fix: Shared compiler restarts no longer leak process handles

[hatayama]

Summary

• Shared compiler worker restarts now release the previous process handle before starting a replacement.
• A failed replacement start no longer leaves the stale process object cached.

User Impact

• Previously, an idle shared compiler worker that exited before the next compile could leave its operating-system process handle undisposed when the worker restarted.
• Repeated recovery now releases each stale handle before acquiring the next worker process.

Changes

• Dispose the cached worker process and clear session ownership before invoking the replacement process starter.
• Add an injectable process starter that follows the session's existing test-seam pattern.
• Add a process-free regression test that observes the previous Process object's synchronous Disposed event without waits or background work.
• Keep the shared compiler wire format and protocol version unchanged.

Verification

• Confirmed the regression test fails before the ownership fix with Expected: True / But was: False for the disposal observation.
• dist/darwin-arm64/uloop compile (0 errors, 0 warnings)
• SharedRoslynCompilerWorkerHostTests.StartProcessLocked_WhenReplacingCachedProcess_ShouldDisposePreviousHandle (1 passed)
• SharedRoslynCompilerWorkerHostTests and StaticFacadeStateGuardTests (36 passed)
• git diff --check

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 06068ad0-8a32-41cd-9884-375c75ab927c

📥 Commits

Reviewing files that changed from the base of the PR and between 764021c and a688326.

📒 Files selected for processing (2)

• Assets/Tests/Editor/DynamicCodeToolTests/SharedRoslynCompilerWorkerHostTests.cs
• Packages/src/Editor/FirstPartyTools/ExecuteDynamicCode/DynamicCompilation/SharedRoslynCompilerWorkerSession.cs

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📝 Walkthrough

Walkthrough

SharedRoslynCompilerWorkerSession now starts processes via an injectable delegate and disposes any previously cached process handle before replacing it. A test-only hook swaps the delegate for testing, and a new test verifies the previous process is disposed when replaced.

Changes

Stale process disposal

Layer / File(s)	Summary
Injectable process starter and disposal logic Packages/src/Editor/.../SharedRoslynCompilerWorkerSession.cs	Adds _startProcess delegate field defaulting to ProcessStartHelper.TryStart, updates StartProcessLocked to dispose the previously stored process before starting a new one via the delegate, and adds SwapProcessStarterForTests to swap the delegate for testing.
Test for previous process disposal Assets/Tests/Editor/DynamicCodeToolTests/SharedRoslynCompilerWorkerHostTests.cs	Adds a test that configures the test starter to return a cached process then null, asserting the first start succeeds, the second fails, and the previous process is disposed.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: disposing leaked process handles during shared compiler restarts.
Description check	✅ Passed	The description is directly related to the changeset and accurately explains the bug fix, test, and verification steps.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/hatayama/dispose-stale-shared-roslyn-worker-process

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[cubic-dev-ai]

No issues found across 2 files

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