[martinrrm]

Summary

Completes the TAP 20 upgrade proposed in #186 rather than changing only the dependency version.

• Upgrade TAP to ^20.0.3, remove unsupported check-coverage and nyc-arg, retain coverage-map: "map.js", and use the modern configuration expected by the existing template-oss version.
• Keep full coverage enforcement enabled.
• Migrate the keys in the four existing snapshot files to TAP 20's hierarchical naming. All 88 recorded snapshot values were compared against the original files and are identical.
• Add a development-only TypeScript 5 dependency: a fresh install otherwise resolves TypeScript 7 through TAP's loader peer dependency, causing Cannot read properties of undefined (reading 'fileExists') before tests run. Default TAP plugins remain enabled.
• Regenerate the Dependabot and branch-protection entries for the newly created release/v5 branch using the pinned template-oss version. Existing main and release/v6 entries are unchanged.

No production source, runtime dependencies, supported Node versions, lockfiles, or workflows were changed.

Validation

• Full TAP suite: 14 files, 174 passing assertions; 100% statements, branches, functions, and lines.
• ESLint passes.
• Template-oss postlint passes after regenerating the maintenance-branch configuration.
• Snapshot key/value comparison passes for all four files.
• Both generated YAML files parse successfully; their release/v5 entries match the existing release/v6 policy, and regeneration is idempotent.
• Validation ran on Linux with Node 24.15.0; the GitHub Actions matrix remains to be verified.

Maintenance-branch configuration

The initial postlint failure was caused by the newly created release/v5 branch not being represented in .github/dependabot.yml and .github/settings.yml.

The same failures were reproduced on unchanged main commit af44cf63cd89291906be6c7d107a06f5583b1203. A separate follow-up commit now regenerates those two files and resolves the lint gate. It does not change workflow definitions, runtime code, or the TAP migration.