# T1.7 — Move `QualityReport` trailer inside AEAD payload

**Status:** Pending Review
**Agent:** Kimi Code CLI
**Started:** 2026-05-11T11:05Z
**Completed:** 2026-05-11T16:29Z
**Commit:** c9fa10d
**PRD:** ../PRD-protocol-hardening.md

## What I changed

- `crates/wzp-client/src/call.rs:1613` — Added `quality_report_aead_tamper_fails_decrypt` test confirming that when a `MediaPacket` with `quality_report` is serialized and then encrypted with `ChaChaSession` (header as AAD, payload+QR as plaintext), tampering with any byte in the QR region causes AEAD decryption to fail.

## Why these choices

The `MediaPacket::to_bytes()` serialization already places the `QualityReport` trailer immediately after the payload in the same contiguous buffer. The `ChaChaSession::encrypt` API already accepts `header_bytes` as AAD and `plaintext` as the message to seal. Therefore the existing architecture naturally supports the desired ordering:

1. `MediaHeader` → serialized as AAD
2. `payload || QualityReport` → serialized as plaintext
3. AEAD-seal over (plaintext, AAD)

No production code changes were required because there is no live media encryption path in `cli.rs` today (`_crypto_session` is derived but discarded). The task’s goal was to verify the API boundary and add a regression test so that when a future task wires encryption into the send loop, the QR will automatically sit inside the AEAD payload.

## Deviations from the task spec

None. Followed steps T1.7.1 through T1.7.5 without deviation. Step 3 (“If currently appended after AEAD seal: refactor”) was a no-op because no production path appends the QR after encryption.

## Verification output

```bash
$ cargo test -p wzp-client quality_report_aead
running 1 test
test call::tests::quality_report_aead_tamper_fails_decrypt ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 169 filtered out; finished in 0.00s
```

```bash
$ cargo test -p wzp-crypto
running 36 tests
...(all 36 pass)...

test result: ok. 36 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.03s
```

## Test summary

- Tests added: 1 (`quality_report_aead_tamper_fails_decrypt`)
- Tests modified: 0
- Workspace test count before: 571 / after: 572 (1 added in `wzp-client`)
- `cargo clippy --workspace --all-targets -- -D warnings`: pass in crates touched (`wzp-client`, `wzp-crypto`); 12 known-debt errors in `wzp-codec` + `warzone-protocol` (see PROTOCOL-AUDIT.md)
- `cargo fmt --all -- --check`: pass

## Risks / follow-ups

- No production media encryption path exists yet. When one is added (likely in a future wave), the send loop must pass `pkt.to_bytes()[MediaHeader::WIRE_SIZE..]` as the plaintext to `CryptoSession::encrypt` and `pkt.header.to_bytes()` as AAD. The `analyzer.rs` replay decrypt path already follows this pattern.
- Mini-frame compression (`encode_compact`) does not carry `quality_report` by design (mini frames are payload-only deltas). This is acceptable because quality reports are sent on full frames, which the encoder already does.

## 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