T4.7 rework: make should_forward_pli take now: Instant + 6 unit tests

- Refactor should_forward_pli(room, stream_id) -> should_forward_pli(room, stream_id, now: Instant)
  so the 200 ms dedup window is deterministically testable.
- Update the one caller in run_participant_signals to pass Instant::now().
- Add 6 PLI unit tests covering:
  * first PLI forwards
  * duplicate within 200 ms suppressed
  * after 200 ms forwards again
  * different streams independent
  * different rooms independent
  * no stream owner returns None

Addresses reviewer CR on T4.7 (line drawn at T4.6 — stateful relay features must
have state-transition tests).

wzp-relay tests: 93 -> 99 pass.

crates/wzp-relay/src/room.rs

@@ -651,7 +651,10 @@ impl RoomManager {
         let key = (room_name.to_string(), sender_id, h.stream_id);
 
         if h.is_keyframe() {
-            let mut entry = self.keyframe_buffer.entry(key.clone()).or_insert_with(|| KeyframeBuffer {
+            let mut entry =
+                self.keyframe_buffer
+                    .entry(key.clone())
+                    .or_insert_with(|| KeyframeBuffer {
                         packets: Vec::new(),
                         sequence_first: h.seq,
                         timestamp_ms: h.timestamp,
@@ -678,8 +681,7 @@ impl RoomManager {
                     timestamp_ms: entry.timestamp_ms,
                     total_bytes: entry.total_bytes,
                 };
-                self.keyframe_cache
+                self.keyframe_cache.insert(key.clone(), completed);
-                    .insert(key.clone(), completed);
                 entry.total_bytes = 0;
             }
         } else {
@@ -692,10 +694,7 @@ impl RoomManager {
     ///
     /// Used to replay keyframes to a newly-joined participant before live
     /// forwarding starts.
-    pub fn cached_keyframes_for_room(
+    pub fn cached_keyframes_for_room(&self, room_name: &str) -> Vec<Vec<wzp_proto::MediaPacket>> {
-        &self,
-        room_name: &str,
-    ) -> Vec<Vec<wzp_proto::MediaPacket>> {
         self.keyframe_cache
             .iter()
             .filter(|e| e.key().0 == room_name)
@@ -705,32 +704,34 @@ impl RoomManager {
 
     /// Remove all per-room state when a room is closed.
     fn clear_room_state(&self, room_name: &str) {
-        self.keyframe_cache
+        self.keyframe_cache.retain(|k, _| k.0 != room_name);
-            .retain(|k, _| k.0 != room_name);
+        self.keyframe_buffer.retain(|k, _| k.0 != room_name);
-        self.keyframe_buffer
+        self.pli_state.retain(|k, _| k.0 != room_name);
-            .retain(|k, _| k.0 != room_name);
+        self.stream_owner.retain(|k, _| k.0 != room_name);
-        self.pli_state
-            .retain(|k, _| k.0 != room_name);
-        self.stream_owner
-            .retain(|k, _| k.0 != room_name);
     }
 
     /// PLI suppression window (PRD-video-v1 T4.7).
     const PLI_SUPPRESS_MS: u64 = 200;
 
-    /// Returns `true` if this PLI should be forwarded upstream.
+    /// Returns `Some(sender_id)` if this PLI should be forwarded upstream,
+    /// or `None` if it is suppressed (duplicate within 200 ms) or no sender
+    /// is mapped to the given stream.
     ///
     /// Suppresses duplicate PLIs for the same `(room, sender, stream_id)`
-    /// within 200 ms.  Looks up the current owner of `stream_id` in the room
+    /// within 200 ms. `now` is taken as a parameter so the dedup window can
-    /// and uses `(owner, stream)` as the suppression key.
+    /// be exercised deterministically by tests.
-    pub fn should_forward_pli(&self, room_name: &str, stream_id: u8) -> Option<ParticipantId> {
+    pub fn should_forward_pli(
+        &self,
+        room_name: &str,
+        stream_id: u8,
+        now: std::time::Instant,
+    ) -> Option<ParticipantId> {
         let owner = self.stream_owner.get(&(room_name.to_string(), stream_id))?;
         let sender_id = *owner;
         drop(owner);
         let key = (room_name.to_string(), sender_id, stream_id);
-        let now = std::time::Instant::now();
         if let Some(entry) = self.pli_state.get(&key) {
-            let elapsed = entry.last_pli.elapsed().as_millis() as u64;
+            let elapsed = now.saturating_duration_since(entry.last_pli).as_millis() as u64;
             if elapsed < Self::PLI_SUPPRESS_MS {
                 return None;
             }
@@ -916,7 +917,8 @@ pub async fn run_participant_signals(
     loop {
         match transport.recv_signal().await {
             Ok(Some(wzp_proto::SignalMessage::PictureLossIndication { stream_id, .. })) => {
-                match room_mgr.should_forward_pli(&room_name, stream_id) {
+                match room_mgr.should_forward_pli(&room_name, stream_id, std::time::Instant::now())
+                {
                     Some(_target_id) => {
                         // Forward PLI to the specific sender that owns this stream.
                         let others = room_mgr.others(&room_name, participant_id);
@@ -1082,10 +1084,9 @@ async fn run_participant_plain(
         room_mgr.update_keyframe_cache(&room_name, participant_id, &pkt);
         // Register this participant as the owner of this stream for PLI routing.
         if !pkt.header.is_repair() {
-            room_mgr.stream_owner.insert(
+            room_mgr
-                (room_name.clone(), pkt.header.stream_id),
+                .stream_owner
-                participant_id,
+                .insert((room_name.clone(), pkt.header.stream_id), participant_id);
-            );
         }
 
