docs: add lessons 110-111 (RLS backfill audit, axios interceptor pattern)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -380,6 +380,10 @@ cd backend && pip install httpx && python -m scripts.seed_trees
 
 **109. `tree_shares.account_id` must equal `tree.account_id`, not the actor's account:** When creating a `TreeShare`, always use `account_id=tree.account_id` (tree owner's tenant). A super admin in tenant A sharing tenant B's tree must produce a share row in tenant B's RLS context — using `current_user.account_id` instead makes the share invisible to the tree owner after RLS is enforced.
 
+**110. Backfill migrations for `account_id` require a service-code audit:** When a migration adds `account_id` to an existing model via backfill (nullable → backfill → NOT NULL), grep for ALL `ModelClass(` instantiation sites in service code and verify `account_id=` is passed. SQLAlchemy accepts `None` silently with no warning; Phase 4 RLS WITH CHECK only surfaces the problem at runtime as `InsufficientPrivilegeError: new row violates row-level security policy`. Fixed example: `AISessionStep` — all 5 creation sites in `flowpilot_engine.py` were missing `account_id` until April 2026.
+
+**111. Global Axios interceptor fires before component `.catch()` — fix optional-data endpoints at the source:** The global 5xx handler in `client.ts` fires for ALL non-401 5xx responses, even when a component does `.catch(() => {})`. If an endpoint returns optional UI data (e.g., board filters, PSA config), return `[]` / `{}` on provider failure rather than raising 502. Silencing the error in the component is not enough — the toast appears anyway. See `list_boards` in `integrations.py` for the fixed pattern.
+
 ## RBAC & Permissions
 
 - **Role hierarchy:** super_admin > team_admin > engineer > viewer