feat(l1): proposal L1-source block + engineer L1-escalations section

- flow-proposal.ts: source_session_id nullable + add l1_session_id (matches backend
  FlowProposalSummary).
- ProposalDetail.tsx: render an 'AI L1 walk (outcome-validated)' note when
  l1_session_id is set instead of the /pilot/{source_session_id} link; fall back to
  the link for ai_session-sourced proposals.
- New L1EscalationsSection.tsx (GET /l1/escalations) — expandable rows with walked-path
  summary; renders nothing if empty. Mounted below the FlowPilot queue on
  EscalationQueuePage. tsc -b + eslint clean.

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

.ai/HANDOFF.md

@@ -9,72 +9,98 @@
 subagent-driven-development on branch `feat/l1-ai-tree-builder-phase-2a`
 (branched from `main` @ `87236b5`; **not pushed**, `main` untouched).
 
-## ⚠️ Tooling note (read first)
-This session repeatedly hit an unreliable **Bash output channel** — intermittently
-returns stale/cached output (e.g. a unique `echo` probe returned a prior `wc`
-result) or fabricated success. The **Read/Write/Edit channel stayed reliable.**
-Two derived lessons:
-- Run backend tests as `docker exec resolutionflow_backend pytest <path> --override-ini="addopts=" -q`.
-  Do **NOT** use `-p no:cov` — `pytest.ini` bakes `--cov` into `addopts`, so disabling
-  the cov plugin makes `--cov` an unrecognized arg and pytest exits non-zero **before
-  running**, which silently mislabels `&& echo PASS || echo FAIL` chains as failures.
-- After any Bash result that matters, cross-check against a `Read`/`grep` of the file.
-  If a probe returns stale output, **stop and recover the shell** before committing.
+## ⚠️ Tooling note (read first — why this session stopped at Task 16)
+The harness's **Bash output channel became intermittently unreliable** — returning
+stale/cached output (a Bash command that wrote `/tmp/perm.txt` instead returned a
+PRIOR command's `/tmp/vc.txt` content; a `cat` returned the wrong commit SHA). The
+Write/Edit channel stayed reliable; Read mostly reliable but occasionally served a
+stale temp file. Work stopped at Task 16 because wiring a new route/nav requires
+accurately reading `router.tsx` + `AccountSettingsPage.tsx` then editing them, and
+read-then-edit against stale reads is exactly what produced the broken Tasks 14–15
+earlier this session. **On resume: confirm the shell is reliable first** — write a
+unique sentinel to a file and read it back; cross-check any Read against a fresh
+`grep`; never commit without a sentinel-wrapped `tsc -b`/pytest verification whose
+unique sentinel you can see in the same output.
 
-## Status: backend complete (Tasks 1–12), frontend not started (Tasks 13–19)
+Earlier-this-session gotcha that cost ~an hour: pytest `-p no:cov` conflicts with the
+`--cov` baked into `pytest.ini` addopts → pytest exits before running → `&& echo PASS`
+chains mislabel. Always use `--override-ini="addopts="`, never `-p no:cov`.
 
-**Tasks 1–12 — DONE & committed** (17 commits `16b9abf`…`04b5511`). Last reliable
-full run: **114 passed** across all 11 Phase 2A backend test files
-(test_l1_ai_build_model, test_account_l1_categories_column, test_flow_proposal_l1_source,
-test_l1_category_service, test_ai_tree_builder, test_match_or_build,
-test_l1_session_service, test_l1_endpoints, test_l1_api_ai_build, test_l1_categories_api,
-test_l1_ai_build_flow). 3 alembic migrations applied; head is `1fd88a68b145`.
+Backend test invocation that works:
+`docker exec resolutionflow_backend pytest <path> --override-ini="addopts=" -q`
+Do **NOT** use `-p no:cov` — `pytest.ini` bakes `--cov` into `addopts`; disabling the
+cov plugin makes `--cov` unrecognized so pytest exits before running, silently turning
+`&& echo PASS || echo FAIL` chains into false FAILs (this cost ~an hour of confusion).
+Frontend gate via file-redirect:
+`docker exec -w /app resolutionflow_frontend sh -c 'npx tsc -b > /app/_o.txt 2>&1; echo EXIT=$? >> /app/_o.txt'`
+then Read `frontend/_o.txt` (frontend is bind-mounted at /app).
 
