Fix: Guard against re-entry in Scheduler (Issue #17355) #35437
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Adds a check for isPerformingWork inside performWorkUntilDeadline. This prevents recursive execution of the work loop when the browser environment (e.g., Firefox) fires message events while the JavaScript main thread is paused by a breakpoint or alert.
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Fixes #17355. This PR adds a re-entrancy guard to
performWorkUntilDeadlinein the Scheduler. This addresses an issue observed in Firefox whereMessageChannelevents may fire recursively when the main thread is paused (e.g. byalert()or breakpoints), causing the 'Should not already be working' invariant violation. Verified by running Scheduler tests (yarn test scheduler).