fix: recover failed Gaussian project builds

tests/test_simulation_projects.py

@@ -228,6 +228,37 @@ def test_service_resumes_a_persisted_provider_job_without_reupload(tmp_path: Pat
     assert provider.submit_calls == 0
 
 
+def test_failed_project_retries_from_retained_source_and_releases_old_job(tmp_path: Path) -> None:
+    store = SimulationProjectStore(tmp_path)
+    project = store.create(
+        name="Retry scene",
+        scene_type="outdoor",
+        source_kind="folder",
+        files=_folder_files(),
+    )
+    _upload_all(store, project)
+    store.begin_build(project["project_id"])
+    store.update_processing(
+        project["project_id"],
+        status="processing",
+        provider_job_id="gsp-20260826000000-deadbeef",
+        provider_state="failed",
+        progress={"completed_steps": 1, "total_steps": 4},
+        bundle_sha256="d" * 64,
+    )
+    store.fail(project["project_id"], "provider failure")
+    provider = _ReadyProvider()
+    service = SimulationProjectService(store, provider_factory=lambda: provider)  # type: ignore[arg-type]
+
+    queued = service.begin_build(project["project_id"])
+
+    assert provider.deleted == ["gsp-20260826000000-deadbeef"]
+    assert queued["status"] == "queued"
+    assert queued["error"] is None
+    assert queued["provider"]["job_id"] is None
+    assert queued["source"]["uploaded_byte_length"] == queued["source"]["total_byte_length"]
+
+
 def test_api_exposes_same_origin_resumable_upload_contract(tmp_path: Path) -> None:
     store = SimulationProjectStore(tmp_path)
     service = SimulationProjectService(store, provider_factory=lambda: None)