-What shipped backend-side:
-- Migrations/models: `ai_build` session kind; `accounts.enabled_l1_categories` (10-key
-  default); `FlowProposal.l1_session_id` (+ `source_session_id` nullable + exactly-one
-  CHECK), `FlowProposalSummary` schema made source_session_id optional + l1_session_id added.
-- Services: `l1_category_service` (defaults + hard floor + get/set), `ai_tree_builder`
-  (constrained node gen, validate, depth cap, `normalize_walked_path`, **skips `meta`
-  entries**), `match_or_build` (match→suggest→build bands; flow_id normalized to str),
-  `l1_session_service.start_ai_build_session` / `advance_ai_build` (records node incl.
-  `node_text`) / flywheel capture in `resolve` / engineer notify in `escalate`.
-- Notifications: `l1.session.escalated` event + link `/escalations` + body/title templates;
-  `_resolve_recipients` now treats an explicit empty `target_user_ids` as "no recipients".
-- API: `/l1/intake` dispatches via `match_or_build` (build seeds a hidden
-  `{"node_type":"meta","category":...}` walked_path entry); `POST /l1/sessions/{id}/next-node`;
-  `GET /l1/escalations` (require_engineer_or_admin); `GET|PATCH /accounts/me/l1-categories`;
-  `require_account_owner_or_admin` dep. Config action keys `l1_realtime_build`/`l1_classify`.
+## Status: Tasks 1–15 DONE & committed. Tasks 16–19 remain (all frontend + final).
 
-## Resume point — Tasks 13–19 (all frontend + final)
+**Backend (Tasks 1–12)** — 17 commits `16b9abf`…`04b5511` + handoff `fdac72e`.
+Last full run: **114 passed** across all 11 Phase 2A backend test files. 3 alembic
+migrations applied; head `1fd88a68b145`. Shipped: `ai_build` session kind;
+`accounts.enabled_l1_categories`; `FlowProposal.l1_session_id` (+ nullable
+source_session_id + exactly-one CHECK + schema made optional); `l1_category_service`;
+`ai_tree_builder` (constrained gen, validate, depth cap, `normalize_walked_path`,
+**skips `meta` entries**); `match_or_build` (bands; flow_id→str); session-service
+`start_ai_build_session`/`advance_ai_build` (stores `node_text`)/flywheel capture in
+`resolve`/engineer notify in `escalate`; `l1.session.escalated` notification (+ link
+`/escalations` + `_resolve_recipients` honors explicit empty list); API
+`/l1/intake` (dispatch; build seeds hidden `{"node_type":"meta","category":...}`
+walked_path entry), `POST /l1/sessions/{id}/next-node`, `GET /l1/escalations`,
+`GET|PATCH /accounts/me/l1-categories`, `require_account_owner_or_admin` dep.
 
-1. **Task 13 — frontend api/types.** `frontend/src/types/l1.ts` + `frontend/src/api/l1.ts`
-   are still **Phase-1 stubs** (api/l1.ts is a rough 36-line stub — read it carefully).
-   Add: `IntakeOutcome`/`IntakeResult` (outcome matched|suggest|out_of_scope|build,
-   optional session fields, near_miss, category), `TreeNode` union, `NextNodeResult`,
-   `L1Categories`; methods `nextNode`, `getCategories`, `setCategories`, `escalations`;
-   retype `intake` to `IntakeResult`. **Carry-forward:** `nextNode` body must include
-   `node_text` (the rendered node text — backend `advance_ai_build` stores it).
-2. **Task 14** — `L1Dashboard.tsx` dispatch on `outcome` (matched/build → walker;
-   suggest → prompt; out_of_scope → adhoc/escalate prompt).
-3. **Task 15** — `L1WalkTreeVariant.tsx` real node rendering via `/next-node` + disclaimer
-   banner; pass `node.text` as `node_text`; terminal nodes → existing Resolve/Escalate.
-4. **Task 16** — new `pages/account/L1CategoriesPage.tsx` + route + nav (owner/admin gated).
-5. **Task 17** — `ProposalDetail.tsx` L1-source block (branch on `l1_session_id`);
-   `EscalationQueuePage.tsx` L1-escalations section via `l1Api.escalations()`.
-6. **Task 18** — extend `frontend/e2e/l1-workspace.spec.ts` (network-stubbed); rely on CI
-   for the run (chromium can't launch here).
-7. **Task 19** — full backend suite + `tsc -b`/`npm run lint`/`npm run build`; migration
-   downgrade/upgrade roundtrip; push branch + open PR to `main` listing deferred items.
+**Frontend (Tasks 13–15) — committed; whole-project `tsc -b` + eslint clean. VERIFIED HEAD `076a9ec`, tree clean.**
+- `03e8748` Task 13 — `types/l1.ts` (+ai_build, IntakeOutcome/Result, NearMiss, TreeNode,
+  NextNodeRequest/Result, L1Categories) + `api/l1.ts` (intake→IntakeResult; nextNode,
+  escalations, getCategories, setCategories). nextNode body carries `node_text`.
+- Tasks 14/15 took THREE commits because the flaky shell caused two broken commits
+  (`df7150f`, `f483196` had missing-export/props errors; `ad9c4c8` was committed with
+  TSC_EXIT=2 because I batched the commit with its own failing verification). The REAL
+  working fix is **`076a9ec`** — confirmed via single-value commands: committed
+  `L1WalkTreeVariant.tsx` has `advanceNode` (grep -c = 3), committed `L1Dashboard.tsx`
+  has `useSuggestedFlow` (= 2); and a sentinel-wrapped `npx tsc -b` returned TSC=0,
+  eslint=0 on the on-disk files before commit. What landed:
+  - `L1Dashboard.tsx`: outcome dispatch on the REAL page (matched/build→walker;
+    suggest→use-flow/build-new; out_of_scope→escalate-without-walk). Original
+    PageMeta/greeting/inputs/open-tickets layout preserved.
+  - `L1WalkTreeVariant.tsx`: real props `{session,onSessionUpdate,onDone}` +
+    ResolveModal/EscalateModal + header + transcript sidebar kept; added ai_build branch
+    that walks nodes via /next-node (passes node_text), disclaimer banner (`bg-warning/10`
+    — NOTE: `*-dim` tokens are NOT `--color-*-dim`; use `/10` opacity), terminal→modals.
+    flow/proposal keep the Phase-1 synthetic path.
+  - `L1WalkPage.tsx` unchanged (already routes ai_build → tree variant).
+  NOT browser-verified (chromium can't launch here).
+- **SHELL DISCIPLINE for resume:** single-value Bash commands (`grep -c`, `wc -l`,
+  `git rev-parse --short`, `git log -1 --format=%s`) are RELIABLE; multi-line
+  `{ echo; … } > file` blocks get GARBLED/interleaved. NEVER batch a commit with its
+  own verification — verify in a separate step and READ the result before committing.
 
