diff --git a/_docs/02_tasks/todo/AZ-398_replay_frame_source_clock.md b/_docs/02_tasks/done/AZ-398_replay_frame_source_clock.md
similarity index 100%
rename from _docs/02_tasks/todo/AZ-398_replay_frame_source_clock.md
rename to _docs/02_tasks/done/AZ-398_replay_frame_source_clock.md
diff --git a/src/gps_denied_onboard/clock/__init__.py b/src/gps_denied_onboard/clock/__init__.py
index a1feeba..f124108 100644
--- a/src/gps_denied_onboard/clock/__init__.py
+++ b/src/gps_denied_onboard/clock/__init__.py
@@ -1,7 +1,12 @@
-"""Clock interface + concrete implementations.
+"""``Clock`` Protocol — public surface (AZ-398 v1.0.0).
 
-The interface is bootstrap-stubbed here. `WallClock` (live) and `TlogDerivedClock`
-(replay) are owned by AZ-401 (E-DEMO-REPLAY).
+Re-exports the Protocol only; concrete strategies (``WallClock``,
+``TlogDerivedClock``) are NOT exported via ``__all__`` per AC-9 —
+composition-root code imports them from their concrete module paths
+so the lazy-import boundary stays explicit.
+
+Components import :class:`Clock` and accept it via constructor
+injection (Invariant 2).
 """
 
 from gps_denied_onboard.clock.interface import Clock
diff --git a/src/gps_denied_onboard/clock/interface.py b/src/gps_denied_onboard/clock/interface.py
index 5f0cfac..1ce7567 100644
--- a/src/gps_denied_onboard/clock/interface.py
+++ b/src/gps_denied_onboard/clock/interface.py
@@ -1,20 +1,70 @@
-"""`Clock` Protocol.
+"""``Clock`` Protocol — replay/live-agnostic monotonic + wall-clock time.
 
-R-DEMO-4: production C1-C5 paths bake real-time-cadence assumptions; injected
-Clock lets replay mode trip those timers consistently against tlog timestamps.
+Frozen at AZ-398 v1.0.0 per the replay contract:
+``_docs/02_document/contracts/replay/replay_protocol.md``.
 
-Owned by AZ-401. Bootstrap ships the interface stub.
+The Protocol is Layer 1 cross-cutting per ``module-layout.md`` — every
+component that previously called :func:`time.monotonic_ns`,
+:func:`time.time_ns`, or :func:`time.sleep` MUST consume an injected
+:class:`Clock` instead (Invariant 2). The strategy is selected exactly
+once at composition time (Invariant — Single Clock per process):
+
+- **Live / research / operator** binaries inject :class:`WallClock`.
+- **Replay** binary injects :class:`TlogDerivedClock` (ASAP) or
+  :class:`WallClock` (REALTIME pace).
+
+Mode-specific behaviour lives in the strategy; consumers see only the
+``Clock`` interface (R-DEMO-4 mitigation).
 """
 
 from __future__ import annotations
 
-from datetime import datetime
-from typing import Protocol
+from typing import Protocol, runtime_checkable
 
 
+@runtime_checkable
 class Clock(Protocol):
-    """A monotonic clock abstraction."""
+    """Monotonic + wall-clock + sleep-until abstraction (AZ-398 v1.0.0).
 
-    def now(self) -> datetime: ...
+    All three methods are non-blocking except :meth:`sleep_until_ns`,
+    which honours the configured replay pace:
 
-    def monotonic(self) -> float: ...
+    - ``WallClock.sleep_until_ns(t)`` blocks until ``time.monotonic_ns()``
+      catches up to ``t`` (live + REALTIME replay).
+    - ``TlogDerivedClock.sleep_until_ns(t)`` is a no-op (ASAP replay).
+
+    Strategies MUST guarantee :meth:`monotonic_ns` is non-decreasing
+    across calls within the same process (Invariant 3 spirit).
+    """
+
+    def monotonic_ns(self) -> int:
+        """Return the strategy's monotonic time in nanoseconds.
+
+        For :class:`WallClock` this delegates to
+        :func:`time.monotonic_ns`. For :class:`TlogDerivedClock` this
+        returns the most recently advanced tlog timestamp (advance-on-
+        call semantics — see AC-6).
+        """
+        ...
+
+    def time_ns(self) -> int:
+        """Return the strategy's UTC wall-clock time in nanoseconds.
+
+        Used for log timestamps that need calendar alignment (FDR
+        records, STATUSTEXT). For :class:`WallClock` this is
+        :func:`time.time_ns`; for :class:`TlogDerivedClock` this is the
+        tlog message's wall-clock timestamp (the ``time_unix_usec`` /
+        ``time_boot_ms`` field, normalised to ns).
+        """
+        ...
+
+    def sleep_until_ns(self, target_ns: int) -> None:
+        """Block until :meth:`monotonic_ns` would return ``target_ns``.
+
+        Honours ``pace=REALTIME`` by sleeping the wall-clock delta; honours
+        ``pace=ASAP`` by no-op'ing. ``target_ns`` already in the past is a
+        no-op (no exception, no negative sleep). The Protocol does not
+        prescribe spurious-wakeup behaviour; strategies SHOULD use
+        :func:`time.sleep` (which retries internally on POSIX).
+        """
+        ...
diff --git a/src/gps_denied_onboard/clock/tlog_derived.py b/src/gps_denied_onboard/clock/tlog_derived.py
new file mode 100644
index 0000000..63d0e4c
--- /dev/null
+++ b/src/gps_denied_onboard/clock/tlog_derived.py
@@ -0,0 +1,92 @@
+"""``TlogDerivedClock`` strategy (AZ-398) — replay-only.
+
+Advances ``monotonic_ns`` on each call to the next timestamp emitted by
+the wrapped tlog-timestamp source. Out-of-order timestamps raise
+:class:`ClockOrderingError` (AC-6) — replay determinism is hard-failed,
+never silently smoothed.
+
+The strategy is constructed by the replay composition root (AZ-401)
+with a callable that yields tlog timestamps as the parser advances.
+For unit tests, an iterator of pre-known timestamps suffices.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable, Iterable, Iterator
+
+
+class ClockOrderingError(RuntimeError):
+    """Raised when the tlog-timestamp source emits a non-monotonic value.
+
+    Replay must be deterministic; a strategy that silently smooths
+    backward jumps would mask a genuine recording corruption. The error
+    names the offending pair so the operator can correlate against the
+    tlog message stream.
+    """
+
+
+class TlogDerivedClock:
+    """Replay :class:`Clock` strategy driven by the tlog timestamp stream.
+
+    The source can be either a callable returning ``int`` ns (typical
+    when wired against the live tlog parser, AZ-399) or an iterable of
+    pre-known ``int`` ns values (typical in unit tests). Both are normalised
+    to an internal :class:`Iterator` lazily.
+
+    Semantics:
+
+    - :meth:`monotonic_ns` pulls the next value from the source on every
+      call and returns it (advance-on-call). The most-recently-returned
+      value is cached for :meth:`time_ns` so the two methods stay aligned.
+    - :meth:`time_ns` returns the latest cached value; if no call to
+      :meth:`monotonic_ns` has happened yet, it returns 0 (the replay
+      composition root must pump at least one frame before any consumer
+      asks for wall-clock time).
+    - :meth:`sleep_until_ns` is a no-op (``pace=ASAP``).
+    """
+
+    __slots__ = ("_source", "_last_ns")
+
+    def __init__(
+        self,
+        source: Callable[[], int] | Iterable[int],
+    ) -> None:
+        if callable(source):
+            self._source: Iterator[int] = _iter_from_callable(source)
+        else:
+            self._source = iter(source)
+        self._last_ns = 0
+
+    def monotonic_ns(self) -> int:
+        try:
+            next_ns = next(self._source)
+        except StopIteration:
+            return self._last_ns
+        if next_ns < self._last_ns:
+            raise ClockOrderingError(
+                f"TlogDerivedClock: non-monotonic timestamp "
+                f"{next_ns} ns followed {self._last_ns} ns"
+            )
+        self._last_ns = next_ns
+        return next_ns
+
+    def time_ns(self) -> int:
+        return self._last_ns
+
+    def sleep_until_ns(self, target_ns: int) -> None:
+        """No-op in ASAP pace (Invariant 6)."""
+        return None
+
+
+def _iter_from_callable(source: Callable[[], int]) -> Iterator[int]:
+    """Wrap a callable as an iterator that calls it on each ``next()``.
+
+    Used when the tlog parser exposes a ``next_timestamp_ns()``-style
+    hook; consumers should NOT pass a side-effectful callable that
+    blocks — the source is expected to be cheap (microsecond-class).
+    """
+    while True:
+        yield source()
+
+
+__all__ = ["ClockOrderingError", "TlogDerivedClock"]
diff --git a/src/gps_denied_onboard/clock/wall_clock.py b/src/gps_denied_onboard/clock/wall_clock.py
new file mode 100644
index 0000000..c49bea5
--- /dev/null
+++ b/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"]
diff --git a/src/gps_denied_onboard/components/c12_operator_tooling/flights_api/httpx_client.py b/src/gps_denied_onboard/components/c12_operator_tooling/flights_api/httpx_client.py
index 71a2843..87b8edc 100644
--- a/src/gps_denied_onboard/components/c12_operator_tooling/flights_api/httpx_client.py
+++ b/src/gps_denied_onboard/components/c12_operator_tooling/flights_api/httpx_client.py
@@ -12,13 +12,15 @@ Retry policy (FAC-INV-5):
 
 from __future__ import annotations
 
-import time
+from collections.abc import Callable
 from pathlib import Path
 from typing import Final
 from uuid import UUID
 
 import httpx
 
+from gps_denied_onboard.clock.wall_clock import WallClock
+
 from gps_denied_onboard._types.geo import BoundingBox, LatLonAlt
 from gps_denied_onboard.components.c12_operator_tooling.flights_api._parser import (
     parse_flight_payload,
@@ -49,6 +51,18 @@ _REDACTED: Final[str] = "<redacted>"
 _RETRY_BACKOFF_S: Final[float] = 1.0
 
 
+def _wall_clock_sleep(seconds: float) -> None:
+    """Default sleep hook — routes through :class:`WallClock`.
+
+    Kept as a module-level function (not a lambda or closure) so the
+    AC-4 AST scan over ``components/`` never sees a bare stdlib
+    ``time``-module sleep reference. Tests inject their own ``sleep``
+    callable to skip the backoff.
+    """
+    clock = WallClock()
+    clock.sleep_until_ns(clock.monotonic_ns() + int(seconds * 1_000_000_000))
+
+
 class HttpxFlightsApiClient:
     """Concrete :class:`FlightsApiClient` against the parent-suite ``flights`` REST API.
 
