# T1.3 — Widen `CodecId` wire representation to u8

**Status:** Approved
**Agent:** Kimi Code CLI
**Started:** 2026-05-11T07:10Z
**Completed:** 2026-05-11T07:11Z
**Commit:** see git log
**PRD:** ../PRD-wire-format-v2.md

## What I changed

- `crates/wzp-proto/src/codec_id.rs:3-6` — updated top-level doc comment to note 4-bit v1 / 8-bit v2 dual encoding
- `crates/wzp-proto/src/codec_id.rs:27-32` — added reserved video codec ID comments (`9..=13`) after `Opus64k = 8`
- `crates/wzp-proto/src/codec_id.rs:174-183` — added `codec_id_unknown_values_rejected` regression test

## Why these choices

Followed steps T1.3.1 through T1.3.3 without deviation. `CodecId::to_wire` already returns `self as u8`, so no code change was needed to support the full 8-bit wire range — only documentation and a regression test.

## Deviations from the task spec

None.

## Verification output

```bash
$ cargo test -p wzp-proto codec_id_unknown_values_rejected
running 1 test
test codec_id::tests::codec_id_unknown_values_rejected ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 108 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 7.56s
```

```bash
$ cargo clippy -p wzp-proto --all-targets -- -D warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.99s
```

```bash
$ cargo fmt --all -- --check
# (clean)
```

## Test summary

- Tests added: 1 (`codec_id_unknown_values_rejected`)
- Tests modified: 0
- Workspace test count before: 567 pass / 0 fail (non-Android subset)
- Workspace test count after: 568 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)

- [x] Code matches PRD intent
- [x] Verification output is real (re-run if suspicious) — re-ran `cargo test -p wzp-proto` (112 passed), clippy + fmt clean.
- [x] No backward-incompat surprises — wire repr is unchanged for IDs 0..=8; only documentation + reservation comments + a regression test.
- [x] Tests cover the new behavior — `codec_id_unknown_values_rejected` covers 9..=255.
- [x] Approved

### Reviewer notes (2026-05-11)

Approved. No follow-ups — this was a docs-and-test-only change with no new public API surface to document. The fmt-driven reflow on `sample_rate_hz` and `is_opus` is collateral from `cargo fmt` and is fine.
