Phase 3.7: paid pairing flow + returning chat + extension flip

- Backend: payment_sessions + pairing_failures tables; payment.service.js
  and pairing-failure.service.js (new); rewritten pairing.service.js
  (payment-gated blast + targeted "Curhat lagi" + cancel + fallback);
  rewritten extension.service.js (data-driven auto-approve with offline
  safeguard, charge-at-approval); pricing.service.js (extension tiers
  without free trial); mitra-status.service.js (countAvailableMitras
  cached path); 60s sweeper for stale payment sessions
- Backend routes: client.payment.routes, client.mitra-availability.routes,
  internal/failed-pairings.routes; client.chat.routes rewritten for
  payment-gated start + /returning + /cancel + /fallback-to-blast;
  internal/config.routes adds 4 new keys with Valkey invalidate publish
- client_app: mitra-availability poll, payment screen + notifier, pairing
  notifier rewrite (PairingTargetedWaiting + PairingFailed states),
  targeted-waiting overlay + bestie-unavailable dialog, "Curhat lagi"
  CTA, failed-pairing terminal, extension via payment-session
- mitra_app: PairingRequestType enum, returning-chat 20s countdown
  auto-dismiss, extension card "otomatis disetujui" copy
- control_center: 4 new config rows in Settings, Failed Pairings page
  (filter + paginate + action menu), sidebar + route registered
- Test infrastructure: Vitest backend (7/7 pass), Playwright CC (4/4
  pass), Maestro mobile scaffold (CLI install pending)
- Bugs found via Playwright + fixed: LoginPage labels not associated
  with inputs (a11y); backend internal CORS missing PATCH/PUT/DELETE
  in allow-methods (silent settings breakage in browsers since Stage 4)
- Docs: phase3.7.md PRD, phase3.7-plan.md, phase3.7-questions.md (Q&A),
  phase3.7-testing.md (E2E checklist), phase3.7-test-run-2026-05-03.md
  (today's run results)

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

backend/src/constants.js

@@ -53,6 +53,48 @@ export const TransactionType = Object.freeze({
   EXTENSION: 'extension',
 })
 
+// Payment session lifecycle
+export const PaymentSessionStatus = Object.freeze({
+  PENDING: 'pending',
+  CONFIRMED: 'confirmed',
+  CONSUMED: 'consumed',
+  FAILED_PAIRING: 'failed_pairing',
+  ABANDONED: 'abandoned',
+  EXPIRED: 'expired',
+})
+
+// Pairing failure cause tags
+export const PairingFailureCause = Object.freeze({
+  NO_MITRA_AVAILABLE: 'no_mitra_available',
+  ALL_MITRAS_REJECTED: 'all_mitras_rejected',
+  TARGETED_MITRA_OFFLINE: 'targeted_mitra_offline',
+  TARGETED_MITRA_REJECTED: 'targeted_mitra_rejected',
+  TARGETED_MITRA_TIMEOUT: 'targeted_mitra_timeout',
+  PAYMENT_SESSION_EXPIRED: 'payment_session_expired',
+  CUSTOMER_CANCELLED: 'customer_cancelled',
+  EXTENSION_REJECTED: 'extension_rejected',
+  EXTENSION_SAFEGUARD_TRIPPED: 'extension_safeguard_tripped',
+})
+
+// Operator actions on failed-pairing rows
+export const PairingFailureOperatorAction = Object.freeze({
+  REFUNDED: 'refunded',
+  CREDITED: 'credited',
+  NO_ACTION: 'no_action',
+})
+
+// Default action when extension request times out (configurable)
+export const ExtensionTimeoutAction = Object.freeze({
+  AUTO_APPROVE: 'auto_approve',
+  AUTO_REJECT: 'auto_reject',
+})
+
+// Pairing request type — distinguishes general blast from targeted "Curhat lagi"
+export const PairingRequestType = Object.freeze({
+  GENERAL: 'general',
+  RETURNING: 'returning',
+})
+
 // Who ended a session
 export const EndedBy = Object.freeze({
   SYSTEM: 'system',
@@ -116,6 +158,16 @@ export const WsMessage = Object.freeze({
   EXTENSION_REQUEST: 'extension_request',
   EXTENSION_RESPONSE: 'extension_response',
 
+  // Returning-chat
+  RETURNING_CHAT_TIMEOUT: 'returning_chat_timeout',
+  RETURNING_CHAT_REJECTED: 'returning_chat_rejected',
+
+  // Sent when the customer is sitting in a searching/waiting state and the server terminates
+  // the payment session out from under them (general blast exhausts, payment expires mid-search,
+  // etc). NOT used for intermediate failures like targeted reject/timeout — those use
+  // RETURNING_CHAT_* events instead.
+  PAIRING_FAILED: 'pairing_failed',
+
   // Topic sensitivity
   SESSION_TOPIC_UPDATED: 'session_topic_updated',