Task DAG with explicit parallel flag¶

The task DAG layer lets a planner hand the orchestrator an authored list of tasks whose parallel-safety is declarative, not inferred from file overlap. Each task carries:

Marker	Meaning
`[T<id>]`	Stable task identifier (required).
`[P]`	Safe to run concurrently with other parallel-safe siblings.
`[US<n>]`	User-story slice used as a rollback grouping.
`-> T###, T###`	Inline dependency arrow at end of line.

File formats¶

Markdown checkbox list¶

# MVP plan

- [ ] [T001] [P] [US1] Add YAML loader
- [ ] [T002] [P] [US1] Add markdown loader
- [ ] [T003]    [US1] Wire orchestrator -> T001, T002
- [ ] [T004] [P] [US2] Render parallel batches

YAML¶

tasks:
  - id: T001
    description: Add YAML loader
    parallel_safe: true
    story_id: US1
  - id: T002
    description: Wire orchestrator
    depends_on: [T001]
    story_id: US1

Walking the DAG¶

bernstein.core.orchestration.task_dag.topological_iter_with_parallel yields one frozenset[TaskNode] per batch:

All-[P] ready tasks merge into a single concurrent batch.
Any serial task in the ready set runs alone; remaining [P] siblings form a pure parallel batch on the next iteration.
Cycles raise TaskDagCycleError with the unresolved task ids.

CLI¶

Render a DAG plan for review:

bernstein plan dag --file specs/mvp-tasks.md
bernstein tasks plan dag --file specs/mvp-tasks.md  # alias

Output marks each batch as SERIAL or PARALLEL and lists user-story rollback groups at the end.

Scheduler consumption¶

bernstein.core.orchestration.adaptive_parallelism.tasks_safe_to_run_in_parallel prefers the declarative parallel_safe flag when both tasks carry it and falls back to the legacy file-overlap heuristic only for legacy tasks that lack the attribute. Tasks generated through the new planner path always set the flag, so the heuristic only runs for older entries.

Rollback grouping¶

Tasks sharing a story_id form a rollback unit: the orchestrator surfaces "story <id> complete" as a single milestone and supports a story-scoped revert. Tasks without story_id remain independent.