fix(whatsapp): messages stuck at Sending - add ACK timeout and retry #1344

Parent: #830 (chat leftovers). Verified against main @ 8e39053.

Bug

WhatsApp messages can stay at "Sending" forever (user report, 14 Sep).

Root cause (verified in code)

• main/services/whatsapp.ts ~L1672 sets the row to typing before sending. After socket.sendMessage (~L1689-1694) it only stores external_message_id: "Do not mark 'sent' immediately; wait for server ACK (status=2) in messages.update" (messages.update handler ~L994).
• Nothing times out a missing ACK: no stale-status sweep, and no queued/typing cleanup on startup or reconnect. If the ACK never arrives (socket drop, app restart, phone offline), the row stays typing, which the UI shows as sending (frontend/src/app/(dashboard)/whatsapp/page.tsx, STATUS_STEPS ~L197).
• feat: add WhatsApp message templates, automated rules, and safety controls #1315 and fix(main): harden WhatsApp offline abort, split-bill deduplication, loyalty rounding, and auto-settlement automation #1323 (main, unreleased) do not cover this.

Fix (decided)

• Add an ACK timeout. If a message is still queued or typing N minutes after its last transition (a named constant, for example 5 minutes), mark it failed with reason ack_timeout.
• Run the sweep on a timer while connected, and once on startup for rows left over from a previous run.
• A late ACK for a message already marked failed should still promote it to sent/delivered (messages.update keys by external_message_id).
• UI: failed rows already render. Add a "Retry" action that re-queues through the same send path, honouring the feat: add WhatsApp message templates, automated rules, and safety controls #1315 safety controls and Offline mode (feat(settings): owner-only Offline mode that closes every optional outbound connection #1306).

Acceptance criteria

• A message without an ACK becomes failed (ack_timeout) after the timeout.
• A late ACK still upgrades it to sent/delivered.
• Rows stuck from before a restart are swept on startup.
• Retry sends once (no duplicates) and is blocked in Offline mode.

Verification

• Extend tests/whatsapp-service.test.ts with fake timers covering the timeout, a late ACK, the startup sweep and retry idempotency.
• npm run lint && npm test