Context

Stage 2b of the hybrid dispatcher (B), on #605 (core) + #606 (scaffold/embed). Flips ax hooks install --all to register the single dispatcher instead of N per-guard hooks, and migrates off legacy per-guard entries. One spawn now multiplexes every guard; guards never double-fire.

What

dispatch-install.ts (pure planning + thin Effect):

• planDispatcherInstall — fan the dispatcher's per-event plan (dispatchInstallPlan, per-event tool matchers UNION-ed) across providers; command = bun <dir>/dispatch.{ts,js}.
• planLegacyRemoval — which rows to drop: only ax-owned entries (an # ax:<id> marker) whose marker-stripped command is bun <dir>/<guard>.{ts,js} for this dir + target provider/scope. A user's own hook is never touched, even on a colliding command.
• resolveDispatcherPath + installDispatcher (idempotent add + migrate).

cli.ts — --all resolves the dispatcher, calls installDispatcher, prints installed/skipped/migrated. Single-file install <file> unchanged.

Tested (no DB)

• 9 pure unit tests — plan fan-out; legacy-removal safety (skips non-ax / different dir / wrong provider+scope / the dispatcher itself).
• Integration test exercises the real config CRUD against a temp settings.json (project scope via repoRoot). readAllHooks(withEvidence:false) returns before it touches SurrealClient, so a never-invoked stub layer suffices — no DB needed. Asserts: dispatcher entries written, legacy ax guard migrated, user hook preserved, re-run idempotent.

bun test apps/axctl/src/hooks/ → 206 pass, 0 fail. bun run typecheck → exit 0.

Migration safety

planLegacyRemoval removes a row only if all hold: has an # ax:<id> marker (ax-owned), command matches a legacy guard path for the exact workspace dir, and provider+scope match. Hand-written hooks and the dispatcher entry itself are left alone — covered by dedicated tests.

Roadmap

1. feat(hooks): dispatcher core — multiplex all guards in one process (B, stage 1) #605 dispatch core ✅
2. feat(hooks): scaffold + embed the single dispatcher (B, stage 2) #606 scaffold + embed ✅
3. This PR — --all installs the dispatcher + migrates legacy.
4. Stage 3 — daemon POST /hooks/eval + effect-free shim (daemon-first, lazy-import bundle on fallback). The latency win.

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