ci: fix flaky Xcode 26 selection killed by SIGPIPE under pipefail

[NuPlay]

Problem

The Select Xcode 26 step tested each candidate with:

if [ -d "${candidate}" ] && DEVELOPER_DIR="${candidate}/Contents/Developer" xcodebuild -version | grep -q '^Xcode 26'; then

under set -euo pipefail.

grep -q exits the moment it matches. xcodebuild is then still writing, takes SIGPIPE, and dies with an uncaught NSFileHandleOperationException (*** -[_NSStdIOFileHandle writeData:]: Broken pipe, Abort trap: 6). pipefail propagates that as the exit status of the whole pipeline, so the condition evaluated false for the candidate that actually was Xcode 26, the loop fell through every entry, and the job failed with Xcode 26 is required for this CI job.

Whether xcodebuild finishes writing before grep closes the pipe is a race, which is why this only failed sometimes. Four pull request runs on the same day:

run	result	Abort trap occurrences in the step log
#78	pass	0
#79	pass	0
#80	fail	4
#81	fail	4

Note the failures are entirely inside this step - nothing was ever compiled, so the failures said nothing about the code in those PRs.

Fix

Capture the version output into a variable and match it with case, so there is no pipe and nothing can be signalled mid-write.

version="$(DEVELOPER_DIR="${candidate}/Contents/Developer" xcodebuild -version 2>/dev/null || true)"

case "${version}" in
  "Xcode 26"*)
    XCODE_APP="${candidate}"
    break
    ;;
esac

Verification

Reproduced the mechanism deterministically with a producer large enough to lose the race every time:

old pattern -> candidate REJECTED even though the version matched   <-- the bug
new pattern -> candidate SELECTED

Should be merged before the other open pull requests, so their runs stop failing at random.

[Copilot]

🟢 Approval recommended

The change removes a known race-prone pipeline pattern in CI and replaces it with a deterministic, low-risk string match without affecting build/test behavior beyond Xcode selection.

Pull request overview

This PR fixes a flaky CI failure in the “Select Xcode 26” workflow step by removing a pipefail-sensitive xcodebuild | grep -q pipeline that could intermittently reject the correct Xcode due to SIGPIPE behavior.

Changes:

• Replace xcodebuild -version | grep -q '^Xcode 26' with capturing xcodebuild -version output into a variable and matching via case.
• Add an in-script rationale explaining the SIGPIPE + pipefail failure mode and why the new approach is race-free.

File summaries

File	Description
.github/workflows/ci.yml	Makes Xcode 26 selection deterministic by avoiding a fragile `xcodebuild

Review details

• Files reviewed: 1/1 changed files
• Comments generated: 0
• Review effort level: Lite

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