feat(orchestrator): compose per-queue speculators and turn speculation on

[behinddwalls]

Summary

Why?

Everything below this commit landed inert: the orchestrator passed the speculate run a placeholder that proposes nothing, so no path was ever funded and no speculative build started. The machinery is all reviewed; nothing configures it per queue or switches it on.

What?

This is the activation switch. Per-queue profiles gain a Scorer and a Speculator: each queue's speculator is composed from its own scorer as standard.New(bestfirst.New(scorer), sticky.New(budget)), with a factory adapter beside the existing ones so routing stays in the wiring layer, and main.go swaps the placeholder for profiles.SpeculatorFactory().

The scorer profiles are the policy knobs: the baseline scores everything 0.5, test-queue buckets by lines changed, and e2e-test-queue exercises the composite scorer. Every scorer is wrapped by scorerfake so a change URI carrying a failure marker forces a scoring error end-to-end. The build budget is a wiring-level constant (4 concurrent builds per queue) with a TODO to move it onto entity.QueueConfig.

With this commit, paths are funded, builds run per path, and batches finalize from their paths — the whole stack goes live in one revertable step.

Test Plan

✅ bazel build //..., make fmt, make gazelle

✅ make e2e-test — the full pipeline lands changes end-to-end with per-path speculation on.

Stack

1. docs(rfc): explain best-first speculation generation #513
2. feat(speculation): generator contract and bestfirst impl #446
3. feat(speculation): allocator contract and sticky impl #450
4. feat(speculation): standard composed speculator #451
5. feat(storage): speculation path set store #501
6. feat(storage): path-build link store for per-path builds #502
7. feat(orchestrator): dispatch builds per speculation path #503
8. feat(orchestrator): poll builds and stop the ones nothing wants #504
9. fix(orchestrator): mint distinct message IDs for cancel re-publishes #505
10. feat(orchestrator): re-plan the queue from the Speculator each run #506
11. feat(orchestrator)!: finalize batches from their speculation paths #507
12. @ feat(orchestrator): compose per-queue speculators and turn speculation on #508