generate_gymfile_from_template emits Apple-deprecated "ad-hoc" export method, rejected by Xcode 26+

Start in packages/build-tools/src/steps/functions/generateGymfileFromTemplate.ts and inspect DEFAULT_CREDENTIALS_TEMPLATE alongside the credentials mapping that sets EXPORT_METHOD. Verify how an internal-distribution credential becomes the generated Gymfile method, then update the behavior so it uses release-testing instead of the deprecated ad-hoc value while preserving other distribution methods.

Summary

packages/build-tools/src/steps/functions/generateGymfileFromTemplate.ts's DEFAULT_CREDENTIALS_TEMPLATE populates the Gymfile's export_options method: field from EXPORT_METHOD, which is set here:

...(credentials
  ? {
      KEYCHAIN_PATH: credentials.keychainPath,
      EXPORT_METHOD: credentials.distributionType,
    }
  : {}),

For an internal-distribution / ad-hoc build, credentials.distributionType stringifies to "ad-hoc". As of Xcode 15.4, Apple's own IDEDistribution tool deprecated that command-line name in favor of "release-testing" (see fastlane/fastlane#22028, which quotes the exact Xcode message: "Command line name 'ad-hoc' is deprecated. Use 'release-testing' instead."). Xcode 26+ now hard-rejects the old value at export time:

exportArchive exportOptionsPlist error for key "method" expected one {} but found ad-hoc

Reproduction

• SDK 56 project (expo@~56.0.14), iOS build with credentialsSource: "remote", distribution: "internal".
• Confirmed via elimination across multiple builds, ruling out every other variable first:
  • Verified this is not downstream of anything else: signing (DEVELOPMENT_TEAM), entitlements/capabilities, and CFBundleShortVersionString version-matching were all independently broken and fixed first, on our own extension targets (Watch app + two extensions) — none of that affected this error.
  • Verified this is not image-recency-dependent: reproduced identically on both macos-tahoe-26.4-xcode-26.4 (the SDK-56-aliased default) and macos-tahoe-26.5-xcode-26.6 (latest), with fastlane/gym at 2.236.1 on the latter — the newest available combination at the time of testing.
  • Archive itself succeeds cleanly (all targets compile, sign, and version-match); only the export step fails, and only on this one value.

Expected

EXPORT_METHOD (and therefore the generated Gymfile's method: value) should resolve to "release-testing" for an ad-hoc/internal-distribution build under Xcode 15.4+, matching Apple's own renamed value, instead of the legacy "ad-hoc" string.

Workaround in use

Supplying a custom template input to generate_gymfile_from_template (via a custom build config), byte-identical to DEFAULT_CREDENTIALS_TEMPLATE except the method: line hardcoded to "release-testing". Happy to remove this workaround once a fix ships — flagging so it can be prioritized and so others hitting the same SDK56 + Xcode 26 combination can find it.