Summary

Add the prioritizer seam and its limit counterpart from the speculation RFC, as vendor-agnostic extension interfaces under submitqueue/extension/speculation/.

prioritizer: the queue-wide policy that rations a shared build budget across every in-flight batch. The controller hands it the queue's candidate paths — every path that is Selected (wants a slot) or Prioritized/Building (holds a slot), each with its score — and it returns sparse decisions: Promote to admit a pending path, Cancel to preempt a running one; omitted paths are left as-is. Whether it preempts is its own per-queue policy (sticky-slots vs preemptive), so the interface is unchanged either way. It never writes; the controller maps each decision to a guarded status transition (Promote → Prioritized, Cancel → Cancelling) and enacts it, staying the single writer. It shares the selector's SpeculationPathDecision output and ranks on the scorer's path Score, so it lives in the same speculation/ family.

prioritizationlimit: the "how much" policy bounding how many builds the queue runs at once — the queue's concurrent-build budget and the ultimate cap on speculation's demand on CI. Injected into the prioritizer at construction and called by it; the value is dynamic, not a fixed constant.

Each follows the repo extension contract: Factory.For(Config) (T, error) with Config carrying only QueueName. Includes READMEs, gomock packages, and programmable fakes. Interfaces only; concrete impls and controller wiring are deferred.

Test Plan

Issues

Stack

1. feat(entity,storage): rework speculation tree model and store #231
2. feat(speculation): add enumerator + dependency-limit extensions #315
3. feat(speculation): add path scorer extension #316
4. feat(speculation): add selector + selection-limit extensions #317
5. @ feat(speculation): add prioritizer + prioritization-limit extensions #320