The backend platform your agents can’t break

Two guests edit the same split at once; last-write-wins drops one change and the bill no longer adds up. Data lost.

Concurrent edits conflict on the same document and retry against the latest state, so no edit is silently dropped and the split always balances. Correct by default.

Two appointments whose times overlap both clear the availability check before either commits — the clash guard locks nothing when it finds no conflict — so one stylist is booked for two customers at once. Double-booked.

Each booking runs as one serializable transaction that reads the overlapping time range; a competing appointment that overlaps conflicts on that read and retries, so a stylist can't be booked twice. Correct by default.

Concurrent card moves reuse the same position index, so several cards land on one slot and the board order silently corrupts. Order corrupted.

Reordering happens inside a serializable mutation; concurrent moves that touch the same position conflict and retry, so no two cards ever claim one slot. Correct by default.

Reversal handlers race on the same entries, applying the reverse multiple times and leaving the ledger balances wrong. Corrupted records.

A reversal is a serializable mutation keyed to its entry; a second reversal of the same entry conflicts and can't apply twice, so balances stay correct. Correct by default.

A cart update mid-checkout drops an item from the paid total while inventory still decrements, so the buyer loses the item unpaid. Unpaid & gone.

Cart edits and checkout mutate the same records transactionally; a mid-checkout change conflicts with the checkout and retries, keeping the paid total and inventory in sync. Correct by default.

Ten simultaneous votes each read the same score and write score+1, so most increments are lost and the tally undercounts. Miscounted.

The vote reads and writes the score in a single transaction; concurrent votes conflict on the document and retry, so every increment lands and the tally is exact. Correct by default.

Two seats freed at the same moment are both offered to the same one-seat waitlister, who buys both — while the next person in line gets none. The offer step reads the waitlist without locking it. Over-allocated.

Offering a freed seat runs in one serializable transaction that reads the next waiter's row; two seats freeing at once conflict on that read and retry, so each waiter is offered exactly one seat and no one is skipped. Correct by default.

The failure branch grabs a 2nd pooled connection while still holding the 1st. With a 10-connection pool, 10 concurrent buys on a sold-out item each hold one and wait forever for another. The whole server deadlocks; /health keeps lying {ok:true}. Deadlocked.

Convex has no connection pool to exhaust, and mutations don't hold connections across awaits, so a flood of buys on a sold-out item can't deadlock the server. Correct by default.

Concurrent picks race past the stock check and each decrement inventory, driving on-hand count negative while every response still returns success. Oversold.

Each pick runs as a serializable transaction, so two picks that read the same stock can't both commit — the loser automatically retries against the updated count. There is no lock to place or forget. Correct by default.