Utix: Create deterministic fee calculation module with explainable breakdowns

[prissca]

Summary

Fees must be calculated consistently and shown with explainable line items so users and maintainers can reconcile outcomes.

This issue is scoped to Utix, a ticketing and event access protocol. Contributors should account for the current stack and integration points: TypeScript, ticket issuance, transfer, redemption, event operations, fraud controls, and organizer dashboards.

Difficulty

High - 200 points

Scope

• Centralize fee calculation logic.
• Expose fee breakdowns before final submission.
• Add rounding and asset precision tests.

Acceptance criteria

• Fee output is deterministic for identical inputs.
• Breakdowns match stored settlement records.
• Tests cover zero fee, minimum fee, multi-line fee, rounding, and invalid asset precision.

Technical notes

• Keep the implementation aligned with the existing repository architecture.
• Include automated tests, fixtures, or a clear validation command.
• Update contributor-facing documentation when behavior, setup, or API contracts change.
• Do not add labels; maintainers will assign labels manually.

Pull request expectations

• Explain design decisions and tradeoffs.
• Include relevant test output, screenshots, logs, or API examples.
• Call out any migration, configuration, or deployment steps.