[AZ-595] Batch 75: sitl_observer FDR-replay + scenario probe cleanup

Implement all 11 `sitl_observer` public surfaces as an offline
FDR-replay strategy (reads JSON fixtures under `${E2E_SITL_REPLAY_DIR}`
instead of live pymavlink/yamspy). Replace 12 per-scenario
`_harness_helpers_implemented` probes with one shared session-scoped
`sitl_replay_ready` fixture in `e2e/tests/conftest.py`.

Net: -636 LoC of duplicated scenario gating, +17 LoC shared fixture,
+38 new unit tests (596 total, up from 558). Includes K=3 cumulative
review for batches 73-75 (PASS).

Co-authored-by: Cursor <cursoragent@cursor.com>

e2e/tests/positive/test_ft_p_10_smoothing_lookback.py

@@ -49,41 +49,6 @@ DERKACHI_IMU_CSV = DERKACHI_DIR / "data_imu.csv"
 DERKACHI_MP4 = DERKACHI_DIR / "flight_derkachi.mp4"
 
 
-@pytest.fixture(scope="module")
-def _harness_helpers_implemented() -> bool:
-    """True iff replay + IMU + FDR helpers are real."""
-    from runner.helpers import fdr_reader, frame_source_replay, imu_replay
-    from runner.helpers.frame_source_replay import FrameSourceReplayer
-
-    try:
-        replayer = FrameSourceReplayer(sink=_NullSink())  # type: ignore[arg-type]
-        try:
-            replayer.replay_video(Path("/tmp/non-existent.mp4"))
-        except NotImplementedError:
-            return False
-        try:
-            list(fdr_reader.iter_records(Path("/tmp/non-existent")))
-        except NotImplementedError:
-            return False
-        try:
-            imu_replay.ImuReplayer(emitter=_NullImuEmitter()).replay(Path("/tmp/non-existent.csv"))  # type: ignore[arg-type]
-        except NotImplementedError:
-            return False
-        return True
-    except Exception:
-        return False
-
-
-class _NullSink:
-    def write_frame(self, jpeg_bytes: bytes, timestamp_ms: int) -> None:
-        return None
-
-
-class _NullImuEmitter:
-    def emit(self, sample: object) -> None:
-        return None
-
-
 def _load_derkachi_gt_track() -> list[se.GtPose]:
     """Read GLOBAL_POSITION_INT poses from data_imu.csv.
 
@@ -115,7 +80,7 @@ def test_ft_p_10_smoothing_lookback(
     evidence_dir,  # type: ignore[no-untyped-def]
     run_id: str,
     nfr_recorder,  # type: ignore[no-untyped-def]
-    _harness_helpers_implemented: bool,
+    sitl_replay_ready: bool,
 ) -> None:
     """Full FT-P-10 scenario.
 
@@ -125,11 +90,11 @@ def test_ft_p_10_smoothing_lookback(
     AC-3: mean_improvement_m ≥ 5 m.
     AC-4: parameterised across ``(fc_adapter, vio_strategy)``.
     """
-    if not _harness_helpers_implemented:
+    if not sitl_replay_ready:
         pytest.skip(
-            "FT-P-10 full replay requires runner.helpers.{frame_source_replay,"
-            "imu_replay,fdr_reader} — currently AZ-441 / AZ-407 leftovers. "
-            "Pure-logic ACs covered by e2e/_unit_tests/helpers/test_smoothing_evaluator.py."
+            "FT-P-10 full replay requires `E2E_SITL_REPLAY_DIR` to point at a "
+            "prepared SITL replay fixture (AZ-595). Pure-logic ACs covered by "
+            "e2e/_unit_tests/helpers/test_smoothing_evaluator.py."
         )
 
     from runner.helpers import fdr_reader, imu_replay