[rush-daemon][WS2.9][8/9] Merge shared builds

[Mo Jazayeri (mojaza)]

Summary

Migrates WS2 layer 8/9 into microsoft/rushstack as a dependent draft that merges compatible concurrent phased SHARED-BUILD requests into one warm operation-graph iteration while preserving client-scoped output and results.

Depends on #5970. Supersedes mojaza#8. Follows merged #5949 and references #5897 without closing it. PBI: https://onedrive.visualstudio.com/EFun/_workitems/edit/3216025

Draft for explicit human review; do not merge without maintainer approval. Do not enable auto-merge.

Details

• Adds a graph-owned coordinator with deterministic event-loop-turn batch boundaries for admitted shared builds.
• Reconciles retained workspace invalidations once per batch, unions each client's dependency closure, and performs one setEnabledStates/schedule/execute cycle.
• Fans raw streams and structured events out only to each client's retained operation subset with independent ordered backpressure.
• Derives exit semantics from each client's subset, isolating disjoint failures while propagating shared failures only to affected clients.
• Removes pre-start cancellations, unsubscribes mid-run cancellations without stopping work needed by live clients, and aborts only when no live client still needs the iteration.
• Preserves WS2.8 FIFO/exclusive admission gating, one-deadline no-wait/timeout semantics, warm retained results, late-arrival batching, exact-once cleanup, and recovery after failed iterations.

Limitations

This remains opt-in and dead-code-safe. It uses the existing injected real graph/shape seam and does not integrate with apps/rush or construct PhasedScriptAction. Command-independent graph/plugin construction and complete per-iteration runner lifetime remain blocked by open #5895. It does not add WS3 lifecycle or WS4 CLI/config integration.

How it was tested

• node common/scripts/install-run-rush.js build --only @rushstack/rush-daemon --verbose
• Focused emitted Jest suites for batching, phased routing, interactive input, admission, result policy, and command classification: 6 suites and 62 tests passed
• node common/scripts/install-run-rush.js change --verify
• API Extractor report validation, git diff --check, source-to-replay range-diff, and conflict-focused read-only review

[Copilot]

Pull request overview

Adds shared-build batching to the warm Rush daemon graph while preserving request-scoped events, results, admission, and cancellation behavior.

Changes:

• Merges compatible phased build requests into one graph iteration.
• Adds per-client event multiplexing, result isolation, and cancellation handling.
• Expands integration and batching test coverage.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
libraries/rush-daemon/src/PhasedRequestRouter.ts	Coordinates merged graph iterations and client-scoped results.
libraries/rush-daemon/src/PhasedRequestEventSink.ts	Reports client output failures to the coordinator.
libraries/rush-daemon/src/PhasedRequestEventMultiplexer.ts	Fans graph events out to multiple request sinks.
libraries/rush-daemon/src/test/PhasedRequestBatching.test.ts	Tests batching, isolation, cancellation, and recovery.
libraries/rush-daemon/src/test/RequestAdmissionIntegration.test.ts	Tests admission timing and exclusive FIFO gating.
libraries/rush-daemon/src/test/PhasedRequestRouterTestUtilities.ts	Supports distinct test session identifiers.
libraries/rush-daemon/README.md	Documents shared-build batching behavior.
common/changes/@rushstack/rush-daemon/mojazayeri-shared-build-merging_2026-08-22-00-11.json	Records the minor package change.

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