[AZ-594] Implement core-three harness stubs (fdr_reader, frame_source_replay, imu_replay)

Replaces the NotImplementedError stubs AZ-406 reserved on three runner-
side helpers; these were stranded from any tracker ticket since
AZ-407/408 never came back to fill them. Concrete bodies:

* fdr_reader.iter_records: JSONL parser + wire-envelope validator;
  recursive *.jsonl walk; projects {schema_version, ts, producer_id,
  kind, payload} to runner-side FdrRecord with record_type/monotonic_ms
  renames; yields oldest-first.
* frame_source_replay.replay_video: OpenCV VideoCapture decode + JPEG
  re-encode; auto-detects file vs directory; injectable sleep_fn for
  unit-test pacing.
* imu_replay.ImuReplayer.replay: csv.DictReader parse; degrees->radians
  attitude conversion; tolerates scientific notation; same sleep_fn
  injection pattern.

Adds 34 unit tests (14 + 10 + 10). Full e2e unit suite: 558 passed (+31).
Existing scenario _harness_helpers_implemented probes still return False
because they also depend on sitl_observer / fc_proxy_runtime stubs that
remain pending; scenario probe cleanup is out of AZ-594 scope.

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

e2e/runner/helpers/imu_replay.py

@@ -3,17 +3,27 @@
 CSV schema (from `_docs/00_problem/input_data/flight_derkachi/data_imu.csv`):
     timestamp_ms,ax,ay,az,gx,gy,gz,roll_deg,pitch_deg,yaw_deg,baro_m
 
-Owned by AZ-406 (public surface) + AZ-407 (concrete file-driver
-implementation). This module commits to the type signatures the
-per-scenario tests will import; the actual MAVLink / MSP2 emission is
-wired up by the downstream task.
+Numeric fields are accepted in any float-parseable form, including
+scientific notation (``-4.44E-16``) — the AZ-408 source CSV uses that
+form for near-zero values.
 """
 
 from __future__ import annotations
 
+import csv
+import math
+import time
 from dataclasses import dataclass
 from pathlib import Path
-from typing import Protocol
+from typing import Callable, Protocol
+
+_REQUIRED_COLUMNS = (
+    "timestamp_ms",
+    "ax", "ay", "az",
+    "gx", "gy", "gz",
+    "roll_deg", "pitch_deg", "yaw_deg",
+    "baro_m",
+)
 
 
 @dataclass(frozen=True)
@@ -34,20 +44,67 @@ class FcInboundEmitter(Protocol):
         ...
 
 
+def _parse_row(row: dict[str, str], source: Path, line_no: int) -> ImuSample:
+    try:
+        return ImuSample(
+            timestamp_ms=int(round(float(row["timestamp_ms"]))),
+            accel_mss=(float(row["ax"]), float(row["ay"]), float(row["az"])),
+            gyro_rps=(float(row["gx"]), float(row["gy"]), float(row["gz"])),
+            attitude_rad=(
+                math.radians(float(row["roll_deg"])),
+                math.radians(float(row["pitch_deg"])),
+                math.radians(float(row["yaw_deg"])),
+            ),
+            baro_alt_m=float(row["baro_m"]),
+        )
+    except (KeyError, ValueError) as exc:
+        raise ValueError(
+            f"IMU CSV row malformed at {source}:{line_no}: {exc}"
+        ) from exc
+
+
 class ImuReplayer:
     """Drives an `FcInboundEmitter` from a CSV file at the recorded cadence."""
 
-    def __init__(self, emitter: FcInboundEmitter, rate_hz: float = 10.0) -> None:
+    def __init__(
+        self,
+        emitter: FcInboundEmitter,
+        rate_hz: float = 10.0,
+        *,
+        sleep_fn: Callable[[float], None] = time.sleep,
+        realtime: bool = True,
+    ) -> None:
+        if rate_hz <= 0:
+            raise ValueError(f"rate_hz must be positive; got {rate_hz}")
         self._emitter = emitter
         self._rate_hz = rate_hz
+        self._sleep = sleep_fn
+        self._realtime = realtime
 
     def replay(self, csv_path: Path) -> int:
         """Replay the CSV file. Returns the number of samples emitted.
 
-        Concrete implementation is owned by AZ-407 (FT-P-02 derkachi-drift
-        + FT-P-04 frame-to-frame registration are the first consumers).
+        Raises ``FileNotFoundError`` on missing CSV. Raises ``ValueError``
+        on missing columns or a row that does not parse. When ``realtime``
+        is True (default), sleeps ``1 / rate_hz`` seconds between
+        emissions; tests should pass ``realtime=False`` or inject a
+        no-op ``sleep_fn`` to keep the unit suite fast.
         """
-        raise NotImplementedError(
-            "ImuReplayer.replay is owned by AZ-407 — AZ-406 supplies only "
-            "the public surface."
-        )
+        if not csv_path.exists():
+            raise FileNotFoundError(f"IMU CSV not found: {csv_path}")
+        emitted = 0
+        period_s = 1.0 / self._rate_hz
+        with csv_path.open() as fh:
+            reader = csv.DictReader(fh)
+            missing = [c for c in _REQUIRED_COLUMNS if c not in (reader.fieldnames or [])]
+            if missing:
+                raise ValueError(
+                    f"IMU CSV {csv_path} missing required columns: {missing}"
+                )
+            for line_no, row in enumerate(reader, start=2):  # +1 for header line
+                sample = _parse_row(row, csv_path, line_no)
+                self._emitter.emit(sample)
+                emitted += 1
+                if self._realtime:
+                    self._sleep(period_s)
+        return emitted