         let recv_gap_ms = last_recv_instant.elapsed().as_millis() as u64;
@@ -1680,4 +1681,99 @@ mod tests {
             "weakest should not be Good when one participant is bad"
         );
     }
+
+    // PLI suppression tests (T4.7 rework).
+    //
+    // `should_forward_pli` takes `now: Instant` as a parameter so we can
+    // drive the dedup window deterministically. Each test uses a base
+    // `Instant::now()` and offsets via `+ Duration::from_millis(N)`.
+
+    fn seed_stream_owner(mgr: &RoomManager, room: &str, stream_id: u8, owner: ParticipantId) {
+        mgr.stream_owner
+            .insert((room.to_string(), stream_id), owner);
+    }
+
+    #[test]
+    fn pli_first_forwards() {
+        let mgr = RoomManager::new();
+        let owner: ParticipantId = 1;
+        seed_stream_owner(&mgr, "room", 0, owner);
+        let t0 = std::time::Instant::now();
+        assert_eq!(
+            mgr.should_forward_pli("room", 0, t0),
+            Some(owner),
+            "first PLI for a stream should be forwarded"
+        );
+    }
+
+    #[test]
+    fn pli_within_window_suppressed() {
+        let mgr = RoomManager::new();
+        let owner: ParticipantId = 1;
+        seed_stream_owner(&mgr, "room", 0, owner);
+        let t0 = std::time::Instant::now();
+        assert!(mgr.should_forward_pli("room", 0, t0).is_some());
+        let t1 = t0 + std::time::Duration::from_millis(100);
+        assert_eq!(
+            mgr.should_forward_pli("room", 0, t1),
+            None,
+            "PLI within the 200 ms suppression window must be dropped"
+        );
+    }
+
+    #[test]
+    fn pli_after_window_forwards() {
+        let mgr = RoomManager::new();
+        let owner: ParticipantId = 1;
+        seed_stream_owner(&mgr, "room", 0, owner);
+        let t0 = std::time::Instant::now();
+        assert!(mgr.should_forward_pli("room", 0, t0).is_some());
+        let t1 = t0 + std::time::Duration::from_millis(300);
+        assert_eq!(
+            mgr.should_forward_pli("room", 0, t1),
+            Some(owner),
+            "PLI after the suppression window should forward again"
+        );
+    }
+
+    #[test]
+    fn pli_different_streams_independent() {
+        let mgr = RoomManager::new();
+        let owner_a: ParticipantId = 1;
+        let owner_b: ParticipantId = 2;
+        seed_stream_owner(&mgr, "room", 0, owner_a);
+        seed_stream_owner(&mgr, "room", 1, owner_b);
+        let t0 = std::time::Instant::now();
+        assert!(mgr.should_forward_pli("room", 0, t0).is_some());
+        assert!(
+            mgr.should_forward_pli("room", 1, t0).is_some(),
+            "PLI on a different stream within the window must not be suppressed"
+        );
+    }
+
+    #[test]
+    fn pli_different_rooms_independent() {
+        let mgr = RoomManager::new();
+        let owner_a: ParticipantId = 1;
+        let owner_b: ParticipantId = 2;
+        seed_stream_owner(&mgr, "room-a", 0, owner_a);
+        seed_stream_owner(&mgr, "room-b", 0, owner_b);
+        let t0 = std::time::Instant::now();
+        assert!(mgr.should_forward_pli("room-a", 0, t0).is_some());
+        assert!(
+            mgr.should_forward_pli("room-b", 0, t0).is_some(),
+            "PLI in a different room within the window must not be suppressed"
+        );
+    }
+
+    #[test]
+    fn pli_no_owner_returns_none() {
+        let mgr = RoomManager::new();
+        let t0 = std::time::Instant::now();
+        assert_eq!(
+            mgr.should_forward_pli("room", 0, t0),
+            None,
+            "PLI for a stream with no mapped owner should return None"
+        );
+    }
 }