-Frontend gate: `docker exec -w /app resolutionflow_frontend npx tsc -b` and
-`docker exec -w /app resolutionflow_frontend npm run build` (per PROJECT_CONTEXT).
+## Resume point — Tasks 16–19
 
-**Working tree:** uncommitted at handoff time — only this `HANDOFF.md` edit (and possibly
-`backend/tests/test_l1_api_ai_build.py` if its last lint-clean edit wasn't committed; verify
-with `git status` once the shell recovers, then commit WIP).
+16. **`pages/account/L1CategoriesPage.tsx`** (does NOT exist yet) — checkbox list of
+    `available` toggling `enabled` via `l1Api.getCategories/setCategories`; read-only
+    hard-floor list. Register lazy route under the `account` children in `router.tsx`
+    (the L1CategoriesPage import is NOT yet there — verify) and add a link card in
+    `AccountSettingsPage.tsx` (AccountLayout has no sidebar nav — see CLAUDE.md
+    "Account sub-page"). Gate visibility to owner/admin via `usePermissions`.
+17. **`ProposalDetail.tsx`** — branch on `l1_session_id` to show an L1-source block
+    instead of the `/pilot/{source_session_id}` link (add `l1_session_id?: string|null`
+    to its proposal type). **`EscalationQueuePage.tsx`** — add an "L1 escalations"
+    section via `l1Api.escalations()`.
+18. **`frontend/e2e/l1-workspace.spec.ts`** — network-stubbed AI-build flow; rely on CI
+    to run it (chromium can't launch here).
+19. **Final:** full backend suite + `tsc -b`/`npm run lint`/`npm run build`; migration
+    downgrade/upgrade roundtrip (head `1fd88a68b145`, down 3); push branch + open PR to
+    `main` listing deferred items (KB grounding/connectors, PSA reassign, escalation
+    package, AI chat handoff, proposal-matching). Then run requesting-code-review +
+    finishing-a-development-branch per the subagent-driven-development skill.
 
