[AZ-894] [AZ-896] Add CSV-driven replay adapter + format docs

Replaces the tlog two-clock replay surface with a single-clock path
driven by the Derkachi-schema CSV. --imu is the new required CLI arg;
--tlog stays as a deprecated alias (warned + ignored when --imu set)
until AZ-895 deletes it.

* csv_ground_truth.py parses the 15-column schema, fails fast at
  startup on every documented schema fault (AC-5).
* CsvReplayFcAdapter slots into ReplayInputBundle.fc_adapter alongside
  the tlog sibling; mirrors Invariant-5 outbound wiring; inbound bus is
  intentionally a no-op since the loop reads CSV directly.
* _run_replay_loop branches on imu_csv_path, stamps
  VioOutput.emitted_at_ns from the CSV-derived frame_end_ns (AC-4),
  closing the AZ-848 two-clock surface for the new path.
* AZ-896 ships the operator-facing format spec at
  _docs/02_document/contracts/replay/csv_replay_format.md plus a
  20-row example CSV (AC-3 regression-locked).

Tests: 11 + 12 new unit tests, plus updates to AZ-401 import-boundary
and AZ-402 CLI suites. Full unit suite 2,327 passed / 86 skipped.

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

tests/e2e/replay/conftest.py

@@ -69,6 +69,7 @@ class DerkachiReplayInputs:
 
     video_path: Path
     tlog_path: Path
+    imu_csv_path: Path
     calibration_path: Path
     config_path: Path
     signing_key_path: Path
@@ -170,6 +171,7 @@ def derkachi_replay_inputs(tmp_path_factory: pytest.TempPathFactory) -> Derkachi
     return DerkachiReplayInputs(
         video_path=video_path,
         tlog_path=tlog_path,
+        imu_csv_path=csv_path,
         calibration_path=_calibration_path(),
         config_path=config_path,
         signing_key_path=signing_key_path,
@@ -241,8 +243,8 @@ def replay_runner(derkachi_replay_inputs: DerkachiReplayInputs) -> Any:
             binary,
             "--video",
             str(derkachi_replay_inputs.video_path),
-            "--tlog",
-            str(derkachi_replay_inputs.tlog_path),
+            "--imu",
+            str(derkachi_replay_inputs.imu_csv_path),
             "--output",
             str(out_path),
             "--camera-calibration",
@@ -254,6 +256,12 @@ def replay_runner(derkachi_replay_inputs: DerkachiReplayInputs) -> Any:
             "--pace",
             pace,
         ]
+        # --tlog is deprecated under AZ-894 but we still forward it
+        # when the synth tlog exists, so the legacy-path e2e tests
+        # (test_derkachi_real_tlog.py) keep exercising the deprecation
+        # warning until AZ-895 deletes the path entirely.
+        if derkachi_replay_inputs.tlog_path.is_file():
+            argv.extend(["--tlog", str(derkachi_replay_inputs.tlog_path)])
         if time_offset_ms is not None:
             argv.extend(["--time-offset-ms", str(time_offset_ms)])
         if skip_auto_sync:

