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 PictureLossIndications, 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

$ cargo build -p wzp-relay
Finished `dev` profile [unoptimized + debuginfo] target(s) in 13.12s

$ cargo test -p wzp-relay
test result: ok. 20 passed; 0 failed

$ cargo test --workspace --exclude wzp-video
# 656 tests passed

$ 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

Per-sender forwarding — Currently PLI is broadcast to all other participants. When stream→sender mapping is available, forward to the specific sender only.
No unit test — The 200 ms window is time-dependent. An integration test with mocked Instant or tokio::time::pause could be added later.
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

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