-## Carry-forward (Phase O — separate, still user-side, gated on EIN)
-Phase O self-serve cutover (Stripe live-mode, apex DNS, Railway prod env, flag flip) remains
-the prior active task — all code blockers closed; blocked on user's EIN. See SESSION_LOG /
-git history for detail. Not touched this session.
+**Working tree:** clean except this HANDOFF.md edit (committing now). Temp `_*.txt`
+files under `frontend/` were scratch — delete any that remain.
+
+## Carry-forward (Phase O — separate, user-side, gated on EIN)
+Phase O self-serve cutover (Stripe live-mode, apex DNS, Railway prod env, flag flip)
+remains the prior active task; all code blockers closed, blocked on user's EIN. Not
+touched this session.

frontend/src/components/l1/L1EscalationsSection.tsx

@@ -0,0 +1,77 @@
+import { useEffect, useState } from 'react'
+import { l1Api } from '@/api/l1'
+import type { WalkSession } from '@/types/l1'
+
+/**
+ * Engineer-visible list of escalated L1 sessions (the Phase 2A handoff queue).
+ * Backed by GET /l1/escalations (engineer-or-above). Pollable, dependency-free —
+ * each row expands to show the walked path summary. Renders nothing if empty.
+ */
+export function L1EscalationsSection() {
+  const [rows, setRows] = useState<WalkSession[]>([])
+  const [loaded, setLoaded] = useState(false)
+  const [expanded, setExpanded] = useState<string | null>(null)
+
+  useEffect(() => {
+    l1Api
+      .escalations()
+      .then(setRows)
+      .catch(() => setRows([]))
+      .finally(() => setLoaded(true))
+  }, [])
+
+  if (!loaded || rows.length === 0) return null
+
+  return (
+    <section className="space-y-3">
+      <div>
+        <h2 className="font-heading text-lg font-bold text-heading">L1 escalations</h2>
+        <p className="text-sm text-text-muted">
+          Tickets an L1 tech escalated mid-walk — pick one up to continue.
+        </p>
+      </div>
+      <div className="rounded-lg border border-default bg-card overflow-hidden">
+        {rows.map((s) => {
+          const isOpen = expanded === s.id
+          return (
+            <div key={s.id} className="border-b border-default last:border-b-0">
+              <button
+                type="button"
+                onClick={() => setExpanded(isOpen ? null : s.id)}
+                className="w-full px-4 py-3 flex items-center justify-between text-left hover:bg-elevated transition-colors"
+              >
+                <div className="flex items-center gap-3 min-w-0">
+                  <span className="font-mono text-xs text-text-muted">#{s.id.slice(0, 8)}</span>
+                  <span className="text-sm text-text-primary truncate">
+                    {s.walked_path.length} step{s.walked_path.length === 1 ? '' : 's'} walked
+                  </span>
+                </div>
+                <span className="text-xs text-text-muted whitespace-nowrap">
+                  {new Date(s.last_step_at).toLocaleString()}
+                </span>
+              </button>
+              {isOpen && (
+                <div className="px-4 pb-3 space-y-1.5">
+                  {s.walked_path.length === 0 ? (
+                    <p className="text-xs text-text-muted">No steps recorded.</p>
+                  ) : (
+                    <ol className="space-y-1.5 text-sm">
+                      {s.walked_path.map((step, i) => (
+                        <li key={i} className="flex flex-col">
+                          <span className="text-text-muted text-xs">{step.question}</span>
+                          {step.answer && (
+                            <span className="font-medium text-text-primary">→ {step.answer}</span>
+                          )}
+                        </li>
+                      ))}
+                    </ol>
+                  )}
+                </div>
+              )}
+            </div>
+          )
+        })}
+      </div>
+    </section>
+  )
+}

frontend/src/components/l1/L1WalkTreeVariant.tsx

@@ -1,8 +1,8 @@
-import { useState } from 'react'
+import { useState, useEffect, useCallback } from 'react'
 import { ChevronLeft } from 'lucide-react'
 import { Link } from 'react-router-dom'
 import { l1Api } from '@/api/l1'
-import type { WalkSession } from '@/types/l1'
+import type { TreeNode, WalkSession } from '@/types/l1'
 import { EscalateModal, ResolveModal } from '@/components/l1/WalkModals'
 
 interface Props {
@@ -16,6 +16,59 @@ export function L1WalkTreeVariant({ session, onSessionUpdate, onDone }: Props) {
   const [showEscalate, setShowEscalate] = useState(false)
   const [note, setNote] = useState('')
 