tests/unit/c8_fc_adapter/test_csv_replay_adapter.py

@@ -0,0 +1,249 @@
+"""AZ-894 — ``CsvReplayFcAdapter`` unit tests.
+
+Focused contract coverage for the thin :class:`FcAdapter` sibling that
+backs the CSV-driven replay input.  The functional inbound/outbound
+plumbing the runtime loop relies on (CSV parsing, frame-stamped IMU
+draining, ESKF cold-start origin) is exercised in
+``tests/unit/replay_input/test_csv_ground_truth.py`` and the AZ-404
+e2e harness; here we pin the Protocol surface (open/close idempotency,
+build-flag refusal, source-set refusal, transport-less emit refusal)
+so a refactor of the adapter cannot silently regress Invariant 5 or
+the FcAdapter Protocol parity that the composition root depends on.
+
+Style: every test follows the Arrange / Act / Assert pattern.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from gps_denied_onboard._types.fc import FcKind, FlightState, Severity
+from gps_denied_onboard.components.c8_fc_adapter.csv_replay_adapter import (
+    CsvReplayFcAdapter,
+)
+from gps_denied_onboard.components.c8_fc_adapter.errors import (
+    FcAdapterConfigError,
+    FcEmitError,
+    FcOpenError,
+    SourceSetSwitchNotSupportedError,
+)
+from gps_denied_onboard.components.c8_fc_adapter.tlog_replay_adapter import (
+    ReplayPace,
+)
+
+
+@pytest.fixture(autouse=True)
+def _build_flag_on(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("BUILD_CSV_REPLAY_ADAPTER", "ON")
+
+
+class _FakeClock:
+    """Minimal Clock stub returning a monotonic counter in ns."""
+
+    def __init__(self) -> None:
+        self._t = 0
+
+    def monotonic_ns(self) -> int:
+        self._t += 1
+        return self._t
+
+    def sleep_until_ns(self, _: int) -> None:  # pragma: no cover — unused.
+        return None
+
+
+class _FakeFdr:
+    """No-op FDR client stand-in (CsvReplayFcAdapter does not emit FDR yet)."""
+
+    def enqueue(self, _record: object) -> None:  # pragma: no cover — unused.
+        return None
+
+
+@pytest.fixture()
+def csv_file(tmp_path: Path) -> Path:
+    # Existence is the only check the adapter does at open() time —
+    # the body never has to be parseable here (parsing lives in
+    # csv_ground_truth.load_csv_ground_truth, tested separately).
+    path = tmp_path / "data_imu.csv"
+    path.write_text("placeholder", encoding="utf-8")
+    return path
+
+
+def _make_adapter(csv_path: Path) -> CsvReplayFcAdapter:
+    return CsvReplayFcAdapter(
+        csv_path=csv_path,
+        target_fc_dialect=FcKind.ARDUPILOT_PLANE,
+        clock=_FakeClock(),
+        fdr_client=_FakeFdr(),
+        pace=ReplayPace.ASAP,
+    )
+
+
+# ----------------------------------------------------------------------
+# Build flag
+
+
+def test_construction_refused_when_build_flag_off(
+    monkeypatch: pytest.MonkeyPatch, csv_file: Path
+) -> None:
+    # Arrange
+    monkeypatch.setenv("BUILD_CSV_REPLAY_ADAPTER", "OFF")
+
+    # Act + Assert
+    with pytest.raises(FcAdapterConfigError, match="BUILD_CSV_REPLAY_ADAPTER"):
+        _make_adapter(csv_file)
+
+
+def test_construction_rejects_non_path(csv_file: Path) -> None:
+    # Arrange — argument intentionally a str rather than Path.
+
+    # Act + Assert
+    with pytest.raises(FcAdapterConfigError, match="csv_path must be a pathlib.Path"):
+        CsvReplayFcAdapter(
+            csv_path=str(csv_file),  # type: ignore[arg-type]
+            target_fc_dialect=FcKind.ARDUPILOT_PLANE,
+            clock=_FakeClock(),
+            fdr_client=_FakeFdr(),
+            pace=ReplayPace.ASAP,
+        )
+
+
+def test_construction_rejects_unknown_dialect(csv_file: Path) -> None:
+    # Act + Assert
+    with pytest.raises(FcAdapterConfigError, match="target_fc_dialect"):
+        CsvReplayFcAdapter(
+            csv_path=csv_file,