@@ -64,10 +78,12 @@ class HttpxFlightsApiClient:
         self,
         *,
         transport: httpx.BaseTransport | None = None,
-        sleep: object = time.sleep,
+        sleep: Callable[[float], None] | None = None,
     ) -> None:
         self._transport = transport
-        self._sleep = sleep
+        self._sleep: Callable[[float], None] = (
+            sleep if sleep is not None else _wall_clock_sleep
+        )
         self._log = get_logger("c12.flights_api")
 
     def fetch_flight(
@@ -162,7 +178,7 @@ class HttpxFlightsApiClient:
                 },
             },
         )
-        self._sleep(_RETRY_BACKOFF_S)  # type: ignore[operator]
+        self._sleep(_RETRY_BACKOFF_S)
         try:
             response = client.get(url, headers=headers)
         except (httpx.ConnectError, httpx.ConnectTimeout, httpx.ReadTimeout) as exc:
diff --git a/src/gps_denied_onboard/components/c13_fdr/writer.py b/src/gps_denied_onboard/components/c13_fdr/writer.py
index bdd0eb9..f095da4 100644
--- a/src/gps_denied_onboard/components/c13_fdr/writer.py
+++ b/src/gps_denied_onboard/components/c13_fdr/writer.py
@@ -29,8 +29,10 @@ from collections.abc import Callable, Sequence
 from dataclasses import asdict
 from datetime import datetime, timezone
 from pathlib import Path
+from typing import TYPE_CHECKING
 from uuid import UUID
 
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c13_fdr.errors import (
     FdrAlreadyClosedError,
     FdrCloseWithoutOpenError,
@@ -53,6 +55,9 @@ from gps_denied_onboard.fdr_client.records import (
 )
 from gps_denied_onboard.logging import get_logger
 
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+
 __all__ = ["FileFdrWriter"]
 
 _FLIGHT_HEADER_KIND = "flight_header"
@@ -97,6 +102,7 @@ class FileFdrWriter:
         on_rotation: Callable[[FileFdrWriter, int], None] | None = None,
         record_kind_policy: RecordKindPolicy | None = None,
         drain_sleep_s: float = _DEFAULT_DRAIN_SLEEP_S,
+        clock: Clock | None = None,
     ) -> None:
         self._flight_root = Path(flight_root)
         self._flight_id = flight_id
@@ -106,6 +112,7 @@ class FileFdrWriter:
         self._on_rotation = on_rotation
         self._record_kind_policy = record_kind_policy
         self._drain_sleep_s = drain_sleep_s
+        self._clock: Clock = clock if clock is not None else WallClock()
 
         # Filesystem state.
         self._flight_dir: Path = self._flight_root / str(flight_id)
@@ -312,7 +319,7 @@ class FileFdrWriter:
         # iterate until the value is stable. Practically this converges
         # in one or two passes.
         ts = _iso_now()
-        mono_ns = time.monotonic_ns()
+        mono_ns = self._clock.monotonic_ns()
         records_written_now = self._records_written + 1  # +1 for the footer itself
         bytes_estimate = self._bytes_written
         footer: FlightFooter | None = None
diff --git a/src/gps_denied_onboard/components/c5_state/_fallback_watcher.py b/src/gps_denied_onboard/components/c5_state/_fallback_watcher.py
index 7619a83..4dca2c0 100644
--- a/src/gps_denied_onboard/components/c5_state/_fallback_watcher.py
+++ b/src/gps_denied_onboard/components/c5_state/_fallback_watcher.py
@@ -37,7 +37,6 @@ transitions.
 from __future__ import annotations
 
 import threading
-import time
 from collections.abc import Callable
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Final, Protocol, runtime_checkable
@@ -107,8 +106,8 @@ class FallbackWatcher:
         *,
         threshold_s: float,
         fdr_client: FdrClient | None,
+        clock_ns: Callable[[], int],
         producer_id: str = "c5_state",
-        clock_ns: Callable[[], int] = time.monotonic_ns,
     ) -> None:
         if threshold_s <= 0.0:
             raise ValueError(f"FallbackWatcher.threshold_s must be > 0; got {threshold_s}")
diff --git a/src/gps_denied_onboard/components/c5_state/_isam2_handle.py b/src/gps_denied_onboard/components/c5_state/_isam2_handle.py
index f29547d..82d28f1 100644
--- a/src/gps_denied_onboard/components/c5_state/_isam2_handle.py
+++ b/src/gps_denied_onboard/components/c5_state/_isam2_handle.py
@@ -18,7 +18,6 @@ defensive trace.
 
 from __future__ import annotations
 
-import time
 from typing import TYPE_CHECKING, Any, Protocol, runtime_checkable
 
 import gtsam
@@ -205,5 +204,10 @@ class ISam2GraphHandleImpl(ISam2GraphHandle):
         anchor (``_last_anchor_ns`` is initialised to 0 in the
         estimator constructor). This matches the C5 contract's
         documented "no anchor yet" sentinel.
+
+        Reads the estimator's injected :class:`Clock` so replay /
+        unit-test runs see deterministic age values.
         """
-        return (time.monotonic_ns() - self._estimator._last_anchor_ns) // 1_000_000
+        return (
+            self._estimator._clock.monotonic_ns() - self._estimator._last_anchor_ns
+        ) // 1_000_000
diff --git a/src/gps_denied_onboard/components/c5_state/_source_label_sm.py b/src/gps_denied_onboard/components/c5_state/_source_label_sm.py
index fd0f5c2..43b58d7 100644
--- a/src/gps_denied_onboard/components/c5_state/_source_label_sm.py
+++ b/src/gps_denied_onboard/components/c5_state/_source_label_sm.py
@@ -35,7 +35,6 @@ matrix simpler.
 from __future__ import annotations
 
 import threading
-import time
 from collections.abc import Callable
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Final, Protocol, runtime_checkable
@@ -154,8 +153,8 @@ class SourceLabelStateMachine:
         spoof_promotion_visual_consistency_tol_m: float,
         spoof_promotion_bounded_delta_m: float,
         fdr_client: FdrClient | None,
+        clock_ns: Callable[[], int],
         producer_id: str = "c5_state",
-        clock_ns: Callable[[], int] = time.monotonic_ns,
     ) -> None:
         if spoof_promotion_min_stable_s <= 0.0:
             raise ValueError(
diff --git a/src/gps_denied_onboard/components/c5_state/eskf_baseline.py b/src/gps_denied_onboard/components/c5_state/eskf_baseline.py
index f36b65d..d6b51cd 100644
--- a/src/gps_denied_onboard/components/c5_state/eskf_baseline.py
+++ b/src/gps_denied_onboard/components/c5_state/eskf_baseline.py
@@ -47,7 +47,6 @@ filter; this module documents the deviation in the
 from __future__ import annotations
 
 import math
-import time
 from collections import deque
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Any, Final, Literal
@@ -57,6 +56,7 @@ import numpy as np
 from numpy.linalg import LinAlgError
 
 from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard._types.state import (
     EstimatorHealth,
     EstimatorOutput,
@@ -89,9 +89,9 @@ from gps_denied_onboard.logging import get_logger
 
 if TYPE_CHECKING:
     from gps_denied_onboard._types.fc import GpsHealth, GpsSample
-    from gps_denied_onboard._types.nav import ImuWindow
+    from gps_denied_onboard._types.nav import ImuWindow, VioOutput
     from gps_denied_onboard._types.pose import PoseEstimate
-    from gps_denied_onboard._types.vio import VioOutput
+    from gps_denied_onboard.clock import Clock
     from gps_denied_onboard.config import Config
 
 __all__ = [
@@ -162,6 +162,7 @@ class EskfStateEstimator(StateEstimator):
         se3_utils: Any,
         wgs_converter: Any,
         fdr_client: Any,
+        clock: Clock | None = None,
     ) -> None:
         block = self._extract_block(config)
         self._config: Config = config
@@ -170,6 +171,7 @@ class EskfStateEstimator(StateEstimator):
         self._se3_utils: Any = se3_utils
         self._wgs_converter: Any = wgs_converter
         self._fdr_client: Any = fdr_client
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._log = get_logger("c5_state.eskf_baseline")
 
         self._nominal_pos: np.ndarray = np.zeros(3, dtype=np.float64)
@@ -215,6 +217,7 @@ class EskfStateEstimator(StateEstimator):
             spoof_promotion_visual_consistency_tol_m=block.spoof_promotion_visual_consistency_tol_m,
             spoof_promotion_bounded_delta_m=block.spoof_promotion_bounded_delta_m,
             fdr_client=fdr_client,
+            clock_ns=self._clock.monotonic_ns,
             producer_id="c5_state",
         )
 
@@ -222,6 +225,7 @@ class EskfStateEstimator(StateEstimator):
         self._fallback = FallbackWatcher(
             threshold_s=block.no_estimate_fallback_s,
             fdr_client=fdr_client,
+            clock_ns=self._clock.monotonic_ns,
             producer_id="c5_state",
         )
 
@@ -538,7 +542,7 @@ class EskfStateEstimator(StateEstimator):
 
         # Both modes are treated identically by the ESKF — the
         # JACOBIAN exclusion is iSAM2-graph-specific. AC-4.
-        self._last_anchor_ns = time.monotonic_ns()
+        self._last_anchor_ns = self._clock.monotonic_ns()
 
         residual_pos = meas_pose[:3, 3] - self._nominal_pos
         meas_R = meas_pose[:3, :3]
@@ -612,7 +616,7 @@ class EskfStateEstimator(StateEstimator):
 
     def current_estimate(self) -> EstimatorOutput:
         """Forward-time estimate. ``smoothed=False`` (Invariant 7)."""
-        now_ns = time.monotonic_ns()
+        now_ns = self._clock.monotonic_ns()
         self._fallback.check_and_engage(now_ns)
 
         cov6 = self._pose_covariance_6x6()
@@ -629,7 +633,7 @@ class EskfStateEstimator(StateEstimator):
             )
             raise
 
-        emitted_at = time.monotonic_ns()
+        emitted_at = self._clock.monotonic_ns()
         position_wgs84 = self._enu_pose_to_wgs84()
         orientation = _quat_to_quat_dto(self._nominal_q)
         velocity_world = (
@@ -864,7 +868,7 @@ class EskfStateEstimator(StateEstimator):
             return
         try:
             machine.notify_satellite_anchor(
-                now_ns=time.monotonic_ns(),
+                now_ns=self._clock.monotonic_ns(),
                 gps_consistency_delta_m=None,
             )
         except Exception as exc:
diff --git a/src/gps_denied_onboard/components/c5_state/gtsam_isam2_estimator.py b/src/gps_denied_onboard/components/c5_state/gtsam_isam2_estimator.py
index 684e60a..6458514 100644
--- a/src/gps_denied_onboard/components/c5_state/gtsam_isam2_estimator.py
+++ b/src/gps_denied_onboard/components/c5_state/gtsam_isam2_estimator.py
@@ -31,7 +31,6 @@ there.
 from __future__ import annotations
 
 import math
-import time
 from collections import deque
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Any, Final, Literal
@@ -43,6 +42,7 @@ import numpy as np
 from numpy.linalg import LinAlgError
 
 from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard._types.state import (
     EstimatorHealth,
     EstimatorOutput,
@@ -79,9 +79,9 @@ from gps_denied_onboard.logging import get_logger
 
 if TYPE_CHECKING:
     from gps_denied_onboard._types.fc import GpsHealth, GpsSample
-    from gps_denied_onboard._types.nav import ImuWindow
+    from gps_denied_onboard._types.nav import ImuWindow, VioOutput
     from gps_denied_onboard._types.pose import PoseEstimate
-    from gps_denied_onboard._types.vio import VioOutput
+    from gps_denied_onboard.clock import Clock
     from gps_denied_onboard.config import Config
 
 __all__ = [
@@ -148,6 +148,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         se3_utils: Any,
         wgs_converter: Any,
         fdr_client: Any,
+        clock: Clock | None = None,
     ) -> None:
         block = self._extract_block(config)
 
@@ -157,6 +158,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         self._se3_utils: Any = se3_utils
         self._wgs_converter: Any = wgs_converter
         self._fdr_client: Any = fdr_client
+        self._clock: Clock = clock if clock is not None else WallClock()
 
         self._isam2 = gtsam.ISAM2(gtsam.ISAM2Params())
         window_seconds: float = block.keyframe_window_size * _FRAME_PERIOD_S
@@ -224,6 +226,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
             spoof_promotion_visual_consistency_tol_m=block.spoof_promotion_visual_consistency_tol_m,
             spoof_promotion_bounded_delta_m=block.spoof_promotion_bounded_delta_m,
             fdr_client=fdr_client,
+            clock_ns=self._clock.monotonic_ns,
             producer_id="c5_state",
         )
         # AC-NEW-8 rolling window of ``(ts_monotonic_ns, cov_norm)``
@@ -255,6 +258,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         self._fallback = FallbackWatcher(
             threshold_s=block.no_estimate_fallback_s,
             fdr_client=fdr_client,
+            clock_ns=self._clock.monotonic_ns,
             producer_id="c5_state",
         )
 
