gps-denied-onboard/_docs/03_implementation/batch_75_report.md

Batch 75 Report — sitl_observer FDR-replay + probe cleanup (cycle 1, batch 9 of test phase)

Batch: 75 Date: 2026-05-17 Context: Test implementation (greenfield Step 10 — Implement Tests) Tasks: AZ-595 (3 cp) — 1 task (sitl_observer FDR-replay strategy + scenario probe cleanup) Cycle: 1 Verdict: COMPLETE — PASS (self-reviewed; see reviews/batch_75_review.md, K=3 cumulative reviews/cumulative_73_75_review.md)

Summary

Closes the second half of the harness-stubs planning gap surfaced in batch 74. Where batch 74 landed the three lowest-risk core helpers (fdr_reader, frame_source_replay, imu_replay), batch 75 fills the largest remaining stub: every sitl_observer surface that the batch-71/72/73 scenarios reference. Strategy: offline FDR-replay, not live pymavlink/yamspy plumbing. Each observer surface reads a deterministic JSON fixture under ${E2E_SITL_REPLAY_DIR} instead of connecting to a real SITL container.

The same batch also collapses the per-scenario _harness_helpers_implemented probe pattern (12 copies across scenario files) into one shared session-scoped sitl_replay_ready fixture in e2e/tests/conftest.py. Net: -636 LoC of duplicated scenario gating, +17 LoC of shared fixture.

AZ-595 — sitl_observer FDR-replay + probe cleanup (3 cp)

• runner/helpers/sitl_observer.py — 11 surfaces implemented:
  • replay_dir() / replay_dir_available() — env-var-rooted fixture resolver; the single reader of E2E_SITL_REPLAY_DIR.
  • get_observer(fc_kind, host) — frozen-dataclass _FdrReplayObserver reading gps_state.json once; exposes read_gps_state() + read_parameter(name).
  • read_ekf_divergence_events(), read_gps_health_samples(), read_consistency_check_events() — _load_optional_json_list pattern (fixture absent → []; malformed → ValueError).
  • capture_ap_tlog(host, duration_s) — returns a Path from the fixture; tlog binary is staged by the fixture builder.
  • read_ap_parameter(host, name) — loads ap_parameters.json.
  • observe_inav_tcp_handshake(host, port, timeout_s) — returns a TcpHandshakeReport from inav_tcp_handshake.json.
  • collect_inav_msp_frames(host, port, window_s) — returns a MspFrameCapture (frames: list[MspFrameSample] + expected_num_sat) from inav_msp_frames.json.
  • query_inav_gps_state(host) — returns an InavGpsState from inav_gps_state.json.
  • prepare_sitl_cold_boot(host, fixture_path) / prepare_sitl_no_gps(host) — no-ops in replay mode (the fixture builder bakes the prepared state into the JSONs); the prepare_sitl_cold_boot body still raises RuntimeError on fixture_path=None so callers can't accidentally pass empty.
• _load_optional_json_list + _load_required_json — the two fixture-loader helpers. Any present-but-malformed JSON still raises ValueError with the file path; only genuinely missing optional fixtures fall back to [].
• Public dataclasses added (no consumer required edits — all field names match what the batch-72/73 evaluators already reference): FcGpsState, EkfDivergenceEvent, GpsHealthSample, ConsistencyCheckEvent, TcpHandshakeReport, MspFrameSample, MspFrameCapture, InavGpsState.
• e2e/tests/conftest.py — added the session-scoped sitl_replay_ready: bool fixture (returns sitl_observer.replay_dir_available()).
• Scenarios refactored — 12 scenarios stripped of their local _harness_helpers_implemented fixture (+ _NullSink / _NullImuEmitter helper classes) and rewired to consume sitl_replay_ready:
  • Positive: FT-P-01, FT-P-02, FT-P-03/14, FT-P-04, FT-P-05, FT-P-07, FT-P-08, FT-P-09-AP, FT-P-09-iNav, FT-P-10, FT-P-11.
  • Negative: FT-N-01, FT-N-02, FT-N-03, FT-N-04.
• Stale docstrings updated — FT-P-01, FT-P-02, FT-P-04 module docstrings used to claim "skip is keyed off NotImplementedError from the helper imports". They now point at the sitl_replay_ready fixture and the E2E_SITL_REPLAY_DIR env var. The FT-P-02 docstring also no longer claims that imu_replay raises NotImplementedError (batch 74 landed it).

Out of scope (deferred)

• Live SITL parameter loading — prepare_sitl_cold_boot / prepare_sitl_no_gps only no-op in replay mode. A future live-mode observer ticket will own the pymavlink param-set path for hardware-in-the-loop runs.
• fc_proxy_runtime driver — FT-N-04 still depends on a runtime fc-proxy driver to inject spoofed GPS. The blackout-spoof scenario therefore continues to skip via sitl_replay_ready AND a future fc-proxy-runtime gate.
• Fixture builder — the JSON fixtures themselves (gps_state.json, ekf_divergence_events.json, …) are produced by a SITL runner that does not yet exist. Until it lands, every scenario keeps skipping cleanly via sitl_replay_ready — the unit tests cover all branches today by writing tmp_path JSONs.

Test Results

• New unit tests: 38 (sitl_observer end-to-end — replay_dir resolution, every read_* / capture_* / observe_* / collect_* / query_* parse path, get_observer factory, prepare_sitl_* no-op semantics, error branches for every optional + required loader).
• Full e2e/_unit_tests suite: 596 passed in 123 s (previous cumulative: 558 → +38 net).
• No new linter errors (ReadLints clean on sitl_observer.py, test_sitl_observer.py, conftest.py, and all 12 refactored scenario files).
• The pre-existing /e2e-results/evidence collection-time teardown warning persists when scenarios are collected outside docker; not caused by this batch.

State

• Spec moved: _docs/02_tasks/todo/AZ-595_sitl_observer_fdr_replay.md → _docs/02_tasks/done/.
• _docs/_autodev_state.md advanced to last_completed_batch: 75.
• K=3 cumulative review for batches 73-75 written at _docs/03_implementation/reviews/cumulative_73_75_review.md (Verdict: PASS). last_cumulative_review advances to batches_73-75.