[codex] Fix Firo Spark Name v2.1 registration

[reubenyap]

What changed

• Builds the v2.1 fee output as P2PKH + OP_SPARKNAMEID <name> OP_DROP <sparkAddress> OP_DROP.
• Adds the measured tagged-script byte difference to Spark Mobile's existing additionalTxSize input.
• Pins flutter_libsparkmobile@53db5a06a7b7f3df68fe6263f1453f77513bec06, whose shared validator rejects underscores before transaction construction.
• Prevents exact-balance registration from subtracting the miner fee from the mandatory name payment.
• Adds focused validation, script-size, and fee-subtraction checks.

Root causes

NAME_FOR_TESTING was rejected because Firo Core accepts only alphanumeric characters, -, and . in a Spark Name. The wrapper incorrectly allowed _, so Stack created a transaction that Core rejected as an invalid name.

The v2.1 tagged fee output also adds bytes that Spark Mobile's standard 34-byte transparent-output model does not include. A confirmed namefortesting registration demonstrates the exact calculation:

base Spark model                         3,083
Spark Name metadata + existing margin     355
without tagged-script delta              3,438
actual serialized transaction            3,473
shortfall                                   35
measured tagged-script delta                164
final fee                                3,602

At Firo Core's default block minimum of 1,000 atomic units/kB, the 3,438-atom form is below the 3,473-byte transaction size and can remain unconfirmed. Measuring taggedScript.length - baseScript.length restores the estimator's existing 129-byte safety margin without hard-coding the tag layout.

The exact-balance path separately attempted to subtract the miner fee from the mandatory name payment. Registration now requires enough balance for both values.

Related

• Spark Mobile v2 payload PR: [codex] Add Spark Name v2 registration payload support firoorg/sparkmobile#10
• Flutter wrapper validation PR: [codex] Fix Spark Name registration compatibility firoorg/flutter_libsparkmobile#1

Validation

• git diff --check passes locally.
• NAME-FOR.TESTING passes the corrected pattern; NAME_FOR_TESTING fails.
• The fee-script regression checks the measured 155-byte delta for alice and the required opcode structure.
• The send-all regression confirms registration never subtracts from the mandatory payment.
• Updated PR workflow passed, including dependency resolution, formatting, and tests: https://github.com/cypherstack/stack_wallet/actions/runs/29501131862/job/87630038975