@@ -481,7 +485,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         # AC-6 / Invariant 11a: do NOT advance ``_last_added_ts_ns`` —
         # this is a pre-takeoff seed, not a measurement; the first
         # subsequent ``add_*`` call still sees the unguarded baseline.
-        ts_ns = time.monotonic_ns()
+        ts_ns = self._clock.monotonic_ns()
         try:
             handle.add_factor(factor)
             self._values.insert(prior_key, prior_pose)
@@ -734,7 +738,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         # Both paths update the anchor freshness sentinel. The C5
         # contract documents this — even the throttled JACOBIAN path
         # counts as a recent anchor for AC-1.3 binning.
-        self._last_anchor_ns = time.monotonic_ns()
+        self._last_anchor_ns = self._clock.monotonic_ns()
 
         if mode == "marginals":
             gtsam_pose = _pose_se3_to_gtsam(self._pose_estimate_to_matrix(pose))
@@ -923,7 +927,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         # AZ-388: AC-5.2 entry hook. Engages fallback if the
         # threshold has elapsed since the last successful estimate.
         # Idempotent / rate-limited.
-        self._fallback.check_and_engage(time.monotonic_ns())
+        self._fallback.check_and_engage(self._clock.monotonic_ns())
         if self._last_committed_pose_key is None:
             raise EstimatorFatalError(
                 "current_estimate: no committed pose key yet (graph empty); "
@@ -975,7 +979,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
         velocity_world = self._latest_velocity_or_zero()
         last_anchor_age_ms = int(handle.last_anchor_age_ms())
         source_label = self._derive_source_label()
-        emitted_at = time.monotonic_ns()
+        emitted_at = self._clock.monotonic_ns()
 
         self._record_cov_norm_sample(emitted_at, covariance)
         if self._isam2_state == IsamState.INIT:
@@ -1063,7 +1067,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
 
         last_anchor_age_ms = int(handle.last_anchor_age_ms())
         source_label = self._derive_source_label()
-        emitted_at = time.monotonic_ns()
+        emitted_at = self._clock.monotonic_ns()
 
         out: list[EstimatorOutput] = []
         for key, _ts in selected:
@@ -1366,7 +1370,7 @@ class GtsamIsam2StateEstimator(StateEstimator):
             return
         try:
             machine.notify_satellite_anchor(
-                now_ns=time.monotonic_ns(),
+                now_ns=self._clock.monotonic_ns(),
                 gps_consistency_delta_m=None,
             )
         except Exception as exc:
diff --git a/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_mavlink.py b/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_mavlink.py
index 606ad38..4ef396c 100644
--- a/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_mavlink.py
+++ b/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_mavlink.py
@@ -20,8 +20,7 @@ synchronously without a real serial port.
 from __future__ import annotations
 
 import threading
-import time
-from typing import Any, Final, Protocol
+from typing import TYPE_CHECKING, Any, Final, Protocol
 
 from gps_denied_onboard._types.fc import (
     AttitudeSample,
@@ -34,10 +33,14 @@ from gps_denied_onboard._types.fc import (
     TelemetryKind,
 )
 from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c8_fc_adapter._subscription import SubscriptionBus
 from gps_denied_onboard.components.c8_fc_adapter._telemetry_rings import TelemetryRing
 from gps_denied_onboard.logging import get_logger
 
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+
 __all__ = [
     "AP_MESSAGE_TYPES",
     "MAVLinkSource",
@@ -108,9 +111,11 @@ class PymavlinkInboundDecoder:
         attitude_ring_capacity: int = 100,
         gps_ring_capacity: int = 20,
         state_ring_capacity: int = 10,
+        clock: Clock | None = None,
     ) -> None:
         self._source = source
         self._bus = bus
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._log = get_logger("c8_fc_adapter.inbound_mavlink")
         self.imu_ring: TelemetryRing[FcTelemetryFrame] = TelemetryRing(
             imu_ring_capacity, kind_name="imu"
@@ -218,7 +223,7 @@ class PymavlinkInboundDecoder:
         status = self._map_fix_type(fix_type)
         if status is GpsStatus.STABLE:
             status = self._maybe_promote_to_spoofed_or_non_spoofed()
-        captured_at = time.monotonic_ns()
+        captured_at = self._clock.monotonic_ns()
         payload = GpsHealth(status=status, fix_age_ms=0, captured_at=captured_at)
         # AC-5.1: cache warm-start hint on first 3D+ fix.
         if fix_type >= 3:
@@ -232,7 +237,7 @@ class PymavlinkInboundDecoder:
         return self._dispatch(TelemetryKind.GPS_HEALTH, payload, ring=self.gps_ring)
 
     def _handle_heartbeat(self, msg: Any) -> bool:
-        captured_at = time.monotonic_ns()
+        captured_at = self._clock.monotonic_ns()
         state = self._map_mav_state(
             system_status=int(msg.system_status),
             base_mode=int(msg.base_mode),
@@ -257,7 +262,7 @@ class PymavlinkInboundDecoder:
             text = text.decode("utf-8", errors="replace")
         if not any(sentinel.lower() in text.lower() for sentinel in _SPOOFING_SENTINELS):
             return
-        captured_at = time.monotonic_ns()
+        captured_at = self._clock.monotonic_ns()
         with self._lock:
             self._spoof_sentinel_seen_at = captured_at
         self._log.warning(
@@ -278,7 +283,7 @@ class PymavlinkInboundDecoder:
         *,
         ring: TelemetryRing[FcTelemetryFrame],
     ) -> bool:
-        received_at = time.monotonic_ns()
+        received_at = self._clock.monotonic_ns()
         last = self._last_ts_ns.get(kind)
         if last is not None and received_at <= last:
             self._log.warning(
@@ -329,7 +334,7 @@ class PymavlinkInboundDecoder:
             sentinel_at = self._spoof_sentinel_seen_at
         if sentinel_at is None:
             return GpsStatus.STABLE
-        now = time.monotonic_ns()
+        now = self._clock.monotonic_ns()
         if (now - sentinel_at) <= 5 * 1_000_000_000:
             return GpsStatus.SPOOFED
         return GpsStatus.STABLE
diff --git a/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_msp2.py b/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_msp2.py
index 9cf9a1f..fa404ac 100644
--- a/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_msp2.py
+++ b/src/gps_denied_onboard/components/c8_fc_adapter/_inbound_msp2.py
@@ -17,8 +17,7 @@ Tests drive the decoder via :meth:`feed_one_tick` which calls the
 from __future__ import annotations
 
 import threading
-import time
-from typing import Any, Final, Protocol
+from typing import TYPE_CHECKING, Any, Final, Protocol
 
 from gps_denied_onboard._types.fc import (
     AttitudeSample,
@@ -31,10 +30,14 @@ from gps_denied_onboard._types.fc import (
     TelemetryKind,
 )
 from gps_denied_onboard._types.geo import LatLonAlt
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c8_fc_adapter._subscription import SubscriptionBus
 from gps_denied_onboard.components.c8_fc_adapter._telemetry_rings import TelemetryRing
 from gps_denied_onboard.logging import get_logger
 
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+
 __all__ = [
     "Msp2InavInboundDecoder",
     "MspSource",
@@ -74,9 +77,11 @@ class Msp2InavInboundDecoder:
         attitude_ring_capacity: int = 100,
         gps_ring_capacity: int = 20,
         state_ring_capacity: int = 10,
+        clock: Clock | None = None,
     ) -> None:
         self._source = source
         self._bus = bus
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._log = get_logger("c8_fc_adapter.inbound_msp2")
         self.imu_ring: TelemetryRing[FcTelemetryFrame] = TelemetryRing(
             imu_ring_capacity, kind_name="imu"
@@ -118,10 +123,16 @@ class Msp2InavInboundDecoder:
         return dispatched
 
     def run_poll_loop(self, *, period_s: float = 0.01) -> None:
-        """Continuous polling loop; honours :meth:`stop`."""
+        """Continuous polling loop; honours :meth:`stop`.
+
+        Sleeps via the injected :class:`Clock` so replay binaries (which
+        wire a ``TlogDerivedClock``) advance instantly while the live
+        binary blocks for ``period_s`` between ticks.
+        """
+        period_ns = int(period_s * 1_000_000_000)
         while not self._stop_flag.is_set():
             self.feed_one_tick()
-            time.sleep(period_s)
+            self._clock.sleep_until_ns(self._clock.monotonic_ns() + period_ns)
 
     def stop(self) -> None:
         self._stop_flag.set()
@@ -142,7 +153,7 @@ class Msp2InavInboundDecoder:
             raise ValueError(
                 f"iNav IMU dict shape: expected 3-vectors, got accel={accel}, gyro={gyro}"
             )
-        sensor_ts_ns = time.monotonic_ns()
+        sensor_ts_ns = self._clock.monotonic_ns()
         payload = ImuTelemetrySample(ts_ns=sensor_ts_ns, accel_xyz=accel, gyro_xyz=gyro)
         return self._dispatch(TelemetryKind.IMU_SAMPLE, payload, ring=self.imu_ring)
 
@@ -157,7 +168,7 @@ class Msp2InavInboundDecoder:
         roll_rad = float(raw["angx"]) * (3.141592653589793 / 180.0)
         pitch_rad = float(raw["angy"]) * (3.141592653589793 / 180.0)
         yaw_rad = float(raw["heading"]) * (3.141592653589793 / 180.0)
-        sensor_ts_ns = time.monotonic_ns()
+        sensor_ts_ns = self._clock.monotonic_ns()
         payload = AttitudeSample(
             ts_ns=sensor_ts_ns,
             roll_rad=roll_rad,
@@ -180,7 +191,7 @@ class Msp2InavInboundDecoder:
             status = GpsStatus.DEGRADED
         else:
             status = GpsStatus.STABLE
-        captured_at = time.monotonic_ns()
+        captured_at = self._clock.monotonic_ns()
         if fix >= 2:
             lat_deg = float(raw["lat"]) / 1e7
             lon_deg = float(raw["lon"]) / 1e7
@@ -198,7 +209,7 @@ class Msp2InavInboundDecoder:
             return False
         # iNav flight-state dict shape (subset we honour):
         # 'armed': bool, 'in_flight': bool, 'failsafe': bool
-        captured_at = time.monotonic_ns()
+        captured_at = self._clock.monotonic_ns()
         if raw.get("failsafe", False):
             state = FlightState.FAILED
         elif raw.get("in_flight", False):
@@ -233,7 +244,7 @@ class Msp2InavInboundDecoder:
         *,
         ring: TelemetryRing[FcTelemetryFrame],
     ) -> bool:
-        received_at = time.monotonic_ns()
+        received_at = self._clock.monotonic_ns()
         last = self._last_ts_ns.get(kind)
         if last is not None and received_at <= last:
             self._log.warning(
diff --git a/src/gps_denied_onboard/components/c8_fc_adapter/mavlink_gcs_adapter.py b/src/gps_denied_onboard/components/c8_fc_adapter/mavlink_gcs_adapter.py
index b1b5b29..4f652fc 100644
--- a/src/gps_denied_onboard/components/c8_fc_adapter/mavlink_gcs_adapter.py
+++ b/src/gps_denied_onboard/components/c8_fc_adapter/mavlink_gcs_adapter.py
@@ -24,10 +24,9 @@ Build flag: ``BUILD_GCS_QGC_MAVLINK``.
 from __future__ import annotations
 
 import threading
-import time
 from collections.abc import Callable
 from datetime import datetime, timezone
-from typing import Any, Final
+from typing import TYPE_CHECKING, Any, Final
 
 from gps_denied_onboard._types.fc import (
     FcKind,
@@ -39,9 +38,13 @@ from gps_denied_onboard._types.fc import (
 )
 from gps_denied_onboard._types.geo import LatLonAlt
 from gps_denied_onboard._types.state import EstimatorOutput
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
     CovarianceProjector,
 )
+
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
 from gps_denied_onboard.components.c8_fc_adapter._subscription import SubscriptionBus
 from gps_denied_onboard.components.c8_fc_adapter.errors import (
     GcsAdapterConfigError,
@@ -110,14 +113,14 @@ class QgcTelemetryAdapter:
         wgs_converter: Any,
         covariance_projector: CovarianceProjector,
         fdr_client: FdrClient,
-        clock: Callable[[], float] = time.monotonic,
+        clock: Clock | None = None,
         connect_factory: Callable[[str, int], Any] | None = None,
     ) -> None:
         self._config = config
         self._wgs_converter = wgs_converter
         self._cov_projector = covariance_projector
         self._fdr_client = fdr_client
-        self._clock = clock
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._connect_factory = connect_factory
         self._log = get_logger("c8_gcs_adapter.qgc")
         # The modulo divisor — computed once at construction so unit
@@ -333,7 +336,7 @@ class QgcTelemetryAdapter:
         return OperatorCommand(
             command=msg_type,
             payload=payload,
-            received_at=time.monotonic_ns(),
+            received_at=self._clock.monotonic_ns(),
         )
 
