[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_09_inav.py

@@ -45,32 +45,6 @@ REPLAY_WINDOW_S = 60
 TCP_HANDSHAKE_BUDGET_S = 5
 
 
-@pytest.fixture(scope="module")
-def _inav_harness_implemented() -> bool:
-    """True iff frame_source_replay + sitl_observer iNav leg are real."""
-    from runner.helpers import sitl_observer
-    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:
-            sitl_observer.observe_inav_tcp_handshake(host="inav-sitl", port=5760, timeout_s=0.01)
-        except (NotImplementedError, AttributeError):
-            return False
-        return True
-    except Exception:
-        return False
-
-
-class _NullSink:
-    def write_frame(self, jpeg_bytes: bytes, timestamp_ms: int) -> None:
-        return None
-
-
 @pytest.mark.traces_to("AC-4.3,AC-1,AC-2,AC-3,AC-4")
 def test_ft_p_09_inav(
     vio_strategy: str,
@@ -78,7 +52,7 @@ def test_ft_p_09_inav(
     run_id: str,
     nfr_recorder,  # type: ignore[no-untyped-def]
     request,  # type: ignore[no-untyped-def]
-    _inav_harness_implemented: bool,
+    sitl_replay_ready: bool,
 ) -> None:
     """Full FT-P-09-iNav scenario; parameterized per vio_strategy.
 
@@ -90,12 +64,11 @@ def test_ft_p_09_inav(
     if fc_adapter != "inav":
         pytest.skip("FT-P-09-iNav is iNav-only; ardupilot variant is FT-P-09-AP (AZ-416)")
 
-    if not _inav_harness_implemented:
+    if not sitl_replay_ready:
         pytest.skip(
-            "FT-P-09-iNav full scenario requires runner.helpers.{frame_source_replay,"
-            "sitl_observer.observe_inav_tcp_handshake} — currently AZ-441 / AZ-407 leftovers. "
-            "Pure-logic AC-2/AC-3 covered by "
-            "e2e/_unit_tests/helpers/test_msp_frame_observer.py."
+            "FT-P-09-iNav full scenario requires `E2E_SITL_REPLAY_DIR` to "
+            "point at a prepared SITL replay fixture (AZ-595). Pure-logic "
+            "AC-2/AC-3 covered by e2e/_unit_tests/helpers/test_msp_frame_observer.py."
         )
 
     from runner.helpers import sitl_observer