Make OpenAI-family strict mode routable and stop redacting payee words

Strict structured-output mode rejects uniqueItems, so every request to a
gpt-5.6-family zero-data-retention endpoint failed with HTTP 400 behind
a generic error; duplicates were already rejected server-side, so the
keyword leaves the wire schemas, pinned by a strict-keyword allowlist
test built from the ledger that hit this.

The bare-BIC redaction pattern deleted every 8- and 11-letter word —
Openbank, BAUMARKT, RACETRACKER — blinding the model to the payee it
was asked to classify and tripping the unsafe-merchant check on honest
answers. BICs now die only labeled or attached to their IBAN, account
labels join the redaction secrets, an identifier-shaped merchant name
degrades to a merchant-less proposal instead of failing the row, and a
provider error inside an HTTP 200 envelope is reported as such (numeric
code only) instead of as envelope corruption.

internal/classification/privacy.go

@@ -12,10 +12,15 @@ import (
 
 var bankingPatterns = []*regexp.Regexp{
 	// Apply before tokenization to capture formatted identifiers as a unit.
-	regexp.MustCompile(`(?i)\b[a-z]{2}\s*\d{2}(?:[ -]?[a-z0-9]){11,30}\b`),
+	// An IBAN may carry its BIC as the next token; both go as one unit. A
+	// *bare* BIC-shaped token is deliberately not redacted: the shape matches
+	// every 8- or 11-letter word ("Openbank", "BAUMARKT", "RACETRACKER"),
+	// which blinded the model to the very payee it should classify, and a
+	// bank code reveals nothing the prompt's institution field does not.
+	// Labeled forms ("BIC ...", "SWIFT ...") die with the label below.
+	regexp.MustCompile(`(?i)\b[a-z]{2}\s*\d{2}(?:[ -]?[a-z0-9]){11,30}\b(?:\s+[a-z]{6}[a-z0-9]{2}(?:[a-z0-9]{3})?\b)?`),
 	regexp.MustCompile(`(?i)\b[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}\b`),
 	regexp.MustCompile(`(?i)\b(?:iban|bic|swift|account(?:\s*(?:number|no))?|konto(?:nummer)?|reference|ref|payment\s*(?:id|reference)|end\s*to\s*end(?:\s*id)?|e2e|eref|mref|kref|cred|mandate|mandat(?:sreferenz)?|kunden(?:nummer|referenz)|kreditornummer|glaeubiger\s*id|gläubiger\s*id)\b[^;\n|]*`),
-	regexp.MustCompile(`(?i)\b[A-Z]{6}[A-Z0-9]{2}(?:[A-Z0-9]{3})?\b`),
 	regexp.MustCompile(`(?i)\b(?:https?://|www\.)\S+|\b[^\s@]+@[^\s@]+\b`),
 }
 
@@ -54,6 +59,9 @@ func redactor(d domain.Dataset, f domain.Facts, private []string) func(string) s
 		addSecret(secrets, a.ID)
 		addSecret(secrets, a.IBAN)
 		addSecret(secrets, a.ExternalAccountID)
+		// People put their own name in the account label; the label is never
+		// sent as a field and its text is own-identity data, like PrivateNames.
+		addSecret(secrets, a.DisplayName)
 	}
 	for _, value := range []string{f.ID, f.ExternalID, f.Fingerprint, f.CounterpartyIBAN} {
 		addSecret(secrets, value)