fix(copilot): reject nested metadata.dry_run with 422 and add contract tests

The CreateSessionRequest accepted extra fields silently, so sending
{"metadata": {"dry_run": true}} resulted in dry_run defaulting to false
instead of returning a validation error. Add `extra="forbid"` to reject
unknown fields and add tests for dry_run=true, default=false, and the
nested-metadata rejection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

autogpt_platform/backend/backend/api/features/chat/routes.py

@@ -11,7 +11,7 @@ from autogpt_libs import auth
 from fastapi import APIRouter, HTTPException, Query, Response, Security
 from fastapi.responses import StreamingResponse
 from prisma.models import UserWorkspaceFile
-from pydantic import BaseModel, Field, field_validator
+from pydantic import BaseModel, ConfigDict, Field, field_validator
 
 from backend.copilot import service as chat_service
 from backend.copilot import stream_registry
@@ -114,7 +114,13 @@ class StreamChatRequest(BaseModel):
 
 
 class CreateSessionRequest(BaseModel):
-    """Request model for creating a new chat session."""
+    """Request model for creating a new chat session.
+
+    ``dry_run`` is a **top-level** field — do not nest it inside ``metadata``.
+    Extra/unknown fields are rejected (422) to prevent silent mis-use.
+    """
+
+    model_config = ConfigDict(extra="forbid")
 
     dry_run: bool = False
 

autogpt_platform/backend/backend/api/features/chat/routes_test.py

@@ -469,3 +469,60 @@ def test_suggested_prompts_empty_prompts(
 
     assert response.status_code == 200
     assert response.json() == {"themes": []}
+
+
+# ─── Create session: dry_run contract ─────────────────────────────────
+
+
+def _mock_create_chat_session(mocker: pytest_mock.MockerFixture):
+    """Mock create_chat_session to return a fake session."""
+    from backend.copilot.model import ChatSession
+
+    async def _fake_create(user_id: str, *, dry_run: bool):
+        return ChatSession.new(user_id, dry_run=dry_run)
+
+    return mocker.patch(
+        "backend.api.features.chat.routes.create_chat_session",
+        new_callable=AsyncMock,
+        side_effect=_fake_create,
+    )
+
+
+def test_create_session_dry_run_true(
+    mocker: pytest_mock.MockerFixture,
+    test_user_id: str,
+) -> None:
+    """Sending ``{"dry_run": true}`` sets metadata.dry_run to True."""
+    _mock_create_chat_session(mocker)
+
+    response = client.post("/sessions", json={"dry_run": True})
+
+    assert response.status_code == 200
+    assert response.json()["metadata"]["dry_run"] is True
+
+
+def test_create_session_dry_run_default_false(
+    mocker: pytest_mock.MockerFixture,
+    test_user_id: str,
+) -> None:
+    """Empty body defaults dry_run to False."""
+    _mock_create_chat_session(mocker)
+
+    response = client.post("/sessions")
+
+    assert response.status_code == 200
+    assert response.json()["metadata"]["dry_run"] is False
+
+
+def test_create_session_rejects_nested_metadata(
+    test_user_id: str,
+) -> None:
+    """Sending ``{"metadata": {"dry_run": true}}`` must return 422, not silently
+    default to ``dry_run=False``. This guards against the common mistake of
+    nesting dry_run inside metadata instead of providing it at the top level."""
+    response = client.post(
+        "/sessions",
+        json={"metadata": {"dry_run": True}},
+    )
+
+    assert response.status_code == 422