docs(audio): specify the phase 3c contract

Phase 3c is delivered in four slices so an interrupted phase never leaves
the runtime worse than it started: contract, lifecycle and voices,
automation, and measured master protection. Slice 2 replaces working
scaffolding, and slice 4 cannot close without user-observed measurement.
Record that split in the implementation plan.

This commit is slice 1, the contract. Format Specification section 16
adds automation tracks with three modes and four interpolation curves,
their placement in the shared resolution pipeline, the seven-state
lifecycle with its permitted transitions, the engine-owned internal
release gain, a per-node table for computing determinable one-shot
endings, voice ceilings with an eviction order that always releases
rather than hard-stops, the master protection contract, and unlock and
pause behavior for audio.

Automation reuses the modulation registry rather than introducing a
second answer to which properties vary over time, and a track is
declared inside the graph that owns its target, so section 14.4 stands:
automation does not widen the external surface of a node property. Close
the container gap the new fields opened by adding `automation` to the
graph object in 14.3 and `release` to the recipe object in 15.16.

Master protection is specified in shape and provisional in value.
Finite-sample handling is normative because a NaN in the output buffer
is unacceptable at any ceiling; the peak ceiling, numerical tolerance,
and release behavior await GC6 measurement.

No runtime change. There is no lifecycle state machine, no voice ceiling
is enforced, and `automation` and `release` are still rejected as
unknown fields. No sound has been heard from any build.

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_011FWPdCqKaaDnP9NC3JAwh6

docs/IMPLEMENTATION_STATUS.md

@@ -1,7 +1,7 @@
 # XZBT implementation status
 
 **Updated:** September 5, 2026
-**State:** Phase 3a/3b audio authoring contract and implementation complete; Phase 3c audio contracts, the Phase 3 audible gates, and the Phase 1 direct-file import/restart observation remain pending
+**State:** The audio subsystem contract is complete through Phase 3c; Phase 3c implementation (slices 2-4), the Phase 3 audible gates, and the Phase 1 direct-file import/restart observation remain pending
 **Planning baseline:** `05fe2b4e021ba86e4a290d05b63c7cae0e386128`
 
 **Exact demarcation:** GC1 direct-file feasibility (10/10 checks), GC2 shared format contracts, GC3 resolution semantics, GC4 clock/PRNG semantics, and GC5 ownership/failure semantics are complete at the Phase 0 contract-oracle level. The Phase 1 production runtime skeleton, the Phase 2 common grammar, and the Phase 3a/3b audio authoring contract and its implementation pass automated checks. Three gates remain open in the completed work: Phase 1's direct-file two-fixture restart observation, Phase 3's audible observation (no sound has been heard from any build), and the Phase 3c audio contracts on which real playback acceptance depends. Visual, cadence/event, scenario, final generated-UI, performance, and soak work remains assigned to later phases.
@@ -13,7 +13,7 @@ The user requested sequential implementation with a stop on problems. The [manua
 | 0 — Contracts and feasibility | Complete | GC1 passed; GC2–GC5 shared contracts and traces passed; GC6/GC7 later gates scheduled and mapped |
 | 1 — Runtime skeleton | Implemented; acceptance pending | [Automated evidence](evidence/phase1/2026-09-05-runtime-skeleton.md) passes production-module, lifecycle, PRNG-vector, cache/restore, fixture-validation, and deterministic-build tests. Direct-file two-fixture import/restart remains a user-observed gate. |
 | 2 — Common grammar | Complete | [Automated evidence](evidence/phase2/2026-09-05-common-grammar.md) covers production GC2 conformance, typed values, signals, actions, same-tick bindings, transitions, override precedence/release, and parameter restoration. |
-| 3 — Audio engine | Phases 3a/3b complete; 3c not started | [Automated evidence](evidence/phase3/2026-09-05-audio-authoring-contract.md) covers Format Specification sections 14-15, all sixteen node types, routing and modulation, twelve legality rules, authoring limits, components, sounds/recipes, and buses. Phase 3c (automation precedence PRD 54, lifecycle PRD 57, safety limits and master protection PRD 58) and the PRD 129 audio acceptance challenge remain. |
+| 3 — Audio engine | Phases 3a/3b complete; 3c contract complete, 3c implementation not started | [Automated evidence](evidence/phase3/2026-09-05-audio-authoring-contract.md) covers Format Specification sections 14-15, all sixteen node types, routing and modulation, twelve legality rules, authoring limits, components, sounds/recipes, and buses. The [Phase 3c contract](evidence/phase3/2026-09-05-phase3c-contract.md) adds section 16: automation tracks and precedence, the seven-state lifecycle and release, determinable one-shot endings, voice ceilings and eviction, master protection, and unlock and pause behavior. Phase 3c implementation slices 2-4 and the PRD 129 audio acceptance challenge remain. |
 | 4 — Visual engine | Not started | Earlier phases and visual contracts |
 | 5 — Events and cadence | Not started | Earlier phases and event/cadence contracts |
 | 6 — Scenario director | Not started | Earlier phases and scenario contracts |
@@ -60,3 +60,9 @@ Implementation lives in `src/runtime/audio-contract.js` (declarative tables), `s
 `npm test` runs 62 tests with zero failures. Two clean builds produce byte-identical artifacts with digest `64d9932ed863dbae66f309504b88e19370ad2c9017e92c32bd61ea1ea39a3f17`.
 
 Phase 3 is not accepted. Audio automation precedence, the lifecycle state machine, unlock behavior, voice ceilings, and the measured master-protection contract are Phase 3c; no sound has been heard from any build, so the PRD 129 audio acceptance challenge, real GC4 synchronization checks, peak and finite-sample capture, and listening observations all remain open.
+
+## Phase 3c contract (slice 1)
+
+Format Specification section 16 completes the audio subsystem contract. Phase 3c is delivered in four slices, recorded in the implementation plan: the contract (done), lifecycle and voices, automation, and measured master protection. Each slice ends green and committable, because slice 2 replaces the working one-shot timer scaffolding and must not be left half-applied.
+
+Section 16 is contract only. The runtime does not implement it: there is no lifecycle state machine, no voice ceiling, and `automation` and `release` are still rejected as unknown fields. Slice 3c-4 and the PRD 129 audio acceptance challenge are user-observed and cannot be closed by automated tests. No sound has been heard from any build.