[AZ-528] Consolidate c1_vio strategy facade orchestration spine

Replace 3-way byte-equivalent orchestration-spine duplication across
okvis2.py / vins_mono.py / klt_ransac.py with a single c1-internal
helper at components/c1_vio/_facade_spine.py. Closes cumulative
review batches 52-54 Finding F1. No behaviour change — all existing
AZ-332 / AZ-333 / AZ-334 AC tests pass unmodified (114 c1_vio tests
green, 237 with adjacent regression suite).

The helper exposes 5 stateless free functions (now_iso, bias_norm,
se3_from_4x4, frame_ts_ns, frame_image) and a FacadeSpine mixin
class providing _classify_state / _tick_lost / _emit_transition.
Concrete strategies inherit the mixin and set spine-required
instance attributes in __init__. Mirrors the AZ-527 precedent for
c2_vpr-side _assert_engine_output_dim consolidation.

New test file test_az528_facade_spine.py covers AC-1..AC-8 with 19
tests, including an AST regression guard that prevents future
re-introduction of the consolidated free functions in any strategy
module, plus a Risk-1 static check that every strategy's __init__
assigns every spine-required attribute.

Archive AZ-528 task spec to done/, bump autodev state to batch 56.

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

_docs/03_implementation/batch_55_cycle1_report.md

@@ -0,0 +1,97 @@
+# Batch 55 — Cycle 1 Report
+
+**Date**: 2026-05-14
+**Tasks**: AZ-528 (Hygiene — c1_vio strategy facade orchestration-spine consolidation)
+**Verdict**: COMPLETE — PASS
+
+## Summary
+
+Consolidated the 3-way orchestration-spine duplication across the
+c1_vio `VioStrategy` modules (`okvis2.py`, `vins_mono.py`,
+`klt_ransac.py`) into a single c1-internal helper module
+`_facade_spine.py`. Closes cumulative review batches 52-54 Finding
+F1 (Medium / Maintainability). Mirrors the AZ-527 precedent for the
+c2_vpr-side `_assert_engine_output_dim` consolidation. No behaviour
+change — every existing AZ-332 / AZ-333 / AZ-334 AC test passes
+unmodified.
+
+## Files added / modified
+
+### Added (2)
+
+- `src/gps_denied_onboard/components/c1_vio/_facade_spine.py` — new
+  c1-internal helper, 225 lines. Exports 5 free functions (`now_iso`,
+  `bias_norm`, `se3_from_4x4`, `frame_ts_ns`, `frame_image`) and the
+  `FacadeSpine` mixin class (`_classify_state`, `_tick_lost`,
+  `_emit_transition`).
+- `tests/unit/c1_vio/test_az528_facade_spine.py` — new test file, 19
+  tests covering AC-1..AC-8 + a Risk-1 mitigation test (each
+  strategy's `__init__` statically asserts that every spine-required
+  attribute is assigned). All pass.
+
+### Modified (3)
+
+- `src/gps_denied_onboard/components/c1_vio/okvis2.py` — inherit from
+  `FacadeSpine`; import the 5 free functions; delete the 5 local
+  module-level definitions, 3 instance methods, and the unused
+  `_BIAS_NORM_FLOOR` constant. Set the 3 spine-required attributes
+  (`_feature_threshold`, `_producer_id`, `_strategy_label`) in
+  `__init__`.
+- `src/gps_denied_onboard/components/c1_vio/vins_mono.py` — same
+  pattern as `okvis2.py`.
+- `src/gps_denied_onboard/components/c1_vio/klt_ransac.py` — same
+  pattern; spine threshold reads `self._cfg.min_features_for_pose`
+  (the KLT-side equivalent of OKVIS2's `degraded_feature_threshold`).
+  Deferred-consolidation comments referencing this PBI removed.
+
+## Tests
+
+- `tests/unit/c1_vio/test_az528_facade_spine.py` — 19 new tests, all
+  pass.
+- `tests/unit/c1_vio/` (full focused suite) — 120 collected, 114
+  pass + 6 tier-2 skipped (unchanged from pre-AZ-528 state).
+- Adjacent regression suite (`test_az270_compose_root`,
+  `test_az272_fdr_record_schema`, `test_az273_fdr_client_ringbuf`,
+  `test_ac1_scaffold_layout`, `tests/unit/c1_vio/`) — 237 pass + 6
+  skipped.
+
+## AC traceability
+
+| AC    | Status | Notes                                                   |
+|-------|--------|---------------------------------------------------------|
+| AC-1  | ✓      | Helper module exposes documented surface.               |
+| AC-2  | ✓      | `now_iso()` returns aware UTC `+00:00` ISO-8601.        |
+| AC-3  | ✓      | `bias_norm` matches L2 formula (accel + gyro).          |
+| AC-4  | ✓      | `se3_from_4x4` builds `gtsam.Pose3` identity correctly. |
+| AC-5  | ✓      | `_classify_state` INIT during warmup, T/D thresholds.   |
+| AC-6  | ✓      | `_tick_lost` demotes T→D first call, escalates to LOST. |
+| AC-7  | ✓      | `_emit_transition` exactly one FDR record per change.   |
+| AC-8  | ✓      | AST guard: 0 module-level free funcs in 3 strategies.   |
+| AC-9  | ✓      | All AZ-332 / AZ-333 / AZ-334 AC tests pass unmodified.  |
+| AC-10 | ✓      | AZ-270 layer-lint regression still passes.              |
+
+## Code review
+
+See `_docs/03_implementation/reviews/batch_55_review.md` — verdict
+PASS, no findings.
+
+## Outcomes & lessons
+
+- Pattern of an "AST regression guard against duplicated free
+  functions" continues to work well (AZ-508 / AZ-526 / AZ-527 /
+  AZ-528 all use it). It catches re-introduction by future authors
+  who don't know the consolidated home exists.
+- Mixin-via-instance-attributes (rather than constructor parameters)
+  keeps strategy `__init__` signatures stable — the AZ-331 factory
+  signature `(config, *, fdr_client)` is preserved across all three
+  strategies post-refactor.
+- A 3-point hygiene PBI was the right granularity: 1 new module,
+  3 small edits to existing strategies, 1 test file with AST + import
+  regression guards. Same shape and complexity as AZ-527.
+
+## Outstanding
+
+None for AZ-528. F2 from cumulative review batches 52-54 (test fake
++ `_patch_pose_recovery` helper consolidation) remains deferred —
+sits at a different abstraction layer and will ride a later hygiene
+pass.