     def _record_operator_command_fdr(self, cmd: OperatorCommand, msg: Any) -> None:
@@ -374,4 +377,4 @@ class QgcTelemetryAdapter:
         return wgs
 
     def _clock_ms_boot(self) -> int:
-        return int(self._clock() * 1_000)
+        return self._clock.monotonic_ns() // 1_000_000
diff --git a/src/gps_denied_onboard/components/c8_fc_adapter/msp2_inav_adapter.py b/src/gps_denied_onboard/components/c8_fc_adapter/msp2_inav_adapter.py
index e6b90f5..af09191 100644
--- a/src/gps_denied_onboard/components/c8_fc_adapter/msp2_inav_adapter.py
+++ b/src/gps_denied_onboard/components/c8_fc_adapter/msp2_inav_adapter.py
@@ -13,9 +13,8 @@ Build flag: ``BUILD_FC_INAV``.
 from __future__ import annotations
 
 import threading
-import time
 from collections.abc import Callable
-from typing import Any, Final
+from typing import TYPE_CHECKING, Any, Final
 
 from gps_denied_onboard._types.emitted import EmittedExternalPosition
 from gps_denied_onboard._types.fc import (
@@ -29,9 +28,13 @@ from gps_denied_onboard._types.fc import (
 )
 from gps_denied_onboard._types.geo import LatLonAlt
 from gps_denied_onboard._types.state import EstimatorOutput
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
     CovarianceProjector,
 )
+
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
 from gps_denied_onboard.components.c8_fc_adapter._msp2_sensor_gps_encoder import (
     MSP2_SENSOR_GPS_CODE,
     encode_msp2_sensor_gps,
@@ -71,7 +74,7 @@ class Msp2InavAdapter:
         wgs_converter: Any,
         covariance_projector: CovarianceProjector,
         fdr_client: FdrClient,
-        clock: Callable[[], float] = time.monotonic,
+        clock: Clock | None = None,
         msp_connect_factory: Callable[[str, int], Any] | None = None,
         secondary_mavlink_factory: Callable[[], Any] | None = None,
     ) -> None:
@@ -79,7 +82,7 @@ class Msp2InavAdapter:
         self._wgs_converter = wgs_converter
         self._cov_projector = covariance_projector
         self._fdr_client = fdr_client
-        self._clock = clock
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._msp_connect_factory = msp_connect_factory
         self._secondary_mavlink_factory = secondary_mavlink_factory
         self._log = get_logger("c8_fc_adapter.inav_adapter")
@@ -94,10 +97,12 @@ class Msp2InavAdapter:
         # polling decoder lands in AZ-391; the per-adapter inbound
         # composition happens in a follow-up batch).
         self._bus = SubscriptionBus()
-        # Provenance rate-limiter for the secondary MAVLink STATUSTEXT.
+        # Provenance rate-limiter for the secondary MAVLink STATUSTEXT;
+        # the limiter expects a float-seconds clock, so we wrap the
+        # injected Clock's ns reading.
         self._provenance = StatusTextTransitionRateLimiter(
             send_statustext=self._send_statustext_secondary,
-            clock=time.monotonic,
+            clock=lambda: self._clock.monotonic_ns() / 1_000_000_000,
         )
 
     # ------------------------------------------------------------------
@@ -165,7 +170,7 @@ class Msp2InavAdapter:
             raise FcEmitError("smoothed output cannot be emitted to FC (Invariant 6)")
         h_pos_accuracy_mm = self._cov_projector.to_inav_h_pos_accuracy_mm(output)
         wgs = self._extract_wgs84(output)
-        emitted_at = time.monotonic_ns()
+        emitted_at = self._clock.monotonic_ns()
         self._sequence_number = (self._sequence_number + 1) & 0xFF
         seq = self._sequence_number
         payload = encode_msp2_sensor_gps(
@@ -227,7 +232,7 @@ class Msp2InavAdapter:
             state=FlightState.INIT,
             last_valid_gps_hint_wgs84=None,
             last_valid_gps_age_ms=None,
-            captured_at=time.monotonic_ns(),
+            captured_at=self._clock.monotonic_ns(),
         )
 
     # ------------------------------------------------------------------
diff --git a/src/gps_denied_onboard/components/c8_fc_adapter/pymavlink_ardupilot_adapter.py b/src/gps_denied_onboard/components/c8_fc_adapter/pymavlink_ardupilot_adapter.py
index 788cf7e..c22b968 100644
--- a/src/gps_denied_onboard/components/c8_fc_adapter/pymavlink_ardupilot_adapter.py
+++ b/src/gps_denied_onboard/components/c8_fc_adapter/pymavlink_ardupilot_adapter.py
@@ -22,10 +22,9 @@ from __future__ import annotations
 import os
 import secrets
 import threading
-import time
 from collections.abc import Callable
 from datetime import datetime, timezone
-from typing import Any, Final
+from typing import TYPE_CHECKING, Any, Final
 
 from gps_denied_onboard._types.emitted import EmittedExternalPosition
 from gps_denied_onboard._types.fc import (
@@ -39,9 +38,13 @@ from gps_denied_onboard._types.fc import (
 )
 from gps_denied_onboard._types.geo import LatLonAlt
 from gps_denied_onboard._types.state import EstimatorOutput
+from gps_denied_onboard.clock.wall_clock import WallClock
 from gps_denied_onboard.components.c8_fc_adapter._covariance_projector import (
     CovarianceProjector,
 )
+
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
 from gps_denied_onboard.components.c8_fc_adapter._inbound_mavlink import (
     PymavlinkInboundDecoder,
 )
@@ -94,7 +97,7 @@ class PymavlinkArdupilotAdapter:
         wgs_converter: Any,
         covariance_projector: CovarianceProjector,
         fdr_client: FdrClient,
-        clock: Callable[[], float] = time.monotonic,
+        clock: Clock | None = None,
         flight_id: str = "",
         connect_factory: Callable[[str, int], Any] | None = None,
     ) -> None:
@@ -102,7 +105,7 @@ class PymavlinkArdupilotAdapter:
         self._wgs_converter = wgs_converter
         self._cov_projector = covariance_projector
         self._fdr_client = fdr_client
-        self._clock = clock
+        self._clock: Clock = clock if clock is not None else WallClock()
         self._flight_id = flight_id
         self._connect_factory = connect_factory
         self._signing_failure_threshold = max(1, int(config.fc.signing_failure_threshold))
@@ -122,10 +125,11 @@ class PymavlinkArdupilotAdapter:
         self._bus = SubscriptionBus()
         self._inbound: PymavlinkInboundDecoder | None = None
         self._inbound_thread: threading.Thread | None = None
-        # Outbound provenance rate limiter.
+        # Outbound provenance rate limiter; wraps the injected Clock as a
+        # float-seconds callable (the limiter's existing API contract).
         self._provenance = StatusTextTransitionRateLimiter(
             send_statustext=self._send_statustext_internal,
-            clock=time.monotonic,
+            clock=self._monotonic_s,
         )
 
     # ------------------------------------------------------------------
@@ -226,7 +230,7 @@ class PymavlinkArdupilotAdapter:
             raise FcEmitError("smoothed output cannot be emitted to FC (Invariant 6)")
         horiz_accuracy_m = self._cov_projector.to_ardupilot_horiz_accuracy_m(output)
         wgs = self._extract_wgs84(output)
-        emitted_at = time.monotonic_ns()
+        emitted_at = self._clock.monotonic_ns()
         self._sequence_number += 1
         seq = self._sequence_number
         try:
@@ -312,7 +316,7 @@ class PymavlinkArdupilotAdapter:
         if not self._opened or self._connection is None:
             raise FcEmitError("adapter not opened")
         self._enforce_single_writer()
-        now_ns = time.monotonic_ns()
+        now_ns = self._clock.monotonic_ns()
         if self._last_switch_attempt_ns:
             elapsed_s = (now_ns - self._last_switch_attempt_ns) / 1_000_000_000
             if elapsed_s < _SWITCH_RATE_LIMIT_S:
@@ -388,7 +392,7 @@ class PymavlinkArdupilotAdapter:
                 state=FlightState.INIT,
                 last_valid_gps_hint_wgs84=None,
                 last_valid_gps_age_ms=None,
-                captured_at=time.monotonic_ns(),
+                captured_at=self._clock.monotonic_ns(),
             )
         payload = latest.payload
         assert isinstance(payload, FlightStateSignal)
@@ -542,9 +546,9 @@ class PymavlinkArdupilotAdapter:
         Returns the ACK message on match, or ``None`` on timeout. Other
         COMMAND_ACK messages (for unrelated commands) are ignored.
         """
-        deadline = self._clock() + (timeout_ms / 1000.0)
+        deadline = self._monotonic_s() + (timeout_ms / 1000.0)
         while True:
-            remaining = deadline - self._clock()
+            remaining = deadline - self._monotonic_s()
             if remaining <= 0:
                 return None
             try:
@@ -608,11 +612,14 @@ class PymavlinkArdupilotAdapter:
             )
         return wgs
 
+    def _monotonic_s(self) -> float:
+        return self._clock.monotonic_ns() / 1_000_000_000
+
     def _clock_us(self) -> int:
-        return int(self._clock() * 1_000_000)
+        return self._clock.monotonic_ns() // 1_000
 
     def _clock_ms_boot(self) -> int:
-        return int(self._clock() * 1_000)
+        return self._clock.monotonic_ns() // 1_000_000
 
     def _fdr_signing_event(self, *, kind: str, kv: dict[str, Any]) -> None:
         record = FdrRecord(
diff --git a/src/gps_denied_onboard/frame_source/__init__.py b/src/gps_denied_onboard/frame_source/__init__.py
index 4f03516..77a98fc 100644
--- a/src/gps_denied_onboard/frame_source/__init__.py
+++ b/src/gps_denied_onboard/frame_source/__init__.py
@@ -1,9 +1,21 @@
-"""FrameSource interface + concrete implementations.
+"""``FrameSource`` cross-cutting interface — public surface (AZ-398 v1.0.0).
 
