[2026 Testing] Enforce per-file coverage thresholds for critical Stellar and signing modules

[Nanle-code]

Objective

Guarantee high test coverage where bugs lose funds or break signing.

Target area

vitest config, scripts/check-coverage.mjs

Context

Global coverage thresholds can hide low coverage in critical files. Stellar SDK wrappers, the transaction builder, fee math, address parsing and signing flows need a higher bar than UI code.

Acceptance criteria

• Per-file thresholds of ≥90% lines/branches for src/lib/stellar*, transactionBuilder.ts, stroop/amount utilities, src/lib/wallet/** and multisig*.
• check-coverage.mjs reports per-file failures clearly in the CI summary.
• Tests are added to meet the thresholds, focused on branches and failure paths.
• Thresholds are documented in contributor docs.
• Automated tests cover the primary flow, at least one boundary case, and at least one failure case.
• User-facing documentation or developer guidance is updated, including compatibility, security, or migration notes where applicable.

Pull request requirements

• All continuous integration checks must pass before a pull request may be merged.
• The branch must be free of merge conflicts with the target branch at the time of merge.
• Do not request merge with failing workflows, skipped required checks, or unresolved conflicts.

[drips-wave]

@Nanle-code This issue could not be added to the Stellar Wave Program because the per-repo points budget would be exceeded (25000 / 25000 points already used). The label has been automatically removed.

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