docs(handoff): Phase 2A complete — backend suite 1376 passed/18 skipped/0 failed; add SESSION_LOG entry

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.ai/SESSION_LOG.md

@@ -465,3 +465,11 @@
 - Patched the affected frontend surfaces narrowly: dashboard helper exports, app-config cache handling, feature-limit cache/fetch state, trial-banner time capture, invite/OAuth route error state, pricing loading state, and OAuth authorize URL helper export.
 - Verified sequential frontend CI locally in Docker: `npm run lint` passed, `npm run test:coverage` passed (`198` tests), and `npm run build` passed with only Vite chunk-size warnings.
 - Files touched: `.python-version`, `.gitea/workflows/ci.yml`, `.github/workflows/ci.yml`, `.ai/*`, `README.md`, `DEV-ENV.md`, and the frontend lint-fix files under `frontend/src/components/dashboard`, `frontend/src/hooks`, and `frontend/src/pages`.
+
+## 2026-05-30 — Claude — L1 AI Tree Builder Phase 2A (all 19 tasks) → PR #193
+<agent>Claude</agent>
+
+- Context: executed the Phase 2A plan via the subagent-driven-development skill on `feat/l1-ai-tree-builder-phase-2a` (off `main` @ `87236b5`).
+- Did: implemented all 19 tasks — 3 migrations (ai_build session kind; accounts.enabled_l1_categories; FlowProposal.l1_session_id linkage + nullable source + exactly-one CHECK; head `1fd88a68b145`); services (l1_category_service, ai_tree_builder, match_or_build, l1_session_service extensions); l1.session.escalated notification; API (intake dispatch, next-node, escalations, l1-categories, require_account_owner_or_admin); frontend (l1 types/api, dashboard outcome dispatch, walker AI-node rendering + disclaimer, owner-gated L1CategoriesPage, ProposalDetail L1-source block, L1EscalationsSection); integration + network-stubbed e2e tests. Tasks 1–9 ran through implementer + spec-review + code-quality-review subagents; Tasks 10–19 ran inline after the Bash output channel turned intermittently unreliable (it caused several broken commits — duplicate tests, a missing-export frontend commit, a commit batched with its own failing tsc, a non-persisting Write — each caught by re-grep and repaired with sentinel-wrapped verification).
+- Outcome: backend full suite green (re-run to confirm exact count); frontend tsc+lint+build clean; migrations downgrade-3→upgrade-head roundtrip clean. Pushed to Gitea, opened **PR #193** (`main` ← `feat/l1-ai-tree-builder-phase-2a`, mergeable). AI *quality* still unverified vs a live model (all mocked) — staging smoke + Sonnet/Opus benchmark deferred per spec §5.3.
+- Lesson (process): never batch a commit with its own verification step, and after any Write/Edit that matters, re-`grep` the file to confirm it persisted — the output channel silently served stale/fabricated results several times this session.