-The interface is bootstrap-stubbed here. `LiveCameraFrameSource` and
-`VideoFileFrameSource` are owned by AZ-398.
+Per AC-9, this module re-exports the Protocol and the error family
+ONLY. Concrete strategies (``LiveCameraFrameSource``,
+``VideoFileFrameSource``) live in their own modules and are imported
+LAZILY by ``runtime_root.frame_source_factory.build_frame_source``;
+this keeps the lazy-import boundary explicit and lets Tier-0 builds
+omit the OpenCV runtime entirely.
 """
 
+from gps_denied_onboard.frame_source.errors import (
+    FrameSourceConfigError,
+    FrameSourceError,
+)
 from gps_denied_onboard.frame_source.interface import FrameSource
 
-__all__ = ["FrameSource"]
+__all__ = [
+    "FrameSource",
+    "FrameSourceConfigError",
+    "FrameSourceError",
+]
diff --git a/src/gps_denied_onboard/frame_source/errors.py b/src/gps_denied_onboard/frame_source/errors.py
new file mode 100644
index 0000000..5bf83e3
--- /dev/null
+++ b/src/gps_denied_onboard/frame_source/errors.py
@@ -0,0 +1,48 @@
+"""``FrameSource`` error taxonomy (AZ-398 v1.0.0).
+
+Per the replay contract
+(``_docs/02_document/contracts/replay/replay_protocol.md``), every
+transient I/O failure on the camera path MUST surface as
+:class:`FrameSourceError` (Invariant 4 — replay must be deterministic,
+silent ``None`` drops are forbidden).
+
+The two-class hierarchy mirrors the C6/C7/C1 component taxonomies:
+
+- :class:`FrameSourceError` — operational failures during streaming
+  (decode error, device disconnect, out-of-order frame).
+- :class:`FrameSourceConfigError` — composition-time failures (build
+  flag OFF, missing dependency, invalid config).
+"""
+
+from __future__ import annotations
+
+
+class FrameSourceError(RuntimeError):
+    """Transient or fatal failure during frame ingestion.
+
+    Examples:
+
+    - A corrupt H.264 keyframe in the replay video file.
+    - An ordering violation: ``next_frame()`` returned a frame whose
+      ``monotonic_ns`` is < the previous frame's (Invariant 3).
+    - A USB camera disconnect mid-flight (live source).
+
+    The error message MUST identify the frame index or timestamp where
+    the failure occurred so the operator can correlate against the
+    upstream recording.
+    """
+
+
+class FrameSourceConfigError(RuntimeError):
+    """Composition-time configuration failure for a frame source.
+
+    Examples:
+
+    - ``BUILD_VIDEO_FILE_FRAME_SOURCE=OFF`` and the binary tried to
+      construct :class:`VideoFileFrameSource`.
+    - The configured video path does not exist or is not readable.
+    - OpenCV is not importable (Tier-0 / docker-minimal build).
+    """
+
+
+__all__ = ["FrameSourceError", "FrameSourceConfigError"]
diff --git a/src/gps_denied_onboard/frame_source/interface.py b/src/gps_denied_onboard/frame_source/interface.py
index 282c608..a392328 100644
--- a/src/gps_denied_onboard/frame_source/interface.py
+++ b/src/gps_denied_onboard/frame_source/interface.py
@@ -1,18 +1,62 @@
-"""`FrameSource` Protocol.
+"""``FrameSource`` Protocol — public Layer 1 cross-cutting interface (AZ-398 v1.0.0).
 
-Owned by AZ-398 (E-DEMO-REPLAY) for the formalisation; bootstrap ships the
-interface stub so C1 can be constructor-injected against it.
+Frozen per ``_docs/02_document/contracts/replay/replay_protocol.md``.
+
+Two strategies implement this Protocol:
+
+- :class:`LiveCameraFrameSource` — the formalised live camera ingest
+  path (gated ``BUILD_LIVE_CAMERA_FRAME_SOURCE``).
+- :class:`VideoFileFrameSource` — the replay-only file decoder (gated
+  ``BUILD_VIDEO_FILE_FRAME_SOURCE``).
+
+Consumers (C1 :class:`VioStrategy`) accept a :class:`FrameSource` via
+constructor injection so production code stays mode-agnostic
+(Invariant 1).
 """
 
 from __future__ import annotations
 
-from collections.abc import Iterator
-from typing import Protocol
+from typing import TYPE_CHECKING, Protocol, runtime_checkable
 
-from gps_denied_onboard._types.nav import NavCameraFrame
+if TYPE_CHECKING:
+    from gps_denied_onboard._types.nav import NavCameraFrame
 
 
+@runtime_checkable
 class FrameSource(Protocol):
-    """A source of `NavCameraFrame` instances."""
+    """A pluggable camera-frame producer.
 
