fix(core): expand merge-blocker statuses to cover all transient states

Audit of task.status assignments across packages/core and packages/engine
surfaced five additional transient/in-flight statuses that should block
auto-merge but weren't in BLOCKING_TASK_STATUSES:

- awaiting-approval — triage spec awaiting user approval
- needs-replan — scheduler/executor/triage signaled re-plan needed
- mission-validation — mission-level validation in flight
- queued — scheduler-side transient state
- stuck-killed — defensive guard; task killed by stuck detector

Each represents a state where finalizing the merge violates user intent
or invariants. Group the set with comments explaining the intent of each
group so future additions can be slotted appropriately.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/core/src/task-merge.ts

@@ -2,15 +2,28 @@ import type { Task, WorkflowStepResult } from "./types.js";
 
 const BLOCKING_TASK_STATUSES = new Set([
   "failed",
+  // ── User-attention / awaiting-handoff states ─────────────────────────
   "awaiting-inspection",
   "awaiting-user-review",
+  "awaiting-approval",       // triage spec awaiting user approval
+  // ── Active merge in-flight ───────────────────────────────────────────
   "merging",
   "merging-pr",
+  // ── Re-planning / triage states (scope not finalized) ────────────────
   // A task in planning/triage hasn't finalized its scope yet — letting it
   // merge skips the work the user moved it back to plan. Same for the legacy
   // "specifying" alias migrated to "planning" in db.ts.
   "planning",
   "specifying",
+  "needs-replan",            // scheduler/executor/triage signaled re-plan
+  // ── Mission-level validation in flight ───────────────────────────────
+  "mission-validation",
+  // ── Scheduler-side transient state ───────────────────────────────────
+  "queued",                  // scheduler placed the task in line; not finalized
+  // ── Abnormal termination — defensive guard ───────────────────────────
+  // Task was killed by the stuck detector. If it surfaces in in-review,
+  // it needs investigation, not auto-merge.
+  "stuck-killed",
 ]);
 
 const NON_TERMINAL_STEP_STATUSES = new Set([