feat(lint): dense motion re-sampling for content_overlap (#2746)

* feat(lint): dense motion re-sampling for content_overlap

Transient text-on-text collisions during continuous motion (e.g. an
orbiting label card crossing the center card) overlap for a fraction of
a second that the sparse 9-point layout grid seeks straight past. The
content_overlap detector is correct; it just never gets a sample at the
crossing moment. Rerun ONLY content_overlap on an 8fps grid (text-only,
cheap) when the composition animates; findings feed the existing
persistence tiering unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(lint): unconditional dense content_overlap pass + honor 500ms floor

Round-1 blocker: the dense motion-overlap re-pass was gated on sparse-grid
geometry fingerprints changing, so an animation aliased to the sparse grid
(identical fingerprints, yet colliding between samples) bypassed the pass —
exactly the transient false-negative it was built to catch. Remove the gate:
the dense pass now runs unconditionally (bounded, text-only), driven by the
composition timeline rather than a fingerprint heuristic.

Round-2 follow-ups:
- Persistence-tier drift: at 8fps, occurrences>=2 spans only ~125ms, not the
  ~500ms the design intends, and it short-circuited before the ms floor.
  content_overlap promotion now requires BOTH occurrences>=2 AND a literal
  firstSeen..lastSeen span >= 500ms, so the wall-clock floor is honored at any
  sampling density. Comment block updated to match.
- Sample cap scales to hold a true 8fps grid up to ~75s (raised 120 -> 600)
  with an explicit note that longer comps degrade below 8fps to stay bounded.

Tests:
- Replaced the trivial "warning at every sample" test with a real between-grid
  regression: a collision living only inside (3.5,4.5) — a gap the sparse grid
  seeks past — is detected and, held ~750ms, promoted to error.
- Replaced the now-invalid "skips when static" test with one asserting the
  dense pass runs even when sparse fingerprints are identical (aliased motion).
- Added a tiering regression: two dense occurrences spanning ~125ms stay a
  warning (not error). Both new guards verified red before the fix.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* perf(lint): settle-free geometry seek for dense content_overlap pass

The dense overlap re-pass did up to OVERLAP_MAX_SAMPLES full-settle seeks
(120ms paint settle each, ~72s of pure sleep at the ceiling) even though
collectOverlap only reads getBoundingClientRect geometry, valid
synchronously after the timeline setTime. Add a settle-free
DENSE_GEOMETRY_SEEK_OPTIONS + driver.seekGeometry used only by the dense
loop; the base grid keeps full-settle driver.seek.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* test(lint): document + cover content_overlap 500ms boundary for sparse callers

The occurrences>=2 AND heldMs>=500 promotion rule is a semantics change for
sparse callers (--samples 20, --at, short comps) whose two samples can land
<500ms apart. Document the change in the tiering comment and add boundary
tests: 499ms span stays warning, 500ms span promotes to error.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* fix(lint): make dense content_overlap seek genuinely geometry-only

Per review: DENSE_GEOMETRY_SEEK_OPTIONS only overrode settleMs, still
inheriting animationFrameSettle:double + waitForFontsMs:500 → ~3 frame
waits + font wait per seek → ~30s at the 600-sample cap. Geometry
(getBoundingClientRect) is valid synchronously post-setTime, so drop all
post-seek waits (animationFrameSettle:none, waitForFontsMs:0, settleMs:0).
Add options-level regression locking the geometry-only contract. Also fix
a stale comment name (detectMotionTextOverlap → collectMotionOverlapSamples).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

* style: collapse multi-line comments to single lines

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

packages/cli/src/utils/checkPipeline.ts

@@ -417,9 +417,42 @@ async function collectGridSamples(
       collected.screenshots.push({ time, pngBase64: capture.pngBase64 });
     }
   }
+  await collectMotionOverlapSamples(driver, grid, collected);
   return collected;
 }
 
+// Dense grid catches mid-motion text collisions the sparse layout grid seeks past; text-only overlap collection is cheap enough to afford it.
+const OVERLAP_SAMPLE_FPS = 8;
+// Ceiling that bounds dense seeks; past ~75s the grid degrades below 8fps rather than growing the seek budget without limit.
+const OVERLAP_MAX_SAMPLES = 600;
+
+function buildOverlapSampleTimes(duration: number): number[] {
+  if (!Number.isFinite(duration) || duration <= 0) return [];
+  const count = Math.min(
+    OVERLAP_MAX_SAMPLES,
+    Math.max(2, Math.ceil(duration * OVERLAP_SAMPLE_FPS) + 1),
+  );
+  const step = duration / (count - 1);
+  return mergeSampleTimes(
+    Array.from({ length: count }, (_, index) => Math.round(index * step * 1000) / 1000),
+  );
+}
+
+/** Reruns content_overlap on a fine grid, unconditionally rather than gated on fingerprint change, since an animation aliased to the sparse grid collides between identical-fingerprint samples. */
+async function collectMotionOverlapSamples(
+  driver: CheckAuditDriver,
+  grid: SampleGrid,
+  collected: GridSamples,
+): Promise<void> {
+  const baseTimes = new Set(grid.layoutSamples);
+  for (const time of buildOverlapSampleTimes(grid.duration)) {
+    if (baseTimes.has(time)) continue;
+    // Settle-free seek: collectOverlap reads getBoundingClientRect geometry, valid synchronously after setTime, so the dense pass skips the per-seek paint settle.
+    await driver.seekGeometry(time);
+    collected.layoutIssues.push(...(await driver.collectOverlap(time)));
+  }
+}
+
 // Frozen-sweep guard (#U10): compositions this short can legitimately hold a
 // single static frame the whole time (a title card) — never flag those.
 const SWEEP_STATIC_MIN_DURATION_SEC = 3;