fix: restore runInBackground on the main thread after input simulation

[hatayama]

Summary

uloop simulate-mouse-input and uloop simulate-keyboard failed on every invocation with UNITY_RPC_ERROR / set_runInBackground can only be called from the main thread (reproduced 5/5 on Windows during the v3 verification pass; the mechanism is platform-independent). The simulation itself succeeded (VibeLogs recorded *_complete with Success:true), but the successful response was discarded, and the escaped exception left PlayMode in Error Pause, blocking subsequent attempts.

Root cause

• PR fix: Harden IPC contracts, empty RPC errors, and Settings async UI #1778's ConfigureAwait guard mechanically added .ConfigureAwait(false) to the executor awaits in SimulateMouseInputUseCase / SimulateKeyboardUseCase.
• Those awaits complete through a TaskCompletionSource created with TaskCreationOptions.RunContinuationsAsynchronously (InputSystemConfiguredUpdateApplier), so with ConfigureAwait(false) the continuation always resumes on a thread-pool thread instead of Unity's main thread.
• The using InputSimulationRunInBackgroundScope Dispose then ran on that pool thread and set Application.runInBackground — a main-thread-only API — which threw, replacing the successful response with an internal error.

Fix

Follow the existing precedent in PlayModeTestExecuter (why-not-using + finally with a main-thread switch):

• SimulateMouseInputUseCase / SimulateKeyboardUseCase: replace using with an explicit scope + try/finally; the finally awaits InputSystemUpdateHelper.SwitchToMainThreadIfNeeded(CancellationToken.None) before Dispose(). (SwitchToMainThreadIfNeeded is a custom awaitable, so it is outside the ConfigureAwait guard's scope — no re-collision.)
• InputSimulationRunInBackgroundScope.Dispose: added Debug.Assert(MainThreadSwitcher.IsMainThread, ...) so any future off-main-thread disposal fails fast. This required referencing the ToolContracts asmdef from the InputSimulation asmdef (same dependency the sibling Common/InputSystem asmdef already has).

Verification (Windows, Unity 2022.3.62f3, native uloop 3.1.0-beta.13)

• Red: existing PlayMode tests SimulateMouseInputTests.LongPress_Should_RestoreRunInBackground_WhenOriginallyDisabled and SimulateKeyboardTests.Press_Should_RestoreRunInBackground_WhenOriginallyDisabled both failed before the fix with exactly set_runInBackground can only be called from the main thread.
• Green: both tests pass after the fix.
• uloop compile: 0 errors, 0 warnings.
• E2E: PlayMode start → uloop simulate-keyboard --action Press --key Space x3 and uloop simulate-mouse-input --action Click x3 → all Success:true / exit 0 (previously 0/5); Unity console shows no errors or warnings afterwards; PlayMode stopped cleanly (no Error Pause).
• Regression: full PlayMode SimulateMouseInputTests + SimulateKeyboardTests suites → 49/49 passed.

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📥 Commits

Reviewing files that changed from the base of the PR and between d578c38 and 47c3c9d.

⛔ Files ignored due to path filters (1)

• Packages/src/Editor/FirstPartyTools/Common/InputSimulation/UnityCLILoop.FirstPartyTools.Common.InputSimulation.Editor.asmdef is excluded by none and included by none

📒 Files selected for processing (3)

• Packages/src/Editor/FirstPartyTools/Common/InputSimulation/InputSimulationRunInBackgroundScope.cs
• Packages/src/Editor/FirstPartyTools/SimulateKeyboard/SimulateKeyboardUseCase.cs
• Packages/src/Editor/FirstPartyTools/SimulateMouseInput/SimulateMouseInputUseCase.cs

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