+  // Phase 2A: ai_build sessions are walked node-by-node against /next-node
+  // (real AI-generated decision tree), not the synthetic stepping below.
+  const isAiBuild = session.session_kind === 'ai_build'
+  const [node, setNode] = useState<TreeNode | null>(null)
+  const [nodeLoading, setNodeLoading] = useState(false)
+  const [nodeError, setNodeError] = useState<string | null>(null)
+
+  useEffect(() => {
+    if (!isAiBuild || session.status !== 'active') return
+    let cancelled = false
+    setNodeLoading(true)
+    l1Api
+      .nextNode(session.id, {})
+      .then((r) => {
+        if (!cancelled) setNode(r.node)
+      })
+      .catch(() => {
+        if (!cancelled) setNodeError('Could not generate the next step.')
+      })
+      .finally(() => {
+        if (!cancelled) setNodeLoading(false)
+      })
+    return () => {
+      cancelled = true
+    }
+  }, [isAiBuild, session.id, session.status])
+
+  const advanceNode = useCallback(
+    async (body: { answer?: 'yes' | 'no'; acknowledged?: boolean }) => {
+      if (!node) return
+      setNodeLoading(true)
+      setNodeError(null)
+      try {
+        const r = await l1Api.nextNode(session.id, {
+          node_id: node.id,
+          node_text: node.text,
+          ...body,
+        })
+        setNode(r.node)
+      } catch {
+        setNodeError('Could not generate the next step.')
+      } finally {
+        setNodeLoading(false)
+      }
+    },
+    [node, session.id],
+  )
+
+  const isTerminalNode =
+    node?.node_type === 'resolved' ||
+    node?.node_type === 'escalate' ||
+    node?.node_type === 'needs_review'
+
   // Phase 1: we don't have the live flow-tree fetch wired up here yet
   // (the tree-navigation pages have their own loader). The walker shows the
   // walked-path side panel, advance buttons stubbed for now — Phase 2 wires
@@ -55,7 +108,7 @@ export function L1WalkTreeVariant({ session, onSessionUpdate, onDone }: Props) {
         <Link to="/l1" className="flex items-center gap-2 text-muted-foreground hover:text-heading transition-colors">
           <ChevronLeft className="w-4 h-4" />
           <span className="font-mono text-xs">#{session.id.slice(0, 8)}</span>
-          {session.session_kind === 'proposal' && (
+          {(session.session_kind === 'proposal' || session.session_kind === 'ai_build') && (
             <span className="ml-2 text-xs bg-accent/10 text-accent px-2 py-0.5 rounded">AI-built</span>
           )}
         </Link>
@@ -80,6 +133,13 @@ export function L1WalkTreeVariant({ session, onSessionUpdate, onDone }: Props) {
       {/* Two-pane body */}
       <div className="flex-1 flex min-h-0">
         <main className="flex-1 p-6 overflow-y-auto min-h-0">
+          {isAiBuild && (
+            <div className="mb-4 max-w-2xl rounded-md border border-warning/30 bg-warning/10 px-4 py-2 text-xs text-warning">
+              These are high-confidence troubleshooting steps, but they come from
+              outside your organization’s knowledge base — review them before acting.
+              When in doubt, escalate early.
+            </div>
+          )}
           <p className="font-sans text-[0.625rem] uppercase tracking-[0.12em] font-semibold text-muted-foreground mb-2">
             Step {session.walked_path.length + 1}
           </p>
@@ -92,6 +152,66 @@ export function L1WalkTreeVariant({ session, onSessionUpdate, onDone }: Props) {
                 Back to workspace
               </button>
             </div>
+          ) : isAiBuild ? (
+            <div className="rounded-lg border border-default bg-card p-6 max-w-2xl space-y-4">
+              {nodeLoading && (
+                <p className="text-sm text-muted-foreground">Thinking through the next step…</p>
+              )}
+              {nodeError && <p className="text-sm text-danger">{nodeError}</p>}
+
+              {!nodeLoading && node?.node_type === 'question' && (
+                <>
+                  <p className="text-lg">{node.text}</p>
+                  <div className="flex gap-3">
+                    <button
+                      onClick={() => advanceNode({ answer: 'yes' })}
+                      className="flex-1 rounded-md bg-accent text-white py-3 text-base font-medium hover:bg-accent/90 min-h-[44px] transition-colors"
+                    >
+                      Yes
+                    </button>
+                    <button
+                      onClick={() => advanceNode({ answer: 'no' })}
+                      className="flex-1 rounded-md border border-default py-3 text-base font-medium hover:bg-elevated min-h-[44px] transition-colors"
+                    >
+                      No
+                    </button>
+                  </div>
+                </>
+              )}
+
+              {!nodeLoading && node?.node_type === 'instruction' && (
+                <>
+                  <p className="text-lg">{node.text}</p>
+                  <button
+                    onClick={() => advanceNode({ acknowledged: true })}
+                    className="rounded-md bg-accent text-white px-5 py-3 text-base font-medium hover:bg-accent/90 min-h-[44px] transition-colors"
+                  >
+                    Done — next step
+                  </button>
+                </>
+              )}
+
+              {!nodeLoading && isTerminalNode && node && (
+                <>
+                  <p className="text-lg">{node.text}</p>
+                  {node.node_type === 'resolved' ? (
+                    <button
+                      onClick={() => setShowResolve(true)}
+                      className="rounded-md bg-accent text-white px-5 py-3 text-base font-medium hover:bg-accent/90 min-h-[44px] transition-colors"
+                    >
+                      Mark resolved ✓
+                    </button>
+                  ) : (
+                    <button
+                      onClick={() => setShowEscalate(true)}
+                      className="rounded-md bg-warning text-white px-5 py-3 text-base font-medium hover:bg-warning/90 min-h-[44px] transition-colors"
+                    >
+                      Escalate to engineering
+                    </button>
+                  )}
+                </>
+              )}
+            </div>
           ) : (
             <div className="rounded-lg border border-default bg-card p-6 max-w-2xl">
               <p className="text-lg mb-6">Continue the walk:</p>

