feat(testing): add max_frames parameter to E2EHarness

Caps the iteration length (and the matching GT slice) when set, so CI
tiers can stay fast on multi-thousand-frame sequences like EuRoC MH_01
(3682 frames ≈ 3+ hours at 3-5s/frame). Also useful for eyeballing a
new adapter's first N frames before committing to a full run.

Three new harness tests cover truncation, explicit None, and over-large
limits. No change to existing adapters or downstream tests.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/e2e/test_harness_smoke.py

@@ -35,3 +35,32 @@ async def test_harness_captures_ground_truth_as_enu():
     east_disp = result.ground_truth[-1, 0] - result.ground_truth[0, 0]
     # Allow 5% tolerance for the lat/lon → ENU conversion approximation
     assert abs(east_disp - 4.0) < 0.5
+
+
+@pytest.mark.asyncio
+async def test_harness_max_frames_truncates_iteration():
+    # Adapter says 10 frames; harness with max_frames=3 should stop at 3.
+    adapter = SyntheticAdapter(num_frames=10, fps=5.0)
+    harness = E2EHarness(adapter, max_frames=3)
+    result = await harness.run()
+    assert result.num_frames_submitted == 3
+    # GT aligned to the same truncation so downstream metrics match lengths
+    assert result.ground_truth.shape[0] == 3
+
+
+@pytest.mark.asyncio
+async def test_harness_max_frames_none_runs_full():
+    # Explicit None = no limit (same as omitting the parameter).
+    adapter = SyntheticAdapter(num_frames=4, fps=5.0)
+    harness = E2EHarness(adapter, max_frames=None)
+    result = await harness.run()
+    assert result.num_frames_submitted == 4
+
+
+@pytest.mark.asyncio
+async def test_harness_max_frames_larger_than_dataset_is_harmless():
+    # Limit above dataset size should not over-extend.
+    adapter = SyntheticAdapter(num_frames=4, fps=5.0)
+    harness = E2EHarness(adapter, max_frames=100)
+    result = await harness.run()
+    assert result.num_frames_submitted == 4