+            target_fc_dialect=FcKind.GCS_QGC,
+            clock=_FakeClock(),
+            fdr_client=_FakeFdr(),
+            pace=ReplayPace.ASAP,
+        )
+
+
+# ----------------------------------------------------------------------
+# open / close
+
+
+def test_open_refused_when_csv_missing(tmp_path: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(tmp_path / "absent.csv")
+
+    # Act + Assert
+    with pytest.raises(FcOpenError, match="CSV file not found"):
+        adapter.open()
+
+
+def test_double_open_raises(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+    adapter.open()
+
+    # Act + Assert
+    with pytest.raises(FcOpenError, match="already opened"):
+        adapter.open()
+
+
+def test_close_is_idempotent_before_open(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+
+    # Act — close() before open() is a documented no-op (parity with tlog).
+    adapter.close()
+    adapter.close()
+
+    # Assert — no exception raised; state remains closeable.
+    assert True
+
+
+def test_close_is_idempotent_after_open(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+    adapter.open()
+
+    # Act
+    adapter.close()
+    adapter.close()
+
+    # Assert
+    assert True
+
+
+# ----------------------------------------------------------------------
+# Protocol parity
+
+
+def test_subscribe_returns_real_subscription_handle(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+    adapter.open()
+
+    # Act
+    subscription = adapter.subscribe_telemetry(lambda _frame: None)
+
+    # Assert — handle exposes the cancel() entry point even though the
+    # bus is intentionally never fed (replay loop reads CSV directly).
+    assert hasattr(subscription, "cancel")
+    subscription.cancel()
+
+
+def test_source_set_switch_unsupported(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+
+    # Act + Assert
+    with pytest.raises(SourceSetSwitchNotSupportedError):
+        adapter.request_source_set_switch()
+
+
+def test_current_flight_state_returns_init_signal(csv_file: Path) -> None:
+    # Arrange — CSV carries no MAVLink HEARTBEAT, so the adapter has
+    # nothing to latch; the contract is to return an INIT-state signal.
+    adapter = _make_adapter(csv_file)
+
+    # Act
+    signal = adapter.current_flight_state()
+
+    # Assert
+    assert signal.state is FlightState.INIT
+    assert signal.last_valid_gps_hint_wgs84 is None
+    assert signal.last_valid_gps_age_ms is None
+
+
+# ----------------------------------------------------------------------
+# Outbound (Invariant 5)
+
+
+def test_emit_external_position_raises_without_transport(csv_file: Path) -> None:
+    # Arrange — no MavlinkTransport injected → adapter falls back to the
+    # AZ-399 raise-on-emit contract, mirroring TlogReplayFcAdapter.
+    adapter = _make_adapter(csv_file)
+    adapter.open()
+
+    # Act + Assert
+    with pytest.raises(FcEmitError, match="does not emit"):
+        adapter.emit_external_position(_dummy_estimator_output())
+
+
+def test_emit_status_text_raises_without_transport(csv_file: Path) -> None:
+    # Arrange
+    adapter = _make_adapter(csv_file)
+    adapter.open()
+
+    # Act + Assert
+    with pytest.raises(FcEmitError, match="does not emit"):
+        adapter.emit_status_text("hello", severity=Severity.INFO)
+
+
+# ----------------------------------------------------------------------
+# Helpers
+
+
+def _dummy_estimator_output() -> object:
+    # The transport-less emit path short-circuits with FcEmitError before
+    # reading any field, so a duck-typed stand-in is enough — duplicating
+    # the full EstimatorOutput (UUID frame_id, 6x6 covariance, etc.)
+    # would only hide the actual contract being tested.
+    from types import SimpleNamespace
+
+    return SimpleNamespace()

