[CI] Dynamically pick latest simulator device

[andrewheard]

Updated build.sh to dynamically select an available simulator for the latest version of the specified OS. For example, get_latest_simulator "iOS" "iPhone" returns iPhone 17 Pro. This may reduce CI failures due to missing devices, requiring fixes like #15992.

Added an install_simulators.sh script that skips downloading when a platform is available already. xcodebuild -downloadPlatform was downloading iOS 26.3.1 runtimes when iOS 26.2 or iOS 26.3 was already available. This added minutes to the CI runs and gigabytes upon gigabytes of bandwidth usage.

#no-changelog

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[andrewheard]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces dynamic simulator selection in scripts/build.sh and adds a new utility script, scripts/install_simulators.sh, to manage simulator runtime installations. The review feedback highlights the need for explicit error handling when using command substitutions and suggests a more robust jq query to handle potential null values when fetching simulator names.

[gemini-code-assist]

When get_latest_simulator fails, it returns a non-zero exit code, but the script doesn't exit because of how set -e handles command substitutions. This can lead to iphone_simulator_name being empty and causing issues later. To ensure the script fails immediately on error, you should explicitly check the exit code.

Suggested change

	iphone_simulator_name=$(get_latest_simulator "iOS" "iPhone")
	iphone_simulator_name=$(get_latest_simulator "iOS" "iPhone") || exit 1

[gemini-code-assist]

When get_latest_simulator fails, it returns a non-zero exit code, but the script doesn't exit because of how set -e handles command substitutions. This can lead to watchos_simulator_name being empty and causing issues later. To ensure the script fails immediately on error, you should explicitly check the exit code.

Suggested change

	watchos_simulator_name=$(get_latest_simulator "watchOS" "Apple Watch")
	watchos_simulator_name=$(get_latest_simulator "watchOS" "Apple Watch") || exit 1

[gemini-code-assist]

When get_latest_simulator fails, it returns a non-zero exit code, but the script doesn't exit because of how set -e handles command substitutions. This can lead to tvos_simulator_name being empty and causing issues later. To ensure the script fails immediately on error, you should explicitly check the exit code.

Suggested change

	tvos_simulator_name=$(get_latest_simulator "tvOS" "Apple TV")
	tvos_simulator_name=$(get_latest_simulator "tvOS" "Apple TV") || exit 1

[gemini-code-assist]

If map(select(.name | contains($dev))) returns an empty array, first will evaluate to null. Attempting to access .name on null will cause jq to error. Using the optional operator ? (.name?) will prevent this error by gracefully returning null instead, making the query more robust.

Suggested change

	first |
	.name
	first | .name?