HKUDS/Vibe-Trading · error · ValueError

DAG contains a cycle: processed {processed}/{len(tasks)} tas

Error message

DAG contains a cycle: processed {processed}/{len(tasks)} tasks

What it means

topological_layers uses Kahn's algorithm; if the processed count is less than the total task count, in-degree never reached zero for some tasks, which can only happen when the dependency graph contains a cycle. ValueError reports processed vs total counts.

Source

Thrown at agent/src/swarm/task_store.py:244

    )

    layers: list[list[str]] = []
    processed = 0

    while queue:
        layer: list[str] = list(queue)
        queue.clear()
        layers.append(layer)
        processed += len(layer)

        for tid in layer:
            for downstream in dependents[tid]:
                in_degree[downstream] -= 1
                if in_degree[downstream] == 0:
                    queue.append(downstream)

    if processed != len(tasks):
        raise ValueError(
            f"DAG contains a cycle: processed {processed}/{len(tasks)} tasks"
        )

    return layers

View on GitHub (pinned to 80ffdda44c)

Solutions

Run validate_dag on the same task list to get the exact cycle path and break it
Audit recently added depends_on entries for backward-pointing edges
Prevent unvalidated task lists from reaching _execute_run

Example fix

# before
topological_layers([t_a_depends_on_b, t_b_depends_on_a])
# after
validate_dag(tasks)  # run first; fix reported cycle, then:
topological_layers([t_a, t_b_depends_on_a])

Defensive patterns

Strategy: validation

Validate before calling

validate_dag(tasks)  # raises with exact cycle path before layering
layers = topological_layers(tasks)

Try / catch

try:
    layers = topological_layers(tasks)
except ValueError as e:
    if 'DAG contains a cycle' in str(e): validate_dag(tasks)  # get precise path, then fix
    else: raise

Prevention

Never let unvalidated task lists reach _execute_run
Validate at preset load (inspect_preset) and again before scheduling
Test dynamic task injection paths with cyclic fixtures

When it happens

Trigger: Executing a run (or inspect_preset) whose task set has a circular depends_on chain; validate_dag was skipped so the cycle survived to layering.

Common situations: Hand-edited presets bypassing validation; dynamic task injection at runtime creating a loop.

Related errors

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/c861b561b341ba12. Report an issue: GitHub.