Add Build EMV TLV operation

[J8k3]

Companion to Parse EMV TLV (closed in #11). A Build EMV TLV operation would accept structured tag-value input and emit BER-TLV encoded hex, completing the round-trip.

Use cases

• Constructing DE 55 payloads for test harnesses or ISO 8583 message simulation
• Editing a parsed TLV structure: parse then modify values then re-encode
• Building GPO responses, READ RECORD data, or other ICC response templates for issuer-side or terminal emulation work

Proposed operation: Build EMV TLV

Input: JSON array of tag-value objects, e.g.:

[
  { "tag": "9F26", "value": "A1B2C3D4E5F60708" },
  { "tag": "9F36", "value": "0001" },
  { "tag": "77", "children": [
    { "tag": "82", "value": "5900" },
    { "tag": "94", "value": "08010401" }
  ]}
]

Output: BER-TLV hex, suitable for piping into Parse EMV TLV for round-trip verification.

Arguments: Output format: Hex | Annotated (human-readable with tag names from the dictionary)

Notes

• Constructed/primitive bit inferred from the EMV tag dictionary (same dict used by Parse EMV TLV), falling back to presence of a children key
• Tag lengths computed automatically from value length
• JSON input format should round-trip cleanly with the JSON output of Parse EMV TLV
• Lower priority than the parse direction; most valuable for issuer simulation and test tooling

Module

Payment