreateDirectory(sessionDir);
+        var eventsFile = Path.Combine(sessionDir, "events.jsonl");
+
+        try
+        {
+            File.WriteAllText(eventsFile,
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{"content":"hello"}}""" + "\n" +
+                """{"type":"assistant.turn_end","data":{}}""");
+            var result = svc.IsSessionStillProcessing(sessionId, tmpDir);
+            Assert.False(result, "Clean turn_end without pending tools should not report still processing");
+        }
+        finally { Directory.Delete(tmpDir, true); }
+    }
+
+    [Fact]
+    public void IsSessionStillProcessing_TurnEndWithPendingTools_ReturnsTrue()
+    {
+        // Turn ended after a tool round. This can still be between rounds, so restore
+        // must stay conservative and keep the session active until the next events arrive.
+        var svc = CreateService();
+        var tmpDir = Path.Combine(Path.GetTempPath(), "polypilot-test-" + Guid.NewGuid().ToString("N"));
+        var sessionId = Guid.NewGuid().ToString();
+        var sessionDir = Path.Combine(tmpDir, sessionId);
+        Directory.CreateDirectory(sessionDir);
+        var eventsFile = Path.Combine(sessionDir, "events.jsonl");
+
+        try
+        {
+            File.WriteAllText(eventsFile,
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{}}""" + "\n" +
+                """{"type":"tool.execution_start","data":{}}""" + "\n" +
+                """{"type":"tool.execution_complete","data":{}}""" + "\n" +
+                """{"type":"assistant.turn_end","data":{}}""");
+            var result = svc.IsSessionStillProcessing(sessionId, tmpDir);
+            Assert.True(result, "turn_end after tool activity in the same sub-turn should report still processing");
+        }
+        finally { Directory.Delete(tmpDir, true); }
+    }
+
+    [Fact]
+    public void IsSessionStillProcessing_TurnEndNoCurrentToolsAfterEarlierToolRound_ReturnsFalse()
+    {
+        // Older tool rounds must not leak across assistant.turn_start boundaries and keep a
+        // later clean no-tool turn alive.
+        var svc = CreateService();
+        var tmpDir = Path.Combine(Path.GetTempPath(), "polypilot-test-" + Guid.NewGuid().ToString("N"));
+        var sessionId = Guid.NewGuid().ToString();
+        var sessionDir = Path.Combine(tmpDir, sessionId);
+        Directory.CreateDirectory(sessionDir);
+        var eventsFile = Path.Combine(sessionDir, "events.jsonl");
+
+        try
+        {
+            File.WriteAllText(eventsFile,
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{}}""" + "\n" +
+                """{"type":"tool.execution_start","data":{}}""" + "\n" +
+                """{"type":"tool.execution_complete","data":{}}""" + "\n" +
+                """{"type":"assistant.turn_end","data":{}}""" + "\n" +
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{"content":"final answer"}}""" + "\n" +
+                """{"type":"assistant.turn_end","data":{}}""");
+            var result = svc.IsSessionStillProcessing(sessionId, tmpDir);
+            Assert.False(result, "A clean no-tool turn_end should not be kept active by tools from an earlier round");
+        }
+        finally { Directory.Delete(tmpDir, true); }
+    }
+
+    [Fact]
+    public void IsSessionStillProcessing_MessageWithContentNoTools_ReturnsFalse()
+    {
+        // Final assistant.message with content, no pending tools — session done.
+        var svc = CreateService();
+        var tmpDir = Path.Combine(Path.GetTempPath(), "polypilot-test-" + Guid.NewGuid().ToString("N"));
+        var sessionId = Guid.NewGuid().ToString();
+        var sessionDir = Path.Combine(tmpDir, sessionId);
+        Directory.CreateDirectory(sessionDir);
+        var eventsFile = Path.Combine(sessionDir, "events.jsonl");
+
+        try
+        {
+            File.WriteAllText(eventsFile,
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{"content":"Here is your answer."}}""");
+            var result = svc.IsSessionStillProcessing(sessionId, tmpDir);
+            Assert.False(result, "assistant.message without pending tools should not report still processing");
+        }
+        finally { Directory.Delete(tmpDir, true); }
+    }
+
+    [Fact]
+    public void IsSessionStillProcessing_MessageWithPendingToolInSameTurn_ReturnsTrue()
+    {
+        // assistant.message as last event, but tool.execution_start earlier in same turn
+        // → smart scan should detect the pending tool and report still processing.
+        var svc = CreateService();
+        var tmpDir = Path.Combine(Path.GetTempPath(), "polypilot-test-" + Guid.NewGuid().ToString("N"));
+        var sessionId = Guid.NewGuid().ToString();
+        var sessionDir = Path.Combine(tmpDir, sessionId);
+        Directory.CreateDirectory(sessionDir);
+        var eventsFile = Path.Combine(sessionDir, "events.jsonl");
+
+        try
+        {
+            File.WriteAllText(eventsFile,
+                """{"type":"assistant.turn_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{}}""" + "\n" +
+                """{"type":"tool.execution_start","data":{}}""" + "\n" +
+                """{"type":"assistant.message","data":{"content":"Running the tool now..."}}""");
+            var result = svc.IsSessionStillProcessing(sessionId, tmpDir);
+            Assert.True(result, "assistant.message with pending tool.execution_start should report still processing");
+        }
+        finally { Directory.Delete(tmpDir, true); }
+    }
+
     // --- Resume branch selection: RESUME-ACTIVE vs RESUME-QUIESCE ---
 
     [Fact]