feat(run): Propagates model_name from the gateway request through the runtime and persistence stack to the SQLite database. (#2775)

* feat(run): propagate model_name from gateway request context to persistence layer

Pass model_name through the full run creation pipeline — from
RunCreateRequest.context in the gateway, through RunManager, to the
RunStore interface and SQL persistence. This enables client-specified
model selection to be recorded per-run in the database.

* feat(run): add model allowlist validation and effective model name capture

- Validate model_name against allowlist in gateway services.py using
  get_app_config().get_model_config()
- Truncate model_name to 128 chars to match DB column constraint
- In worker.py, capture effective model name from agent.metadata after
  agent creation and persist if resolved differently than requested

* feat(run): add defense-in-depth model_name normalization and round-trip persistence tests

- Add _normalize_model_name() to RunRepository for whitespace stripping
  and 128-char truncation before DB writes.
- Add round-trip unit tests for model_name creation and default None
  in test_run_manager.py.

* fix(run): coerce non-string model_name values before strip/truncate in _normalize_model_name

* fix(gateway): add runtime type guard for model_name coercion in gateway services

Add isinstance check and str() coercion before calling .strip() to prevent
AttributeError when non-string types (int, None, etc.) flow through the
gateway. Paired with SQL integration test for end-to-end model_name
persistence across gateway → langgraph → persistence layer.

* fix(run): drop Alembic migration for model_name (no-op) and expose public update method on RunManager

- Drop a1b2c3d4e5f6 migration: model_name already exists in RunRow schema
  and is auto-created via Base.metadata.create_all() at startup
- Add update_model_name() public method to RunManager to replace the private
  _persist_to_store call in worker.py, preserving internal locking/persistence

backend/packages/harness/deerflow/runtime/runs/manager.py

@@ -36,6 +36,7 @@ class RunRecord:
     abort_event: asyncio.Event = field(default_factory=asyncio.Event, repr=False)
     abort_action: str = "interrupt"
     error: str | None = None
+    model_name: str | None = None
 
 
 class RunManager:
@@ -65,6 +66,7 @@ class RunManager:
                 metadata=record.metadata or {},
                 kwargs=record.kwargs or {},
                 created_at=record.created_at,
+                model_name=record.model_name,
             )
         except Exception:
             logger.warning("Failed to persist run %s to store", record.run_id, exc_info=True)
@@ -137,6 +139,18 @@ class RunManager:
                 logger.warning("Failed to persist status update for run %s", run_id, exc_info=True)
         logger.info("Run %s -> %s", run_id, status.value)
 
+    async def update_model_name(self, run_id: str, model_name: str | None) -> None:
+        """Update the model name for a run."""
+        async with self._lock:
+            record = self._runs.get(run_id)
+            if record is None:
+                logger.warning("update_model_name called for unknown run %s", run_id)
+                return
+            record.model_name = model_name
+            record.updated_at = _now_iso()
+        await self._persist_to_store(record)
+        logger.info("Run %s model_name=%s", run_id, model_name)
+
     async def cancel(self, run_id: str, *, action: str = "interrupt") -> bool:
         """Request cancellation of a run.
 
@@ -171,6 +185,7 @@ class RunManager:
         metadata: dict | None = None,
         kwargs: dict | None = None,
         multitask_strategy: str = "reject",
+        model_name: str | None = None,
     ) -> RunRecord:
         """Atomically check for inflight runs and create a new one.
 
@@ -221,6 +236,7 @@ class RunManager:
                 kwargs=kwargs or {},
                 created_at=now,
                 updated_at=now,
+                model_name=model_name,
             )
             self._runs[run_id] = record