# Batch 54 — Cycle 1 Report

**Date**: 2026-05-14
**Tasks**: AZ-334 (C1 KLT/RANSAC Strategy)
**Verdict**: COMPLETE — PASS_WITH_WARNINGS

## Summary

Implemented `KltRansacStrategy`, the ADR-002 engine-rule mandatory
simple-baseline VIO for C1. Pure-Python facade over OpenCV's
`cv2.goodFeaturesToTrack` / `cv2.calcOpticalFlowPyrLK` /
`cv2.findEssentialMat` / `cv2.recoverPose` pipeline — no C++/pybind11
binding by design so a Tier-0 workstation can run the strategy with
`pip install opencv-python` and the AZ-331 factory's
`BUILD_KLT_RANSAC=ON` gate. Mirrors the AZ-332 OKVIS2 + AZ-333
VINS-Mono facade pattern on the orchestration spine so the AZ-331
factory + IT-12 comparative harness treat all three strategies as
drop-in substitutable.

## Files added / modified

### Added (3)

- `src/gps_denied_onboard/components/c1_vio/klt_ransac.py` —
  Python facade, ~770 lines.
- `tests/unit/c1_vio/test_klt_ransac_strategy.py` — AC-1..AC-11 +
  NFR-perf + KltRansacConfig validation tests, ~990 lines, 25 tests
  (23 pass + 2 tier-2 skipped on dev/CI runners).
- `_docs/03_implementation/reviews/batch_54_review.md` — code review
  report.

### Modified (4)

- `src/gps_denied_onboard/components/c1_vio/config.py` — add
  `KltRansacConfig` dataclass + `klt_ransac` field on `C1VioConfig`;
  `__all__` updated. (Pre-existing `KNOWN_STRATEGIES` already had
  `klt_ransac` from AZ-331.)
- `src/gps_denied_onboard/components/c1_vio/__init__.py` — export
  `KltRansacConfig`.
- `cpp/klt_ransac/CMakeLists.txt` — replace AZ-263 placeholder with
  a deliberate "pure-Python; no native target" STATUS message so
  the build graph stays symmetric with `cpp/okvis2/` and
  `cpp/vins_mono/` while the `BUILD_KLT_RANSAC=ON` flag only gates
  the Python module import at the AZ-331 composition-root factory.
- `tests/unit/c1_vio/test_protocol_conformance.py` — introduce the
  `_STRATEGIES_WITHOUT_NATIVE_BINDING` category and route
  `klt_ransac` through it inside
  `test_ac5_build_vio_strategy_flag_on_but_module_missing` so the
  parametrised factory test correctly handles the pure-Python
  shape (no native binding to fail on; the construction should
  succeed and return a `VioStrategy` instance instead).

## AC coverage (AC-1..AC-11 + NFR-perf)

All 11 ACs + NFR-perf mapped to passing tests (see
`batch_54_review.md` Phase 2 table). AC-9 + NFR-perf are
tier-2-tagged per the task spec; they skip on macOS dev + GitHub
Actions Linux runner with `Tier-2-only test; set GPS_DENIED_TIER=2
to run`. AC-3 / AC-6 / AC-9 / AC-10 / AC-11 / NFR-perf monkeypatch
`cv2.findEssentialMat` + `cv2.recoverPose` +
`RansacFilter.filter_correspondences` to deterministic values so
the unit suite exercises the FACADE's state machine without
depending on real OpenCV geometry on synthetic correspondences;
real-geometry validation lives in C1-IT-12 (Jetson Tier-2 fixture).

## Test results

### Focused suite — `tests/unit/c1_vio/`

```
95 passed, 6 skipped in 1.67s
```

The 6 skips are the 2 OKVIS2 tier-2 tests + the 2 VINS-Mono tier-2
tests + the 2 new KLT/RANSAC tier-2 tests (`test_ac9_*` and
`test_nfr_perf_*`).

### Adjacent regression — config / compose-root

```
17 passed in 1.96s
```

(`test_az269_config_loader.py`, `test_az270_compose_root.py` — all
green; the new `KltRansacConfig` registration did not break the
schema-loader or compose-root layered-import guards.)

### Tier-2 verification

```
GPS_DENIED_TIER=2 pytest tests/unit/c1_vio/test_klt_ransac_strategy.py
→ 25 passed in 0.43s
```

All 25 tests pass under the tier-2 gate (including AC-9 honest-
covariance monotonicity over 48 synthetic frames + NFR-perf p95
record).

