fix: remediate end-to-end app reliability issues

[AnganSamadder]

Summary

• harden account deletion so retries are safe, shared history is preserved, and realtime/auth teardown cannot resurrect stale state
• validate link-request provenance and keep friend discovery, requests, and synchronization private and retry-safe
• persist expense notes across local and Convex flows
• fix add-expense alert presentation, settlement-share totals, navigation resets, destructive debug-data confirmation, friend-name editing, and the inactive receipt-camera control
• add and repair focused backend/iOS regression coverage for each behavior

Why

End-to-end testing exposed several independent reliability problems around identity state, account switching, destructive cleanup, and transient UI state. The main root causes were client-trusted link targets, non-idempotent account teardown, stale realtime data crossing session boundaries, total-vs-current-user settlement calculations, and UI state surviving account changes.

Impact

These changes reduce cross-account data leakage, make destructive and retryable flows deterministic, preserve shared financial history during account deletion, and eliminate the tested UI glitches without changing the intended product model.

Validation

• FAIL_ON_WARNINGS=1 ./scripts/test-ci-locally.sh
  • backend: 63/63
  • iOS: 2,581/2,581
  • web smoke: passed
  • overall coverage: 48.97% (CI threshold: 48%)
  • warnings: 0
• SANITIZER=thread FAIL_ON_WARNINGS=1 ./scripts/test-ci-locally.sh
  • iOS: 2,581/2,581
  • Thread Sanitizer findings: 0
• SANITIZER=address FAIL_ON_WARNINGS=1 ./scripts/test-ci-locally.sh
  • iOS: 2,581/2,581
  • Address Sanitizer findings: 0

Review

Independent backend/security, iOS/lifecycle, and PR-architecture reviews were completed. All actionable findings were resolved before publication.

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Project	Deployment	Actions	Updated (UTC)
payback	Ready	Preview	Jul 31, 2026 3:04am