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Document FANTOM_FORCE_CI_MODE for full local runs (#56531)#56531

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Document FANTOM_FORCE_CI_MODE for full local runs (#56531)#56531
rubennorte wants to merge 1 commit into
react:mainfrom
rubennorte:export-D101795648

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@rubennorte

@rubennorte rubennorte commented Apr 21, 2026

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Summary:

Add a section to the Fantom __docs__/README.md that recommends running the full suite locally with FANTOM_FORCE_CI_MODE=1. In CI mode, globalSetup pre-builds the entire (hermesVariant × enableOptimized) binary matrix once up-front and per-test buck2 invocations are skipped, which eliminates buck2 daemon contention from the worker pool — a common source of sporadic build failures when many workers race to build different binary variants at the same time.

CI environments (SANDCASTLE, GITHUB_ACTIONS) already auto-detect this mode; this just documents it for local use.

Changelog: [Internal]

Reviewed By: andrewdacenko

Differential Revision: D101795648

@meta-cla meta-cla Bot added the CLA Signed This label is managed by the Facebook bot. Authors need to sign the CLA before a PR can be reviewed. label Apr 21, 2026
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meta-codesync Bot commented Apr 21, 2026

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@rubennorte has exported this pull request. If you are a Meta employee, you can view the originating Diff in D101795648.

@meta-codesync meta-codesync Bot changed the title Document FANTOM_FORCE_CI_MODE for full local runs Document FANTOM_FORCE_CI_MODE for full local runs (#56531) Apr 21, 2026
rubennorte added a commit to rubennorte/react-native that referenced this pull request Apr 21, 2026
Summary:

Add a section to the Fantom `__docs__/README.md` that recommends running the full suite locally with `FANTOM_FORCE_CI_MODE=1`. In CI mode, `globalSetup` pre-builds the entire `(hermesVariant × enableOptimized)` binary matrix once up-front and per-test buck2 invocations are skipped, which eliminates buck2 daemon contention from the worker pool — a common source of sporadic build failures when many workers race to build different binary variants at the same time.

CI environments (`SANDCASTLE`, `GITHUB_ACTIONS`) already auto-detect this mode; this just documents it for local use.

Changelog: [Internal]

Reviewed By: andrewdacenko

Differential Revision: D101795648
Summary:
Pull Request resolved: react#56531

Add a section to the Fantom `__docs__/README.md` that recommends running the full suite locally with `FANTOM_FORCE_CI_MODE=1`. In CI mode, `globalSetup` pre-builds the entire `(hermesVariant × enableOptimized)` binary matrix once up-front and per-test buck2 invocations are skipped, which eliminates buck2 daemon contention from the worker pool — a common source of sporadic build failures when many workers race to build different binary variants at the same time.

CI environments (`SANDCASTLE`, `GITHUB_ACTIONS`) already auto-detect this mode; this just documents it for local use.

Changelog: [Internal]

Reviewed By: andrewdacenko

Differential Revision: D101795648
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This pull request was successfully merged by @rubennorte in 5f69a91

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@react-native-bot react-native-bot added the Merged This PR has been merged. label Apr 21, 2026
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