A build run's dependent lane cannot start until its predecessor has merged into the default branch: readiness reads a predecessor as landed only when its lane is done, its pull request an ancestor of the default branch, so a step that needs another waits a whole preflight and merge-queue cycle (about one to two and a half hours each on 2026-10-22) before it opens. Stacked changes are standard practice for dependent work (Graphite, Sapling and ghstack stacks, and merge queues taking a stack in order), and on 2026-10-22/23 that shape was rolled by hand twice: merge-gate steps 2 and 3, and model-matrix step 2 stacked on the route branch. Building it is more than a fix: the dependent lane's pull request is based on the predecessor's branch, the stack merges in order, and a lane rebases (and re-stamps what it resolved) when the predecessor changes.

Press Release

Seeded by promotion from iss-2610230856272073. Expand into the full press-release narrative before planning.

Why This Matters

Graduated from iss-2610230856272073: A build run's dependent lane cannot start until its predecessor has merged into the default branch: readiness reads a predecessor as landed only when its lane is done, its pull request an ancestor of the default branch, so a step that needs another waits a whole preflight and merge-queue cycle (about one to two and a half hours each on 2026-10-22) before it opens. Stacked changes are standard practice for dependent work (Graphite, Sapling and ghstack stacks, and merge queues taking a stack in order), and on 2026-10-22/23 that shape was rolled by hand twice: merge-gate steps 2 and 3, and model-matrix step 2 stacked on the route branch. Building it is more than a fix: the dependent lane's pull request is based on the predecessor's branch, the stack merges in order, and a lane rebases (and re-stamps what it resolved) when the predecessor changes.. Read that issue record for the source observation.

Mechanism

Prompted (the claim-recording gradient): why the authors expect this to work, as a falsifiable "we expect X because Y" — not the outcome restated. Replace this line with the claim, or with the exact token None stated. alone on its line to record the claim as considered and declined.

Scope Conditions

Required (the claim-recording gradient): the population, platform, scale, or assumptions this claim holds under, one per top-level bullet — abcd intent plan stamps each with a persistent identity. Replace this line with those bullets, or with the exact token None stated. alone on its line.

Acceptance Criteria

Required (the itd-1 discipline): add at least one Given-When-Then bullet describing the verifiable bar for "shipped" before this draft can be planned.

Open Questions

None recorded yet.

Audit Notes

Empty. Populated by intent-auditor when intent moves to shipped/.