Implements the mandatory simple-baseline StateEstimator per AC-2.1a
engine-rule at C5 (IT-12 comparative study vs iSAM2). NumPy-only;
no GTSAM dependency so BUILD_STATE_ESKF=ON binaries ship without
GTSAM at all.
- 16-state error vector (pos 3 + vel 3 + rot 3 + ba 3 + bg 3 + dt 1)
over a textbook nominal-state / error-state ESKF split.
- add_fc_imu: full nonlinear IMU integration + linearised F P F^T + Q
covariance propagation per IMU sample.
- add_vio: simplified relative-pose update (snapshot-based; baseline
scope, documented).
- add_pose_anchor: absolute-pose update; integrates BOTH marginals and
jacobian modes (no skip — ESKF has no graph; AC-4).
- AC-9 divergence test: Mahalanobis r^T S^-1 r > 100 (10 sigma) on the
innovation covariance S = H P H^T + R.
- AC-5 SPD: Cholesky-positive enforcement on every emitted covariance;
non-SPD raises EstimatorFatalError and locks state to LOST.
- AC-6 honesty: smoothed_history entries carry smoothed=False; deviation
from C5 contract Invariant 7 documented in module + report.
- AC-7 / AC-10 BUILD_STATE_ESKF gating: works through existing factory
infra (state_factory._STATE_BUILD_FLAGS).
- AC-8: SourceLabelStateMachine + FallbackWatcher auto-wired eagerly
in __init__, same pattern as the iSAM2 estimator.
Tests: 20 new unit tests covering AC-1..AC-10 + robustness checks.
Full suite: 660 passed, 2 skipped (CI-only).
The AZ-386 Jira transition to Done is deferred (Atlassian MCP returned
'Not connected'); recorded in _docs/_process_leftovers/ for replay on
the next autodev invocation per the Leftovers Mechanism.
Co-authored-by: Cursor <cursoragent@cursor.com>
Oleksandr Bezdieniezhnykh