### Full suite

Deferred per the implement skill's Test-Run Cadence — the full
unit-suite gate runs exactly once at Step 16 (end of implementation
phase), not per-batch. Focused tests + cumulative review (every K
batches) catch cross-batch regressions before then.

## Architectural decisions

- **No native binding by design**: KLT/RANSAC is pure Python over
  OpenCV's Python bindings. The `cpp/klt_ransac/CMakeLists.txt`
  placeholder is preserved (with an explanatory STATUS message) for
  build-graph symmetry with `cpp/okvis2/` and `cpp/vins_mono/`; the
  `BUILD_KLT_RANSAC=ON` flag only gates the Python module import at
  the AZ-331 composition-root factory.
- **Constructor shape matches factory**: `KltRansacStrategy(config,
  *, fdr_client, clock=None)` mirrors `Okvis2Strategy` +
  `VinsMonoStrategy` so the AZ-331 factory invokes all three via the
  same call shape. The task spec's illustrative constructor
  (with explicit injection of `CameraCalibration` / `ImuPreintegrator`
  / `RansacFilter` / `Logger`) was deliberately not adopted because
  it would diverge from the existing factory contract; the same
  dependencies are resolved internally instead — `RansacFilter` is
  static (AZ-282 stateless helper) and `ImuPreintegrator` is
  constructed lazily on the first `process_frame` call (it needs
  the per-call `CameraCalibration` which is not available at
  construction time).
- **Honest covariance, AC-9 compliant**: per-frame covariance =
  `np.eye(6) * (sigma_sq + inlier_penalty) / max(inlier_count - 5, 1)`
  where `sigma_sq = median_residual_px**2` and `inlier_penalty =
  threshold_px / max(inlier_count, 1)`. No client-side floor or
  smoother; the formula grows monotonically as inliers drop or
  residuals scatter. Tier-2 test walks 48 scripted-inlier frames
  through the DEGRADED window and verifies monotonicity.
- **Camera agnostic, AC-11 enforced**: no `adti20` / `adti26`
  literals in executable source (docstring mentions are excluded
  from the CI grep via AST-aware stripping in the test). The
  per-call `CameraCalibration` argument carries intrinsics; the
  same code path produces sensible `VioOutput` for two distinct
  calibrations (different f, cx, cy).
- **State machine mirrors OKVIS2 / VINS-Mono**: `INIT` until
  `warm_start_max_frames` is exhausted, then `TRACKING` if inlier
  count ≥ `min_features_for_pose`, else `DEGRADED`; sustained
  pose-recovery failure for `lost_frame_threshold` consecutive
  frames raises `VioFatalError` with state == `LOST`. Exactly one
  `vio.health` FDR record per transition (AC-10).
- **Error envelope closed**: every OpenCV `cv2.error` is caught at
  each call site and rewrapped into `VioFatalError` with
  `__cause__` chaining (AC-4). `RansacFilterError` +
  `ImuPreintegrationError` are also caught and rewrapped.

## Out of scope / deferred

- Real geometry validation against Derkachi fixtures — Tier-2
  follow-up; C1-IT-12 binds KLT/RANSAC alongside OKVIS2.
- Warm-start hint persistence (AZ-335) — separate batch.
- Strategy-facade consolidation hygiene PBI — now formally in scope
  for the cumulative review covering batches 52-54 (next trigger).
  All three strategy shapes (OKVIS2, VINS-Mono, KLT/RANSAC) are
  now visible so the right factoring (template-method base class
  for the orchestration spine + per-strategy geometry hook) can be
  scoped without over-fitting.

## Honest-covariance numeric envelope (AC-9 evidence)

Tier-2 test walks the following inlier-count sequence through the
DEGRADED gate (`min_features_for_pose=50`):

| Frame range | Inlier count | State    | Cov Frobenius (approx) |
|-------------|--------------|----------|------------------------|
| 1           | first-frame  | INIT     | 24.49 (10·√6)          |
| 2..29       | 80           | TRACKING | ≈ 0.0056               |
| 30          | 40           | DEGRADED | ≈ 0.013                |
| 31..43      | 35..12       | DEGRADED | strictly increasing    |
| 44..49      | 10           | DEGRADED | ≈ 0.127                |

The Frobenius norm grows monotonically across the entire DEGRADED
window — the AC-9 honest-covariance invariant is upheld by the
formula's structure, not by a floor clamp.
