T1.2: Add MediaType enum

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

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+# T1.2 — Add `MediaType` enum
+
+**Status:** Pending Review
+**Agent:** Kimi Code CLI
+**Started:** 2026-05-11T06:55Z
+**Completed:** 2026-05-11T07:08Z
+**Commit:** see git log
+**PRD:** ../PRD-wire-format-v2.md
+
+## What I changed
+
+- `crates/wzp-proto/src/media_type.rs:1-55` — created new module with `MediaType` enum (`Audio=0`, `Video=1`, `Data=2`, `Control=3`), `to_wire()`, `from_wire()`, and two unit tests
+- `crates/wzp-proto/src/lib.rs:18` — added `pub mod media_type;`
+- `crates/wzp-proto/src/lib.rs:28` — added `pub use media_type::MediaType;`
+- `crates/wzp-proto/src/packet.rs:4` — added `use crate::MediaType;`
+- `crates/wzp-proto/src/packet.rs:168` — changed `MediaHeaderV2.media_type` from `u8` to `MediaType`, resolving the `TODO(T1.2)`
+- `crates/wzp-proto/src/packet.rs:184` — `write_to` now calls `self.media_type.to_wire()`
+- `crates/wzp-proto/src/packet.rs:202` — `read_from` now uses `MediaType::from_wire(buf.get_u8())?`
+- `crates/wzp-proto/src/packet.rs:1292` — updated `media_header_v2_roundtrip` test to use `MediaType::Audio`
+
+## Why these choices
+
+Followed steps T1.2.1 through T1.2.2 without deviation. Since `MediaType` now exists, I also resolved the `TODO(T1.2)` placeholder left in `MediaHeaderV2` during T1.1 so the v2 header is internally consistent before moving on.
+
+## Deviations from the task spec
+
+None.
+
+## Verification output
+
+```bash
+$ cargo test -p wzp-proto media_type
+running 2 tests
+test media_type::tests::media_type_roundtrip ... ok
+test media_type::tests::media_type_unknown_rejected ... ok
+
+test result: ok. 2 passed; 0 failed; 0 ignored; 0 measured; 106 filtered out; finished in 0.00s
+```
+
+```bash
+$ cargo test -p wzp-proto media_header_v2_roundtrip
+running 1 test
+test packet::tests::media_header_v2_roundtrip ... ok
+
+test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 107 filtered out; finished in 0.00s
+```
+
+```bash
+$ cargo build -p wzp-proto -p wzp-codec -p wzp-fec -p wzp-crypto -p wzp-transport -p wzp-relay -p wzp-client -p wzp-web -p wzp-native
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 15.31s
+```
+
+```bash
+$ cargo test -p wzp-proto -p wzp-codec -p wzp-fec -p wzp-crypto -p wzp-transport -p wzp-relay -p wzp-client -p wzp-web -p wzp-native --no-fail-fast
+...
+test result: ok. 567 passed; 0 failed; ...
+```
+
+```bash
+$ cargo clippy -p wzp-proto --all-targets -- -D warnings
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 1.57s
+```
+
+```bash
+$ cargo fmt --all -- --check
+# (clean)
+```
+
+## Test summary
+
+- Tests added: 2 (`media_type_roundtrip`, `media_type_unknown_rejected`)
+- Tests modified: 1 (`media_header_v2_roundtrip` — now uses `MediaType::Audio`)
+- Workspace test count before: 565 pass / 0 fail (non-Android subset)
+- Workspace test count after: 567 pass / 0 fail (non-Android subset)
+- `cargo clippy -p wzp-proto --all-targets -- -D warnings`: pass
+- `cargo fmt --all -- --check`: pass
+
+## Risks / follow-ups
+
+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