77 lines
3.0 KiB
Markdown
77 lines
3.0 KiB
Markdown
# T3.2 — Document `timestamp_ms` rebase across rekey (W3)
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**Status:** Pending Review
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**Agent:** Kimi Code CLI
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**Started:** 2026-05-11T21:15Z
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**Completed:** 2026-05-11T21:25Z
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**Commit:** (see git log)
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**PRD:** ../PRD-protocol-hardening.md
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## What I changed
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- `crates/wzp-proto/src/packet.rs` — Updated doc comment on `MediaHeader::timestamp`:
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```rust
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/// Milliseconds since session start. Monotonic for the full session lifetime;
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/// NOT reset by rekey (rekey changes only key material, not framing state).
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pub timestamp: u32,
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```
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- `crates/wzp-crypto/src/rekey.rs` — Added inline comment on `perform_rekey()`:
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```rust
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/// NOTE: Rekeying changes **only** the symmetric key material. Sequence
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/// numbers and timestamps in the media framing layer (e.g. `MediaHeader`)
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/// are untouched — they continue monotonically across the rekey boundary.
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```
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- `docs/WZP-SPEC.md` — Updated `timestamp_ms` field description:
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```
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| timestamp_ms | 32 | ms since session start. Monotonic across the full session; **not reset by rekey** |
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```
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- `crates/wzp-client/tests/long_session.rs` — Added `rekey_timestamp_monotonic` test:
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- Simulates a 3000-frame session with two conceptual rekey boundaries at frames 1000 and 2000.
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- Collects all `MediaHeader::timestamp` values across the three phases.
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- Asserts strict monotonicity (non-decreasing) with `windows(2)`.
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- Sanity-checks that at least 3000 timestamps were collected.
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## Why these choices
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The test uses `CallEncoder` (which owns `timestamp_ms`) rather than `ChaChaSession` (which owns `RekeyManager`) because the property we care about is at the **framing layer**: regardless of what happens in crypto, the media header timestamps must not jump backwards or reset. `CallEncoder` is the component that actually emits timestamps, and it has no knowledge of rekeying — which is exactly the invariant we want to verify.
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## Deviations from the task spec
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None.
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## Verification output
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```bash
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$ cargo test -p wzp-client --test long_session
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running 4 tests
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test rekey_timestamp_monotonic ... ok
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test long_session_no_drift ... ok
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test long_session_with_simulated_loss ... ok
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test long_session_stats_consistency ... ok
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test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 14.62s
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```
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## Test summary
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- Tests added: 1
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- `rekey_timestamp_monotonic` — 3000-frame session, two rekey boundaries, verifies timestamp monotonicity
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- Tests modified: 0
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- `wzp-client` integration test count: 4 (was 3 before T3.2)
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- `cargo fmt --all -- --check`: pass
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## Risks / follow-ups
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- The test simulates rekeys conceptually (phase boundaries) rather than invoking `RekeyManager::perform_rekey()` directly. This is correct because `CallEncoder` doesn't touch crypto state; a more integration-level test could be added later if the encoder/decoder ever gains explicit rekey hooks.
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## Reviewer checklist (filled in by reviewer)
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- [ ] Code matches PRD intent
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- [ ] Verification output is real
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- [ ] No backward-incompat surprises
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- [ ] Tests cover the new behavior
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- [ ] Approved
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