frontend/src/pages/AccountSettingsPage.tsx

@@ -18,6 +18,7 @@ import {
   RefreshCw,
   Server,
   Shield,
+  Wand2,
   UserCog,
   X,
 } from 'lucide-react'
@@ -662,6 +663,12 @@ export function AccountSettingsPage() {
                 title="Team categories"
                 description="Shared flow categories for your workspace"
               />
+              <SettingsRow
+                to="/account/l1-categories"
+                icon={<Wand2 className="h-4 w-4" />}
+                title="L1 AI build categories"
+                description="Which problem types the L1 assistant may build trees for"
+              />
               <SettingsRow
                 to="/account/target-lists"
                 icon={<Server className="h-4 w-4" />}

frontend/src/pages/account/L1CategoriesPage.tsx

@@ -0,0 +1,98 @@
+import { useEffect, useState } from 'react'
+import { PageMeta } from '@/components/common/PageMeta'
+import { l1Api } from '@/api/l1'
+import { toast } from '@/lib/toast'
+import type { L1Categories } from '@/types/l1'
+
+const prettify = (key: string) =>
+  key.replace(/_/g, ' ').replace(/\b\w/g, (c) => c.toUpperCase())
+
+export default function L1CategoriesPage() {
+  const [data, setData] = useState<L1Categories | null>(null)
+  const [saving, setSaving] = useState<string | null>(null)
+
+  useEffect(() => {
+    l1Api
+      .getCategories()
+      .then(setData)
+      .catch(() => toast.error('Failed to load L1 categories.'))
+  }, [])
+
+  const toggle = async (cat: string) => {
+    if (!data) return
+    const next = data.enabled.includes(cat)
+      ? data.enabled.filter((c) => c !== cat)
+      : [...data.enabled, cat]
+    setSaving(cat)
+    try {
+      const updated = await l1Api.setCategories(next)
+      setData({ ...data, enabled: updated.enabled })
+      toast.success('L1 categories updated.')
+    } catch {
+      toast.error('Could not update categories.')
+    } finally {
+      setSaving(null)
+    }
+  }
+
+  if (!data) {
+    return (
+      <div className="max-w-2xl">
+        <PageMeta title="L1 AI Build Categories" />
+        <p className="text-sm text-muted-foreground">Loading…</p>
+      </div>
+    )
+  }
+
+  return (
+    <div className="max-w-2xl space-y-6">
+      <PageMeta title="L1 AI Build Categories" />
+      <div>
+        <h1 className="font-heading text-2xl font-bold text-heading">
+          L1 AI build categories
+        </h1>
+        <p className="mt-2 text-sm text-muted-foreground">
+          When an L1 tech describes a problem with no matching published flow, the
+          assistant can build a troubleshooting tree on the fly — but only for the
+          categories you enable here. Disabled categories fall back to an ad-hoc walk
+          or escalation.
+        </p>
+      </div>
+
+      <div className="space-y-2">
+        {data.available.map((cat) => {
+          const checked = data.enabled.includes(cat)
+          return (
+            <label
+              key={cat}
+              className="flex items-center gap-3 rounded-md border border-default bg-card px-4 py-3 cursor-pointer hover:bg-elevated transition-colors"
+            >
+              <input
+                type="checkbox"
+                checked={checked}
+                disabled={saving === cat}
+                onChange={() => toggle(cat)}
+                className="h-4 w-4 accent-accent"
+              />
+              <span className="text-sm text-primary">{prettify(cat)}</span>
+            </label>
+          )
+        })}
+      </div>
+
+      <div>
+        <h2 className="font-heading text-sm font-semibold text-heading mb-2">
+          Always excluded (safety)
+        </h2>
+        <p className="text-xs text-muted-foreground mb-2">
+          These action classes are never built automatically and cannot be enabled.
+        </p>
+        <ul className="list-disc pl-5 text-xs text-muted-foreground space-y-1">
+          {data.hard_floor.map((h) => (
+            <li key={h}>{prettify(h)}</li>
+          ))}
+        </ul>
+      </div>
+    </div>
+  )
+}

