feat(#175): validate fiat code before submitting an order

[codaMW]

Problem

create_order took the selected fiat code straight into the outgoing request with no submit-time validation. The currency picker constrains the happy path, but if the saved default fiat code becomes stale or is tampered with, the request could still go out with an unsupported code and come back as a daemon-side CantDo instead of being rejected locally.

Fix

A local preflight in create_order, reusing settings::validate_fiat_code (made pub(crate)):

• orders.rs create_order validates the fiat code before publishing. This replaces the previous empty-only check and covers empty and malformed codes alike, failing with the stable InvalidFiatCode marker so every caller inherits the check (per @grunch's note, same pattern as BondRequired).
• settings.rs validate_fiat_code is now pub(crate); added validate_fiat_code_marker_cases covering valid codes plus empty / short / long / lowercase / mixed / symbol / non-ASCII, all rejected with the marker.
• daemon_errors.dart maps InvalidFiatCode to a localized message through the existing localizedDaemonError helper.
• l10n invalidFiatCode in all five locales.

Testing

cargo test (256 pass) + cargo clippy clean; flutter analyze clean. Verified on device (Nokia C31): a normal order with a valid currency still creates successfully. The bad-code path is a defense-in-depth guard against a tampered/stale saved default it can't be reached through the picker in normal use, so it's covered by the Rust test rather than a device repro.

Scope question for @grunch

This validates the fiat code's format (ISO 4217 shape), which catches the stale/tampered cases the issue describes and emits the InvalidFiatCode marker as you suggested. Full membership validation (rejecting valid-format-but-unsupported codes like "XYZ") would mean porting the bundled fiat list into Rust, creating a second source of truth to keep in sync with the Dart asset. Happy to add that here or as a follow-up which would you prefer?

Closes #175.

Summary by CodeRabbit

• Bug Fixes

  • Order creation now detects unsupported or incorrectly formatted fiat currencies before submission.
  • Clear localized guidance is shown when the selected currency must be changed.

• Localization

  • Added messages for invalid fiat currencies in English, German, Spanish, French, and Italian.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 02e28990-4de1-40f1-a0c4-91336ed81000

📥 Commits

Reviewing files that changed from the base of the PR and between 7625b24 and 7bad547.

📒 Files selected for processing (8)

• lib/core/daemon_errors.dart
• lib/l10n/app_de.arb
• lib/l10n/app_en.arb
• lib/l10n/app_es.arb
• lib/l10n/app_fr.arb
• lib/l10n/app_it.arb
• rust/src/api/orders.rs
• rust/src/api/settings.rs

Included review availability: Your plan includes up to 1 review per rolling hour; 0 remain after this review.

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Walkthrough

The order API now validates trimmed fiat codes before publication. The validator is reused across the crate and has expanded unit coverage. Invalid-code errors now map to dedicated English, German, Spanish, French, and Italian messages.

Changes

Fiat code validation

Layer / File(s)	Summary
Fiat code validation contract rust/src/api/settings.rs	validate_fiat_code is available within the crate. Tests cover valid ISO-shaped codes and invalid formats.
Order creation preflight rust/src/api/orders.rs	create_order trims and validates fiat_code before publishing the order.
Localized invalid-code error lib/core/daemon_errors.dart, lib/l10n/app_*.arb	InvalidFiatCode maps to a dedicated localized message in English, German, Spanish, French, and Italian.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: 🟡 Moderate · up to 7bad5

This PR adds submit-time fiat-format validation and a localized rejection path for malformed saved or tampered currency codes. The change is localized, but merge readiness remains moderate until the required binding, Flutter test, and localization regeneration checks are completed.

Suggested reviewers: grunch, catrya, andreadiazcorreia

Poem

A rabbit checked the coins with care,
And trimmed each code from hidden wear.
Bad fiat stayed outside the door,
While clear translations said what for.
Order paths now hop secure.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Linked Issues check	⚠️ Warning	The PR validates format before publishing, but it does not reject valid-format codes that are unsupported or stale.	Validate fiat-code membership against the supported currency set, or clarify that the create-order contract requires format validation only.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes submit-time fiat-code validation before order submission.
Out of Scope Changes check	✅ Passed	The validation, tests, error mapping, and translations directly support the linked issue and its local rejection flow.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[codaMW]

@coderabbitai full review

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Full review finished.