docs: record the ledger-duplicate guard and why awaitsStatementLine is gone

CLAUDE.md

@@ -146,15 +146,24 @@ Only cash is excluded on payment method. Bank transfers *do* appear on a
 statement now that transaction accounts are imported, and NULL means unknown —
 both stay candidates, preserving the behaviour of every pre-existing row.
 
-**Account-feed rows are excluded separately, and for a different reason**
-(`awaitsStatementLine()`, added with the Frollo importer). A feed row is the
-account's own ledger entry, not a receipt awaiting a statement line: the importer
-only covers accounts whose statements are deliberately *not* imported. Without
-the exclusion those ~600 rows a year sit in the queue forever and bury the
-receipts that genuinely need a decision — measured, the queue went from 8 to 558.
-It is scoped to a named list (`ACCOUNT_FEED_SOURCES`) rather than to
-`source IS NOT NULL`, so a future source that *does* await a statement is not
-swept up by it.
+**Account-feed rows are NOT excluded, and the removed exclusion is worth
+knowing about.** There was an `awaitsStatementLine()` predicate here, added with
+the Frollo importer on the premise that a feed row is the account's own ledger
+entry with no statement line coming. That premise was asserted and never tested.
+It was false for almost every account: 422 of the first 550 imported rows already
+had a statement twin.
+
+What matters is how it got in. The queue jumped from 8 to 558 the moment the feed
+landed, and that jump was read as noise and filtered out. **The queue was right** —
+those rows genuinely were provisional entries awaiting statement lines — and
+filtering it removed the only mechanism that would ever have collapsed them, so
+the duplicates became permanent instead of transient and stayed invisible until a
+human saw one salary payment listed twice in two currencies.
+
+A feed row belongs in the queue. Queue volume is solved **upstream**, by not
+importing rows the ledger already holds (`LEDGER_MATCH_DAYS`), never downstream
+by hiding the ones that are there. If a genuinely statement-less feed is ever
+added, give it its own predicate and prove the premise with a query first.
 
 ATM withdrawals stay categorised as spend rather than `transfers`. Treating them
 as transfers only works if every cash purchase is logged; with partial logging
@@ -636,7 +645,44 @@ statements already cover them and are authoritative, and a second producer for
 the same rows would only create reconciliation work.
 
 - Logic: `src/lib/frollo-csv.ts` (pure, parsing + scoping + de-duplication) and
-  `src/lib/frollo-ingest.ts` (report + insert). 42 unit tests.
+  `src/lib/frollo-ingest.ts` (report + insert + the ledger-duplicate guard).
+  53 unit tests across `frollo-csv.test.ts` and `frollo-ingest.test.ts`.
+
+**There are TWO de-duplications and they solve different problems.** `dedupe()`
+compares the file against itself (CDR re-consent twins, below). The
+ledger-duplicate guard compares the file against `transactions`, and its absence
+is what made the first import write 422 duplicates out of 550 — $1,023,824.63
+counted twice — because "these accounts issue no statements" had been asserted
+rather than queried. The check that would have caught it is one SQL statement.
+The check run instead compared each row's date to the statement's min–max window,
+which for accounts whose statements span 182 to 460 days swallows a year and
+cannot distinguish covered from uncovered at all.
+
+The guard matches on **amount + direction, within `LEDGER_MATCH_DAYS` (3)**, and
+consumes each ledger row once so a genuine repeat survives. Three details, each
+of which was wrong first and each caught only by rehearsing against the real
+database rather than fixtures:
+
+- **`pg` returns a DATE as a JS `Date`; Prisma and the CSV give strings.**
+  `String(date).slice(0, 10)` is `"Wed Mar 10"` → NaN → every comparison skipped,
+  silently. The first dry run reported 550 to insert against a ledger holding 422
+  of them. `dayMs()` accepts both, and both shapes are tested because both
+  drivers are in use.
+- **Direction must be in the key.** This ledger is full of internal transfers
+  between the owner's own accounts and the feed carries *both legs*: 2026-05-18
+  has +3076.04 into ANZ and −3076.04 out of AMP. On amount alone the credit leg
+  consumed the ledger's debit row and the real duplicate was written — 20 rows.
+- **`refund` is money in.** Ledger types are debit | credit | payment | fee |
+  interest | refund; the feed calls a reversed account fee a `credit` while the
+  statement importer types it `refund`. Classifying it as an outflow left every
+  ANZ servicing-fee reversal behind.
+
+Residual after all three: **4 rows / $15.01**, all sub-$5 account fees where
+several identical amounts fall in overlapping windows and greedy consumption
+picks the wrong one. Left alone deliberately at this scale.
+
+The count is printed by the CLI even when zero. A number you have to go looking
+for is a number nobody looks at.
 - Two callers share that module so they cannot drift: `scripts/import-frollo.mts`
   (dry run by default) and `POST /api/frollo/ingest` (token auth, called daily by
   the n8n `Frollo Import` workflow). The DB is reached through an injected