[fix] Fix HTML logger parallel file collision

[nohwnd]

Summary

Fixes #15404

When multiple vstest.console processes run in parallel with the HTML logger, temporary XML result files can collide because:

1. The timestamp format (yyyyMMdd_HHmmss) only has second-level precision
2. The in-process lock (FileCreateLockObject) doesn't prevent cross-process races
3. Two processes finishing in the same second generate identical filenames

Changes

src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs

• Add millisecond precision to timestamp - changes format from HHmmss to HHmmssfff, greatly reducing collision likelihood across parallel processes
• Use FileMode.CreateNew for atomic file creation - replaces the File.Exists + File.Create pattern with an atomic create-if-not-exists operation that retries on IOException
• Remove unused FileCreateLockObject - the cross-process lock was ineffective

test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs

• Added XmlFilePathShouldContainMillisecondTimestampForCrossProcessUniqueness test

Documentation

• Updated .github/copilot-instructions.md with build/test commands, repo structure, and logger architecture
• Updated .github/skills/vstest-build-test/SKILL.md with logger-specific notes

Testing

All 34 HTML logger unit tests pass on both net9.0 and net48.

[Copilot]

Pull request overview

Fixes cross-process temp XML filename collisions in the HTML logger when multiple vstest.console instances run in parallel.

Changes:

• Adds PID to the temp XML filename and switches to FileMode.CreateNew for atomic “create if not exists”.
• Adds a unit test to validate the PID is present in the generated XML path.
• Updates build/doc tooling and authoring docs for repo build/test guidance.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
test/Microsoft.TestPlatform.Extensions.HtmlLogger.UnitTests/HtmlLoggerTests.cs	Adds a unit test asserting PID is included in the temp XML filename.
src/Microsoft.TestPlatform.Extensions.HtmlLogger/HtmlLogger.cs	Adds PID to filename and uses FileMode.CreateNew for atomic file creation; removes ineffective in-proc lock.
eng/common/tools.ps1	Adds an extra console message when exiting with an exit code.
eng/build.ps1	Attempts to forward the exit code from the invoked Arcade build script.
.github/skills/vstest-build-test/SKILL.md	Adds repo-specific build/test instructions and logger notes.
.github/skills/validate-skills/SKILL.md	Adds a procedure for validating that documented skill commands work.
.github/skills/creating-skills/SKILL.md	Adds guidance for creating skill files and frontmatter.
.github/copilot-instructions.md	Adds build/test command guidance and repository structure notes.

[nohwnd]

needs merge of #15434

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

[Copilot]

Same issue as in copilot-instructions.md: the documented filename pattern includes {pid} but the actual code does not add a PID to the filename. The uniqueness strategy relies on millisecond timestamps plus FileMode.CreateNew with retry. This documentation should be corrected to match the actual implementation.

Suggested change

	- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}_{pid}.xml` — PID ensures cross-process uniqueness
	- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision
	- **Temp XML naming:** `TestResult_{user}_{machine}_{timestamp}.xml` — timestamp-based name only (no PID)
	- **File creation:** Uses `FileMode.CreateNew` for atomic creation with retry on collision; millisecond timestamps + `CreateNew` retries provide uniqueness

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.