## What
Fixes the N+1 flagged by Sentry **PHP-LARAVEL-3Y** in
`App\Jobs\SyncBankingConnectionJob`.
`TransactionSyncService::importTransaction()` ran one `exists()` probe
**per incoming bank transaction** to detect duplicates:
```sql
select exists(
select * from transactions
where account_id = ?
and (dedup_fingerprint = ? or external_transaction_id = ?)
) as exists
```
A sync importing N transactions issued N dedup `SELECT`s. As transaction
volume per sync grows, so does the query count.
## How
Preload the account's existing dedup keys **once** at the start of
`sync()` and match against in-memory sets:
- `loadExistingDedupKeys()` streams (`cursor()`) the two dedup columns
for the account — including soft-deleted rows (`withTrashed()`) — into
two keyed sets. One query instead of N.
- `importTransaction()` checks membership in memory (`isset()`), an
exact mirror of the old `fingerprint OR external_id` predicate.
- Keys from successful inserts are folded back into the sets, so
duplicates **within the same sync** (e.g. the same transaction repeated
across pages) are still caught in memory.
- The `(account_id, dedup_fingerprint)` unique index +
`UniqueConstraintViolationException` catch still backstop concurrent
syncs (`SyncBankingConnectionJob` is already `ShouldBeUnique` per
connection).
## Commits
1. `perf(banking): preload dedup keys to kill per-transaction N+1` — the
core fix + a query-count regression test.
2. `perf(banking): stream dedup key preload with a cursor` — avoids
buffering every historical row into a Collection on top of the sets
(memory guard for very large accounts).
3. `fix(banking): match external ids case-insensitively in dedup` — the
old query compared `external_transaction_id` under the production
`utf8mb4_unicode_ci` collation; the in-memory `isset()` is byte-exact.
With no unique index on `external_transaction_id`, a legacy id stored as
`ABC` vs an incoming `abc` would have silently double-imported.
Normalized with `mb_strtolower()` on both sides + a test.
4. `test(banking): cover intra-run cross-page dedup` — new coverage for
the same transaction appearing on two pages of one sync.
## Testing
- 303/303 in `tests/Feature/OpenBanking/` green; full backend suite
green except one **pre-existing, unrelated** failure on `main`
(`DashboardTest` returns 409 locally — an Inertia asset-version artifact
that resolves once `bun run build` runs in CI).
- New tests: dedup runs as a single preload SELECT regardless of batch
size; case-insensitive external-id dedup; cross-page intra-run dedup.
- `pint` clean; `larastan` clean on the changed file.
## Reviewed by two independent agents (architecture +
product/correctness)
Both rated the change behavior-preserving and shippable. Follow-ups they
surfaced, intentionally **not** bundled here to keep this fix focused
and low-risk:
- **`WiseTransactionSyncService` has the identical latent N+1**
(`:149-158`). It is not currently firing in Sentry (lower volume). Worth
a separate PR — possibly extracting a shared dedup-set helper once both
call sites need it.
- **Residual collation divergence**: accent/width folding from
`utf8mb4_unicode_ci` is not replicated in PHP. Irrelevant for real bank
reference ids (ASCII), accepted.
- The test comment referencing a "cleanup command" that repoints orphan
fingerprinted rows describes a command that does not exist in the repo —
pre-existing, worth correcting separately.
Fixes PHP-LARAVEL-3Y
84bad76316