GatewayTransactionRequest class

Normalized request the SDK hands to a GatewayClient when forwarding an encrypted payload to the merchant backend.

Strict allow-list. This object carries only the fields below; there is no extras map, no escape hatch, no "passthrough TLV". The backend reconstructs anything else it needs from the encrypted blob (which it can decrypt; the SDK cannot).

• encryptedPayload — opaque encrypted blob produced by the reader (hex-encoded). The SDK never decodes this.
• ksn — opaque DUKPT key serial number. The SDK never uses this to derive a key.
• entryMode — chip / tap / swipe / manual. The backend uses this to route to the right processor adapter.
• amountMinorUnits, currency — what was asked for at startTransaction time. The backend authoritatively verifies against its own expectation.
• reader — device metadata (id, vendor, modelKey, transport, serial, battery) for the backend's audit trail. Provided as a Map<String, dynamic> so the gateway layer does not have to depend on the ReaderDevice model.
• transactionMetadata — POS-supplied per-transaction metadata (order id, ticket id, ...). Opaque to the SDK.
• idempotencyKey — caller-supplied key from the originating TransactionRequest. The backend MUST dedupe on this.

Banned fields. This object MUST NOT carry:

• PAN / masked PAN / last4,
• cardholder name,
• track 1 / track 2 / track 3,
• CVV / CVC / CID,
• expiry,
• service code,
• discretionary data,
• ARQC plaintext,
• plaintext EMV tags.

The constructor accepts only the named fields above. There is no Map<String, dynamic> field for "everything else" - adding banned data would require modifying this class, which makes the audit boundary the class signature itself.