[AZ-398] Replay: FrameSource + Clock Protocols + Clock injection

Ship the two Layer-1 cross-cutting Protocols replay mode needs to leave
production C1-C5 components mode-agnostic (Invariant 1) and replay-
deterministic (Invariant 2). Live + replay binaries see the same
interfaces; only the strategy differs.

* Clock Protocol (monotonic_ns / time_ns / sleep_until_ns) +
  WallClock (live + REALTIME replay) + TlogDerivedClock (ASAP replay;
  advance-on-call; non-monotonic source → ClockOrderingError).
* FrameSource Protocol (next_frame -> NavCameraFrame | None / close)
  + LiveCameraFrameSource (cv2.VideoCapture device index) +
  VideoFileFrameSource (cv2.VideoCapture file).
* Build-flag gating: BUILD_VIDEO_FILE_FRAME_SOURCE,
  BUILD_LIVE_CAMERA_FRAME_SOURCE (constructor-time check; Tier-0 OFF
  refuses construction with FrameSourceConfigError).
* Composition-root factories: build_clock + build_frame_source.
* Injected Clock across every component that previously called
  time.monotonic_ns() / time.sleep() directly: c5_state (estimator,
  ESKF, fallback watcher, source-label SM, isam2 handle), c8_fc_adapter
  (inbound MAVLink + MSP2, AP outbound, iNav outbound, QGC GCS),
  c13_fdr writer, c12_operator_tooling httpx flights client. All
  constructors default to WallClock() so existing call sites keep
  live-binary behaviour without a wiring change.
* AC-4 CI guard (tests/_meta/test_no_direct_time_in_components.py)
  AST-scans components/**/*.py for direct time.monotonic_ns /
  time.time_ns / time.sleep references and fails loudly with file:line.
* Conformance + factory tests: tests/unit/clock + tests/unit/frame_source.
* Test fixture updates: FallbackWatcher / SourceLabelStateMachine
  clock_ns is now required (removed time.monotonic_ns default);
  test_az388 patches estimator._clock instead of a module-level time;
  test_az393 ardupilot adapter uses a _FixedClock test double.

Excluded per the task spec: TlogReplayFcAdapter (AZ-399), ReplaySink
(AZ-400), compose_replay (AZ-401), CLI (AZ-402), Docker/CI (AZ-403),
E2E fixture (AZ-404), IMU auto-sync (AZ-405).

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

src/gps_denied_onboard/clock/wall_clock.py

@@ -0,0 +1,42 @@
+"""``WallClock`` strategy (AZ-398) — live + REALTIME replay.
+
+Thin :class:`Clock` adapter over the standard-library :mod:`time`
+module. Owned by ``clock/`` so the AC-4 AST scan over ``components/``
+remains clean: components MUST NOT call :func:`time.monotonic_ns`
+directly; they call :meth:`WallClock.monotonic_ns` via injection.
+"""
+
+from __future__ import annotations
+
+import time
+
+
+class WallClock:
+    """Default :class:`Clock` strategy backed by :mod:`time`.
+
+    Stateless; constructable without arguments. All three methods are
+    trivially Liskov-clean over the Protocol.
+    """
+
+    __slots__ = ()
+
+    def monotonic_ns(self) -> int:
+        return time.monotonic_ns()
+
+    def time_ns(self) -> int:
+        return time.time_ns()
+
+    def sleep_until_ns(self, target_ns: int) -> None:
+        """Block until ``time.monotonic_ns() >= target_ns``.
+
+        A target already in the past is a no-op. Sub-millisecond
+        oversleep is accepted (AC-5: ≤ 5 ms drift on a 100 ms sleep).
+        """
+        now = time.monotonic_ns()
+        delta_ns = target_ns - now
+        if delta_ns <= 0:
+            return
+        time.sleep(delta_ns / 1_000_000_000.0)
+
+
+__all__ = ["WallClock"]