Make build/test worktree-aware and add same-worktree lock

[johnml1135]

Summary

• Scope process cleanup in build/test flows to the current worktree root.
• Add lightweight same-worktree exclusivity using a named mutex plus Output/WorktreeRun.lock.json metadata.
• Add optional actor tagging via FW_BUILD_STARTED_BY or -StartedBy.
• Keep build.ps1 -RunTests working by having child test.ps1 reuse the parent lock (-SkipWorktreeLock).
• Default build.ps1 -NodeReuse to false for safer multi-worktree behavior.
• Document behavior in build/testing instructions and README.

Files

• build.ps1
• test.ps1
• Build/Agent/FwBuildHelpers.psm1
• .github/instructions/build.instructions.md
• .github/instructions/testing.instructions.md
• ReadMe.md

Validation

• Ran diagnostics checks on changed PowerShell files.
• No new diagnostics in build.ps1 or Build/Agent/FwBuildHelpers.psm1.
• Existing pre-existing warning remains in test.ps1 (vstestOutput assigned but not used).

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This change is 

[Copilot]

Pull request overview

This PR updates the repo’s PowerShell build/test tooling to be worktree-aware, enabling safer concurrent workflows across multiple git worktrees while enforcing single active scripted workflow per worktree via a lock.

Changes:

• Add same-worktree exclusivity using a named mutex + Output/WorktreeRun.lock.json metadata (with optional FW_BUILD_STARTED_BY / -StartedBy actor tagging).
• Scope process cleanup and file-lock retry cleanup to the current worktree root ($PSScriptRoot) so other worktrees aren’t affected.
• Change build.ps1 default MSBuild node reuse to -NodeReuse $false to reduce cross-worktree contention, and document the new behavior.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
build.ps1	Acquires worktree lock, scopes cleanup by repo root, defaults -NodeReuse to false, and passes -SkipWorktreeLock to child test.ps1 under -RunTests.
test.ps1	Adds optional -StartedBy, supports -SkipWorktreeLock, scopes cleanup by repo root, and releases lock in finally.
Build/Agent/FwBuildHelpers.psm1	Implements Enter-WorktreeLock/Exit-WorktreeLock, adds worktree-aware filtering to Stop-ConflictingProcesses, and extends Invoke-WithFileLockRetry with optional -RepoRoot.
.github/instructions/build.instructions.md	Documents worktree-aware cleanup, same-worktree lock behavior, and -NodeReuse default change.
.github/instructions/testing.instructions.md	Documents worktree-aware behavior and lock reuse for build.ps1 -RunTests.
ReadMe.md	Adds a concise overview of concurrent worktree behavior and lock tagging.

[Copilot]

In Enter-WorktreeLock, if the mutex has already been acquired ($hasHandle = $true) and an exception occurs after that (e.g., failing to create Output/ or write WorktreeRun.lock.json), the catch block rethrows without releasing/disposing the mutex. In a long-lived PowerShell session this can leave the mutex held and block subsequent build/test runs. Ensure the error path releases the mutex (when owned) and disposes it before throwing (or wrap the whole acquisition/write flow in a try/finally that always cleans up on failure).

Suggested change

	if (-not $hasHandle -and $mutex) {
	if ($mutex) {
	if ($hasHandle) {
	try {
	$mutex.ReleaseMutex()
	}
	catch {
	# Ignore release failures on error path
	}
	}

[github-actions]

NUnit Tests

    1 files  ±0      1 suites  ±0   5m 50s ⏱️ +2s
4 407 tests ±0  4 320 ✅ ±0  87 💤 ±0  0 ❌ ±0 
4 416 runs  ±0  4 329 ✅ ±0  87 💤 ±0  0 ❌ ±0 

Results for commit f14a7c6. ± Comparison against base commit fe415b8.