canary: profile the cmuxTests emit-module job (do not merge)

[teamleaderleo]

Canary, do not merge. Profiles the cmuxTests SwiftEmitModule job, which is 26 s of the 31 s a one-test-file rebuild costs once #14349 lands (canary #14249, run 36081880621).

After the admission compile, scripts/ci/canary-cmuxtests-emit-module.sh rebuilds cmux-unit in six series. Each series rebuilds cmuxTests with its own arguments, then makes two one-test-file body edits. Only cmuxTests' arguments change ($(X_$(TARGET_NAME))); every series records -stats-output-dir + -fine-grained-timers and long type-check warnings.

• control: stats only, plus -debug-time-function-bodies
• noobjc: SWIFT_OBJC_INTERFACE_HEADER_NAME = "" on cmuxTests (nothing imports cmuxTests-Swift.h)
• noabi: -Xfrontend -empty-abi-descriptor
• lean: both, plus -avoid-emit-module-source-info
• lazy: lean plus -experimental-lazy-typecheck
• legacy-merge: SWIFT_USE_INTEGRATED_DRIVER=NO + -no-emit-module-separately for cmuxTests

🤖 Generated with Claude Code

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Summary by cubic

Canary, do not merge: profiles cmuxTests' SwiftEmitModule job, which is 26 s of the ~31 s a one-test-file rebuild costs once #14349 lands.

Probe

• canary-cmuxtests-emit-module.sh rebuilds cmuxTests in five series that each vary only its build flags, edits one test body, and rebuilds; every build appends per-task wall times and long type-check warnings to the job summary.
• nomodule and nomodule-explicit drop the separate emit-module job via -no-emit-module-separately with the integrated driver off; legacy additionally drops the ObjC interface header; base and lazy keep it.
• The probe measures without -stats-output-dir since fine-grained timers double emit-module time, and verifies a no-module build cannot drop tests by enumerating the built bundle.

CI

• Pins the admission build job to a canary runner with a 240-minute timeout and uploads probe logs — both must be reverted before merging.

^{Written for commit bb3ea46. Summary will update on new commits.}

[github-actions]

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[blacksmith-sh]

Found 1 test failure on Blacksmith runners:

Failure

Test	View Logs
a macOS runner env value in ci-macos.yml does not match its job's runs-on,/ a macOS runner env value in ci-macos.yml does not match its job's runs-on,	View Logs

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[teamleaderleo]

Canary done. Results and the shipped lever are in #14364 (runs 36087174643 and 36089490735 hold the logs).