Phase 4 Stage 6: chat-room countdown UX + voice-call mode pill

Customer chat screen:
- Voice-call header pill (mode == 'call' renders accent-colored pill;
  chat mode renders no pill).
- HaloSnackbar fires once per session at 180s remaining ('sisa 3 menit
  lagi ya 🤍'), driven by the backend session_warning WS event.
- Last-2-min danger styling: timer pill flips to HaloTokens.danger +
  bold JetBrainsMono when remaining <= 120s.
- Floating ChatExpiredBanner widget injected above the input bar when
  remaining hits 0 in closing-grace state. perpanjang -> existing
  pricing bottom sheet.
- pricing_bottom_sheet.dart rewritten to the 5-option layout with
  chat|call mode toggle (mirrors duration-pick from Stage 3).

Mitra chat screen: voice-call header pill only (no countdown UX per PRD).

Backend:
- session.service.js getSessionById JOINs payment_sessions so mode +
  expires_at ship in /api/shared/chat/:id/info.
- session-timer.service.js onThreeMinuteWarning now emits expires_at +
  remaining_seconds for client resync.
- Dev-only POST /internal/_test/force-session-expires-at clears the
  3-min flag, reschedules the timer, and broadcasts WS resync. Lets
  the Maestro flow drive 175s -> 90s -> 0s without waiting live.

New chatRemainingSeconds StreamProvider derived from expiresAt, fed by
session_warning / session_timer / session_expired resync messages
(plan referenced a secondsLeftProvider that didn't actually exist).

Maestro 06_chat_countdown.yaml + force_session_expires_at.js helper.

Out of scope: meet.google.com URL launching - url_launcher isn't a
client_app dependency and message bubbles render plain Text. Defer.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/routes/internal/_test.routes.js

@@ -7,6 +7,7 @@
 
 import { peekStubOtp } from '../../services/otp.service.js'
 import { expirePairingRequest } from '../../services/pairing.service.js'
+import { startSessionTimer, _resetThreeMinFiredForTest, _broadcastTimerResyncForTest } from '../../services/session-timer.service.js'
 import { getDb } from '../../db/client.js'
 import { PairingFailureCause, SessionStatus } from '../../constants.js'
 
@@ -108,4 +109,49 @@ export const internalTestRoutes = async (fastify) => {
     await expirePairingRequest(target, PairingFailureCause.NO_MITRA_AVAILABLE)
     return { ok: true, session_id: target }
   })
+
+  // Force-set the expires_at of an active chat_session to drive Phase 4
+  // Stage 6 countdown UX (3-min snackbar, last-2-min danger, expired banner)
+  // without waiting in real time. Reschedules the in-memory session timer so
+  // `session_warning` / `session_timer` / `session_expired` WS events fire on
+  // the new schedule.
+  //
+  // Body shape:
+  //   { seconds_from_now: 175 }                  → expire latest active session in N seconds
+  //   { session_id: '<uuid>', seconds_from_now } → expire specific session
+  fastify.post('/force-session-expires-at', async (request, reply) => {
+    const { session_id, seconds_from_now } = request.body ?? {}
+    if (typeof seconds_from_now !== 'number') {
+      return reply.code(400).send({ error: 'seconds_from_now (number) required' })
+    }
+    let target = session_id
+    if (!target) {
+      const [row] = await sql`
+        SELECT id FROM chat_sessions
+        WHERE status = ${SessionStatus.ACTIVE}
+        ORDER BY created_at DESC
+        LIMIT 1
+      `
+      if (!row) {
+        return reply.code(404).send({ error: 'no_active_session' })
+      }
+      target = row.id
+    }
+    const [updated] = await sql`
+      UPDATE chat_sessions
+      SET expires_at = NOW() + (${seconds_from_now} || ' seconds')::interval
+      WHERE id = ${target} AND status = ${SessionStatus.ACTIVE}
+      RETURNING id, expires_at
+    `
+    if (!updated) {
+      return reply.code(404).send({ error: 'no_active_session_for_id', session_id: target })
+    }
+    // Allow the 3-min warning to fire again on the new schedule.
+    _resetThreeMinFiredForTest(updated.id)
+    startSessionTimer(updated.id, updated.expires_at)
+    // Push an immediate WS resync so the customer UI's local ticker tracks
+    // the new schedule without waiting for the next scheduled event.
+    _broadcastTimerResyncForTest(updated.id, updated.expires_at)
+    return { ok: true, session_id: updated.id, expires_at: updated.expires_at }
+  })
 }