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/persistence/run/sql.py

@@ -23,6 +23,18 @@ class RunRepository(RunStore):
     def __init__(self, session_factory: async_sessionmaker[AsyncSession]) -> None:
         self._sf = session_factory
 
+    @staticmethod
+    def _normalize_model_name(model_name: str | None) -> str | None:
+        """Normalize model_name for storage: strip whitespace, truncate to 128 chars."""
+        if model_name is None:
+            return None
+        if not isinstance(model_name, str):
+            model_name = str(model_name)
+        normalized = model_name.strip()
+        if len(normalized) > 128:
+            normalized = normalized[:128]
+        return normalized
+
     @staticmethod
     def _safe_json(obj: Any) -> Any:
         """Ensure obj is JSON-serializable. Falls back to model_dump() or str()."""
@@ -70,6 +82,7 @@ class RunRepository(RunStore):
         thread_id,
         assistant_id=None,
         user_id: str | None | _AutoSentinel = AUTO,
+        model_name: str | None = None,
         status="pending",
         multitask_strategy="reject",
         metadata=None,
@@ -85,6 +98,7 @@ class RunRepository(RunStore):
             thread_id=thread_id,
             assistant_id=assistant_id,
             user_id=resolved_user_id,
+            model_name=self._normalize_model_name(model_name),
             status=status,
             multitask_strategy=multitask_strategy,
             metadata_json=self._safe_json(metadata) or {},