tests/unit/replay_input/test_csv_ground_truth.py

@@ -0,0 +1,287 @@
+"""AZ-894 — CSV-driven IMU + GPS ground-truth extractor.
+
+Covers AC-1 (parses 4,899 IMU + 4,899 GPS samples on a single monotonic
+clock) and AC-5 (clear ``ReplayInputAdapterError`` at startup for schema
+faults) of ``_docs/02_tasks/todo/AZ-894_csv_driven_replay_adapter.md``.
+
+The happy-path test is gated on the committed Derkachi fixture
+(``_docs/00_problem/input_data/flight_derkachi/data_imu.csv``, 4,899
+rows + header).  Schema-fault tests use synthetic CSV strings written
+to ``tmp_path`` so they remain deterministic and do not depend on the
+fixture being present.
+
+Style: every test follows the Arrange / Act / Assert pattern.
+"""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+import pytest
+
+from gps_denied_onboard.replay_input.csv_ground_truth import (
+    CSV_SOURCE_LABEL,
+    REQUIRED_COLUMNS,
+    load_csv_ground_truth,
+)
+from gps_denied_onboard.replay_input.errors import ReplayInputAdapterError
+
+
+_DERKACHI_CSV: Path = (
+    Path(__file__).resolve().parents[3]
+    / "_docs"
+    / "00_problem"
+    / "input_data"
+    / "flight_derkachi"
+    / "data_imu.csv"
+)
+
+
+_EXAMPLE_CSV: Path = (
+    Path(__file__).resolve().parents[3]
+    / "_docs"
+    / "02_document"
+    / "contracts"
+    / "replay"
+    / "example_data_imu.csv"
+)
+
+
+# ---------------------------------------------------------------------
+# Header + minimal-row helpers
+
+
+def _write_csv(path: Path, header: str, rows: list[str]) -> Path:
+    path.write_text(header + "\n" + "\n".join(rows) + "\n", encoding="utf-8")
+    return path
+
+
+def _full_header() -> str:
+    return ",".join(REQUIRED_COLUMNS)
+
+
+def _row(time_s: float, *, prefix_ms: float = 0.0) -> str:
+    # 15 fields total matching REQUIRED_COLUMNS ordering. Values are
+    # picked to be valid floats; the exact magnitudes do not matter
+    # for these tests (the loader only validates parseability + range).
+    fields = [
+        str(prefix_ms),
+        str(time_s),
+        "10",
+        "-3",
+        "-980",
+        "50",
+        "30",
+        "-5",
+        "50.0809634",
+        "36.1115442",
+        "141290",
+        "-4",
+        "-6",
+        "-88",
+        "35041",
+    ]
+    return ",".join(fields)
+
+
+# ---------------------------------------------------------------------
+# AC-1: happy path on the real Derkachi CSV
+
+
+@pytest.mark.skipif(
+    not _DERKACHI_CSV.is_file(),
+    reason="Derkachi fixture data_imu.csv not present",
+)
+def test_ac1_loads_derkachi_csv_emits_paired_samples() -> None:
+    # Arrange — committed fixture path; nothing to set up.
+    # Note: AZ-894 spec mentions "4,899 samples"; the actual fixture
+    # spans Time=0.0..489.9 s in 0.1 s steps → 4,900 rows.  We pin the
+    # concrete count so the test catches truncation, plus the
+    # span-derived invariant so future fixtures with a different
+    # length still pass for the right reason.
+    expected_count = 4900
+
+    # Act
+    gt = load_csv_ground_truth(_DERKACHI_CSV)
+
+    # Assert
+    assert gt.source == CSV_SOURCE_LABEL
+    assert len(gt.records) == expected_count
+    assert len(gt.imu_samples) == expected_count
+    # First row of the fixture has Time=0; last is 489.9 s (10 Hz).
+    assert gt.records[0].ts_ns == 0
+    assert gt.records[-1].ts_ns == int(489.9 * 1e9)
+    # IMU samples share the same canonical clock as the GPS records.
+    for gps, imu in zip(gt.records, gt.imu_samples, strict=True):
+        assert gps.ts_ns == imu.ts_ns
+
+
+# ---------------------------------------------------------------------
+# AZ-896 AC-3: the shipped example CSV stays parser-clean
+
+@pytest.mark.skipif(
+    not _EXAMPLE_CSV.is_file(),
+    reason="AZ-896 example_data_imu.csv not present",
+)
+def test_az896_example_csv_loads_clean() -> None:
+    # Arrange — committed AZ-896 example; nothing to set up.
+
+    # Act
+    gt = load_csv_ground_truth(_EXAMPLE_CSV)
+
+    # Assert
+    assert gt.source == CSV_SOURCE_LABEL
+    assert len(gt.records) >= 10
+    assert len(gt.records) == len(gt.imu_samples)
+    assert gt.records[0].ts_ns == 0
+
+
+# ---------------------------------------------------------------------
+# AC-1 (small fixture): paired-sample invariants
+
+
+def test_paired_imu_and_gps_share_clock(tmp_path: Path) -> None:
+    # Arrange
+    csv = _write_csv(
+        tmp_path / "ok.csv",
+        _full_header(),
+        [
