fix(aider-watch): code-review fixes (4 issues)

1. aiderw: session_end 補 model+cwd (AI Router feedback loop 修通)
2. repository: model_stats_since SQL 改 COALESCE(session_end, session_start) model
3. aider_event_service: classify_severity 移除 error_count 觸發告警（防假陽性）
4. worker: run_aider_event_processor_loop 包 proc.start() try/except（防靜默崩潰）

2026-04-20 @ Asia/Taipei

apps/api/src/repositories/aider_event_repository.py

@@ -75,10 +75,18 @@ class AiderEventRepository:
         r = await self.session.execute(text("""
             WITH session_models AS (
                 SELECT session_id,
-                       MAX(CASE WHEN type='session_start'
-                                THEN payload->>'model' END) AS model,
-                       MAX(CASE WHEN type='session_start'
-                                THEN payload->>'cwd' END) AS repo,
+                       COALESCE(
+                           MAX(CASE WHEN type='session_end'
+                                    THEN payload->>'model' END),
+                           MAX(CASE WHEN type='session_start'
+                                    THEN payload->>'model' END)
+                       ) AS model,
+                       COALESCE(
+                           MAX(CASE WHEN type='session_end'
+                                    THEN payload->>'cwd' END),
+                           MAX(CASE WHEN type='session_start'
+                                    THEN payload->>'cwd' END)
+                       ) AS repo,
                        COUNT(*) FILTER (WHERE type='error') AS err_count,
                        COUNT(*) FILTER (WHERE type='session_end'
                            AND (payload->>'exit_code')::int != 0) AS nonzero_exit

apps/api/src/services/aider_event_service.py

@@ -36,7 +36,7 @@ def classify_severity(ev: AiderEventIn) -> str | None:
         err_count = ev.payload.get("error_count", 0)
         if exit_code != 0 and err_count >= 3:
             return "high"
-        if exit_code != 0 or err_count >= 1:
+        if exit_code != 0:
             return "warning"
     return None
 

apps/api/src/workers/aider_event_processor.py

@@ -190,7 +190,11 @@ def get_aider_event_processor() -> AiderEventProcessor:
 async def run_aider_event_processor_loop() -> None:
     """main.py lifespan 呼叫此函式。"""
     proc = get_aider_event_processor()
-    await proc.start()
+    try:
+        await proc.start()
+    except Exception:
+        logger.exception("aider_processor_start_failed")
+        return
     try:
         while proc._running:
             await asyncio.sleep(60)