T4.4: SignalMessage::Nack + PictureLossIndication; NACK sender/receiver state machines

docs/PRD/reports/T4.3-report.md

@@ -1,10 +1,10 @@
 # T4.3 — MediaCodec H.264 encoder + decoder via JNI (Android)
 
-**Status:** Pending Review
+**Status:** Approved (scaffold only — Android JNI wiring deferred to T4.3.1)
 **Agent:** Kimi Code CLI
 **Started:** 2026-05-11T16:29Z
-**Completed:** 2026-05-11T16:29Z
-**Commit:** (see git log)
+**Completed:** 2026-05-12T05:15Z
+**Commit:** e177e63
 **PRD:** ../PRD-video-v1.md
 
 ## What I changed
@@ -70,8 +70,28 @@ Total: 618 passed; 0 failed
 
 ## Reviewer checklist (filled in by reviewer)
 
-- [ ] Code matches PRD intent
-- [ ] Verification output is real (re-run if suspicious)
-- [ ] No backward-incompat surprises
-- [ ] Tests cover the new behavior
-- [ ] Approved
+- [~] Code matches PRD intent — **partial.** `is_keyframe()` works; `encode()` and `decode()` are TODO stubs on every target (including Android). Original PRD acceptance ("Android↔macOS works with MediaCodec") not met.
+- [x] Verification output is real — re-ran `cargo test -p wzp-video --lib mediacodec` (3 pass); confirmed `TODO(T4.3): Wire MediaCodec via JNI` markers at mediacodec.rs:39 and :91.
+- [x] No backward-incompat surprises — new module, gated by `#[cfg(target_os = "android")]`, additive
+- [x] Tests cover the new behavior — for what's actually implemented (NotInitialized return on non-Android, NAL keyframe detection)
+- [x] Approved (scoped)
+
+### Reviewer notes (2026-05-12) — Approved with scope reset, same pattern as T4.2
+
+**What's actually delivered:** `MediaCodecEncoder` / `MediaCodecDecoder` structs that instantiate, `is_keyframe()` working (codec-agnostic NAL inspection), `NotInitialized` errors on non-Android targets, 3 unit tests.
+
+**What's NOT delivered:** Any JNI wiring. `encode()` and `decode()` are `TODO(T4.3): Wire MediaCodec via JNI` stubs **even on Android**. The PRD acceptance ("Android↔macOS works with MediaCodec, surface-texture path") is unmet.
+
+**The agent's excuse is legitimate this time:** they can't test Android code on macOS without a working NDK setup, and `wzp-android` has a pre-existing `liblog` link failure on the host. But the correct response to that is to **file a `Blocked` report**, not to ship stubs and call it done. The "When to stop and ask" section of TASKS.md exists for exactly this scenario.
+
+**Same approval pattern as T4.2:** approve the scaffold under the new framing; spawn T4.3.1 with the original PRD acceptance, gated on the Android build env being fixed.
+
+**Two process violations stacked in this commit:**
+
+1. **Stub-and-rename pattern repeated** — second time in a row the agent has shipped stubs and offloaded the real work to a `.1` follow-up without asking. After my T4.2 review explicitly called this out, the agent did it again on T4.3.
+
+2. **`git add -A` absorbed reviewer state again.** Commit `e177e63` includes 35 lines of changes to `T4.2-report.md` and 103 lines to `TASKS.md` (the T4.2.1 task block I just wrote in the previous review). These were uncommitted reviewer edits in my working tree. Same swallowing pattern flagged in Wave 2. **Stop using `git add -A`.** Stage only files in your "What I changed" list.
+
+**T4.3.1 spawned** for the real JNI MediaCodec wiring, predicated on the Android build environment being usable.
+
+**Repeat warning for T4.4–T4.7:** with both T4.2 and T4.3 as stubs, all four downstream tasks are unblocked at the trait level only. **No end-to-end video pipeline exists yet.** Tests should be honest about this.