+            _row(0.0, prefix_ms=4551116.348),
+            _row(0.1, prefix_ms=4551216.348),
+            _row(0.2, prefix_ms=4551316.348),
+        ],
+    )
+
+    # Act
+    gt = load_csv_ground_truth(csv)
+
+    # Assert
+    assert len(gt.records) == 3 and len(gt.imu_samples) == 3
+    expected_ns = [0, 100_000_000, 200_000_000]
+    assert [r.ts_ns for r in gt.records] == expected_ns
+    assert [s.ts_ns for s in gt.imu_samples] == expected_ns
+
+
+def test_gps_unit_conversion(tmp_path: Path) -> None:
+    # Arrange — values exercise the deg/mm/cm-s/cdeg conversions.
+    header = _full_header()
+    row = ",".join([
+        "0.0", "0.0",
+        "10", "-3", "-980", "50", "30", "-5",  # IMU stays raw
+        "50.0809634",   # lat already in degrees
+        "36.1115442",   # lon already in degrees
+        "141290",       # alt in mm   → 141.290 m
+        "-400",         # vx in cm/s  → -4.0 m/s
+        "600",          # vy in cm/s  → 6.0 m/s
+        "-88",          # vz in cm/s  → -0.88 m/s
+        "35041",        # hdg in cdeg → 350.41 deg
+    ])
+    csv = _write_csv(tmp_path / "units.csv", header, [row])
+
+    # Act
+    gt = load_csv_ground_truth(csv)
+
+    # Assert
+    fix = gt.records[0]
+    assert fix.lat_deg == pytest.approx(50.0809634)
+    assert fix.lon_deg == pytest.approx(36.1115442)
+    assert fix.alt_m == pytest.approx(141.290)
+    assert fix.vx_m_s == pytest.approx(-4.0)
+    assert fix.vy_m_s == pytest.approx(6.0)
+    assert fix.vz_m_s == pytest.approx(-0.88)
+    assert fix.hdg_deg == pytest.approx(350.41)
+
+
+# ---------------------------------------------------------------------
+# AC-5: schema faults raise ReplayInputAdapterError at startup
+
+
+def test_ac5_file_not_found_raises(tmp_path: Path) -> None:
+    # Arrange
+    missing = tmp_path / "absent.csv"
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="CSV file not found"):
+        load_csv_ground_truth(missing)
+
+
+def test_ac5_missing_required_column_raises(tmp_path: Path) -> None:
+    # Arrange — drop one required column from the header.
+    bad_header = ",".join(c for c in REQUIRED_COLUMNS if c != "SCALED_IMU2.xacc")
+    csv = _write_csv(
+        tmp_path / "missing_col.csv",
+        bad_header,
+        ["0,0,-3,-980,50,30,-5,50.0,36.0,141290,-4,-6,-88,35041"],
+    )
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="missing required columns"):
+        load_csv_ground_truth(csv)
+
+
+def test_ac5_nan_in_time_raises(tmp_path: Path) -> None:
+    # Arrange
+    csv = _write_csv(
+        tmp_path / "nan_time.csv",
+        _full_header(),
+        [_row(0.0), _row(float("nan"))],
+    )
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="Time=.*is NaN/Inf"):
+        load_csv_ground_truth(csv)
+
+
+def test_ac5_non_monotonic_time_raises(tmp_path: Path) -> None:
+    # Arrange
+    csv = _write_csv(
+        tmp_path / "non_monotonic.csv",
+        _full_header(),
+        [_row(0.1), _row(0.0)],
+    )
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="non-monotonic Time"):
+        load_csv_ground_truth(csv)
+
+
+def test_ac5_repeated_time_also_non_monotonic(tmp_path: Path) -> None:
+    # Arrange — equal timestamps still violate strict monotonicity so
+    # the preintegrator never gets fed a zero-delta window.
+    csv = _write_csv(
+        tmp_path / "repeated.csv",
+        _full_header(),
+        [_row(0.0), _row(0.0)],
+    )
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="non-monotonic Time"):
+        load_csv_ground_truth(csv)
+
+
+def test_ac5_non_numeric_imu_value_raises(tmp_path: Path) -> None:
+    # Arrange — substitute a non-parseable token in the IMU column.
+    row = ",".join([
+        "0.0", "0.0",
+        "not-a-number",  # SCALED_IMU2.xacc
+        "-3", "-980", "50", "30", "-5",
+        "50.0", "36.0", "141290", "-4", "-6", "-88", "35041",
+    ])
+    csv = _write_csv(tmp_path / "bad_imu.csv", _full_header(), [row])
+
+    # Act + Assert
+    with pytest.raises(
+        ReplayInputAdapterError,
+        match=r"SCALED_IMU2\.xacc=.*is not a number",
+    ):
+        load_csv_ground_truth(csv)
+
+
+def test_ac5_header_only_raises(tmp_path: Path) -> None:
+    # Arrange — header but no data rows.
+    csv = tmp_path / "header_only.csv"
+    csv.write_text(_full_header() + "\n", encoding="utf-8")
+
+    # Act + Assert
+    with pytest.raises(ReplayInputAdapterError, match="no data rows"):
+        load_csv_ground_truth(csv)

