update GPS-denied onboard research docs

_docs/00_problem/acceptance_criteria.md

@@ -1,8 +1,9 @@
 # Acceptance Criteria
 
-> **Last revised**: 2026-04-26 (post Mode B Solution Assessment + user-driven addendum on VPR granularity & change-robustness + user lock-in of Mode B open items Q1–Q5).
+> **Last revised**: 2026-04-29 (visual-blackout / GPS-spoofing degraded-mode addendum).
 > Changes vs. previous version (2026-04-25): AC-1.2 split into hard-floor + stretch; AC-1.4 made quantitative; AC-2.2 split per pipeline stage; AC-3.4 dual-trigger; AC-4.3 autopilot-pinned; AC-5.2 N pinned; AC-7.1 scoped to level flight; AC-8.2 freshness by sector; six new AC added (AC-NEW-1 … AC-NEW-6).
 > Changes 2026-04-26: AC-4.3 extended to dual-channel hybrid (GPS_INPUT primary + ODOMETRY auxiliary); AC-8.6 added (VPR retrieval-unit + change-robustness); AC-NEW-7 added with confirmed numeric thresholds (cache-poisoning safety budget).
+> Changes 2026-04-29: AC-3.5 and AC-NEW-8 added for temporary visual blackout/cloud occlusion during GPS spoofing, including IMU-only degraded navigation, covariance growth, and failover limits.
 
 ## Position Accuracy
 
@@ -26,6 +27,7 @@
 - **AC-3.2** — The system shall correctly continue work during sharp turns where the next photo overlaps **<5%** with the previous, drifts **<200 m**, and changes heading **<70°**. Sharp-turn frames are expected to fail VO and shall be handled by satellite-based re-localization (place recognition over the satellite tile cache).
 - **AC-3.3** — The system shall handle **≥3 disconnected segments** per flight, connecting each new segment to the previous trajectory via global descriptor retrieval + RANSAC pose-graph relocalization. This is a core capability, not a degraded mode.
 - **AC-3.4** — When the system cannot determine position for **≥3 consecutive frames AND ≥2 s**, it shall send a re-localization request to the ground station via telemetry. While waiting, it continues VO/IMU dead reckoning and the flight controller uses last known position + IMU extrapolation.
+- **AC-3.5** — During temporary **visual blackout** where the navigation camera provides no usable ground signal (e.g., clouds/occlusion/whiteout) while GPS is denied or spoofed, the system shall switch to `{dead_reckoned}` within **≤1 processed frame OR ≤400 ms**, reject the spoofed GPS as an estimator input, and propagate position solely from the last trusted state + flight-controller IMU/attitude/airspeed/altitude inputs until visual or satellite anchoring recovers. During this mode, covariance shall grow monotonically, `GPS_INPUT.horiz_accuracy` shall not under-report the 95% covariance semi-major axis, and QGroundControl shall receive a `VISUAL_BLACKOUT_IMU_ONLY` status at **1–2 Hz**.
 
 ## Real-Time Onboard Performance
 
@@ -153,3 +155,18 @@
 - Eligibility check (Component 1b) tightens generation gate from σ_xy ≤ 10 m to σ_xy ≤ 5 m.
 
 **Validation.** Multi-flight Monte Carlo replay over AerialVL + Mavic + AerialExtreMatch with **synthetic over-confidence injection** (artificially deflate EKF covariance by 1.5×–3×): assert both probabilities below budget across ≥100 simulated flights worth of frames. Independently, Service-side voting layer is exercised in F-T3 to verify candidate tiles are not promoted to trusted basemap before N-flight confirmation.
+
+### AC-NEW-8 — Visual blackout + GPS spoofing degraded-mode budget
+
+**Statement.** When the navigation camera is fully unusable for visual localization and the flight controller simultaneously reports GPS denial/spoofing, the onboard system shall:
+
+- continue emitting `GPS_INPUT` from IMU-only propagation for **up to 30 s** after the last trusted visual/satellite anchor, unless the estimator covariance exceeds the fail threshold earlier;
+- label every estimate `{dead_reckoned}` and set `fix_type=2` or lower when the 95% covariance semi-major axis exceeds **100 m**;
+- emit `fix_type=0`, `horiz_accuracy=999.0`, and `STATUSTEXT: VISUAL_BLACKOUT_FAILSAFE` when the 95% covariance semi-major axis exceeds **500 m** OR visual blackout exceeds **30 s** without a trusted re-anchor;
+- never promote spoofed real-GPS measurements back into the estimator during blackout unless the FC GPS health has been stable and non-spoofed for **≥10 s** and a visual/satellite consistency check has succeeded.
+
+**Why it matters.** A cloud/whiteout period removes all visual correction exactly when spoofed GPS cannot be trusted. The only safe behavior is honest IMU-only dead reckoning with rapidly growing uncertainty, not pretending that a stale visual position or spoofed GPS remains valid.
+
+**Implementation drivers.** Add an image-quality/occlusion classifier before VO/VPR, a blackout state in the ESKF mode machine, covariance floors for IMU-only propagation, strict GPS health gating, and QGC/FDR logging for blackout start, every degraded estimate, and blackout recovery/failsafe.
+
+**Validation.** SITL/replay: inject a 5 s, 15 s, and 35 s full-camera blackout while spoofing `GPS_RAW_INT`; assert mode transition ≤400 ms, spoofed GPS is ignored, covariance grows monotonically, `GPS_INPUT` fields degrade at the thresholds above, and recovery only occurs after a trusted visual/satellite anchor or the 10 s GPS-health + visual-consistency gate.