[AZ-599] Batch 79: FT-P-02 Derkachi builder + _common.py extraction

- Add build_p02_fixtures.py: IMU CSV → tlog conversion (RAW_IMU +
  ATTITUDE pairs, centidegrees→radians yaw) and orchestrator that
  runs gps-denied replay against Derkachi MP4 + generated tlog,
  verifying ≥1 record_type="estimate" in the FDR archive.
- Extract run_gps_denied_replay + FDR-parent-dir helpers into
  sitl_replay_builder/_common.py; refactor build_p01_fixtures.py
  to import from _common (b78 tests preserved).
- Add 20 unit tests under e2e/_unit_tests/fixtures/test_sitl_
  replay_builder_p02.py covering AC-1..AC-5; total unit suite
  686/686 passing (regression gate AC-6).
- README updated to document FT-P-01 + FT-P-02 builders.
- Advance autodev state: last_completed_batch=79, current_batch=80;
  prune verbose detail blob.

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

_docs/02_tasks/done/AZ-599_ft_p_02_derkachi_builder.md

@@ -0,0 +1,77 @@
+# FT-P-02 Derkachi fixture builder (IMU CSV → tlog, real-motion replay)
+
+**Task**: AZ-599_ft_p_02_derkachi_builder
+**Complexity**: 3 points
+**Dependencies**: AZ-598 (shared `run_gps_denied_replay` helper)
+**Component**: Blackbox Tests / Test Infrastructure (epic AZ-262)
+**Tracker**: AZ-599
+
+## Problem
+
+FT-P-02 (Derkachi continuous-flight drift) needs an offline-replay
+FDR archive so the scenario can compute drift between satellite
+anchors. The b78 FT-P-01 builder doesn't apply directly — FT-P-02
+uses real video + real IMU CSV instead of still images + synthetic
+stationary tlog.
+
+## Strategy
+
+Same overall shape as b78 (drive `gps-denied-replay` against a video
++ tlog pair), with two differences:
+
+1. **Video is already MP4** — skip the OpenCV encoding step.
+2. **IMU is real recorded telemetry** — `data_imu.csv` has 10 Hz
+   `SCALED_IMU2` + `GLOBAL_POSITION_INT` columns. Need a CSV → tlog
+   conversion that packs each row as a `RAW_IMU` + `ATTITUDE`
+   MAVLink pair, with yaw synthesised from `GLOBAL_POSITION_INT.hdg`
+   and roll/pitch=0 (acceptable for fixed-wing cruise).
+
+Output: the SUT's natural FDR archive directory (the b78 schema-
+projection step is dropped because FT-P-02 reads the FDR directly).
+
+## Files Touched
+
+* `e2e/fixtures/sitl_replay_builder/_common.py` (new) — extracts
+  `run_gps_denied_replay` + `write_observer_fixture` from
+  `build_p01_fixtures.py` so b78 + b79 share one implementation.
+* `e2e/fixtures/sitl_replay_builder/build_p01_fixtures.py` (edit)
+  — re-export the moved helpers from `_common.py` for backwards
+  compatibility; b78 tests must still pass unchanged.
+* `e2e/fixtures/sitl_replay_builder/build_p02_fixtures.py` (new) —
+  the FT-P-02 builder.
+* `e2e/fixtures/sitl_replay_builder/README.md` (edit) — document
+  both flows.
+* `e2e/_unit_tests/fixtures/test_sitl_replay_builder_p02.py` (new)
+  — b79 builder tests.
+* `e2e/_unit_tests/test_directory_layout.py` (edit) — register
+  the three new paths.
+
+## Acceptance Criteria
+
+**AC-1**: `convert_imu_csv_to_tlog` parses every row of
+`data_imu.csv` and writes one RAW_IMU + one ATTITUDE pair per row.
+
+**AC-2**: `convert_imu_csv_to_tlog` raises `ValueError` on missing
+required columns OR malformed numeric rows OR empty CSV.
+
+**AC-3**: Heading conversion uses centidegrees → radians
+(`hdg_cdeg * pi / 18000`).
+
+**AC-4**: `build_p02_fixtures` invokes `run_gps_denied_replay` with
+the Derkachi MP4 + the generated tlog; the resulting FDR archive
+contains ≥1 `record_type="estimate"` record (`verify_fdr_has_estimates`
+helper).
+
+**AC-5**: `run_gps_denied_replay` is in `_common.py`; b78 +
+b79 both import it from there; b78 tests still pass.
+
+**AC-6**: Full e2e unit-test suite passes.
+
+## Out of Scope
+
+* Live capture EXECUTION (manual operator step, same as b78).
+* FT-P-04 / FT-P-05 (also use Derkachi but each needs its own
+  builder; deferred).
+* iNav adapter.
+* True SCALED_IMU2 → RAW_IMU unit conversion (pass-through; will
+  re-visit if the SUT's tlog parser rejects).