apply_state_sync delta path mutates SMT forest without rollback on IndexedDB write failure

[Sertug17]

Bug

apply_state_sync in crates/idxdb-store/src/sync/mod.rs uses replace_roots (immediate mutation) on the SMT forest when applying public account delta updates. If the subsequent apply_transaction_delta IndexedDB write fails, the SMT forest is already mutated while the persisted data is stale.

Unlike the transaction path (apply_transaction/apply_transaction_batch_atomic), which uses stage_roots/commit_roots/discard_roots, the sync delta path mutates the forest inline via replace_roots with no rollback mechanism:

// From sync/mod.rs — delta path
smt_forest.replace_roots(...)  // immediate mutation
// ... then writes to IndexedDB
apply_transaction_delta(...)   // If this fails, forest is already inconsistent

Impact

• SMT forest (in-memory) diverges from IndexedDB (persisted)
• Future SMT witness computations produce wrong results
• Account storage/vault verification fails
• Inconsistency persists until client reset and full re-sync

Root cause

replace_roots mutates the forest immediately instead of staging the changes. Compare with the transaction path which properly stages first and only commits after DB success.

This is the same class of bug as #190 (apply_transaction rollback), but in the sync code path rather than the transaction code path.