diff --git a/prisma/migrations/0036_normalize_foreign_currency_code/migration.sql b/prisma/migrations/0036_normalize_foreign_currency_code/migration.sql
new file mode 100644
index 0000000..affd250
--- /dev/null
+++ b/prisma/migrations/0036_normalize_foreign_currency_code/migration.sql
@@ -0,0 +1,73 @@
+-- Normalise foreign_currency_code to ISO-4217, and clear two sentinel values.
+--
+-- WHY THIS MATTERS: exact-code equality is the whole basis of FX reconciliation.
+-- ingestion-engine's order_transaction_bridge matches foreign orders with
+--   AND t.foreign_currency_code = %(ccy)s
+--   AND t.foreign_currency_amount = %(total)s
+-- so a row labelled 'BAHT' can never match a THB order, and a row labelled
+-- 'null' can never match anything. 226 of 1,632 coded rows (14%) were
+-- unmatchable for this reason alone, which silently degrades a shipped job.
+--
+-- THE SENTINELS. 187 rows carry the literal 4-character STRING 'null' rather
+-- than SQL NULL, and 42 of those also carry foreign_currency_amount = -1.00
+-- exactly. Neither is data: they are "no value" markers that survived a truthy
+-- guard. Root cause is in the CC statement processors' Parse node, which does
+--   foreign_currency_code: t.foreign_currency_code || null
+-- and a non-empty string is truthy, so a model that answers with the STRING
+-- "null" (rather than JSON null) passes straight through. Same for -1. Fixed
+-- workflow-side in the same change; this migration cleans what already landed.
+-- Not purely historical -- 155 rows in 2026-03, but also 8 in May, 3 in July
+-- and 21 in August 2026.
+--
+-- MAPPINGS WERE VERIFIED AGAINST IMPLIED RATE, NOT TRUSTED FROM THE LABEL,
+-- because a row whose rate contradicts its claimed currency is a broken ledger
+-- row rather than a mislabelled one (the trap order_transaction_bridge's rate
+-- guard exists for: 2 of its first 73 matches were broken rows, not bad
+-- matches). Median amount/foreign_currency_amount per raw code vs the ISO
+-- median over statement rows (n>=5):
+--   BAHT          0.0433  vs THB 0.0470   INDIAN RUPEE 0.0183 vs INR 0.0180
+--   U.A.E. DIRHAM 0.4287  vs AED 0.4184   US DOLLAR    1.4054 vs USD 1.5513
+--   NZ DOLLAR     0.8243  vs NZD 0.9311   EURO         1.6342 vs EUR 1.6964
+-- Every label agrees with its rate. foreign_currency_amount is untouched by the
+-- relabels -- only the code was ever wrong, so this is a relabel, never a
+-- recompute.
+--
+-- EXPECTED ROW COUNTS (verified pre-flight, includes superseded rows):
+--   code 'null'    -> NULL   187      BAHT          -> THB   13
+--   amount -1.00   -> NULL    42      U.A.E. DIRHAM -> AED   10
+--   NZ DOLLAR      -> NZD      6      US DOLLAR     -> USD    4
+--   INDIAN RUPEE   -> INR      4      EURO          -> EUR    2
+-- Pre-flight also confirmed: no -1.00 amount exists outside the 'null'-code
+-- rows, and no other non-ISO code exists.
+
+BEGIN;
+
+-- Sentinels first: the -1.00 amounts live only on 'null'-code rows, so clear
+-- them before that code is nulled and the set becomes unfindable.
+UPDATE transactions SET foreign_currency_amount = NULL
+ WHERE foreign_currency_amount = -1.00 AND foreign_currency_code = 'null';
+
+UPDATE transactions SET foreign_currency_code = NULL
+ WHERE foreign_currency_code = 'null';
+
+-- Word-form relabels.
+UPDATE transactions SET foreign_currency_code = 'THB' WHERE foreign_currency_code = 'BAHT';
+UPDATE transactions SET foreign_currency_code = 'AED' WHERE foreign_currency_code = 'U.A.E. DIRHAM';
+UPDATE transactions SET foreign_currency_code = 'NZD' WHERE foreign_currency_code = 'NZ DOLLAR';
+UPDATE transactions SET foreign_currency_code = 'USD' WHERE foreign_currency_code = 'US DOLLAR';
+UPDATE transactions SET foreign_currency_code = 'INR' WHERE foreign_currency_code = 'INDIAN RUPEE';
+UPDATE transactions SET foreign_currency_code = 'EUR' WHERE foreign_currency_code = 'EURO';
+
+-- Postcondition: every remaining code is ISO-4217 shaped. Fails the whole
+-- transaction rather than leaving a partial normalisation behind.
+DO $$
+DECLARE bad int;
+BEGIN
+  SELECT count(*) INTO bad FROM transactions
+   WHERE foreign_currency_code IS NOT NULL AND foreign_currency_code !~ '^[A-Z]{3}$';
+  IF bad <> 0 THEN
+    RAISE EXCEPTION 'normalisation incomplete: % non-ISO codes remain', bad;
+  END IF;
+END $$;
+
+COMMIT;