[AZ-698] Tlog trim + mid-flight alignment for replay

Adds find_aligned_window cross-correlation (NCC, per-window unit norm)
between IMU energy and video optical-flow magnitude. Returns
AlignedWindow{tlog_start_ns, tlog_end_ns, offset_ms, confidence,
used_fallback}, with fallback to head-takeoff on low confidence to
preserve AZ-405 behavior. TlogReplayFcAdapter honors tlog_start_ns and
skips pre-window messages. New --auto-trim CLI flag, mutex with
--time-offset-ms. AC-1..AC-4 covered by unit tests; AC-5 skipped (no
real flight_derkachi.mp4 in repo). 106 tests pass in regression slice.
Zero new mypy --strict errors.

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

src/gps_denied_onboard/components/c8_fc_adapter/tlog_replay_adapter.py

@@ -202,6 +202,7 @@ class TlogReplayFcAdapter:
         "_clock",
         "_wgs_converter",
         "_time_offset_ns",
+        "_tlog_start_ns",
         "_pace",
         "_fdr_client",
         "_log",
@@ -218,6 +219,7 @@ class TlogReplayFcAdapter:
         "_latest_flight_state",
         "_last_received_at_ns",
         "_dispatched_count",
+        "_skipped_pre_window_count",
         "_mavlink_transport",
         "_outbound_mav",
         "_sequence_number",
@@ -234,6 +236,7 @@ class TlogReplayFcAdapter:
         wgs_converter: "WgsConverter",
         fdr_client: "FdrClient",
         time_offset_ms: int = 0,
+        tlog_start_ns: int | None = None,
         pace: ReplayPace = ReplayPace.ASAP,
         source_factory: Any | None = None,
         mavlink_transport: "MavlinkTransport | None" = None,
@@ -254,12 +257,23 @@ class TlogReplayFcAdapter:
                 f"target_fc_dialect must be ARDUPILOT_PLANE or INAV; "
                 f"got {target_fc_dialect!r}"
             )
+        if tlog_start_ns is not None and not isinstance(tlog_start_ns, int):
+            raise FcAdapterConfigError(
+                "tlog_start_ns must be int or None; "
+                f"got {type(tlog_start_ns).__name__}"
+            )
         self._tlog_path = tlog_path
         self._target_fc_dialect = target_fc_dialect
         self._clock = clock
         self._wgs_converter = wgs_converter
         self._fdr_client = fdr_client
         self._time_offset_ns: int = int(time_offset_ms) * 1_000_000
+        # AZ-698: pre-window seek bound. Messages with raw
+        # ``_timestamp`` (NOT offset-shifted) below this value are
+        # silently skipped by ``feed_one_message`` so the runtime
+        # loop only sees the mid-flight slice the aligner located.
+        # ``None`` preserves the historical "stream from t=0" behaviour.
+        self._tlog_start_ns: int | None = tlog_start_ns
         self._pace = pace
         self._log = get_logger("c8_fc_adapter.tlog_replay")
         self._bus = SubscriptionBus()
@@ -275,6 +289,7 @@ class TlogReplayFcAdapter:
         self._latest_flight_state: FlightStateSignal | None = None
         self._last_received_at_ns: int = -1
         self._dispatched_count: int = 0
+        self._skipped_pre_window_count: int = 0
         # AZ-558: outbound MAVLink seam. When ``mavlink_transport`` is
         # injected (replay branch wires NoopMavlinkTransport in), every
         # ``emit_external_position`` / ``emit_status_text`` call routes
@@ -634,9 +649,24 @@ class TlogReplayFcAdapter:
         Test-friendly entrypoint mirroring AZ-391's
         :meth:`PymavlinkInboundDecoder.feed_one_message`. Production
         replay uses :meth:`_run_decode_loop`.
+
+        AZ-698: when ``tlog_start_ns`` was set at construction, every
+        message with a raw ``_timestamp`` below that bound is silently
+        skipped before its type-specific handler runs — the runtime
+        loop only sees the trimmed window.
         """
         if msg is None:
             return False
+        if self._tlog_start_ns is not None:
+            try:
+                raw_ts_ns = _msg_timestamp_ns(msg)
+            except FcOpenError:
+                # Malformed timestamp — let the handler raise so the
+                # error path matches the no-trim case verbatim.
+                raw_ts_ns = None
+            if raw_ts_ns is not None and raw_ts_ns < self._tlog_start_ns:
+                self._skipped_pre_window_count += 1
+                return False
         try:
             msg_type = self._safe_msg_type(msg)
             if msg_type in ("RAW_IMU", "SCALED_IMU2"):