[AZ-271] [AZ-276] [AZ-278] [AZ-282] Finish cross-cutting helpers + relax opencv pin

E-CC-HELPERS closes with the three remaining Layer-1 helpers and
E-CC-CONF closes with the env > YAML > defaults precedence test
gate. All four tickets ship with frozen public surfaces, hermetic
unit tests, and no upward (components.*) imports.

* AZ-271 — tests/unit/shared/config/test_precedence.py (5 ACs + smoke
  test + helper that names the layer in failure messages).
* AZ-282 — helpers/ransac_filter.py: static RansacFilter +
  RansacResult; cv2.setRNGSeed(0) for byte-equal determinism;
  median residual semantics pinned by contract.
* AZ-276 — helpers/imu_preintegrator.py + make_imu_preintegrator;
  GTSAM PreintegratedCombinedMeasurements; strict-monotonic ts_ns
  guard runs before any state mutation. Adjacent hygiene:
  _types/nav.py ImuSample/ImuWindow now use ts_ns:int and the
  spec-mandated ImuBias dataclass.
* AZ-278 — helpers/lightglue_runtime.py: structural R14 fix.
  LightGlueRuntime + non-blocking concurrent-access guard that
  raises rather than serialising. EngineHandle Protocol in
  _types/manifests.py + KeypointSet/CorrespondenceSet in
  _types/matching.py (Protocol surface adds approved by spec).

Dependency conflict (Finding 1, user-approved): gtsam 4.2 (PyPI) is
numpy-1.x-ABI only; opencv-python>=4.12 needs numpy>=2 at runtime.
Resolution: opencv-python pin relaxed to >=4.11.0.86,<4.12. The
D-CROSS-CVE-1 ratchet at ci/opencv_pin_gate.py is held at 4.11.0
with the original 4.12.0 floor restored once a numpy-2-compatible
gtsam wheel ships. Full replay procedure in
_docs/_process_leftovers/2026-05-11_d_cross_cve_1_opencv_pin_deferred.md.

Tests: 294 passed, 2 skipped (cmake/actionlint env-skips,
pre-existing). 43 new tests added for batch 5. Ruff check + format
clean.

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

src/gps_denied_onboard/helpers/__init__.py

@@ -16,6 +16,22 @@ from gps_denied_onboard.helpers.engine_filename_schema import (
     EngineFilenameSchema,
     EngineFilenameSchemaError,
 )
+from gps_denied_onboard.helpers.imu_preintegrator import (
+    CombinedImuFactor,
+    ImuPreintegrationError,
+    ImuPreintegrator,
+    make_imu_preintegrator,
+)
+from gps_denied_onboard.helpers.lightglue_runtime import (
+    LightGlueConcurrentAccessError,
+    LightGlueRuntime,
+    LightGlueRuntimeError,
+)
+from gps_denied_onboard.helpers.ransac_filter import (
+    RansacFilter,
+    RansacFilterError,
+    RansacResult,
+)
 from gps_denied_onboard.helpers.se3_utils import (
     SE3,
     Se3InvalidMatrixError,
@@ -46,10 +62,19 @@ __all__ = [
     "SE3",
     "SIDECAR_SUFFIX",
     "WEB_MERCATOR_MAX_LAT_DEG",
+    "CombinedImuFactor",
     "DescriptorNormaliser",
     "DescriptorNormaliserError",
     "EngineFilenameSchema",
     "EngineFilenameSchemaError",
+    "ImuPreintegrationError",
+    "ImuPreintegrator",
+    "LightGlueConcurrentAccessError",
+    "LightGlueRuntime",
+    "LightGlueRuntimeError",
+    "RansacFilter",
+    "RansacFilterError",
+    "RansacResult",
     "Se3InvalidMatrixError",
     "Sha256Sidecar",
     "Sha256SidecarError",
@@ -59,6 +84,7 @@ __all__ = [
     "exp_map",
     "is_valid_rotation",
     "log_map",
+    "make_imu_preintegrator",
     "matrix_to_se3",
     "se3_to_matrix",
 ]