tests/unit/test_az401_compose_root_replay.py

@@ -491,12 +491,14 @@ def test_ac8_replay_branch_imports_only_public_apis() -> None:
     tree = ast.parse(text)
 
     # Allowed deep imports: into the c8_fc_adapter component (the
-    # noop transport + the JSONL sink) and into the `replay_input`
-    # cross-cutting coordinator (Layer-4). Both are documented in
-    # module-layout.md as the replay strategy homes.
+    # noop transport + the JSONL sink + the AZ-894 CSV replay adapter)
+    # and into the `replay_input` cross-cutting coordinator (Layer-4).
+    # All of these are documented in module-layout.md as the replay
+    # strategy homes.
     allowed_deep_prefixes = (
         "gps_denied_onboard.components.c8_fc_adapter.noop_mavlink_transport",
         "gps_denied_onboard.components.c8_fc_adapter.replay_sink",
+        "gps_denied_onboard.components.c8_fc_adapter.csv_replay_adapter",
         "gps_denied_onboard.replay_input.tlog_video_adapter",
     )
 
@@ -632,9 +634,14 @@ def test_replay_branch_rejects_empty_video_path(
         build_replay_components(config)
 
 
-def test_replay_branch_rejects_empty_tlog_path(
+def test_replay_branch_rejects_both_inputs_empty(
     _airborne_replay_env: Path,
 ) -> None:
+    # AZ-894: the validation gate now accepts either imu_csv_path
+    # (canonical) or tlog_path (legacy) — rejecting only when both
+    # are empty. Keeping the historical name pattern (test_*_rejects_*)
+    # for grep parity but renamed to reflect the new semantics.
+
     # Arrange
     runtime_cfg = RuntimeConfig(camera_calibration_path=str(_airborne_replay_env))
     config = Config(
@@ -642,6 +649,7 @@ def test_replay_branch_rejects_empty_tlog_path(
         replay=ReplayConfig(
             video_path="/dev/null/fake.mp4",
             tlog_path="",
+            imu_csv_path="",
             output_path="/tmp/out.jsonl",
             pace="asap",
             target_fc_dialect="ardupilot_plane",
@@ -650,7 +658,7 @@ def test_replay_branch_rejects_empty_tlog_path(
     )
 
     # Act / Assert
-    with pytest.raises(CompositionError, match="tlog_path is empty"):
+    with pytest.raises(CompositionError, match="imu_csv_path is empty"):
         build_replay_components(config)
 
 

tests/unit/test_az402_replay_cli.py

@@ -57,6 +57,10 @@ def _required_files(tmp_path: Path, _calib_payload: dict[str, Any]) -> dict[str,
     video.write_bytes(b"\x00\x00\x00\x18ftypmp42")  # placeholder
     tlog = tmp_path / "flight.tlog"
     tlog.write_bytes(b"\x00")
+    imu_csv = tmp_path / "data_imu.csv"
+    # Minimal placeholder — the CLI only validates existence, parsing
+    # happens later inside the runtime loop.
+    imu_csv.write_text("placeholder", encoding="utf-8")
     output = tmp_path / "out.jsonl"
     calib = tmp_path / "calib.json"
     calib.write_text(json.dumps(_calib_payload))
@@ -67,6 +71,7 @@ def _required_files(tmp_path: Path, _calib_payload: dict[str, Any]) -> dict[str,
     return {
         "video": video,
         "tlog": tlog,
+        "imu": imu_csv,
         "output": output,
         "camera_calibration": calib,
         "config": config_yaml,
@@ -95,6 +100,7 @@ def _argv(files: dict[str, Path], **overrides: Any) -> list[str]:
     """Build a CLI argv from the required-files fixture + overrides."""
     base = {
         "--video": str(files["video"]),
+        "--imu": str(files["imu"]),
         "--tlog": str(files["tlog"]),
         "--output": str(files["output"]),
         "--camera-calibration": str(files["camera_calibration"]),
@@ -477,6 +483,7 @@ def test_ac10_console_script_runs_help() -> None:
     # Required-arg surface check
     for arg in (
         "--video",
+        "--imu",
         "--tlog",
         "--output",
         "--camera-calibration",