Add Build EMV TLV operation

[J8k3]

Summary

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 → modify values → 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 should be inferred from the EMV tag dictionary (same dict used by Parse EMV TLV), with a fallback based on whether a children key is present
• Tag lengths should be computed automatically from the value length
• The JSON input format should round-trip cleanly with the JSON output of Parse EMV TLV
• Lower priority than the parse direction — acquirer flows primarily receive and parse TLV rather than construct it; most valuable for issuer simulation and test tooling

Module

Payment