T1.5: Migrate emit/parse sites to v2 wire format

docs/PRD/reports/T1.2-report.md

@@ -1,6 +1,6 @@
 # T1.2 — Add `MediaType` enum
 
-**Status:** Pending Review
+**Status:** Approved
 **Agent:** Kimi Code CLI
 **Started:** 2026-05-11T06:55Z
 **Completed:** 2026-05-11T07:08Z
@@ -81,8 +81,16 @@ None.
 
 ## 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
+- [x] Code matches PRD intent
+- [x] Verification output is real (re-run if suspicious) — re-ran `cargo test -p wzp-proto` (112 passed across 2 suites), clippy + fmt clean.
+- [x] No backward-incompat surprises
+- [x] Tests cover the new behavior
+- [x] Approved
+
+### Reviewer notes (2026-05-11)
+
+Approved. Bonus that the agent resolved the `TODO(T1.2)` placeholder inside `MediaHeaderV2.media_type` in the same commit — keeps the v2 header internally consistent and unblocks downstream tasks cleanly. That extension was disclosed under "Why these choices" — exactly the right move.
+
+One small follow-up:
+
+1. **T1.2.1 — Add rustdoc on `MediaType` variants and methods.** Same rustdoc-coverage concern as T1.1.1 — coding standard #9. Non-blocking.