frontend/src/pages/l1/L1Dashboard.tsx

@@ -6,7 +6,7 @@ import { l1Api } from '@/api/l1'
 import { toast } from '@/lib/toast'
 import { EmptyStateCard } from '@/components/l1/EmptyStateCard'
 import { ResumeInProgress } from '@/components/l1/ResumeInProgress'
-import type { QueueRow } from '@/types/l1'
+import type { NearMiss, QueueRow } from '@/types/l1'
 
 export default function L1Dashboard() {
   const user = useAuthStore((s) => s.user)
@@ -17,6 +17,8 @@ export default function L1Dashboard() {
   const [submitting, setSubmitting] = useState(false)
   const [queue, setQueue] = useState<QueueRow[]>([])
   const [isEmpty, setIsEmpty] = useState(false)
+  const [suggestion, setSuggestion] = useState<NearMiss | null>(null)
+  const [outOfScope, setOutOfScope] = useState<string | null>(null)
 
   useEffect(() => {
     l1Api.queue('open').then(setQueue).catch(() => setQueue([]))
@@ -37,8 +39,42 @@ export default function L1Dashboard() {
     }
   }, [queue])
 
+  const resetPrompts = () => {
+    setSuggestion(null)
+    setOutOfScope(null)
+  }
+
   const handleStart = async () => {
     if (!problem.trim()) return
+    setSubmitting(true)
+    resetPrompts()
+    try {
+      // Phase 2A: intake dispatches via match_or_build and returns an `outcome`.
+      const response = await l1Api.intake({
+        problem_statement: problem.trim(),
+        customer_name: customerName.trim() || undefined,
+        customer_contact: customerContact.trim() || undefined,
+      })
+      if (response.outcome === 'matched' || response.outcome === 'build') {
+        navigate(`/l1/walk/${response.session_id}`)
+      } else if (response.outcome === 'suggest') {
+        setSuggestion(response.near_miss ?? null)
+      } else if (response.outcome === 'out_of_scope') {
+        setOutOfScope(response.category ?? 'unknown')
+      }
+    } catch (err) {
+      const detail = (err as { response?: { data?: { detail?: string } } }).response?.data?.detail
+      const msg =
+        typeof detail === 'string' ? detail : 'Failed to start walk. Try again.'
+      toast.error(msg)
+    } finally {
+      setSubmitting(false)
+    }
+  }
+
+  // "Use this flow" — re-run intake with the same text; it matches again and
+  // returns a `matched` outcome with a started flow session (acceptable Phase 2A).
+  const useSuggestedFlow = async () => {
     setSubmitting(true)
     try {
       const response = await l1Api.intake({
@@ -46,12 +82,54 @@ export default function L1Dashboard() {
         customer_name: customerName.trim() || undefined,
         customer_contact: customerContact.trim() || undefined,
       })
-      navigate(`/l1/walk/${response.session_id}`)
-    } catch (err) {
-      const detail = (err as { response?: { data?: { detail?: string } } }).response?.data?.detail
-      const msg =
-        typeof detail === 'string' ? detail : 'Failed to start walk. Try again.'
-      toast.error(msg)
+      if (response.session_id) navigate(`/l1/walk/${response.session_id}`)
+      else resetPrompts()
+    } catch {
+      toast.error('Could not start the matched flow. Try again.')
+    } finally {
+      setSubmitting(false)
+    }
+  }
+
+  // "Build new" — skip the match pass (force_build); still gated by enabled categories.
+  const buildNew = async () => {
+    setSubmitting(true)
+    resetPrompts()
+    try {
+      const response = await l1Api.intake({
+        problem_statement: problem.trim(),
+        customer_name: customerName.trim() || undefined,
+        customer_contact: customerContact.trim() || undefined,
+        force_build: true,
+      })
+      if (response.outcome === 'build' && response.session_id) {
+        navigate(`/l1/walk/${response.session_id}`)
+      } else if (response.outcome === 'out_of_scope') {
+        setOutOfScope(response.category ?? 'unknown')
+      }
+    } catch {
+      toast.error('Failed to start walk. Try again.')
+    } finally {
+      setSubmitting(false)
+    }
+  }
+
+  // out-of-scope fallback: escalate straight to engineering (no walk).
+  const escalateOutOfScope = async () => {
+    if (!problem.trim()) return
+    setSubmitting(true)
+    try {
+      const session = await l1Api.escalateWithoutWalk({
+        problem_statement: problem.trim(),
+        customer_name: customerName.trim() || undefined,
+        customer_contact: customerContact.trim() || undefined,
+        reason_category: 'out_of_scope',
+        reason: 'Problem is outside the enabled L1 AI-build categories.',
+      })
+      toast.success('Escalated to engineering.')
+      navigate(`/l1/walk/${session.id}`)
+    } catch {
+      toast.error('Could not escalate. Try again.')
     } finally {
       setSubmitting(false)
     }
@@ -160,6 +238,63 @@ export default function L1Dashboard() {
           </section>
         )}
 