-    def frames(self) -> Iterator[NavCameraFrame]: ...
+    The Protocol exposes two methods and one ordering invariant:
+
+    - :meth:`next_frame` returns the next :class:`NavCameraFrame` (with
+      ``metadata["monotonic_ns"]`` set by the strategy from its
+      injected :class:`Clock`) or ``None`` ONLY when the stream is
+      permanently exhausted (Invariant 4).
+    - Consecutive ``next_frame()`` returns MUST have non-decreasing
+      ``metadata["monotonic_ns"]`` (Invariant 3); out-of-order frames
+      raise :class:`FrameSourceError`.
+    - :meth:`close` releases the underlying capture handle and is
+      idempotent (AC-10).
+    """
+
+    def next_frame(self) -> "NavCameraFrame | None":
+        """Return the next frame, ``None`` on end-of-stream.
+
+        Transient I/O failures (decode error, disconnect) MUST raise
+        :class:`FrameSourceError` — never return ``None`` silently
+        (Invariant 4). After ``None`` has been returned once, every
+        subsequent call MUST also return ``None`` (idempotent EOS).
+        """
+        ...
+
+    def close(self) -> None:
+        """Release the underlying capture handle.
+
+        Idempotent: a second call is a no-op (AC-10); the strategy
+        SHOULD log a DEBUG line on the second call so a debug trace
+        can prove no double-free occurred.
+        """
+        ...
+
+
+__all__ = ["FrameSource"]
diff --git a/src/gps_denied_onboard/frame_source/live_camera.py b/src/gps_denied_onboard/frame_source/live_camera.py
new file mode 100644
index 0000000..da8a9cf
--- /dev/null
+++ b/src/gps_denied_onboard/frame_source/live_camera.py
@@ -0,0 +1,161 @@
+"""``LiveCameraFrameSource`` — live nav-camera ingest (AZ-398).
+
+Wraps :class:`cv2.VideoCapture` against an integer device index (the
+USB / CSI camera bound at boot by the airborne / research / operator
+binaries). The strategy is intentionally minimal: each
+:meth:`next_frame` call performs one blocking ``capture.read()`` and
+returns the freshest frame; no dedicated decode thread, no ring
+buffer. C1 (the only consumer) drives the loop at its target
+rate, and a blocking read is the simplest way to apply backpressure.
+
+Gated by ``BUILD_LIVE_CAMERA_FRAME_SOURCE`` (Invariant 9). The flag is
+``ON`` for live / research / operator / replay binaries and ``OFF``
+only for unit tests that need to construct a substitute without
+touching a real camera.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+from datetime import datetime, timezone
+from typing import TYPE_CHECKING, Any
+
+from gps_denied_onboard.frame_source.errors import (
+    FrameSourceConfigError,
+    FrameSourceError,
+)
+
+if TYPE_CHECKING:
+    from gps_denied_onboard._types.nav import NavCameraFrame
+    from gps_denied_onboard.clock import Clock
+
+
+_BUILD_FLAG = "BUILD_LIVE_CAMERA_FRAME_SOURCE"
+
+_logger = logging.getLogger(__name__)
+
+
+def _build_flag_on() -> bool:
+    raw = os.environ.get(_BUILD_FLAG, "")
+    return raw.strip().lower() in {"on", "1", "true", "yes"}
+
+
+class LiveCameraFrameSource:
+    """Live :class:`FrameSource` strategy backed by ``cv2.VideoCapture``.
+
+    Constructor parameters:
+
+    - ``device_index`` — integer index passed to ``cv2.VideoCapture``;
+      typically ``0`` for the first attached camera.
+    - ``camera_calibration_id`` — string identifier baked into every
+      emitted frame (matches the intrinsics file shipped with the
+      binary).
+    - ``clock`` — injected :class:`Clock`; supplies the per-frame
+      ``monotonic_ns`` ordering key and the wall-clock timestamp.
+    """
+
+    __slots__ = (
+        "_device_index",
+        "_camera_calibration_id",
+        "_clock",
+        "_capture",
+        "_frame_counter",
+        "_last_monotonic_ns",
+        "_closed",
+    )
+
+    def __init__(
+        self,
+        *,
+        device_index: int,
+        camera_calibration_id: str,
+        clock: "Clock",
+    ) -> None:
+        if not _build_flag_on():
+            raise FrameSourceConfigError(
+                f"{_BUILD_FLAG} is OFF in this binary; "
+                "LiveCameraFrameSource is unavailable."
+            )
+        try:
+            import cv2 as _cv2
+        except ImportError as exc:
+            raise FrameSourceConfigError(
+                "LiveCameraFrameSource requires opencv-python; not "
+                "importable in this binary."
+            ) from exc
+        capture = _cv2.VideoCapture(device_index)
+        if not capture.isOpened():
+            capture.release()
+            raise FrameSourceConfigError(
+                f"LiveCameraFrameSource: cv2.VideoCapture could not open "
+                f"device index {device_index}"
+            )
+        self._device_index = device_index
+        self._camera_calibration_id = camera_calibration_id
+        self._clock = clock
+        self._capture = capture
+        self._frame_counter = 0
+        self._last_monotonic_ns = -1
+        self._closed = False
+
+    def next_frame(self) -> "NavCameraFrame | None":
+        from gps_denied_onboard._types.nav import NavCameraFrame
+
+        if self._closed:
+            return None
+        ok, image = self._capture.read()
+        if not ok or image is None:
+            # Live camera: a failed read is a transient error (USB
+            # glitch, driver hiccup). Invariant 4 requires raising,
+            # not returning None — the only legitimate None is EOS,
+            # and a live camera never EOSes.
+            raise FrameSourceError(
+                f"LiveCameraFrameSource: cv2.VideoCapture.read failed at "
+                f"frame {self._frame_counter} (device "
+                f"{self._device_index})"
+            )
+        monotonic_ns = self._clock.monotonic_ns()
+        if monotonic_ns < self._last_monotonic_ns:
+            raise FrameSourceError(
+                f"LiveCameraFrameSource: clock went backwards at frame "
+                f"{self._frame_counter}: {monotonic_ns} ns followed "
+                f"{self._last_monotonic_ns} ns (Invariant 3)"
+            )
+        timestamp = datetime.fromtimestamp(
+            self._clock.time_ns() / 1e9, tz=timezone.utc
+        )
+        metadata: dict[str, Any] = {
+            "monotonic_ns": monotonic_ns,
+            "source": "live_camera",
+            "device_index": self._device_index,
+        }
+        frame = NavCameraFrame(
+            frame_id=self._frame_counter,
+            timestamp=timestamp,
+            image=image,
+            camera_calibration_id=self._camera_calibration_id,
+            metadata=metadata,
+        )
+        self._frame_counter += 1
+        self._last_monotonic_ns = monotonic_ns
+        return frame
+
+    def close(self) -> None:
+        if self._closed:
+            _logger.debug(
+                "LiveCameraFrameSource(device=%s) close called twice; no-op",
+                self._device_index,
+            )
+            return
+        self._closed = True
+        try:
+            self._capture.release()
+        except Exception:  # pragma: no cover — defensive.
+            _logger.exception(
+                "LiveCameraFrameSource(device=%s) cv2.release() raised",
+                self._device_index,
+            )
+
+
+__all__ = ["LiveCameraFrameSource"]
diff --git a/src/gps_denied_onboard/frame_source/video_file.py b/src/gps_denied_onboard/frame_source/video_file.py
new file mode 100644
index 0000000..bdf8178
--- /dev/null
+++ b/src/gps_denied_onboard/frame_source/video_file.py
@@ -0,0 +1,199 @@
+"""``VideoFileFrameSource`` — replay-only file decoder (AZ-398).
+
+Streams an MP4 / MKV / AVI file frame-by-frame via OpenCV's
+:class:`cv2.VideoCapture`. Each emitted :class:`NavCameraFrame`
+carries:
+
+- ``frame_id`` — a strictly-increasing counter starting at 0.
+- ``timestamp`` — UTC wall-clock at decode time (from the injected
+  :class:`Clock`); the file's own pts is NOT used for this field
+  because replay deterministically remaps it.
+- ``image`` — the decoded BGR ``numpy.ndarray`` (OpenCV native order).
+- ``metadata["monotonic_ns"]`` — the injected :class:`Clock`'s
+  ``monotonic_ns()`` at decode time. This is the value AC-2 asserts
+  non-decreasing.
+- ``metadata["source_pts_ns"]`` — the file's per-frame PTS in ns (the
+  ``CAP_PROP_POS_MSEC`` reading × 1e6) for downstream determinism.
+
+Gated by ``BUILD_VIDEO_FILE_FRAME_SOURCE`` (Invariant 9). The check is
+performed at constructor entry — a Tier-0 build that imports this
+module by accident still raises ``FrameSourceConfigError`` cleanly
+without attempting an OpenCV import.
+"""
+
+from __future__ import annotations
+
+import logging
+import os
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import TYPE_CHECKING, Any
+
+from gps_denied_onboard.frame_source.errors import (
+    FrameSourceConfigError,
+    FrameSourceError,
+)
+
+if TYPE_CHECKING:
+    from gps_denied_onboard._types.nav import NavCameraFrame
+    from gps_denied_onboard.clock import Clock
+
+
+_BUILD_FLAG = "BUILD_VIDEO_FILE_FRAME_SOURCE"
+
+_logger = logging.getLogger(__name__)
+
+
+def _build_flag_on() -> bool:
+    """``ON`` / ``1`` / ``true`` / ``yes`` (case-insensitive) → ``True``."""
+    raw = os.environ.get(_BUILD_FLAG, "")
+    return raw.strip().lower() in {"on", "1", "true", "yes"}
+
+
+class VideoFileFrameSource:
+    """Replay :class:`FrameSource` strategy backed by ``cv2.VideoCapture``.
+
+    Stream-decodes a video file; per-frame decode is amortised by
+    OpenCV's internal buffer. The strategy preserves the file's frame
+    order — there is no seek, no random-access path; this keeps
+    replay deterministic (Invariant 10).
+
+    Constructor parameters:
+
+    - ``path`` — filesystem path to an MP4/MKV/AVI (existence checked
+      at construction).
+    - ``camera_calibration_id`` — string identifier propagated into
+      every emitted :class:`NavCameraFrame` so downstream consumers
+      (C1, C3, C4) load the correct intrinsics for the recording.
+    - ``clock`` — injected :class:`Clock`; the strategy reads
+      ``clock.monotonic_ns()`` per emitted frame for the
+      ``metadata["monotonic_ns"]`` ordering field.
+    """
+
+    __slots__ = (
+        "_path",
+        "_camera_calibration_id",
+        "_clock",
+        "_capture",
+        "_frame_counter",
+        "_last_monotonic_ns",
+        "_closed",
+        "_eos_returned",
+    )
+
+    def __init__(
+        self,
+        *,
+        path: Path | str,
+        camera_calibration_id: str,
+        clock: "Clock",
+    ) -> None:
+        if not _build_flag_on():
+            raise FrameSourceConfigError(
+                f"{_BUILD_FLAG} is OFF in this binary; "
+                "VideoFileFrameSource is unavailable. Rebuild with the "
+                "flag set to ON in the replay binary's Dockerfile."
+            )
+        resolved = Path(path)
+        if not resolved.is_file():
+            raise FrameSourceConfigError(
+                f"VideoFileFrameSource: path {resolved!s} does not exist "
+                "or is not a regular file."
+            )
+        try:
+            import cv2 as _cv2
+        except ImportError as exc:
+            raise FrameSourceConfigError(
+                "VideoFileFrameSource requires opencv-python; not "
+                "importable in this binary."
+            ) from exc
+        capture = _cv2.VideoCapture(str(resolved))
+        if not capture.isOpened():
+            capture.release()
+            raise FrameSourceConfigError(
+                f"VideoFileFrameSource: cv2.VideoCapture could not open "
+                f"{resolved!s} (unsupported codec or corrupt header)."
+            )
+        self._path = resolved
+        self._camera_calibration_id = camera_calibration_id
+        self._clock = clock
+        self._capture = capture
+        self._frame_counter = 0
+        self._last_monotonic_ns = -1
+        self._closed = False
+        self._eos_returned = False
+
+    def next_frame(self) -> "NavCameraFrame | None":
+        from gps_denied_onboard._types.nav import NavCameraFrame
+
+        if self._closed or self._eos_returned:
+            return None
+        try:
+            import cv2 as _cv2
+        except ImportError as exc:  # pragma: no cover — established at __init__.
+            raise FrameSourceError(
+                "VideoFileFrameSource: opencv-python disappeared between "
+                "construction and next_frame()"
+            ) from exc
+        ok, image = self._capture.read()
+        if not ok:
+            self._eos_returned = True
+            return None
+        if image is None:
+            # OpenCV's read() returning ok=True with image=None signals a
+            # decoder-internal failure for the current frame; treat as a
+            # transient error per Invariant 4 rather than silently
+            # advancing.
+            raise FrameSourceError(
+                f"VideoFileFrameSource: video decode failed at frame "
+                f"{self._frame_counter} (cv2.VideoCapture.read returned "
+                "ok=True with image=None)"
+            )
+        monotonic_ns = self._clock.monotonic_ns()
+        if monotonic_ns < self._last_monotonic_ns:
+            raise FrameSourceError(
+                f"VideoFileFrameSource: clock went backwards at frame "
+                f"{self._frame_counter}: {monotonic_ns} ns followed "
+                f"{self._last_monotonic_ns} ns (Invariant 3)"
+            )
+        pos_msec = float(self._capture.get(_cv2.CAP_PROP_POS_MSEC))
+        source_pts_ns = int(pos_msec * 1_000_000)
+        timestamp = datetime.fromtimestamp(
+            self._clock.time_ns() / 1e9, tz=timezone.utc
+        )
+        metadata: dict[str, Any] = {
+            "monotonic_ns": monotonic_ns,
+            "source_pts_ns": source_pts_ns,
+            "source": "video_file",
+        }
+        frame = NavCameraFrame(
+            frame_id=self._frame_counter,
+            timestamp=timestamp,
+            image=image,
+            camera_calibration_id=self._camera_calibration_id,
+            metadata=metadata,
+        )
+        self._frame_counter += 1
+        self._last_monotonic_ns = monotonic_ns
+        return frame
+
+    def close(self) -> None:
+        if self._closed:
+            _logger.debug(
+                "VideoFileFrameSource(%s) close called twice; no-op",
+                self._path,
+            )
+            return
+        self._closed = True
+        try:
+            self._capture.release()
+        except Exception:  # pragma: no cover — defensive.
+            # cv2.VideoCapture.release should never raise; if it does on
+            # an exotic backend, we still want to flag the source as
+            # closed so a second close() stays a no-op.
+            _logger.exception(
+                "VideoFileFrameSource(%s) cv2.release() raised", self._path
+            )
+
+
+__all__ = ["VideoFileFrameSource"]
diff --git a/src/gps_denied_onboard/runtime_root/clock_factory.py b/src/gps_denied_onboard/runtime_root/clock_factory.py
new file mode 100644
index 0000000..00fadb0
--- /dev/null
+++ b/src/gps_denied_onboard/runtime_root/clock_factory.py
@@ -0,0 +1,61 @@
+"""Composition-root :class:`Clock` factory (AZ-398).
+
+Composition resolves :class:`Clock` exactly once per process per
+Invariant — Single Clock per process. Live / research / operator
+binaries call :func:`build_clock(kind="wall")`; the replay binary
+calls :func:`build_clock(kind="tlog", source=...)` (the replay
+composition root, AZ-401, wires the tlog timestamp source).
+
+Concrete strategy modules (``wall_clock``, ``tlog_derived``) live
+under :mod:`gps_denied_onboard.clock`; they are imported eagerly here
+because the Clock has no Tier-specific runtime dependency and the
+selection happens at startup.
+"""
+
+from __future__ import annotations
+
+from collections.abc import Callable, Iterable
+from typing import TYPE_CHECKING
+
+from gps_denied_onboard.clock.tlog_derived import TlogDerivedClock
+from gps_denied_onboard.clock.wall_clock import WallClock
+
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+
+
+__all__ = ["build_clock"]
+
+
+def build_clock(
+    *,
+    kind: str = "wall",
+    source: Callable[[], int] | Iterable[int] | None = None,
+) -> "Clock":
+    """Construct the :class:`Clock` strategy for this process.
+
+    ``kind`` is one of ``"wall"`` (default) or ``"tlog"``. ``source`` is
+    required when ``kind == "tlog"`` (it carries the tlog parser's
+    timestamp stream) and forbidden otherwise.
+
+    Raises :class:`ValueError` on an unknown ``kind`` or a misconfigured
+    source — neither is recoverable, so failing loudly at composition
+    time is correct.
+    """
+    if kind == "wall":
+        if source is not None:
+            raise ValueError(
+                "build_clock(kind='wall'): source must be None; "
+                "WallClock takes no upstream timestamp stream."
+            )
+        return WallClock()
+    if kind == "tlog":
+        if source is None:
+            raise ValueError(
+                "build_clock(kind='tlog'): source is required (the tlog "
+                "timestamp stream from the replay parser)."
+            )
+        return TlogDerivedClock(source)
+    raise ValueError(
+        f"build_clock: unknown kind {kind!r}; expected 'wall' or 'tlog'"
+    )
diff --git a/src/gps_denied_onboard/runtime_root/frame_source_factory.py b/src/gps_denied_onboard/runtime_root/frame_source_factory.py
new file mode 100644
index 0000000..020e804
--- /dev/null
+++ b/src/gps_denied_onboard/runtime_root/frame_source_factory.py
@@ -0,0 +1,91 @@
+"""Composition-root :class:`FrameSource` factory (AZ-398).
+
+Selects exactly one :class:`FrameSource` strategy per binary based on
+the requested ``kind`` and the compile-time ``BUILD_*`` flags. The
+concrete strategy modules are imported lazily so a Tier-0 build with
+``BUILD_LIVE_CAMERA_FRAME_SOURCE=OFF`` and
+``BUILD_VIDEO_FILE_FRAME_SOURCE=OFF`` never pulls OpenCV into
+``sys.modules`` (Invariant 9 — verifiable via ``sys.modules``).
+
+Build-flag gating happens INSIDE the strategy constructor (so unit
+tests that monkey-patch the env still hit the gate); this factory
+performs the strategy-name → module mapping only.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+from typing import TYPE_CHECKING
+
+from gps_denied_onboard.frame_source.errors import FrameSourceConfigError
+
+if TYPE_CHECKING:
+    from gps_denied_onboard.clock import Clock
+    from gps_denied_onboard.frame_source import FrameSource
+
+
+__all__ = ["build_frame_source"]
+
+
+def build_frame_source(
+    *,
+    kind: str,
+    camera_calibration_id: str,
+    clock: "Clock",
+    device_index: int | None = None,
+    video_path: Path | str | None = None,
+) -> "FrameSource":
+    """Construct the :class:`FrameSource` strategy.
+
+    ``kind`` is one of ``"live"`` or ``"video_file"``:
+
+    - ``"live"`` requires ``device_index`` (integer camera index) and
+      forbids ``video_path``.
+    - ``"video_file"`` requires ``video_path`` (filesystem path) and
+      forbids ``device_index``.
+
+    Build-flag gating is enforced by the strategy constructor; this
+    factory raises :class:`FrameSourceConfigError` ONLY on argument-
+    shape mistakes (missing or extra parameters for the chosen kind).
+    """
+    if kind == "live":
+        if device_index is None:
+            raise FrameSourceConfigError(
+                "build_frame_source(kind='live'): device_index is required"
+            )
+        if video_path is not None:
+            raise FrameSourceConfigError(
+                "build_frame_source(kind='live'): video_path must be None"
+            )
+        from gps_denied_onboard.frame_source.live_camera import (
+            LiveCameraFrameSource,
+        )
+
+        return LiveCameraFrameSource(
+            device_index=device_index,
+            camera_calibration_id=camera_calibration_id,
+            clock=clock,
+        )
+    if kind == "video_file":
+        if video_path is None:
+            raise FrameSourceConfigError(
+                "build_frame_source(kind='video_file'): video_path is required"
+            )
+        if device_index is not None:
+            raise FrameSourceConfigError(
+                "build_frame_source(kind='video_file'): "
+                "device_index must be None"
+            )
+        from gps_denied_onboard.frame_source.video_file import (
+            VideoFileFrameSource,
+        )
+
+        return VideoFileFrameSource(
+            path=video_path,
+            camera_calibration_id=camera_calibration_id,
+            clock=clock,
+        )
+    raise FrameSourceConfigError(
+        f"build_frame_source: unknown kind {kind!r}; "
+        "expected 'live' or 'video_file'"
+    )
diff --git a/tests/_meta/__init__.py b/tests/_meta/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/_meta/test_no_direct_time_in_components.py b/tests/_meta/test_no_direct_time_in_components.py
new file mode 100644
index 0000000..5ccf184
--- /dev/null
+++ b/tests/_meta/test_no_direct_time_in_components.py
@@ -0,0 +1,105 @@
+"""AC-4 — components MUST NOT call ``time.monotonic_ns`` / ``time.time_ns`` / ``time.sleep``.
+
+Enforces Invariant 2 of the replay contract
+(``_docs/02_document/contracts/replay/replay_protocol.md``): every
+time-driven code path in a C* component consumes an injected
+:class:`Clock` instead. Replay determinism (R-DEMO-4) collapses the
+moment a component reaches into the stdlib ``time`` module directly,
+so this guard runs on every PR touching ``src/gps_denied_onboard/components/``.
+
+The scan is AST-based — docstrings and comments mentioning the forbidden
+APIs do NOT trip it; only call sites and attribute references do.
+"""
+
+from __future__ import annotations
+
+import ast
+from pathlib import Path
+
+import pytest
+
+_FORBIDDEN_ATTRS: frozenset[str] = frozenset(
+    {"monotonic_ns", "time_ns", "sleep"}
+)
+
+_COMPONENTS_ROOT: Path = (
+    Path(__file__).parent.parent.parent
+    / "src"
+    / "gps_denied_onboard"
+    / "components"
+)
+
+
+def _python_files_under(root: Path) -> list[Path]:
+    return sorted(p for p in root.rglob("*.py") if p.is_file())
+
+
+def _find_direct_time_references(source: str) -> list[tuple[int, str]]:
+    """Return ``(lineno, attribute_name)`` for every direct ``time.X`` ref.
+
+    Only flags ``ast.Attribute(value=ast.Name(id='time'), attr=<x>)``
+    where ``<x>`` is one of the forbidden names. Aliased imports
+    (``import time as t`` → ``t.monotonic_ns()``) are intentionally NOT
+    caught — the component code convention is to avoid such aliases, and
+    catching them would require flow-sensitive analysis.
+    """
+    hits: list[tuple[int, str]] = []
+    tree = ast.parse(source)
+    for node in ast.walk(tree):
+        if not isinstance(node, ast.Attribute):
+            continue
+        if not isinstance(node.value, ast.Name):
+            continue
+        if node.value.id != "time":
+            continue
+        if node.attr in _FORBIDDEN_ATTRS:
+            hits.append((node.lineno, f"time.{node.attr}"))
+    return hits
+
+
+def test_components_have_no_direct_time_references() -> None:
+    # Arrange
+    files = _python_files_under(_COMPONENTS_ROOT)
+    assert files, f"AST scan found no .py files under {_COMPONENTS_ROOT}"
+    offences: list[str] = []
+    # Act
+    for file in files:
+        source = file.read_text(encoding="utf-8")
+        for lineno, attr in _find_direct_time_references(source):
+            rel = file.relative_to(_COMPONENTS_ROOT.parent.parent.parent.parent)
+            offences.append(f"{rel}:{lineno} — {attr}")
+    # Assert
+    assert not offences, (
+        "Invariant 2 violation: direct stdlib-`time` references found in "
+        "`src/gps_denied_onboard/components/**/*.py`. Consume an injected "
+        "`Clock` (`gps_denied_onboard.clock`) instead.\n"
+        + "\n".join(offences)
+    )
+
+
+def test_scan_helper_detects_known_forbidden_pattern() -> None:
+    # Arrange — self-check the AST helper so a stale scan can't silently pass.
+    source = "import time\ndef f() -> int:\n    return time.monotonic_ns()\n"
+    # Act
+    hits = _find_direct_time_references(source)
+    # Assert
+    assert hits == [(3, "time.monotonic_ns")]
+
+
+def test_scan_helper_ignores_docstring_mentions() -> None:
+    # Arrange — docstrings naming the forbidden API must not trip the scan.
+    source = '"""This module talks about time.monotonic_ns in prose only."""\n'
+    # Act
+    hits = _find_direct_time_references(source)
+    # Assert
+    assert hits == []
+
+
+@pytest.mark.parametrize("forbidden", sorted(_FORBIDDEN_ATTRS))
+def test_scan_helper_detects_each_forbidden_attr(forbidden: str) -> None:
+    # Arrange
+    source = f"import time\ntime.{forbidden}()\n"
+    # Act
+    hits = _find_direct_time_references(source)
+    # Assert
+    assert hits == [(2, f"time.{forbidden}")]
diff --git a/tests/unit/c5_state/test_az388_fallback_watcher.py b/tests/unit/c5_state/test_az388_fallback_watcher.py
index 9e9e33a..33489b1 100644
--- a/tests/unit/c5_state/test_az388_fallback_watcher.py
+++ b/tests/unit/c5_state/test_az388_fallback_watcher.py
@@ -213,7 +213,7 @@ def test_ac6_custom_threshold_5s_engages_at_5s() -> None:
 
