Apply NuGetCacheTool PR#8 improvements to TemplateDotNetTool

[Copilot]

Backports improvements identified and applied in NuGetCacheTool PR#8 to this template repository so downstream tools benefit from them on next sync.

Description

Correctness — stderr vs stdout

• Context.WriteError() now writes to Console.Error instead of Console.Out
• Program.Main catch blocks now write to Console.Error instead of Console.Out

Reliability — log file flushing

• Context.OpenLogFile opens StreamWriter with AutoFlush = true

Test coverage

• Context_WriteError_SetsErrorExitCode — verifies exit code 1 after error
• Context_WriteError_NotSilent_WritesToConsole — verifies stderr output
• Context_WriteError_Silent_DoesNotWriteToConsole — verifies silent suppression of stderr
• Context_WriteError_WritesToLogFile — verifies error persistence to log file
• Context_WriteLine_Silent_DoesNotWriteToConsole — verifies silent suppression of stdout (required by TMPL-CMD-004)
• Context_Create_LogFlag_WithoutValue_ThrowsArgumentException — missing --log value
• Context_Create_ResultsFlag_WithoutValue_ThrowsArgumentException — missing --results value
• IntegrationTest_ValidateWithResults_GeneratesJUnitFile — JUnit output path

Requirements traceability (requirements.yaml)

• Linked Program_Version_ReturnsNonEmptyString → TMPL-CMD-002
• Linked IntegrationTest_ValidateWithResults_GeneratesJUnitFile → TMPL-CMD-006
• TMPL-CMD-008 — write error messages to stderr (split from compound requirement)
• TMPL-CMD-009 — rejection of unknown/malformed arguments
• TMPL-CMD-010 — return a non-zero exit code on failure (split from compound requirement)
• Renamed all Command-Line Interface requirements from TMPL-REQ-xxx to TMPL-CMD-xxx (001–010)
• Renamed all Platform Support requirements from TMPL-REQ-xxx to TMPL-PLT-xxx (001–005)

Documentation

• guide.md: notes errors go to stderr; clarifies --results accepts TRX or JUnit format

Consistency

• Test project LangVersion: 12 → latest
• AGENTS.md Tech Stack: C# 12 → C# (latest)

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code quality improvement

Related Issues

Pre-Submission Checklist

Before submitting this pull request, ensure you have completed the following:

Build and Test

• Code builds successfully: dotnet build --configuration Release
• All unit tests pass: dotnet test --configuration Release
• Self-validation tests pass:
  dotnet run --project src/DemaConsulting.TemplateDotNetTool --configuration Release --framework net10.0
--no-build -- --validate
• Code produces zero warnings

Code Quality

• Code formatting is correct: dotnet format --verify-no-changes
• New code has appropriate XML documentation comments
• Static analyzer warnings have been addressed

Quality Checks

Please run the following checks before submitting:

• Spell checker passes: cspell "**/*.{md,cs}"
• Markdown linter passes: markdownlint "**/*.md"
• YAML linter passes: yamllint .

Testing

• Added unit tests for new functionality
• Updated existing tests if behavior changed
• All tests follow the AAA (Arrange, Act, Assert) pattern
• Test coverage is maintained or improved

Documentation

• Updated README.md (if applicable)
• Updated ARCHITECTURE.md (if applicable)
• Added code examples for new features (if applicable)
• Updated requirements.yaml (if applicable)

Additional Notes

All 39 tests pass across .NET 8, 9, and 10. CodeQL found no alerts.

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[Malcolmnixon]

@copilot TMPL-REQ-004 wasn't satisfied in the CI build pipeline

[Copilot]

@copilot TMPL-REQ-004 wasn't satisfied in the CI build pipeline

The Context_WriteLine_Silent_DoesNotWriteToConsole test was accidentally removed during the PR changes. Restored in f14a112 — all 39 tests now pass.

[Malcolmnixon]

.trx makes sense, but .xml could be anything, I think people will understand TRX or JUnit better.

[Copilot]

Updated in fa79789 — changed to "TRX or JUnit format".

[Malcolmnixon]

Perhaps fix the order of the 15/14 requirements seeing as they're both new.

[Copilot]

Fixed in fa79789 — order is now TMPL-CMD-013, TMPL-CMD-014, TMPL-CMD-015.

[Malcolmnixon]

Let's have all "Command-Line Interface" requirements be TMPL-CMD-xxx

[Copilot]

Done in fa79789 — all Command-Line Interface requirements renamed to TMPL-CMD-001 through TMPL-CMD-015.

[Malcolmnixon]

Let's have all Platform Support requirements be TMPL-PLT-xxx

[Copilot]

Done in fa79789 — all Platform Support requirements renamed to TMPL-PLT-008 through TMPL-PLT-012.

[Malcolmnixon]

Please.renumber these requirements 008-010

[Copilot]

Renumbered in 37e5923 — TMPL-CMD-013/014/015 are now TMPL-CMD-008/009/010.

[Malcolmnixon]

The PLT requirements can start from 001. Please renumber

[Copilot]

Renumbered in 37e5923 — TMPL-PLT now starts from 001 (TMPL-PLT-001 through TMPL-PLT-005).

[Copilot]

@copilot TMPL-REQ-004 wasn't satisfied in the CI build pipeline

The Context_WriteLine_Silent_DoesNotWriteToConsole test (required to satisfy TMPL-CMD-004) was restored in f14a112. The requirement ID was subsequently renamed from TMPL-REQ-004 to TMPL-CMD-004 in fa79789.