feat(§8.12/§8.3): main-view Ask cuts an edit branch and runs the question there (v0.54.0)

The AI "Ask" affordance (selection tooltip + prompt bar) had no response
surface on an entry's canonical `main` view: RFCView renders the human-
discussion panel there, not the chat panel, so a chat turn posted from the
reading view had nowhere to render — asking-while-reading silently did
nothing. AI chat is an editing activity (a turn can emit <change> proposals)
and only runs on an edit branch.

Option B: when Ask is invoked from main, transparently cut an edit branch via
the same dispatch as Start Contributing (promote-to-branch for active,
start-edit-branch for super-draft; idempotent — reuse an existing edit
branch), navigate onto it so the chat panel mounts, and run the question
(text + selected quote) as the branch's first chat turn once its view and
main_thread_id resolve. The turn fires from the message-load effect's
continuation (not a parallel effect) so a late message load can't clobber the
optimistic turn; a live ref keeps the latest submitChatTurn closure in reach.

Degrades gracefully: signed-out → login; a viewer who can't contribute has the
cut rejected server-side and the error surfaced (no spurious branch); asking
from a branch already, and Flag on main (human discussion thread), unchanged.

Frontend-only; the branch chat endpoints already work on a branch. SPEC §8.3
records the behavior; new RFCView unit tests + an e2e spec cover the flow.
backend 677 / frontend 66 / e2e 5 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

e2e/main-view-ask.spec.js

@@ -0,0 +1,53 @@
+import { test, expect } from './lib/fixtures.js'
+import { signIn, OWNER_EMAIL } from './lib/auth.js'
+import { dismissCookies } from './lib/ui.js'
+
+// §8.12 Option B — asking-while-reading on the canonical `main` view.
+//
+// Before this fix, the AI "Ask" affordance had no chat surface on main (the
+// human-discussion panel renders there, not the chat panel), so asking from the
+// reading view silently did nothing. Option B transparently cuts an edit branch,
+// navigates to it, and runs the question there.
+//
+// This spec asserts the model-independent core: the branch cut + navigation
+// (old code did NOTHING here — the silent no-op), and that the question turn
+// actually FIRED against the branch. The turn's outcome is environment-specific
+// — PPE/prod (a model is configured) streams an answer and the optimistic
+// question persists; the Tier-1 stack has no AI provider, so the turn errors
+// with "Chat failed". Either outcome proves the turn fired; we match both so the
+// one spec passes in both environments. The quote-passthrough + answer rendering
+// are covered deterministically by the RFCView unit tests (model mocked).
+//
+// Driven through the prompt bar, which shares handlePrompt → handleMainAsk with
+// the selection tooltip's onAsk. Runs against the faceted `bdd` collection entry
+// (collection-scoped — the same three-tier path G-15 hardened).
+const ENTRY = '/p/ohm/c/bdd/e/checkout-returning'
+
+test('Ask from the canonical view cuts an edit branch and lands the question in chat', async ({ page }) => {
+  await signIn(page, OWNER_EMAIL)
+  await page.goto(ENTRY)
+  await dismissCookies(page)
+
+  // We start on the canonical (main) view: read-only, no chat surface — the
+  // discuss-mode banner is the canonical-view tell, and the URL has no branch.
+  await expect(page.locator('.discuss-mode-banner')).toContainText('read-only')
+  expect(new URL(page.url()).searchParams.get('branch')).toBeNull()
+
+  // Ask a question from the prompt bar.
+  const question = `What problem does this entry solve? (${Date.now()})`
+  await page.locator('.prompt-input').fill(question)
+  await page.getByRole('button', { name: 'Ask', exact: true }).click()
+
+  // Option B: an edit branch is cut and we navigate onto it (no silent no-op).
+  await expect(async () => {
+    expect(new URL(page.url()).searchParams.get('branch')).toMatch(/^edit/)
+  }).toPass({ timeout: 30_000 })
+
+  // The question turn fired against the new branch: either the optimistic
+  // question is showing (model answered / answering) or the turn surfaced a
+  // chat error (no AI provider in Tier-1). Both prove it ran — the pre-fix
+  // silent no-op showed neither.
+  await expect(
+    page.getByText(question).or(page.getByText(/Chat failed|No AI providers/i)),
+  ).toBeVisible({ timeout: 30_000 })
+})