# Code Review Report

**Batch**: 79 — AZ-599 (FT-P-02 Derkachi fixture builder + b78 helper extraction)
**Date**: 2026-05-17
**Verdict**: PASS

## Findings

(none blocking)

### Non-blocking notes

* **Roll/pitch=0 simplification in synthesised ATTITUDE**: acceptable
  for the Derkachi fixed-wing cruise data but unrealistic for
  aggressive manoeuvres. Documented as a Limitation in the README;
  re-visit if FT-P-04 (Derkachi F2F registration) or other
  manoeuvre-sensitive scenarios show fusion drift from this gap.
* **`SCALED_IMU2` → `RAW_IMU` pass-through (no unit conversion)**:
  the builder passes scaled accelerometer (mg) and gyro (mrad/s)
  values straight into RAW_IMU fields. Documented as a Limitation;
  if the SUT's tlog parser rejects, a units conversion pass needs to
  be added. Surfaced as a follow-up rather than fixed speculatively.
* **Disk-full incident during regression gate**: not a code issue;
  surfaced to the user, who freed space, after which the full
  suite (686 tests) passed cleanly.

## Findings Sweep

### Phase 1 — Context Loading

Read the FT-P-02 scenario to confirm: it (a) skips when
`sitl_replay_ready` is false; (b) calls
`fdr_reader.iter_records(fdr_root)` to walk the FDR archive; (c)
filters for `record_type == "estimate"` and projects into
`apd.FdrEstimate`. Confirmed FT-P-02 does NOT call
`wait_for_outbound` (so the b78 schema doesn't apply). Read
`data_imu.csv` to confirm column names + units (10 Hz; ms
timestamps; SCALED_IMU2 in mg / mrad/s; GLOBAL_POSITION_INT.hdg
in centidegrees). Inspected the production
`replay_input/auto_sync.py` AC-13 contract for required tlog
message types (RAW_IMU + ATTITUDE) — this drove the choice of
which messages to pack per CSV row. Verified `pymavlink>=2.4`
already in `pyproject.toml`. Read the b78
`build_p01_fixtures.py` to identify the helper extraction
boundary (`run_gps_denied_replay` + `write_observer_fixture` had
no FT-P-01-specific code, ideal candidates).

### Phase 2 — Spec Compliance

| AC | Coverage | Status |
|----|----------|--------|
| AC-1 (parse every row, one pair per row) | `test_convert_imu_csv_writes_pair_per_row`, `test_convert_imu_csv_real_pymavlink_round_trip` | Covered |
| AC-2 (ValueError on missing cols / malformed numerics / empty CSV) | `test_convert_imu_csv_empty_raises`, `test_convert_imu_csv_missing_required_column_raises`, `test_convert_imu_csv_malformed_numeric_raises`, `test_convert_imu_csv_missing_file_raises` | Covered (4 distinct error paths) |
| AC-3 (heading centideg → rad) | `test_hdg_centideg_to_rad` (5 parametric cases: 0, π/2, π, 3π/2, near-2π) | Covered |
| AC-4 (build_p02 invokes replay + verifies ≥1 estimate) | `test_build_p02_end_to_end_with_mocks`, `test_build_p02_propagates_verify_failure`, `test_verify_fdr_no_estimates_raises`, `test_verify_fdr_counts_estimates`, `test_verify_fdr_tolerates_malformed_lines` | Covered |
| AC-5 (`_common.py` shared between b78 + b79) | `test_common_module_exports_used_by_b01` + b78 suite (24/24) still passes | Covered |
| AC-6 (full unit-test suite passes) | 686/686 in 123 s (previous: 664) | Covered |

### Phase 3 — Code Quality

* **Single responsibility**: `convert_imu_csv_to_tlog` parses CSV +
  packs MAVLink (one cohesive concern: CSV row → tlog pair).
  `verify_fdr_has_estimates` does one thing. `build_p02_fixtures`
  is the only orchestrator. Helper extraction into `_common.py`
  removed duplicate definitions cleanly — no copy-pasted code
  remains.
* **No suppressed errors**: every JSON-decode in
  `verify_fdr_has_estimates` is wrapped in a `try / except
  json.JSONDecodeError` that explicitly `continue`s with a comment
  explaining the tolerance (real FDR archives can contain partial
  writes at the tail). Every CSV parse error wraps in `ValueError`
  with row context. `subprocess.run` uses `check=True`.
* **AAA test discipline**: all 20 new tests use
  `# Arrange / # Act / # Assert`; omitted when redundant.
* **Comments**: every public function has a docstring documenting
  contract + raises; no narrating comments in function bodies.
  The yaw conversion uses a named helper (`_hdg_centideg_to_rad`)
  rather than an inline magic-formula comment.
* **Public boundary**: b79 module does NOT import any
  `src/gps_denied_onboard` symbol (verified by grep). pymavlink
  imports are deferred to function bodies so the test factory
  injections don't need the real library available.