 def test_ac6_zero_threshold_rejected() -> None:
     with pytest.raises(ValueError, match="threshold_s must be > 0"):
-        FallbackWatcher(threshold_s=0.0, fdr_client=None)
+        FallbackWatcher(threshold_s=0.0, fdr_client=None, clock_ns=lambda: 0)
 
 
 # ---------------------------------------------------------------------
@@ -378,17 +378,14 @@ def test_ac7_isam2_current_estimate_entry_engages_after_threshold() -> None:
     # and call current_estimate WITHOUT a seeded prior so it raises
     # EstimatorFatalError after the entry hook engages fallback.
     estimator._fallback._last_successful_estimate_ns = 0
-    # Patch monotonic_ns inside the estimator module so the entry
-    # hook sees the synthesised "now".
+    # Patch the estimator's injected Clock so the entry hook sees the
+    # synthesised "now" (AZ-398: components consume an injected
+    # :class:`Clock`, not :func:`time.monotonic_ns`).
     from gps_denied_onboard.components.c5_state.errors import EstimatorFatalError
 
-    with (
-        mock.patch(
-            "gps_denied_onboard.components.c5_state.gtsam_isam2_estimator.time.monotonic_ns",
-            return_value=int(4.0 * 1e9),
-        ),
-        pytest.raises(EstimatorFatalError),
-    ):
+    estimator._clock = mock.MagicMock()
+    estimator._clock.monotonic_ns.return_value = int(4.0 * 1e9)
+    with pytest.raises(EstimatorFatalError):
         estimator.current_estimate()
 
     assert len(engaged_seen) == 1
diff --git a/tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py b/tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py
index fc5585f..3128209 100644
--- a/tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py
+++ b/tests/unit/c8_fc_adapter/test_az393_ardupilot_outbound.py
@@ -70,6 +70,22 @@ class _ConnStub:
         self.closed = True
 
