fix(perception): isolate recorded decode from realtime admission

tests/test_perception_graph.py

@@ -62,9 +62,12 @@ from k1link.perception.providers import (
 from k1link.perception.recorded_source import (
     DecodedFrameTiming,
     DecodedRecordedSource,
+    DecodePhase,
+    PrefetchedRecordedImageDecoder,
     RecordedRavnoves00Source,
     RecordedSourceError,
     ReplayPacing,
+    SourcePacingTiming,
 )
 
 
@@ -839,6 +842,7 @@ def test_recorded_source_target_rate_changes_only_wall_clock_pacing(tmp_path: Pa
     camera_path, timeline_path = _write_recorded_fixture(tmp_path)
     now = [1_000_000_000]
     waits: list[float] = []
+    pacing: list[SourcePacingTiming] = []
 
     def wait(stop_event: Event, seconds: float) -> bool:
         waits.append(seconds)
@@ -852,6 +856,7 @@ def test_recorded_source_target_rate_changes_only_wall_clock_pacing(tmp_path: Pa
         target_rate_hz=20.0,
         expected_frame_count=2,
         expected_source_pack_sha256=None,
+        pacing_observer=pacing.append,
         clock_ns=lambda: now[0],
         wait=wait,
     )
@@ -859,6 +864,8 @@ def test_recorded_source_target_rate_changes_only_wall_clock_pacing(tmp_path: Pa
     packets = list(source.packets(Event()))
 
     assert waits == pytest.approx([0.05])
+    assert [sample.sequence for sample in pacing] == [0, 1]
+    assert [sample.lateness_ns for sample in pacing] == [0, 0]
     assert (
         packets[1].envelope.timestamps.source_ns
         - packets[0].envelope.timestamps.source_ns
@@ -879,6 +886,44 @@ def test_recorded_source_rejects_target_rate_for_uncapped_replay(tmp_path: Path)
         )
 
 
+def test_prefetched_decoder_moves_cold_decode_before_source_admission() -> None:
+    observed: list[DecodedFrameTiming] = []
+
+    class Decoder:
+        def frames(self, stop_event: Event) -> Iterator[np.ndarray]:
+            for index in range(4):
+                if stop_event.is_set():
+                    return
+                yield np.full((2, 3, 3), index, dtype=np.uint8)
+
+    decoder = PrefetchedRecordedImageDecoder(
+        Decoder(),
+        capacity_frames=2,
+        ready_frames=2,
+        timing_observer=observed.append,
+    )
+    stop_event = Event()
+
+    snapshot = decoder.prepare(stop_event)
+
+    assert snapshot.buffered_frames == 2
+    assert snapshot.capacity_frames == 2
+    assert [sample.phase for sample in observed] == [
+        DecodePhase.PREADMISSION,
+        DecodePhase.PREADMISSION,
+    ]
+    decoder.mark_admission_started()
+    frames = list(decoder.frames(stop_event))
+    decoder.close()
+
+    assert [int(frame[0, 0, 0]) for frame in frames] == [0, 1, 2, 3]
+    assert [sample.sequence for sample in observed] == [0, 1, 2, 3]
+    assert [sample.phase for sample in observed[2:]] == [
+        DecodePhase.HOT_LOOP,
+        DecodePhase.HOT_LOOP,
+    ]
+
+
 def test_recorded_source_rejects_timeline_mismatch(tmp_path: Path) -> None:
     camera_path, timeline_path = _write_recorded_fixture(tmp_path, mismatched=True)
     source = RecordedRavnoves00Source(