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/__tests__/task-merge.test.ts

@@ -60,6 +60,34 @@ describe("getTaskMergeBlocker", () => {
       .toContain("specifying");
   });
 
+  it("returns reason when task is awaiting-approval", () => {
+    expect(getTaskMergeBlocker({ ...baseTask, status: "awaiting-approval" }))
+      .toContain("awaiting-approval");
+  });
+
+  it("returns reason when task needs-replan", () => {
+    // scheduler/executor/triage move a task here when its plan must be revisited.
+    expect(getTaskMergeBlocker({ ...baseTask, status: "needs-replan" }))
+      .toContain("needs-replan");
+  });
+
+  it("returns reason when task is in mission-validation", () => {
+    expect(getTaskMergeBlocker({ ...baseTask, status: "mission-validation" }))
+      .toContain("mission-validation");
+  });
+
+  it("returns reason when task is queued (scheduler transient)", () => {
+    expect(getTaskMergeBlocker({ ...baseTask, status: "queued" }))
+      .toContain("queued");
+  });
+
+  it("returns reason when task is stuck-killed", () => {
+    // Defensive: if this transient marker surfaces in in-review, the task
+    // needs investigation rather than auto-merge.
+    expect(getTaskMergeBlocker({ ...baseTask, status: "stuck-killed" }))
+      .toContain("stuck-killed");
+  });
+
   it("returns reason when task has incomplete steps", () => {
     expect(getTaskMergeBlocker({
       ...baseTask,