feat: add topic summarize endpoint

src/backend/api/routes/topics.py

@@ -9,8 +9,10 @@ from src.backend.db.database import (
     get_topic,
     update_topic,
     delete_topic,
+    list_requests,
 )
 from src.backend.models.api import TopicCreate, TopicUpdate, ok, fail
+from src.backend.services.worker_client import WorkerClient
 
 router = APIRouter(
     prefix="/topics",
@@ -91,3 +93,38 @@ async def delete(topic_id: str, db=Depends(_get_db)):
             content=fail("NOT_FOUND", "Topic not found or has active requests"),
         )
     return ok({"deleted": True})
+
+
+@router.post("/{topic_id}/summarize", summary="Regenerate topic summary")
+async def summarize_topic(topic_id: str, db=Depends(_get_db)):
+    topic = await get_topic(db, topic_id)
+    if not topic:
+        return JSONResponse(
+            status_code=404,
+            content=fail("NOT_FOUND", "Topic not found"),
+        )
+
+    completed = await list_requests(db, status="completed", topic_id=topic_id)
+    if not completed:
+        return JSONResponse(
+            status_code=400,
+            content=fail("NO_DATA", "No completed requests to summarize"),
+        )
+
+    exchanges = [
+        {"prompt": r["prompt"], "result": r["result"]}
+        for r in completed
+        if r["result"]
+    ]
+
+    worker = WorkerClient()
+    result = await worker.summarize(exchanges=exchanges, mode="complete")
+
+    if not result.get("success"):
+        return JSONResponse(
+            status_code=502,
+            content=fail("WORKER_ERROR", "Worker failed to generate summary"),
+        )
+
+    updated = await update_topic(db, topic_id, summary=result["summary"])
+    return ok(updated)