+        {/* Suggest: near-miss flow found */}
+        {suggestion && (
+          <div className="space-y-3 rounded-lg border border-default bg-card p-4">
+            <p className="text-sm text-primary">
+              Found a similar flow: <strong>{suggestion.flow_name}</strong>. Use it, or
+              build a new troubleshooting tree for this problem?
+            </p>
+            <div className="flex gap-2">
+              <button
+                type="button"
+                onClick={useSuggestedFlow}
+                disabled={submitting}
+                className="rounded-md bg-accent text-white px-4 py-2 text-sm font-medium hover:bg-accent/90 transition-colors disabled:opacity-50"
+              >
+                Use this flow
+              </button>
+              <button
+                type="button"
+                onClick={buildNew}
+                disabled={submitting}
+                className="rounded-md border border-default px-4 py-2 text-sm hover:bg-elevated transition-colors disabled:opacity-50"
+              >
+                Build new
+              </button>
+            </div>
+          </div>
+        )}
+
+        {/* Out of scope: category disabled/unknown */}
+        {outOfScope && (
+          <div className="space-y-3 rounded-lg border border-default bg-card p-4">
+            <p className="text-sm text-primary">
+              This problem isn’t in your account’s enabled L1 categories
+              {outOfScope !== 'unknown' ? ` (${outOfScope.replace(/_/g, ' ')})` : ''}, so
+              there’s no AI-built walk for it. You can escalate it to engineering.
+            </p>
+            <div className="flex gap-2">
+              <button
+                type="button"
+                onClick={escalateOutOfScope}
+                disabled={submitting}
+                className="rounded-md bg-accent text-white px-4 py-2 text-sm font-medium hover:bg-accent/90 transition-colors disabled:opacity-50"
+              >
+                Escalate to engineering
+              </button>
+              <button
+                type="button"
+                onClick={resetPrompts}
+                disabled={submitting}
+                className="rounded-md border border-default px-4 py-2 text-sm hover:bg-elevated transition-colors disabled:opacity-50"
+              >
+                Cancel
+              </button>
+            </div>
+          </div>
+        )}
+
         {/* Resume in progress */}
         <ResumeInProgress />
       </div>

frontend/src/router.tsx

@@ -114,6 +114,7 @@ const IntegrationsPage = lazyWithRetry(() => import('@/pages/account/Integration
 const BrandingSettingsPage = lazyWithRetry(() => import('@/pages/account/BrandingSettingsPage'))
 const BillingPage = lazyWithRetry(() => import('@/pages/account/BillingPage'))
 const SelectPlanPage = lazyWithRetry(() => import('@/pages/account/SelectPlanPage'))
+const L1CategoriesPage = lazyWithRetry(() => import('@/pages/account/L1CategoriesPage'))
 
 /** Wraps a lazy-loaded page with Suspense + ErrorBoundary */
 function page(Component: React.LazyExoticComponent<React.ComponentType>) {
@@ -363,6 +364,14 @@ export const router = sentryCreateBrowserRouter([
               </ProtectedRoute>
             ),
           },
+          {
+            path: 'l1-categories',
+            element: (
+              <ProtectedRoute requiredRole="owner">
+                {page(L1CategoriesPage)}
+              </ProtectedRoute>
+            ),
+          },
           {
             path: 'chat-retention',
             element: (

frontend/src/types/flow-proposal.ts

@@ -10,7 +10,10 @@ export interface FlowProposalSummary {
   supporting_session_count: number
   status: 'pending' | 'approved' | 'modified' | 'rejected' | 'dismissed' | 'auto_reinforced'
   target_flow_id: string | null
-  source_session_id: string
+  // Exactly one source is set: source_session_id (FlowPilot ai_session) XOR
+  // l1_session_id (L1 ai_build walk). Both nullable on the backend (Phase 2A).
+  source_session_id: string | null
+  l1_session_id: string | null
   created_at: string
 }