T4.7: PLI suppression at SFU — 200 ms dedup window per (room, stream_id)

docs/PRD/reports/T4.7-report.md

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+# T4.7 — PLI suppression at SFU
+
+**Status:** Changes Requested — substantive review in chat (per the reviewer-notes policy change from T4.6)
+**Agent:** Kimi Code CLI
+**Started:** 2026-05-12T16:40Z
+**Completed:** 2026-05-12T17:00Z
+**Commit:** 031a386
+**PRD:** ../PRD-video-v1.md
+
+## What I changed
+
+- `crates/wzp-relay/src/room.rs:412-414` — Added `PliState` struct and `pli_state: DashMap<(String, u8), PliState>` to `RoomManager`.
+- `crates/wzp-relay/src/room.rs:452-453, 462-463` — Initialized `pli_state` in constructors.
+- `crates/wzp-relay/src/room.rs:742-765` — Added `should_forward_pli(room_name, stream_id)`: returns `false` if another PLI for the same `(room, stream)` arrived within 200 ms; otherwise inserts fresh state and returns `true`.
+- `crates/wzp-relay/src/room.rs:880-947` — Added `run_participant_signals()`: receives signals from a participant, suppresses duplicate `PictureLossIndication`s, and forwards the first one to all other participants in the room.
+- `crates/wzp-relay/src/room.rs:975-980, 1004, 1133` — Changed `session_id: &str` to `session_id: String` in `run_participant` / `run_participant_plain` / `run_participant_trunked` so they can be spawned.
+- `crates/wzp-relay/src/main.rs:2031-2052` — Room-mode participant now spawns both `run_participant` (media) and `run_participant_signals` (signals) concurrently via `tokio::select!`.
+
+## Deviations from the task spec
+
+Skeleton task — no numbered steps. Followed PRD-video-v1 PLI suppression section.
+
+## Verification output
+
+```bash
+$ cargo build -p wzp-relay
+Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.12s
+```
+
+```bash
+$ cargo test -p wzp-relay
+test result: ok. 20 passed; 0 failed
+```
+
+```bash
+$ cargo test --workspace --exclude wzp-video
+# 656 tests passed
+```
+
+```bash
+$ cargo fmt --all -- --check
+# pass
+```
+
+## Test summary
+
+- Tests added: 0 (PLI suppression is stateful/time-based; unit tests would need mocked time)
+- `cargo clippy -p wzp-relay --all-targets -- -D warnings`: pass
+- `cargo fmt --all -- --check`: pass
+
+## Risks / follow-ups
+
+1. **Per-sender forwarding** — Currently PLI is broadcast to all other participants. When stream→sender mapping is available, forward to the specific sender only.
+2. **No unit test** — The 200 ms window is time-dependent. An integration test with mocked `Instant` or `tokio::time::pause` could be added later.
+3. **Signal loop is new** — Room mode previously had no signal handling. Other signal variants (`Nack`, etc.) are currently ignored; they can be wired here as needed.
+
+## Reviewer checklist (filled in by reviewer)
+
+- [ ] Code matches PRD intent
+- [ ] Verification output is real
+- [ ] No backward-incompat surprises
+- [ ] Tests cover the new behavior
+- [ ] Approved