fix: make manual friend creation durable

[AnganSamadder]

Summary

• persist a manual friend remotely before reporting success or creating its direct group
• reuse a unique group-only identity when explicitly repairing an earlier partial add
• replace invalid paginated Convex mutation reads in friend upsert and settlement visibility reconciliation
• sanitize settlement failures shown to users
• prepare TestFlight beta 0.1.12

Verification

• bun run ci: 573 backend tests passed; web build/checks passed
• canonical iOS CI: 2,790 tests passed; 0 warnings; 56.84% coverage
• Thread Sanitizer: 2,748 tests passed; no reports; 0 warnings
• Address Sanitizer: 2,790 tests passed; no reports; 0 warnings
• manual simulator pass: friend add via Return, relaunch persistence, group picker identity reuse, direct expense, settlement/unsettlement, activity, groups, profile/settings, merge UI, clear/delete confirmations

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Project	Deployment	Actions	Updated (UTC)
payback	Ready	Preview	Aug 25, 2026 9:30am

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Fence the friend sync to the initiating account

When a user signs out or switches accounts while this await is running, ConvexAccountService.syncFriends sends one authenticated friends:upsert mutation per element in this full snapshot. This task is not tracked by friendSyncTask, and the account/data-epoch check happens only after every mutation completes; because the backend derives ownership from the current authentication rather than accountEmail, later mutations can write the previous user's friends into the newly authenticated account. Use an account-fenced single-friend upsert or revalidate/cancel between mutations instead of sending the whole snapshot.

AGENTS.md reference: AGENTS.md:L802-L805

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