fix: Fail control-play-mode fast when unsaved changes cannot be quietly saved

[hatayama]

Summary

• control-play-mode --action Play no longer waits the full timeout (up to 180s) when Play mode cannot start because unsaved editor changes could not be quietly saved (for example, an Untitled scene).

User Impact

• Before: if the active scene had no path (an Untitled scene) or otherwise could not be saved, Unity's synchronous handler gave up in milliseconds, but the response looked identical on the wire to "no state change yet." The CLI then polled Unity's status for the full wait timeout before finally reporting a generic "did not complete" error, hiding the real cause.
• After: the CLI recognizes this failure immediately and returns an actionable error listing exactly which scene/prefab changes could not be saved, with guidance to save or discard them (or give an Untitled scene a path) before retrying.

Changes

• Packages/src/Editor/FirstPartyTools/ControlPlayMode: added a BlockedByUnsavedChanges response field, set when SaveDirtyEditorChangesBeforePlayStart fails, mirroring the existing BlockedByCompileErrors field.
• cli/project-runner: runControlPlayModeWithStateWait now checks BlockedByUnsavedChanges on the initial response and fails fast with a new CONTROL_PLAY_MODE_UNSAVED_CHANGES error instead of entering the state-wait poll loop.

Verification

• Root-caused via a live reproduction in this checkout: created an Untitled dirty scene with execute-dynamic-code, then ran control-play-mode --action Play, which hung for the full timeout before this fix (EditorApplication.isPlaying stayed false throughout, confirming Unity had already given up).
• TDD: added a failing Go test (TestRunControlPlayModeWithStateWaitFailsImmediatelyWhenUnsavedChangesBlockPlay) reproducing the fall-through-to-polling bug against the pre-fix code, confirmed it failed with a generic timeout, then implemented the fix. Added assertions to the existing C# unit tests (ExecuteAsync_WhenPlayStartSaveFails_DoesNotEnterPlayMode, ExecuteAsync_WhenPlayStartLeavesUnsavedChanges_DoesNotEnterPlayMode) confirming BlockedByUnsavedChanges is set; confirmed both failed (Expected: True / But was: False) before the fix.
• Re-ran the live repro after the fix: control-play-mode --action Play against the same Untitled dirty scene now returns the new error in well under a second instead of hanging.
• sh scripts/check-go-cli.sh: format/vet/lint 0 issues, all Go packages pass (including the new test).
• go test -run TestProductionGoFilesStayFocused ./... (release-automation): pass.
• sh scripts/stamp-release-inputs.sh: re-run and committed, since cli/common changed.
• dist/darwin-arm64/uloop compile: 0 errors / 0 warnings.
• uloop run-tests (EditMode, ControlPlayModeUseCaseTests): 18/18 passed after the fix.

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 69a8f70c-5cbb-4ddb-9cf5-f156998c65cb

📥 Commits

Reviewing files that changed from the base of the PR and between ac70353 and d19a254.

📒 Files selected for processing (8)

• Assets/Tests/Editor/ControlPlayModeUseCaseTests.cs
• Packages/src/Editor/FirstPartyTools/ControlPlayMode/ControlPlayModeResponse.cs
• Packages/src/Editor/FirstPartyTools/ControlPlayMode/ControlPlayModeUseCase.cs
• cli/common/errors/error_envelope.go
• cli/dispatcher/shared-inputs-stamp.json
• cli/project-runner/internal/projectrunner/control_play_mode_wait.go
• cli/project-runner/internal/projectrunner/control_play_mode_wait_test.go
• cli/project-runner/shared-inputs-stamp.json

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/control-play-mode-unsaved-changes-fast-fail

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