Coverage improvement follow-ups (post-refactor)

[jongalloway]

Coverage dropped after recent refactors / consolidation work. This meta issue tracks targeted follow-ups to regain confidence by:

• adding tests where behavior is stable and deterministic,
• refactoring “hard to test” helpers into pure functions where appropriate,
• clarifying any intentional coverage exclusions (generated sources, etc.).

Context / tooling:

• CI artifact-based coverage diagnostics script (Cobertura): scripts/download-coverage-artifact.ps1 (see PR Add coverage diagnostics section and download script for CI artifacts #246)

Related prior work:

• Consolidated tools: update tests + conformance expectations #217 (closed) did the broad consolidated-tool test updates/strategy alignment.

Work items:

• Increase coverage: consolidated tool routing/validation (follow-up) #252 Increase coverage: consolidated tool routing/validation (follow-up)
• TemplateEngineHelper: refactor formatting into pure functions + deterministic tests #251 TemplateEngineHelper: refactor formatting into pure functions + deterministic tests
• DotNetResources: add unit tests for mappings + lookup error paths #250 DotNetResources: add unit tests for mappings + lookup error paths
• ProjectAnalysisHelper: make testable with minimal on-disk fixtures #253 ProjectAnalysisHelper: make testable with minimal on-disk fixtures
• Define coverage exclusions policy (generated sources, obj/, source generators) #248 Define coverage exclusions policy (generated sources, obj/, source generators)

Acceptance:

• Each sub-issue has clear scope + acceptance criteria.
• Closing this meta issue implies each sub-issue is closed (or explicitly deferred with rationale).