T1.4: Add v2 MiniHeader with seq_delta

docs/PRD/reports/T1.4-report.md

@@ -0,0 +1,92 @@
+# T1.4 — Add v2 `MiniHeader` with `seq_delta`
+
+**Status:** Pending Review
+**Agent:** Kimi Code CLI
+**Started:** 2026-05-11T07:12Z
+**Completed:** 2026-05-11T07:16Z
+**Commit:** see git log
+**PRD:** ../PRD-wire-format-v2.md
+
+## What I changed
+
+- `crates/wzp-proto/src/packet.rs:580-611` — renamed `MiniHeader` → `MiniHeaderV1`, kept all impls intact
+- `crates/wzp-proto/src/packet.rs:613` — added `pub type MiniHeader = MiniHeaderV1;` backward-compat alias
+- `crates/wzp-proto/src/packet.rs:616-640` — added new `MiniHeaderV2` struct (5 bytes: `seq_delta` + `timestamp_delta_ms` + `payload_len`) with `write_to`/`read_from`
+- `crates/wzp-proto/src/packet.rs:642-666` — renamed `MiniFrameContext` → `MiniFrameContextV1`, kept all impls intact
+- `crates/wzp-proto/src/packet.rs:668` — added `pub type MiniFrameContext = MiniFrameContextV1;` backward-compat alias
+- `crates/wzp-proto/src/packet.rs:670-695` — added new `MiniFrameContextV2` tracking `MediaHeaderV2` baseline, with `update` and `expand` using explicit `seq_delta`
+- `crates/wzp-proto/src/lib.rs:31` — re-exported `MiniHeaderV1`, `MiniHeaderV2`, `MiniFrameContextV1`, `MiniFrameContextV2`
+- `crates/wzp-proto/src/packet.rs:1968-2014` — added 3 v2 tests: `mini_header_v2_roundtrip`, `mini_frame_context_v2_expand`, `mini_frame_context_v2_no_baseline`
+
+## Why these choices
+
+Same naming collision as T1.1: Rust does not allow a type alias and a struct with the same name in the same module. The new structs are named `MiniHeaderV2` and `MiniFrameContextV2` with temporary aliases preserving the old names; T1.5 will delete the v1 types and rename.
+
+The v2 `MiniFrameContextV2::expand` uses `base.seq.wrapping_add(m.seq_delta as u32)` instead of the hard-coded `wrapping_add(1)` from v1, which resolves audit W4 (a missed full header no longer desyncs the sequence).
+
+## Deviations from the task spec
+
+1. **Step 2 / Step 3 (struct names):** The new mini struct is `MiniHeaderV2` and the new context is `MiniFrameContextV2` instead of `MiniHeader` / `MiniFrameContext`. Required because `pub type MiniHeader = MiniHeaderV1;` and `pub type MiniFrameContext = MiniFrameContextV1;` occupy the base names. T1.5 will resolve.
+
+## Verification output
+
+```bash
+$ cargo test -p wzp-proto mini
+running 12 tests
+test packet::tests::full_vs_mini_size_comparison ... ok
+test packet::tests::mini_frame_context_expand ... ok
+test packet::tests::mini_frame_context_no_baseline ... ok
+test packet::tests::mini_frame_context_v2_expand ... ok
+test packet::tests::mini_frame_context_v2_no_baseline ... ok
+test packet::tests::mini_frame_disabled ... ok
+test packet::tests::mini_frame_encode_decode_sequence ... ok
+test packet::tests::mini_frame_periodic_full ... ok
+test packet::tests::mini_header_encode_decode ... ok
+test packet::tests::mini_header_v2_roundtrip ... ok
+test packet::tests::mini_header_wire_size ... ok
+test packet::tests::candidate_update_minimal_roundtrip ... ok
+
+test result: ok. 12 passed; 0 failed; 0 ignored; 0 measured; 100 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 15.71s
+```
+
+```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. 571 passed; 0 failed; ...
+```
+
+```bash
+$ cargo clippy -p wzp-proto --all-targets -- -D warnings
+    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.19s
+```
+
+```bash
+$ cargo fmt --all -- --check
+# (clean)
+```
+
+## Test summary
+
+- Tests added: 3 (`mini_header_v2_roundtrip`, `mini_frame_context_v2_expand`, `mini_frame_context_v2_no_baseline`)
+- Tests modified: 0
+- Workspace test count before: 568 pass / 0 fail (non-Android subset)
+- Workspace test count after: 571 pass / 0 fail (non-Android subset)
+- `cargo clippy -p wzp-proto --all-targets -- -D warnings`: pass
+- `cargo fmt --all -- --check`: pass
+
+## Risks / follow-ups
+
+- `MiniHeaderV2` / `MiniFrameContextV2` must be renamed to `MiniHeader` / `MiniFrameContext` in T1.5 after v1 types are deleted.
+
+## 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