fix(lab): stabilize recorded spatial playback

apps/control-station/test/m4ReplayThreat.test.mjs

@@ -12,6 +12,7 @@ let fetchM4ThreatTimelineChunk;
 let selectM4ThreatTimelineFrame;
 let selectM4ThreatTimelineSequence;
 let advanceRecordedEvidencePlayback;
+let m4ThreatChunkWindowStarts;
 
 const resultId = `m4-threat-replay-${"a".repeat(64)}`;
 
@@ -32,6 +33,9 @@ before(async () => {
   ({ advanceRecordedEvidencePlayback } = await server.ssrLoadModule(
     "/src/components/laboratory/useRecordedEvidencePlayback.ts",
   ));
+  ({ m4ThreatChunkWindowStarts } = await server.ssrLoadModule(
+    "/src/workspaces/laboratory/useM4ThreatTimeline.ts",
+  ));
 });
 
 after(async () => {
@@ -243,6 +247,7 @@ test("M4.6 timeline keeps only a compact index and decodes bounded spatial chunk
     recorded_source: {
       session_id: "20260720T065719Z_viewer_live",
       source_id: "RAVNOVES00",
+      representation_id: "registered-map-increment-v1",
       synchronization: "host-arrival-best-effort",
     },
       image_width: 800,
@@ -254,18 +259,24 @@ test("M4.6 timeline keeps only a compact index and decodes bounded spatial chunk
       nominal_frame_interval_seconds: 0.1,
       nominal_rate_hz: 10,
       max_chunk_frames: 24,
-      point_sample_limit: 2000,
+      point_sample_limit: 4096,
+      maximum_source_points_per_frame: 3092,
+      point_delivery: "exact-current-increment",
       rig: { length_m: 1, width_m: 0.6, nominal_sensor_height_m: 1.25 },
       corridor: {
         forward_length_m: 8,
         rear_margin_m: 0.5,
         half_width_m: 0.5,
+        occupied_voxel_size_m: 0.45,
         prediction_horizon_seconds: 5,
       },
       authority: "replay-simulated",
     }), { status: 200 }),
   });
   assert.equal(timeline.frameTimesNs.length, 4489);
+  assert.equal(timeline.pointDelivery, "exact-current-increment");
+  assert.equal(timeline.maximumSourcePointsPerFrame, 3092);
+  assert.equal(timeline.occupiedVoxelSizeM, 0.45);
   assert.equal(selectM4ThreatTimelineSequence(timeline.frameTimesNs, 35.50), 1);
 
   const chunk = await fetchM4ThreatTimelineChunk(resultId, 0, 2, {
@@ -289,6 +300,11 @@ test("M4.6 timeline keeps only a compact index and decodes bounded spatial chunk
   assert.equal(selectM4ThreatTimelineFrame(chunk.frames, 35.50).sequence, 1);
 });
 
+test("M4.6 spatial buffering keeps previous, active and two future chunks", () => {
+  assert.deepEqual(m4ThreatChunkWindowStarts(48, 24, 4489), [24, 48, 72, 96]);
+  assert.deepEqual(m4ThreatChunkWindowStarts(0, 24, 4489), [0, 24, 48]);
+});
+
 test("recorded evidence clock advances by selected rate and stops at the sealed end", () => {
   const range = { startSeconds: 10, endSeconds: 20 };
   assert.deepEqual(
@@ -319,6 +335,8 @@ test("M4.6 viewer reuses shared camera, video and metric evidence renderers", as
   assert.match(visual, /<RecordedEvidenceVideoScene/);
   assert.match(visual, /<RecordedEvidenceImageScene/);
   assert.match(visual, /<LaboratoryMetricEvidenceScene/);
+  assert.match(visual, /m4-replay-threat-visual__deck/);
+  assert.match(visual, /lastFrameRef/);
   assert.match(visual, /<ObservationTimeline/);
   assert.match(visual, /useM4ThreatTimelineFrame/);
   assert.match(visual, /label: "VIDEO"/);