fix: singleton WorkflowService + mark task failed on load error

[devteamaegis]

What

Two independent logic bugs in workflows/backend/:

Bug 1 — get_service() creates a new instance on every request

# before
def get_service() -> WorkflowService:
    return WorkflowService()   # fresh empty state every call!

active_tasks, workflow_tasks, and cancel_events are stored on the instance.
A POST /execute request builds service A and stores the task there.
Any follow-up GET /tasks/{id}/status or POST /tasks/{id}/cancel builds service B (empty) and always returns 404 / "Task not found" — the task status and cancel endpoints are effectively broken.

Fix: promote to a module-level singleton.

Bug 2 — load failure leaves task stuck as 'running'

# before
except Exception as e:
    print(f'Error loading workflow: {e}')
    return   # active_tasks[task_id].status stays 'running' forever

If Workflow.load_from_file raises (corrupt file, missing deps, schema error), the task is never marked 'failed'. Callers poll forever seeing status: running with no error details. The message also went to stdout instead of the structured log.

Fix: set status = 'failed', populate error, write to the log file.

Tests

workflows/backend/tests/test_service_singleton_and_load_failure.py — 6 unit tests, no browser/LLM required:

Test	What it checks
test_returns_workflow_service_instance	get_service() returns a WorkflowService
test_same_instance_on_repeated_calls	second call returns the exact same object
test_task_state_survives_across_calls	task written in call 1 visible in call 2
test_singleton_reset_creates_new_instance	sanity — reset gives a new object
test_load_failure_sets_status_to_failed	status is 'failed' after load raises
test_load_failure_logs_error	error message appears in the log

PASSED  test_returns_workflow_service_instance
PASSED  test_same_instance_on_repeated_calls
PASSED  test_task_state_survives_across_calls
PASSED  test_singleton_reset_creates_new_instance
PASSED  test_load_failure_sets_status_to_failed
PASSED  test_load_failure_logs_error
6 passed in 0.XX s

---

Summary by cubic

Fixes two backend bugs: make WorkflowService a module-level singleton and mark tasks as failed (with logged errors) when workflow loading fails. This restores persistent task state across requests and prevents tasks from getting stuck as running.

• Bug Fixes
  • get_service() now returns a shared WorkflowService instance, so active_tasks, workflow_tasks, and cancel_events persist and status/cancel/log endpoints find tasks instead of 404.
  • If Workflow.load_from_file throws, set task status to 'failed', populate error, and write the message to the task log (no stdout), so clients stop polling and see the failure reason.

^{Written for commit 10fc4e1. Summary will update on new commits. Review in cubic}

[cubic-dev-ai]

1 issue found across 3 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="workflows/backend/tests/test_service_singleton_and_load_failure.py">

<violation number="1" location="workflows/backend/tests/test_service_singleton_and_load_failure.py:64">
P2: Module-level mocking of `aiofiles` and `yaml` leaks stubbed modules into the shared test process and can break unrelated tests.</violation>
</file>

<sub>Reply with feedback, questions, or to request a fix.

Fix all with cubic | Re-trigger cubic</sub>

[cubic-dev-ai]

P2: Module-level mocking of aiofiles and yaml leaks stubbed modules into the shared test process and can break unrelated tests.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At workflows/backend/tests/test_service_singleton_and_load_failure.py, line 64:

<comment>Module-level mocking of `aiofiles` and `yaml` leaks stubbed modules into the shared test process and can break unrelated tests.</comment>

<file context>
@@ -0,0 +1,222 @@
+_aiofiles_open_cm.__aenter__ = AsyncMock(return_value=_aiofiles_file)
+_aiofiles_open_cm.__aexit__ = AsyncMock(return_value=False)
+_aiofiles_mock.open = MagicMock(return_value=_aiofiles_open_cm)
+sys.modules["aiofiles"] = _aiofiles_mock
+
+sys.modules["yaml"].safe_load = MagicMock(return_value={})
</file context>