[rush-daemon] Add request scheduler foundation

[Mo Jazayeri (mojaza)]

Summary

Issue #5897 requires daemon requests to queue instead of failing when another Rush command is active. This PR introduces the initial @rushstack/rush-daemon package and its request admission scheduler as an independently reviewable foundation for that workstream.

Details

The scheduler defines SHARED-BUILD, SHARED-READ, and EXCLUSIVE compatibility classes. Requests in the same shared class can run concurrently, incompatible classes serialize, and a queued exclusive request gates later admissions to preserve FIFO fairness.

Admission supports queue position notifications, clean cancellation through AbortSignal, bounded waits, and fail-fast --no-wait semantics. Leases are idempotently released so a completed request cannot corrupt scheduler state.

This is intentionally a partial implementation of #5897: transport, workspace session routing, command classification, graph integration, and shared-build selection merging depend on the WS0/WS1 prerequisites and are not included here. The package is registered but not connected to the Rush CLI, so existing behavior is unchanged.

How it was tested

• Built @rushstack/rush-daemon with Rush/Heft, including TypeScript, ESLint, and API Extractor.
• Ran 7 scheduler unit tests covering shared concurrency, incompatible serialization, exclusive FIFO gating, fail-fast admission, timeout, cancellation, and queue position updates.

Impacted documentation

N/A. The package is not yet exposed through the Rush CLI.

[Sean Larkin (TheLarkInn)]

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[Copilot]

Pull request overview

Introduces the publishable @rushstack/rush-daemon package and foundational request admission scheduler.

Changes:

• Adds scheduler compatibility classes, FIFO admission, cancellation, timeouts, and queue notifications.
• Adds scheduler unit tests and public API exports.
• Registers and configures the package within the Rush monorepo.

Show a summary per file

File	Description
rush.json	Registers the daemon project.
README.md	Lists the new package.
libraries/rush-daemon/tsconfig.json	Configures TypeScript.
libraries/rush-daemon/src/test/RequestScheduler.test.ts	Tests scheduler behavior.
libraries/rush-daemon/src/RequestScheduler.ts	Implements request scheduling.
libraries/rush-daemon/src/index.ts	Exports the public API.
libraries/rush-daemon/README.md	Describes package status.
libraries/rush-daemon/package.json	Defines package metadata and builds.
libraries/rush-daemon/LICENSE	Adds MIT licensing.
libraries/rush-daemon/eslint.config.js	Configures linting.
libraries/rush-daemon/config/rig.json	Selects the shared rig.
libraries/rush-daemon/config/jest.config.json	Configures Jest.
libraries/rush-daemon/config/api-extractor.json	Configures API Extractor.
libraries/rush-daemon/CHANGELOG.md	Initializes the changelog.
libraries/rush-daemon/CHANGELOG.json	Initializes changelog metadata.
libraries/rush-daemon/.npmignore	Defines published files.
common/reviews/api/rush-daemon.api.md	Records the public API surface.
common/config/subspaces/default/pnpm-lock.yaml	Adds the package importer.
common/changes/@rushstack/rush-daemon/mojazayeri-rush-daemon-scheduler_2026-08-13-22-30.json	Records the minor change.

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• Comments generated: 3
• Review effort level: Balanced