D34 — Synchronization: Layer 3 push over stdio + codex/kiro materialization

Decision. Two pieces of the sync model (D27) completed: - codex/kiro providers: skillDestDir (internal/provisioning) now also maps codex → .codex/skills/<nome>/ and kiro → .kiro/skills/<nome>/ — they move out of needs_approval to direct materialization like claude/opencode. Everything else (manifest, lockfile, diff, prune) was already provider-generic. - Layer 3 (push): Server.Notify(method, params) emits a JSON-RPC notification on the shared stdio encoder (serialized by writeMu); the notifyWrap helper wraps skill_install (outside gitWrap, fires after the commit, only on success) and emits notifications/skills/list_changed. Capability skills.listChanged: true announced in initialize.

Rationale. On the hand-rolled HTTP transport (D16: request/response, no SSE) the server has no channel for unsolicited pushes → Server.Notify is a no-op when not inside Run (enc == nil), and Layer 3 applies only to stdio, degrading gracefully to Layers 1–2 over HTTP (consistent with the "additive" design of sync.md). The crucial choice is the lock discipline: writeMu protects each individual Encode but is never held during dispatch (where Notify is called, same goroutine) → no nested locks and no deadlock; verified with go test -race. The practical value over stdio is limited (the agent calling skill_install is also the consumer), but the Notify infrastructure is the hook-in point for future emitters (server-side git pull, bundle hot-reload) with no further changes to the loop.