fix(pin): coalesce concurrent PIN check/confirm (lockout under-count + torn salt/hash)#669
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…-count and torn salt+hash Concurrent VerifyPinCubit.checkPin() calls for one submission shared no serialization, so two parallel wrong attempts both read the same failed-attempts baseline and persisted the same incremented value — under-counting the lockout cascade and widening the brute-force window. SetupPinCubit._confirmPin() could likewise run twice (a confirm re-typed during the slow PBKDF2 hash), interleaving two salt+hash writes into a torn pair that no longer verifies and locks the user out of their own wallet. Both critical sections are now wrapped in a private in-flight Future that coalesces concurrent callers onto one round-trip and clears on completion, so the counter advances exactly once and the salt+hash pair is always written atomically from a single run. No public API added. Regression: test/screens/pin/verify_pin_cubit_test.dart:267 Regression: test/screens/pin/setup_pin_cubit_test.dart:163 Boundary: Tier 1 Architect-spec: fixer/fix-spec.md (loop fleet-20260603-190231-84831-2, iter 1) mandate-hash: b59fe886f6702d4c loop-id: fleet-20260603-190231-84831-2 iteration: 1
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Addresses Issue #657 — Part 2 Auth & PIN, findings F-01 (HIGH, security) and F-09 (HIGH).
Problem
verify_pin_cubit.dart): concurrentcheckPin()calls for one submission shared no serialization → two parallel wrong attempts read the same failed-attempts baseline and persisted the same incremented value, under-counting the lockout cascade and widening the brute-force window.setup_pin_cubit.dart):_confirmPin()could run twice (confirm re-typed during the slow PBKDF2 hash), interleaving two salt+hash writes into a torn pair that no longer verifies → user locked out of their own wallet.Fix
Both critical sections are wrapped in a private in-flight
Futurethat coalesces concurrent callers onto one round-trip and clears on completion → the lockout counter advances exactly once and the salt+hash pair is always written atomically. No public API added.Tests (RED→GREEN)
verify_pin_cubit_test.dart— F-01: two parallelcheckPinof one submission advance the counter oncesetup_pin_cubit_test.dart— F-09: confirm re-typed during the in-flight hash writes one atomic salt+hashflutter analyzeclean.