Update autodev state and lessons documentation

- Changed current step from 16 (Deploy) to 9 (New Task) and updated cycle from 1 to 2 in _docs/_autodev_state.md.
- Closed Cycle 1 (Phase B) and noted that Steps 14, 15, and 16 were skipped due to no changes in auth, wire, or performance surfaces.
- Added new lessons to _docs/LESSONS.md, including insights on architecture gates and handling state discrepancies during session resumes, sourced from recent retrospectives.

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

_docs/LESSONS.md

@@ -1,8 +1,32 @@
 # Lessons
 
-Short, actionable retros from past sessions. Newest at top. Each entry: one
-line title + ≤6 lines body. The `autodev` orchestrator surfaces the top 3
-entries on every invocation.
+Short, actionable retros from past sessions. Newest at top. Ring buffer of
+the last 15 entries. The `autodev` orchestrator surfaces the top 3 entries
+on every invocation.
+
+Categories: estimation · architecture · testing · dependencies · tooling · process
+
+---
+
+- [2026-05-12] [architecture] When adding an architecture gate (STC-ARCH-*),
+  extend the existing single-script dispatcher with a new `--mode` flag
+  instead of forking a second script; same walker, same comment-skip, same
+  test harness — half the drift surface.
+  Source: _docs/06_metrics/retro_2026-05-12.md
+
+- [2026-05-12] [architecture] When a barrel re-export causes a runtime
+  circular import, treat the carve-out as a structural exemption documented
+  in five coupled places (barrel, consumer, script regex, layout doc, gate
+  test), not as a re-order hack — the exemption clears when the deeper
+  structural fix lands and never silently drifts in the meantime.
+  Source: _docs/06_metrics/retro_2026-05-12.md
+
+- [2026-05-12] [process] When autodev detects state ↔ working-tree
+  disagreement on session resume (`state.cycle` / `state.step` ≠ on-disk
+  artifact set), ALWAYS surface as a Choose block before resuming work —
+  never silently merge or restart; the rule in `state.md` "trust folders
+  over state file" worked end-to-end on the AZ-486 resume.
+  Source: _docs/06_metrics/retro_2026-05-12.md
 
 ---