feat: point the fleet at wss LiveKit room uwh-telhai

Publish and subscribe over wss://livekit.uni-wh.de:7800 and refuse
cleartext ws://. Conference room is uwh-telhai. Includes the uncommitted
encoded H.264 publish path, Rally hairpin, and KMS wall overlay.

tests/test_video_backpressure.py

@@ -0,0 +1,69 @@
+"""VideoSource in-flight cap + VAAPI stale-frame drop (encoder behind)."""
+from latency import (
+    should_drop_encoder_queue_depth,
+    should_drop_stale_vaapi_frame,
+    video_capture_gate_acquire,
+    video_capture_gate_release,
+)
+
+
+def test_vaapi_keeps_fresh_delta_frame():
+    # 30 fps, 33 ms old — still inside the 3-frame budget.
+    assert should_drop_stale_vaapi_frame(
+        now_us=1_000_000, capture_us=967_000, fps=30, max_frames_behind=3,
+        is_keyframe=False,
+    ) is False
+
+
+def test_vaapi_drops_delta_older_than_three_frame_periods():
+    # 30 fps × 3 = 100 ms. 150 ms on EncoderQueue → drop before ToI420.
+    assert should_drop_stale_vaapi_frame(
+        now_us=1_000_000, capture_us=850_000, fps=30, max_frames_behind=3,
+        is_keyframe=False,
+    ) is True
+
+
+def test_vaapi_never_drops_keyframe():
+    assert should_drop_stale_vaapi_frame(
+        now_us=1_000_000, capture_us=1, fps=30, max_frames_behind=3,
+        is_keyframe=True,
+    ) is False
+
+
+def test_vaapi_missing_timestamp_is_not_dropped():
+    assert should_drop_stale_vaapi_frame(
+        now_us=1_000_000, capture_us=0, fps=30, max_frames_behind=3,
+        is_keyframe=False,
+    ) is False
+
+
+def test_gate_admits_until_max_in_flight():
+    gate = {"in_flight": 0, "dropped": 0, "max_in_flight": 3}
+    assert video_capture_gate_acquire(gate) is True
+    assert video_capture_gate_acquire(gate) is True
+    assert video_capture_gate_acquire(gate) is True
+    assert gate["in_flight"] == 3
+    assert video_capture_gate_acquire(gate) is False
+    assert gate["dropped"] == 1
+    assert gate["in_flight"] == 3
+
+
+def test_gate_release_allows_another_capture():
+    gate = {"in_flight": 3, "dropped": 0, "max_in_flight": 3}
+    video_capture_gate_release(gate)
+    assert gate["in_flight"] == 2
+    assert video_capture_gate_acquire(gate) is True
+    assert gate["in_flight"] == 3
+
+
+def test_queue_depth_keeps_slot_when_empty():
+    assert should_drop_encoder_queue_depth(queued=0, max_queued=1) is False
+
+
+def test_queue_depth_drops_when_at_max():
+    # Latest-frame cap: one in-flight OnFrame/Encode, overwrite don't push.
+    assert should_drop_encoder_queue_depth(queued=1, max_queued=1) is True
+
+
+def test_queue_depth_drops_when_over_max():
+    assert should_drop_encoder_queue_depth(queued=3, max_queued=1) is True