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Implements docs/todo/work-graph-time-travel-debugging-design.md, backend and console together (user confirmed 2026-08-06). Key finding that shrank the v1 scope: ux_work_graph_run_active is a PARTIAL unique index (only covers non-terminal statuses), not a blanket one -- forking from a parent run that's already reached a terminal status never collides with it at all. v1 restricts forking to exactly that case, so no index/constraint change is needed, only two new nullable columns (parent_run_id, fork_of_node_exec_id). Resolved the requirements doc's FR-1 ambiguity ("override input_payload, re-trigger execution") as OUTPUT SUBSTITUTION instead: the fork point's own output_payload is replaced with the human-supplied content directly, it is never re-executed via a new claude -p call -- only the strict downstream subgraph actually re-runs. This sidesteps reconciling the different build_prompt/input_payload conventions each caller uses (Planner's artifact_type lookup, E's generic task_prompt field, F's jury) -- work_graph_fork.py only needs the persisted graph_manifest and each node's output_payload. Implementation needs ZERO changes to the execution engine: pre-seeding every non-downstream node as a 'done' work_node_execution row before calling the unmodified run_graph() on the unmodified graph_manifest is enough -- run_work_node()'s existing REQ-06 breakpoint-recovery short-circuit (already-'done' nodes return their persisted output without calling run_fn) does all the "reuse without re-executing" work for free. _reconstruct_build_prompt supports two graph shapes generically from persisted state alone (Planner's canonical doc chain via e2e_pipeline._planner_prompt_builder, and E's generic task_prompt field); anything else raises ForkGraphShapeUnsupportedError rather than producing broken prompts. New: src/work_graph_fork.py (create_fork/execute_fork/fork_work_graph_run/ start_fork_in_background, the last splitting fast DB-only setup from slow real execution so an HTTP caller gets run_id back immediately, same pattern task_execution.start_task_execution_in_background already uses). work_graph_run gets parent_run_id/fork_of_node_exec_id (SCHEMA_SQL + migrate_add_work_graph_fork_columns for existing databases). work_graph_run_query.py/task_query.py surface both fields. New endpoint POST /api/work-nodes/:node_exec_id/fork. Console: a "从这里分叉" form on each 'done' node in v_run_detail, a fork badge linking back to the parent run, and a 🔀 marker on v_graph_console's run list -- no diff/merge UI (non-goal #3), read-only branch visibility only. Verified end-to-end for real: started the actual backend, sent a real HTTP fork request, confirmed the new run persisted with correct parent_run_id/fork_of_node_exec_id lineage. Tests cover requirements doc acceptance standards 1-3 (PRD swapped -> SDD/Benchmark genuinely re-execute, BRD untouched; original run completely unaffected; the same node forked twice produces independent branches) plus schema migration idempotency, query-layer field surfacing, the HTTP route, and 3 frontend smoke-test assertions. Full src suite (608 tests) + all 3 frontend smoke tests pass. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