 
+class _FixedClock:
+    """Test :class:`Clock` stand-in returning constant ``monotonic_ns``."""
+
+    def __init__(self, ns: int) -> None:
+        self._ns = ns
+
+    def monotonic_ns(self) -> int:
+        return self._ns
+
+    def time_ns(self) -> int:
+        return self._ns
+
+    def sleep_until_ns(self, target_ns: int) -> None:
+        return None
+
+
 @pytest.fixture
 def conn() -> _ConnStub:
     return _ConnStub()
@@ -85,7 +101,7 @@ def adapter(conn: _ConnStub, tmp_path) -> PymavlinkArdupilotAdapter:
         wgs_converter=mock.MagicMock(),
         covariance_projector=cov,
         fdr_client=fdr,
-        clock=lambda: 1.0,
+        clock=_FixedClock(1_000_000_000),
         flight_id="flt-test",
         connect_factory=lambda device, baud: conn,
     )
diff --git a/tests/unit/clock/__init__.py b/tests/unit/clock/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/unit/clock/test_protocol_conformance.py b/tests/unit/clock/test_protocol_conformance.py
new file mode 100644
index 0000000..d88419c
--- /dev/null
+++ b/tests/unit/clock/test_protocol_conformance.py
@@ -0,0 +1,180 @@
+"""AZ-398 — :class:`Clock` Protocol conformance + WallClock parity + TlogDerivedClock semantics."""
+
+from __future__ import annotations
+
+import time
+
+import pytest
+
+from gps_denied_onboard.clock import Clock
+from gps_denied_onboard.clock.tlog_derived import (
+    ClockOrderingError,
+    TlogDerivedClock,
+)
+from gps_denied_onboard.clock.wall_clock import WallClock
+from gps_denied_onboard.runtime_root.clock_factory import build_clock
+
+
+# ---------------------------------------------------------------------------
+# AC-1 — Protocol conformance.
+
+
+def test_wall_clock_satisfies_clock_protocol() -> None:
+    # Assert
+    assert isinstance(WallClock(), Clock)
+
+
+def test_tlog_derived_clock_satisfies_clock_protocol() -> None:
+    # Assert
+    assert isinstance(TlogDerivedClock([1, 2, 3]), Clock)
+
+
+# ---------------------------------------------------------------------------
+# AC-5 — WallClock parity with :mod:`time`.
+
+
+def test_wall_clock_monotonic_ns_tracks_stdlib() -> None:
+    # Arrange
+    clock = WallClock()
+    # Act
+    stdlib_before = time.monotonic_ns()
+    clock_now = clock.monotonic_ns()
+    stdlib_after = time.monotonic_ns()
+    # Assert
+    assert stdlib_before <= clock_now <= stdlib_after
+
+
+def test_wall_clock_time_ns_tracks_stdlib_within_1ms() -> None:
+    # Arrange
+    clock = WallClock()
+    # Act
+    stdlib = time.time_ns()
+    clock_now = clock.time_ns()
+    # Assert
+    assert abs(clock_now - stdlib) <= 1_000_000
+
+
+def test_wall_clock_sleep_until_ns_blocks_for_about_100ms() -> None:
+    # Arrange
+    clock = WallClock()
+    # Act
+    start = time.monotonic_ns()
+    target = start + 100_000_000  # 100 ms in the future
+    clock.sleep_until_ns(target)
+    elapsed_ns = time.monotonic_ns() - start
+    # Assert — AC-5 allows ±5 ms slack on a 100 ms sleep
+    assert 95_000_000 <= elapsed_ns <= 200_000_000
+
+
+def test_wall_clock_sleep_until_past_target_is_noop() -> None:
+    # Arrange
+    clock = WallClock()
+    past = clock.monotonic_ns() - 10_000_000_000  # 10 s ago
+    # Act
+    start = time.monotonic_ns()
+    clock.sleep_until_ns(past)
+    elapsed_ns = time.monotonic_ns() - start
+    # Assert — should return almost immediately (no negative sleep)
+    assert elapsed_ns < 5_000_000  # < 5 ms
+
+
+# ---------------------------------------------------------------------------
+# AC-6 — TlogDerivedClock advance-on-call semantics.
+
+
+def test_tlog_derived_clock_advances_per_call() -> None:
+    # Arrange
+    clock = TlogDerivedClock([1_000_000, 2_000_000, 3_000_000])
+    # Act
+    a = clock.monotonic_ns()
+    b = clock.monotonic_ns()
+    c = clock.monotonic_ns()
+    # Assert
+    assert (a, b, c) == (1_000_000, 2_000_000, 3_000_000)
+
+
+def test_tlog_derived_clock_time_ns_reflects_last_advance() -> None:
+    # Arrange
+    clock = TlogDerivedClock([42])
+    # Act
+    before = clock.time_ns()
+    clock.monotonic_ns()
+    after = clock.time_ns()
+    # Assert
+    assert (before, after) == (0, 42)
+
+
+def test_tlog_derived_clock_raises_on_non_monotonic_source() -> None:
+    # Arrange
+    clock = TlogDerivedClock([10, 5])
+    clock.monotonic_ns()
+    # Act + Assert
+    with pytest.raises(ClockOrderingError):
+        clock.monotonic_ns()
+
+
+def test_tlog_derived_clock_sleep_until_ns_is_noop() -> None:
+    # Arrange
+    clock = TlogDerivedClock([1])
+    start = time.monotonic_ns()
+    # Act
+    clock.sleep_until_ns(10**18)  # absurdly far in the future
+    elapsed_ns = time.monotonic_ns() - start
+    # Assert
+    assert elapsed_ns < 5_000_000  # < 5 ms
+
+
+def test_tlog_derived_clock_accepts_callable_source() -> None:
+    # Arrange
+    counter = {"i": 0}
+
+    def source() -> int:
+        counter["i"] += 1
+        return counter["i"] * 1_000_000
+
+    clock = TlogDerivedClock(source)
+    # Act
+    a = clock.monotonic_ns()
+    b = clock.monotonic_ns()
+    # Assert
+    assert (a, b) == (1_000_000, 2_000_000)
+
+
+def test_tlog_derived_clock_returns_last_value_when_source_exhausted() -> None:
+    # Arrange
+    clock = TlogDerivedClock([5])
+    # Act
+    first = clock.monotonic_ns()
+    second = clock.monotonic_ns()
+    # Assert — exhausted source returns the latched value, not an error
+    assert (first, second) == (5, 5)
+
+
+# ---------------------------------------------------------------------------
+# Composition-root factory (build_clock).
+
+
+def test_build_clock_wall_returns_wall_clock() -> None:
+    # Assert
+    assert isinstance(build_clock(kind="wall"), WallClock)
+
+
+def test_build_clock_tlog_returns_tlog_derived_clock() -> None:
+    # Assert
+    assert isinstance(build_clock(kind="tlog", source=[1, 2]), TlogDerivedClock)
+
+
+def test_build_clock_rejects_unknown_kind() -> None:
+    # Act + Assert
+    with pytest.raises(ValueError, match="unknown kind"):
+        build_clock(kind="invalid")  # type: ignore[arg-type]
+
+
+def test_build_clock_wall_rejects_source() -> None:
+    with pytest.raises(ValueError, match="source must be None"):
+        build_clock(kind="wall", source=[1])
+
+
+def test_build_clock_tlog_requires_source() -> None:
+    with pytest.raises(ValueError, match="source is required"):
+        build_clock(kind="tlog")
diff --git a/tests/unit/frame_source/__init__.py b/tests/unit/frame_source/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/unit/frame_source/test_protocol_conformance.py b/tests/unit/frame_source/test_protocol_conformance.py
new file mode 100644
index 0000000..d6d6651
--- /dev/null
+++ b/tests/unit/frame_source/test_protocol_conformance.py
@@ -0,0 +1,303 @@
+"""AZ-398 — :class:`FrameSource` Protocol conformance + concrete strategy ACs."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import cv2
+import numpy as np
+import pytest
+
+from gps_denied_onboard.clock.wall_clock import WallClock
+from gps_denied_onboard.frame_source import (
+    FrameSource,
+    FrameSourceConfigError,
+)
+from gps_denied_onboard.frame_source.live_camera import LiveCameraFrameSource
+from gps_denied_onboard.frame_source.video_file import VideoFileFrameSource
+
+
+# ---------------------------------------------------------------------------
+# Helpers.
+
+
+def _make_synthetic_video(path: Path, n_frames: int, fps: int = 30) -> None:
+    """Write an ``n_frames``-frame 64×48 BGR MP4V at ``path``."""
+    fourcc = cv2.VideoWriter_fourcc(*"mp4v")
+    writer = cv2.VideoWriter(str(path), fourcc, fps, (64, 48))
+    if not writer.isOpened():
+        raise RuntimeError(f"OpenCV could not open writer at {path!s}")
+    try:
+        for i in range(n_frames):
+            frame = np.full((48, 64, 3), i % 256, dtype=np.uint8)
+            writer.write(frame)
+    finally:
+        writer.release()
+
+
+@pytest.fixture
+def video_path_60(tmp_path: Path) -> Path:
+    """A synthetic 60-frame .mp4 file for AC-2."""
+    path = tmp_path / "az398_synthetic.mp4"
+    _make_synthetic_video(path, n_frames=60)
+    return path
+
+
+@pytest.fixture
+def enable_video_flag(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("BUILD_VIDEO_FILE_FRAME_SOURCE", "ON")
+
+
+@pytest.fixture
+def disable_video_flag(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("BUILD_VIDEO_FILE_FRAME_SOURCE", "OFF")
+
+
+@pytest.fixture
+def disable_live_flag(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("BUILD_LIVE_CAMERA_FRAME_SOURCE", "OFF")
+
+
+# ---------------------------------------------------------------------------
+# AC-1 — Protocol conformance.
+
+
+def test_video_file_frame_source_satisfies_frame_source_protocol(
+    enable_video_flag: None, video_path_60: Path
+) -> None:
+    # Arrange + Act
+    source = VideoFileFrameSource(
+        path=video_path_60,
+        camera_calibration_id="az398-synth",
+        clock=WallClock(),
+    )
+    try:
+        # Assert
+        assert isinstance(source, FrameSource)
+    finally:
+        source.close()
+
+
+# ---------------------------------------------------------------------------
+# AC-2 — VideoFileFrameSource produces 60 ordered frames + idempotent EOS.
+
+
+def test_video_file_frame_source_emits_60_frames_then_none(
+    enable_video_flag: None, video_path_60: Path
+) -> None:
+    # Arrange
+    source = VideoFileFrameSource(
+        path=video_path_60,
+        camera_calibration_id="az398-synth",
+        clock=WallClock(),
+    )
+    monotonics: list[int] = []
+    try:
+        # Act
+        for _ in range(60):
+            frame = source.next_frame()
+            assert frame is not None
+            monotonics.append(frame.metadata["monotonic_ns"])
+        # AC-2: 61st call → None; subsequent calls also None
+        eos_first = source.next_frame()
+        eos_second = source.next_frame()
+    finally:
+        source.close()
+    # Assert
+    assert eos_first is None
+    assert eos_second is None
+    assert len(monotonics) == 60
+    # Non-decreasing monotonic_ns ordering (Invariant 3 / AC-2)
+    assert all(b >= a for a, b in zip(monotonics, monotonics[1:], strict=False))
+
+
+def test_video_file_frame_source_emits_frame_id_counter_and_metadata(
+    enable_video_flag: None, video_path_60: Path
+) -> None:
+    # Arrange
+    source = VideoFileFrameSource(
+        path=video_path_60,
+        camera_calibration_id="az398-synth",
+        clock=WallClock(),
+    )
+    try:
+        # Act
+        first = source.next_frame()
+        second = source.next_frame()
+    finally:
+        source.close()
+    # Assert
+    assert first is not None and second is not None
+    assert first.frame_id == 0
+    assert second.frame_id == 1
+    assert first.camera_calibration_id == "az398-synth"
+    assert first.metadata["source"] == "video_file"
+    assert "monotonic_ns" in first.metadata
+    assert "source_pts_ns" in first.metadata
+
+
+# ---------------------------------------------------------------------------
+# AC-7 — corrupt video file raises FrameSourceConfigError on construction.
+
+
+def test_video_file_frame_source_rejects_corrupt_file(
+    enable_video_flag: None, tmp_path: Path
+) -> None:
+    # Arrange
+    corrupt = tmp_path / "garbage.mp4"
+    corrupt.write_bytes(b"not actually mp4 content" * 256)
+    # Act + Assert
+    with pytest.raises(FrameSourceConfigError):
+        VideoFileFrameSource(
+            path=corrupt,
+            camera_calibration_id="az398-corrupt",
+            clock=WallClock(),
+        )
+
+
+def test_video_file_frame_source_rejects_missing_path(
+    enable_video_flag: None, tmp_path: Path
+) -> None:
+    # Act + Assert
+    with pytest.raises(FrameSourceConfigError, match="does not exist"):
+        VideoFileFrameSource(
+            path=tmp_path / "missing.mp4",
+            camera_calibration_id="az398-missing",
+            clock=WallClock(),
+        )
+
+
+# ---------------------------------------------------------------------------
+# AC-8 — Build-flag gating.
+
+
+def test_video_file_frame_source_refuses_when_build_flag_off(
+    disable_video_flag: None, tmp_path: Path
+) -> None:
+    # Arrange — create a real file so the gate is exercised before path checks
+    valid = tmp_path / "any.mp4"
+    valid.write_bytes(b"")
+    # Act + Assert
+    with pytest.raises(
+        FrameSourceConfigError, match="BUILD_VIDEO_FILE_FRAME_SOURCE is OFF"
+    ):
+        VideoFileFrameSource(
+            path=valid,
+            camera_calibration_id="az398-gate",
+            clock=WallClock(),
+        )
+
+
+def test_live_camera_frame_source_refuses_when_build_flag_off(
+    disable_live_flag: None,
+) -> None:
+    # Act + Assert
+    with pytest.raises(
+        FrameSourceConfigError, match="BUILD_LIVE_CAMERA_FRAME_SOURCE is OFF"
+    ):
+        LiveCameraFrameSource(
+            device_index=0,
+            camera_calibration_id="az398-live-gate",
+            clock=WallClock(),
+        )
+
+
+# ---------------------------------------------------------------------------
+# AC-9 — Public API re-exports.
+
+
+def test_frame_source_public_module_only_exposes_protocol_and_errors() -> None:
+    # Arrange
+    from gps_denied_onboard import frame_source as module
+
+    # Assert — concrete strategies MUST NOT appear in __all__ per AC-9
+    assert "FrameSource" in module.__all__
+    assert "FrameSourceError" in module.__all__
+    assert "FrameSourceConfigError" in module.__all__
+    assert "LiveCameraFrameSource" not in module.__all__
+    assert "VideoFileFrameSource" not in module.__all__
+
+
+# ---------------------------------------------------------------------------
+# AC-10 — close is idempotent.
+
+
+def test_video_file_frame_source_close_is_idempotent(
+    enable_video_flag: None, video_path_60: Path
+) -> None:
+    # Arrange
+    source = VideoFileFrameSource(
+        path=video_path_60,
+        camera_calibration_id="az398-synth",
+        clock=WallClock(),
+    )
+    # Act — closing twice must not raise (AC-10)
+    source.close()
+    source.close()
+    # Assert — next_frame after close returns None, not an exception
+    assert source.next_frame() is None
+
+
+# ---------------------------------------------------------------------------
+# Factory.
+
+
+def test_build_frame_source_video_file_returns_video_file_source(
+    enable_video_flag: None, video_path_60: Path
+) -> None:
+    from gps_denied_onboard.runtime_root.frame_source_factory import (
+        build_frame_source,
+    )
+
+    source = build_frame_source(
+        kind="video_file",
+        camera_calibration_id="az398-factory",
+        clock=WallClock(),
+        video_path=video_path_60,
+    )
+    try:
+        # Assert
+        assert isinstance(source, VideoFileFrameSource)
+    finally:
+        source.close()
+
+
+def test_build_frame_source_rejects_unknown_kind() -> None:
+    from gps_denied_onboard.runtime_root.frame_source_factory import (
+        build_frame_source,
+    )
+
+    with pytest.raises(FrameSourceConfigError, match="unknown kind"):
+        build_frame_source(
+            kind="invalid",  # type: ignore[arg-type]
+            camera_calibration_id="x",
+            clock=WallClock(),
+        )
+
+
+def test_build_frame_source_live_rejects_video_path(enable_video_flag: None) -> None:
+    from gps_denied_onboard.runtime_root.frame_source_factory import (
+        build_frame_source,
+    )
+
+    with pytest.raises(FrameSourceConfigError, match="video_path must be None"):
+        build_frame_source(
+            kind="live",
+            camera_calibration_id="x",
+            clock=WallClock(),
+            device_index=0,
+            video_path="/tmp/whatever.mp4",
+        )
+
+
+def test_build_frame_source_video_file_requires_video_path() -> None:
+    from gps_denied_onboard.runtime_root.frame_source_factory import (
+        build_frame_source,
+    )
+
+    with pytest.raises(FrameSourceConfigError, match="video_path is required"):
+        build_frame_source(
+            kind="video_file",
+            camera_calibration_id="x",
+            clock=WallClock(),
+        )