After a red merge batch, the queue gates the halves `restack` plans, so both land when both are green #6534

Part of #5994, the second half of #6515.

Done:

• [ ] Where src/checks/queue.ts re-forms a red batch, it gates the two candidates restack returns (the second built on the first's merge) and acts on afterVerdicts; nothing else in the queue changes.
• [ ] A queue test drives an 8-pull batch with one bad pull through the injected gate and sees the 7 good ones land in at most 2 rounds after the red.
• [ ] Every existing queue test still passes unchanged; if one must change, the pull says which and why.

Files: src/checks/queue.ts, the queue test under test/.

Before pushing: bun x tsc --noEmit and every test file that imports the queue.

Parked by the crew: the run ended without a pull: declined: #6534 is blocked by #6533, and #6533 isn't done. This issue asks src/checks/queue.ts to gate the two candidates that restack returns and to act on afterVerdicts. Neither function exists on `main

Parked by the crew: the run ended without a pull: declined: the second Done item can't be met by gating what restack and afterVerdicts return, so I made no change. The queue's red-batch search is judged in src/checks/queue.ts, and nothing else in the f

Parked twice since a person last spoke here, so it is the planner's now. Every reason:

1. the run ended without a pull: declined: #6534 is blocked by #6533, and #6533 isn't done. This issue asks src/checks/queue.ts to gate the two candidates that restack returns and to act on afterVerdicts. Neither function exists on `main
2. the run ended without a pull: declined: the second Done item can't be met by gating what restack and afterVerdicts return, so I made no change. The queue's red-batch search is judged in src/checks/queue.ts, and nothing else in the f

The planner splits it, replaces it with a fresh issue, or defers it; a person can also say what to try. Nothing starts here until then, and the board lists it.

Replaced by #6651. Both runs were right that this could not be built as written: the queue's red-batch search, judged in src/checks/queue.ts, already re-gates a red batch by stacked prefixes (#5994), and test/merge-queue-search.test.ts already proves the 8-pull, one-bad case lands the 7 good in 2 gate rounds — the second Done item. Wiring restack/afterVerdicts in would replace a more general search with a narrower one. #6651 removes the unused planner instead, so nothing on main is imported only by its test.