Phase 4 checkpoint: chat-screen perf refactor + retryable blast-failure + repo-wide dispose-ref guardrail

Chat-screen performance (customer + mitra):
- Parent screens have zero `ref.watch` — only `ref.listen` for side effects
- Body extracted into its own `ConsumerStatefulWidget`; AppBar parts split
  into narrow `.select` consumers (mode, sensitivity, timer)
- Per-second timer ticks routed to dedicated providers
  (`chatRemainingSecondsProvider` + new `mitraChatRemainingSecondsProvider`)
  so WS `session_tick` frames don't invalidate the rest of the chat state

Dispose-in-ref bug fix:
- `home_screen.dart`, `payment_screen.dart`, `mitra_chat_screen.dart` —
  ref-using cleanup moved from `dispose()` to `deactivate()`. Modern
  Riverpod invalidates `ref` the moment `dispose()` runs; the resulting
  silent error corrupts the widget-tree finalize and the next screen
  appears frozen
- `halo_lints` package added at repo root with `no_ref_in_dispose` rule
  to catch this pattern in CI / IDE analysis
- `custom_lint` activated in both apps' `analysis_options.yaml`
  (was installed but never wired in — also brings `riverpod_lint`'s
  `avoid_ref_inside_state_dispose` online)
- CLAUDE.md Pitfalls section added to client_app + mitra_app

Phase 4 §3 retryable blast-failure (Option A):
- Backend `expirePairingRequest` + all-rejected use
  `recordIntermediateFailure` instead of `failPaymentSession` so the
  payment session stays `confirmed` for re-blast
- WS `pairing_failed` payload carries `is_terminal: false` on the
  retryable paths; client parses the flag and exposes `retryBlast()`
- "Coba cari lagi" CTA on S7 Timeout now re-blasts on the same payment
- Pairing service test updated to reflect the new semantics

Customer waiting-payment screen navigation patch:
- `_navigateTerminal` uses `Future.microtask` + `addPostFrameCallback`
  redundancy after a release-mode bug where polling stopped but
  `context.go` never fired, leaving the screen visually stuck on
  "menunggu pembayaran"

See requirement/resume-2026-05-15.md for next-day pickup checklist
(mitra release rebuild + S21 Ultra install + retest is the gating item).

Bundles unrelated in-flight Phase 4 §2.x work that was already on disk
(ESP screen removal, USP one-time gate scaffolding, bestie-availability
public route, OTP service edits, Maestro flow tweaks) — kept together
to avoid a partial-rebase mess.

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

mitra_app/lib/core/chat/mitra_chat_notifier.dart

@@ -10,6 +10,28 @@ import '../constants.dart';
 
 part 'mitra_chat_notifier.g.dart';
 
+/// Per-second session countdown, decoupled from `mitraChatProvider` so the
+/// `session_tick` WS frame doesn't invalidate the entire chat state (which
+/// would force `ref.watch(mitraChatProvider)` callers — including the chat
+/// screen — to rebuild every second). Watched only by the small timer
+/// indicator in the chat AppBar. See mitra_app/CLAUDE.md for the wider perf
+/// rationale.
+///
+/// Manually declared (no @Riverpod annotation) to keep .g.dart codegen
+/// minimal — one-line Notifier with no special config.
+class MitraChatRemainingSecondsNotifier
+    extends AutoDisposeNotifier<int?> {
+  @override
+  int? build() => null;
+  void update(int? seconds) => state = seconds;
+  void clear() => state = null;
+}
+
+final mitraChatRemainingSecondsProvider =
+    NotifierProvider.autoDispose<MitraChatRemainingSecondsNotifier, int?>(
+  MitraChatRemainingSecondsNotifier.new,
+);
+
 // States
 sealed class MitraChatData {
   const MitraChatData();
@@ -304,7 +326,11 @@ class MitraChat extends _$MitraChat {
         break;
 
       case WsMessage.sessionTimer:
-        state = current.copyWith(remainingSeconds: data['remaining_seconds'] as int?);
+        // Route timer ticks to the dedicated provider so the chat state isn't
+        // invalidated every second. See [mitraChatRemainingSecondsProvider].
+        ref
+            .read(mitraChatRemainingSecondsProvider.notifier)
+            .update(data['remaining_seconds'] as int?);
         break;
 
       case WsMessage.sessionExpired: