chore: WIP pre-implement

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

_docs/LESSONS.md

@@ -6,6 +6,30 @@ Ring buffer: trim to the last 15 entries. Categories: `estimation · architectur
 
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+## 2026-05-26 — [testing] Removing `@pytest.mark.xfail` must be paired with a same-batch run on the actual hardware tier the test targets
+
+**Trigger**: AZ-848 root cause re-diagnosis (2026-05-26). In cycle 2, commit `8de2716 [AZ-776] Open-loop ESKF composition profile via c4_pose.enabled` removed `@xfail` decorators from AC-1/AC-2/AC-5/AC-6 in `test_derkachi_1min.py` with AC-7 in the spec stating "tests run on Jetson after this task → All five pass". The Jetson run was never executed before AZ-776 closed. The latent C1 contract bug (`VioOutput.emitted_at_ns` uses `monotonic_ns` instead of FC-boot-relative timestamps) was therefore not detected until cycle-3 Step 11 — three weeks later. AZ-848 is 5 SP and now blocks all real airborne work in cycle 4.
+
+**What changed**: `.cursor/skills/implement/SKILL.md` batch self-review should add a check — **if the batch removes any `@pytest.mark.xfail` decorator**, the same batch MUST include a green test execution against the test's target tier (or explicit `tier-2-only` skip documentation if the hardware is unavailable in the batch session). Block PASS verdict without this evidence. Predates the 2026-05 `meta-rule.mdc` "Real Results, Not Simulated Ones" rule but the implement skill's own gate should also enforce.
+
+Source: `_docs/06_metrics/retro_2026-05-26.md`
+
+## 2026-05-26 — [process] Autodev must block Step-N+1 entry if the previous cycle's retro file is missing
+
+**Trigger**: cycle-2 retro was never filed. The autodev orchestrator silently auto-chained from cycle-2 Step 17 (if it ran at all) straight into cycle-3 Step 9 without producing `retro_<cycle2-date>.md`. As a result, cycle-1 retro's Top-3 Improvement Actions sat invisible across cycle 2 and were re-discovered, all three still undelivered, only at cycle-3 close — including `architecture_compliance_baseline.md` (action #3) which is now in its third cycle of being un-delivered.
+
+**What changed**: `.cursor/skills/autodev/state.md` Re-Entry After Completion (or `flows/existing-code.md`) should verify that `_docs/06_metrics/retro_<YYYY-MM-DD>.md` exists for the previous cycle (`state.cycle`) before incrementing the cycle counter and entering Step 9 of cycle N+1. If absent, BLOCK and surface the gap with an A/B/C choice: (A) author the missing retro now, (B) stub a backfilled retro and proceed, (C) abort and ask the user.
+
+Source: `_docs/06_metrics/retro_2026-05-26.md`
+
+## 2026-05-26 — [tooling] When investigating bug X reveals a separate latent bug Y, file Y as a new ticket immediately — do not fold Y's scope into X
+
+**Trigger**: AZ-848 evidence-based investigation (2026-05-26) used a pymavlink probe against the Derkachi tlog to verify the original "IMU-vs-IMU clock mismatch" hypothesis. The probe REFUTED the original hypothesis (both `RAW_IMU` and `SCALED_IMU2` share the FC-boot timebase) and SIMULTANEOUSLY surfaced a separate latent bug — `c8_fc_adapter._handle_imu` mis-reads `SCALED_IMU2.time_boot_ms` as `time_usec`, defaulting to 0 for ~half of all IMU samples. Both bugs are real and orthogonal in their fix paths. The decision was to split — AZ-883 (2 SP) gets its own ticket, AZ-848 (5 SP) keeps its tightly-scoped contract repair.
+
+**What changed**: when a deep investigation surfaces a second latent issue that's orthogonal to the primary bug, file the second issue as its own ticket in the same session (with full evidence + reproduction protocol), then resume the primary investigation. Resist the temptation to fold the second issue into the primary ticket's scope "for convenience" — it inflates SP estimates and couples fix landings unnecessarily.
+
+Source: `_docs/06_metrics/retro_2026-05-26.md`
+
 ## 2026-05-20 — [testing] Two-tier test policy retired — all tests run on Jetson only
 
 **Trigger**: a `/test-run` invocation on the workstation Tier-1 Docker stack uncovered eight categorically distinct, sequential bugs in the supposedly-supported workstation path (Dockerfile `COPY` ordering before editable install, base-image pip too old for `gtsam` pre-release wheels, runtime stage missing the `python3` metapackage that `python3 -m venv` symlinks against, missing `libgl1` / `libglib2.0-0` for `cv2` import, missing `runtime_root/__main__.py` shim, lazy import that never registered the `c6_tile_cache` config block, and a `BUILD_FAISS_INDEX` env flag gap in `docker-compose.test.jetson.yml`). None of these had been hit before because no one had actually executed the workstation Docker stack end-to-end since it was authored — the colocated Jetson Woodpecker agent was the only test environment that ever ran. Maintaining the divergent x86 path was producing only false-negative signal and engineering time, never honest test coverage.