fix: session handling and SDK async iteration

- Add sdk_conversation_id column to track SDK conversation separately from user session_id
- Queue processor looks up SDK conversation ID for resume instead of passing user session_id
- session_id "new" stores NULL initially, gets set from SDK on completion
- Custom session_ids are preserved (not overwritten by SDK)
- Worker catches SDK process exit error after messages are collected

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/backend/db/database.py

@@ -19,6 +19,7 @@ CREATE TABLE IF NOT EXISTS topics (
 CREATE TABLE IF NOT EXISTS requests (
     id TEXT PRIMARY KEY,
     session_id TEXT,
+    sdk_conversation_id TEXT,
     topic_id TEXT NOT NULL REFERENCES topics(id),
     prompt TEXT NOT NULL,
     model TEXT,
@@ -156,7 +157,7 @@ async def create_request(
     now = _now()
 
     if session_id == "new":
-        session_id = _new_id()
+        session_id = None
 
     await db.execute(
         "INSERT INTO requests (id, session_id, topic_id, prompt, model, summarize, status, created_at) "
@@ -246,19 +247,14 @@ async def complete_request(
     db: aiosqlite.Connection,
     request_id: str,
     result: str,
-    session_id: str | None = None,
+    sdk_conversation_id: str | None = None,
 ) -> None:
     now = _now()
-    if session_id:
-        await db.execute(
-            "UPDATE requests SET status = 'completed', result = ?, completed_at = ?, session_id = ? WHERE id = ?",
-            (result, now, session_id, request_id),
-        )
-    else:
-        await db.execute(
-            "UPDATE requests SET status = 'completed', result = ?, completed_at = ? WHERE id = ?",
-            (result, now, request_id),
-        )
+    await db.execute(
+        "UPDATE requests SET status = 'completed', result = ?, completed_at = ?, "
+        "sdk_conversation_id = ?, session_id = COALESCE(session_id, ?) WHERE id = ?",
+        (result, now, sdk_conversation_id, sdk_conversation_id, request_id),
+    )
     await db.commit()
 
 
@@ -297,6 +293,17 @@ async def list_sessions(db: aiosqlite.Connection) -> list[dict]:
     return [dict(row) for row in rows]
 
 
+async def get_session_sdk_id(db: aiosqlite.Connection, session_id: str) -> str | None:
+    cursor = await db.execute(
+        "SELECT sdk_conversation_id FROM requests "
+        "WHERE session_id = ? AND status = 'completed' AND sdk_conversation_id IS NOT NULL "
+        "ORDER BY completed_at DESC LIMIT 1",
+        (session_id,),
+    )
+    row = await cursor.fetchone()
+    return row[0] if row else None
+
+
 async def session_exists(db: aiosqlite.Connection, session_id: str) -> bool:
     cursor = await db.execute(
         "SELECT 1 FROM requests WHERE session_id = ? LIMIT 1", (session_id,)

src/backend/services/queue.py

@@ -9,6 +9,7 @@ from src.backend.db.database import (
     complete_request,
     fail_request,
     append_topic_summary,
+    get_session_sdk_id,
 )
 from src.backend.services.worker_client import WorkerClient
 
@@ -38,6 +39,11 @@ async def process_one(worker: WorkerClient) -> bool:
             return True
 
         model = resolve_model(req["model"], topic["model"])
+
+        # Only resume if there's a previous completed request with an SDK conversation ID
+        resume_id = None
+        if req["session_id"]:
+            resume_id = await get_session_sdk_id(db, req["session_id"])
     finally:
         await db.close()
 
@@ -46,7 +52,7 @@ async def process_one(worker: WorkerClient) -> bool:
             prompt=req["prompt"],
             system_prompt=topic["system_prompt"],
             model=model,
-            session_id=req["session_id"],
+            session_id=resume_id,
         )
     except Exception as e:
         db = await get_db()
@@ -63,7 +69,7 @@ async def process_one(worker: WorkerClient) -> bool:
                 db,
                 req["id"],
                 result["result"],
-                session_id=result.get("session_id"),
+                sdk_conversation_id=result.get("session_id"),
             )
 
             if req["summarize"]: