fix(engine): make the planning->plan-review handoff atomic so planned cards stop stranding in Todo

Triage announced specification completion before its finally block marked the
plan work item terminal, so the Plan Review seeder saw its own still-running
predecessor as an "active continuation", bailed, and the discarded result
silently stranded the card until FN-8592 self-healing re-seeded it ~10 minutes
later (529 occurrences in 18 days).

- seedStrandedPlanReviewContinuation gains retirePredecessorId: idle check
  excludes the named predecessor, then retires it and installs the successor in
  ONE transaction under the task lock; a bailed seed mutates nothing.
- triage threads planningWorkItemId through PlanningHandoffReport; the runtime
  reaction passes it as retirePredecessorId.
- reactToSpecificationComplete consumes the seed result: typed quiet parks
  (incl. new "no-pre-release-plan-review"), bounded retries with a fresh
  task/IR snapshot per attempt (mid-retry pause/needs-replan honored), loud
  warning naming self-healing on exhaustion.
- Tests: PG both-orderings/no-mutation-on-bail/cross-task cases, direct engine
  seeder handoff cases, reaction retry/park/pause/replan cases.
- docs/solutions: new planning-handoff-race writeup; graph-entry-contract doc
  reclassifies the FN-8592 sweep as backstop-only.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/solutions/architecture-patterns/workflow-node-column-placement-and-graph-entry-contract.md

@@ -91,7 +91,11 @@ own column, so the node must be where the card rests.
   `passed` `plan-review` entry to `workflowStepResults`. A held unreviewed card is the gate working;
   that path belongs to `pre-release-plan-review.test.ts`.
 - **Pre-existing cards** sitting in Todo with a real spec and no continuation are re-seeded
-  automatically by FN-8592's stranded-hold-continuation sweep.
+  automatically by FN-8592's stranded-hold-continuation sweep. Since 2026-08-13 that sweep is a pure
+  backstop: the primary handoff retires its own planning work item atomically with the successor
+  install (`retirePredecessorId`), so routine post-planning stranding — which once made the sweep
+  the de facto handoff at a ~10-minute delay per card — is a bug, not expected behavior. See
+  [planning-handoff-race-silently-strands-plan-review](../logic-errors/planning-handoff-race-silently-strands-plan-review.md).
 - **The trace no longer starts at `start`** for a card past intake. Assertions on `visitedNodeIds`
   should expect the card's column entry point.
 - **Coding (Ideas) no longer has a private planning shape.** Its planning-node re-home is deleted —

docs/solutions/logic-errors/planning-handoff-race-silently-strands-plan-review.md

@@ -0,0 +1,69 @@
+---
+category: logic-errors
+module: "@fusion/engine (triage planning handoff), @fusion/core (workflow work items)"
+tags: [workflow-work-items, continuation, race-condition, silent-drop, self-healing-backstop, plan-review]
+problem_type: race_condition
+applies_when: "A node-completion handoff installs its successor continuation outside the transaction that terminalizes the predecessor, or a fire-and-forget reaction discards a seed/install result."
+---
+
+# Planning handoff race silently strands Plan Review
+
+## Symptom
+
+Every freshly planned (or replanned) card sat idle in Todo for ~10 minutes with
+"Execution dispatch refused — task is still unplanned" in its log, then moved on
+after `task:reconcile-stranded-hold-continuation` fired. 529 self-healing
+recoveries in 18 days — self-healing had silently become the PRIMARY handoff,
+each one costing the card the sweep's full staleness grace.
+
+## Root cause
+
+Two independent defects compounded:
+
+1. **Ordering race.** Triage's `specifyTask` announced completion
+   (`onSpecifyComplete`) BEFORE its `finally` block transitioned the planning
+   work item to `succeeded`. The seed reaction fired concurrently, and
+   `seedPreReleasePlanReviewContinuation`'s all-kinds idle check counted the
+   caller's own still-`running` plan row as an "active continuation" and bailed.
+2. **Silent drop.** `reactToSpecificationComplete` awaited the seed but
+   discarded its result, so the bail was invisible — no log, no retry, no audit.
+   The card stranded until FN-8592 self-healing re-seeded it.
+
+## Fix (2026-08-13)
+
+- `seedStrandedPlanReviewContinuation` gained `retirePredecessorId`: in ONE
+  transaction under the task advisory lock it excludes the named predecessor
+  from the idle check, re-verifies no OTHER active row and no passed Plan
+  Review, transitions the predecessor to `succeeded`, and installs the
+  successor. Checks run BEFORE the retirement, so a bailed seed mutates nothing.
+- Triage threads `planningWorkItemId` through `PlanningHandoffReport`; the
+  runtime reaction passes it as `retirePredecessorId`.
+- The reaction consumes the seed result: quiet parks (`awaiting-approval`,
+  `paused`, `plan-review-passed`, `no-pre-release-plan-review`) log and exit;
+  anomalies retry (1s, 5s) with a fresh task/IR snapshot per attempt (so a
+  mid-retry pause or `needs-replan` is honored) and warn loudly on exhaustion,
+  naming self-healing as the recovery owner.
+
+## Lessons
+
+- **A node transition is a handoff, not two writes.** Terminalizing the
+  predecessor and installing the successor must be one transaction; any code
+  that does them separately has an ordering race with every observer between.
+- **A discarded result is a silent stall.** Fire-and-forget reactions must
+  consume the outcome and surface non-success loudly (see
+  [branch-group-name-collision-strands-mission-triage](branch-group-name-collision-strands-mission-triage.md)).
+- **Self-healing frequency is a bug signal.** A "backstop" firing hundreds of
+  times is the primary path failing quietly; alert on recovery-event volume.
+- **Reason-less bails poison retry loops.** Every refusal needs a named reason
+  so consumers can distinguish legitimate configuration (no pre-release Plan
+  Review node) from genuine anomalies worth retrying/warning.
+
+## Verification
+
+- `packages/core/src/__tests__/workflow-work-items-conditional-seed.test.ts` —
+  "planning handoff retires its own predecessor atomically": both race
+  orderings, only-the-named-predecessor, cross-task safety, no-mutation-on-bail.
+- `packages/engine/src/__tests__/plan-approval-hold-invariant.test.ts` — "#2b
+  the handoff seeder does not bail on its own named predecessor".
+- `packages/engine/src/__tests__/specify-complete-reaction.test.ts` — result
+  consumption, bounded retries, quiet parks, mid-retry pause/replan honoring.