### Phase 4 — Security

* No new credentials / secrets / network surfaces.
* `convert_imu_csv_to_tlog` uses `csv.DictReader` — no `eval`, no
  shell injection. Numeric fields go through `int(float(s))` so
  bad input raises ValueError rather than executing arbitrary code.
* `verify_fdr_has_estimates` uses `json.loads` (safe) and silently
  ignores malformed lines (documented as tolerance for partial
  writes; not a security risk because we never act on the data).
* `subprocess` invocation uses a list-argument `cmd` (no shell
  injection surface; same pattern as b78).

### Phase 5 — Performance

* `convert_imu_csv_to_tlog` is O(N) over CSV rows; for the Derkachi
  4,900-row file → ~5 s wall-clock estimate (pymavlink packing is
  the bottleneck). Bounded by input size; no hidden quadratic
  behaviour.
* `verify_fdr_has_estimates` is single-pass O(N) over JSONL lines.
* `_iter_imu_rows` validates the header once and then streams rows;
  doesn't materialize the entire CSV in memory until the orchestrator
  asks for `list(...)` (could be optimized later if Derkachi data
  ever grows orders of magnitude larger; currently 4,900 rows is
  trivial).

### Phase 6 — Cross-Task Consistency

* **Builder shape parity with b78**: `BuilderConfig` /
  `P02BuilderConfig` dataclass; `build_pXX_fixtures(cfg, *, _runner=...,
  _mavlink_writer_factory=..., _verify_fdr=...)` signature; same
  underscore-prefixed dependency-injection convention. A future
  contributor reading both side-by-side will see the same pattern.
* **`_common.py` extraction validated by both**: b78's existing
  `test_run_gps_denied_replay_builds_correct_cmd` /
  `test_run_gps_denied_replay_creates_fdr_parent_dir` /
  `test_run_gps_denied_replay_passes_extra_args` /
  `test_write_observer_fixture_schema` tests pass unchanged against
  the moved implementation. b79 adds
  `test_common_module_exports_used_by_b01` to lock in the import
  relationship.
* **No drift in `observer_<fc_kind>_<host>.json` schema**: same
  payload structure as b75/b78.

### Phase 7 — Architecture Compliance

* **Module placement**: new files under
  `e2e/fixtures/sitl_replay_builder/` (existing package from b78);
  new tests under `e2e/_unit_tests/fixtures/`. All registered in
  `test_directory_layout.py`.
* **No `src/gps_denied_onboard` imports**.
* **No new top-level dependencies** — pymavlink already there from
  b78/b76; `csv` is stdlib; `math` is stdlib.
* **`__init__.py` not modified** — the b78 docstring already
  documents why we don't re-export symbols on the package namespace,
  and that's still the right choice for b79.
* **Refactor preserves backwards compatibility**: `build_p01_fixtures`
  re-imports `run_gps_denied_replay` + `write_observer_fixture`
  from `_common.py`. Any caller (test or production) doing
  `bp01.run_gps_denied_replay(...)` still works because the symbol
  is present in the module namespace via the `from … import …`
  re-export.

## Test Results

* New unit tests: **20** (5 `convert_imu_csv_to_tlog` + 5
  `_hdg_centideg_to_rad` parametric + 4 `verify_fdr_has_estimates`
  + 4 `build_p02_fixtures` end-to-end + 1 export-relationship
  + 1 missing-file negative).
* Full `e2e/_unit_tests` suite: **686 passed in 123 s** (previous:
  664 → +22 net = +20 new + +2 directory-layout entries).
* No new linter errors (`ReadLints` clean on all touched files).
* No regression in the b78 builder tests (24/24 still pass after
  the helper extraction).
