[AZ-228] [AZ-229] Add VIO and satellite sync boundaries

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

_docs/02_tasks/done/AZ-228_vio_adapter.md

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+# VIO Adapter
+
+**Task**: AZ-228_vio_adapter
+**Name**: VIO Adapter
+**Description**: Wrap the selected relative VIO backend as a replaceable component with health and error behavior.
+**Complexity**: 5 points
+**Dependencies**: AZ-221_shared_geometry_time_sync, AZ-222_runtime_config_errors_telemetry, AZ-223_camera_ingest_calibration, AZ-224_mavlink_gcs_gateway
+**Component**: VIO Adapter
+**Tracker**: AZ-228
+**Epic**: AZ-213
+
+## Problem
+
+The safety wrapper needs relative VIO state from calibrated frames and FC IMU without inheriting backend-specific internals.
+
+## Outcome
+
+- Backend initialization, processing, and health behavior are exposed through a replaceable adapter.
+- Tracking loss and timestamp mismatch are explicit.
+- The adapter never emits WGS84 coordinates or safety decisions.
+
+## Scope
+
+### Included
+- Initialization and runtime health.
+- Frame + IMU processing behavior.
+- Relative pose/velocity/bias output and quality metadata.
+- Native bridge boundary.
+
+### Excluded
+- Absolute anchor fusion and covariance authority.
+- Satellite matching fallback implementation.
+
+## Dependencies
+
+### Document Dependencies
+- `_docs/02_document/contracts/shared/runtime_contracts.md`
+- `_docs/02_document/contracts/shared/geometry_time_sync.md`
+- `_docs/02_document/contracts/shared/config_errors_telemetry.md`
+
+## Acceptance Criteria
+
+**AC-1: VIO state emitted**
+Given synchronized frame and IMU samples
+When processing succeeds
+Then a relative VIO state packet with tracking quality is emitted.
+
+**AC-2: Timestamp mismatch is explicit**
+Given frame/IMU timestamps are inconsistent
+When processing is requested
+Then the adapter rejects the packet with a timestamp mismatch error.
+
+**AC-3: Health is observable**
+Given initialization or tracking quality changes
+When health is requested
+Then the adapter reports current VIO readiness and degradation state.
+
+## Non-Functional Requirements
+
+**Performance**
+- Adapter processing must be profiled against Jetson latency/memory limits.
+
+**Reliability**
+- Backend failures are surfaced, not hidden.
+
+## Unit Tests
+
+| AC Ref | What to Test | Required Outcome |
+|--------|--------------|------------------|
+| AC-1 | Valid synchronized packet | VIO state emitted |
+| AC-2 | Bad timestamp window | Explicit error |
+| AC-3 | Tracking loss | Health reports degraded |
+
+## Blackbox Tests
+
+| AC Ref | Initial Data/Conditions | What to Test | Expected Behavior | NFR References |
+|--------|-------------------------|--------------|-------------------|----------------|
+| AC-1 | Derkachi/public replay | Relative VIO path | Continuous estimates where data supports it | Performance |
+
+## Constraints
+
+- BASALT remains the current selected backend, but package and folder names must stay backend-neutral.
+- The VIO adapter is not the safety authority.
+- GPL VIO dependencies remain reference-only unless explicitly approved.
+
+## Risks & Mitigation
+
+**Risk 1: Nadir fixed-wing fit**
+- *Risk*: The selected VIO backend underperforms on low-parallax terrain.
+- *Mitigation*: Representative replay and reference comparisons gate acceptance.