[edusperoni]

Depends on NativeScript/v8-buildscripts#10. This stays a draft until that PR is merged and tagged, and V8_RELEASE here is bumped to the new release.

What

• Runtime (Catalyst only): before V8::Initialize, the runtime tries one small mmap(MAP_JIT) allocation. If it fails, the runtime passes --jitless. "ios": { "jit": false } in the app's package.json forces the interpreter. iOS is unchanged: its V8 is lite mode, which implies --jitless.
• Catalyst test lane: TestRunner and its dependencies build for Mac Catalyst (arm64), ad-hoc signed with hardened runtime and allow-jit, like a shipped app. ./run_tests.sh --catalyst runs the suite on the host Mac, and a new test-catalyst CI job does the same on macos-15. CatalystJitTests asserts that V8 holds executable memory, which it only maps with the JIT on.
• Fixed along the way:
  • The arm64 Catalyst slice was linking Apple's /usr/lib/libffi.dylib. build_libffi.sh had no arm64-maccatalyst slice, so -lffi fell back to the SDK's libffi.tbd, while the runtime compiled against our fork's headers; the published 9.1.0 framework shows this with otool -L. The slice is now built and committed.
  • The metadata generator produced 0-byte metadata in Catalyst builds without failing them. Xcode doesn't export IPHONEOS_DEPLOYMENT_TARGET to Catalyst script phases, so the fix(metadata-generator): emit UIKit metadata for Mac Catalyst #433 fallback raised KeyError. It now falls back to LLVM_TARGET_TRIPLE_OS_VERSION. User Catalyst apps run the same script.

Why the runtime check is needed

V8 doesn't fall back to the interpreter on its own. In a hardened-runtime process without allow-jit (or allow-unsigned-executable-memory), the JIT build dies at its first code allocation; I saw a SIGTRAP at startup in a probe. With the entitlement, or without hardened runtime, the JIT runs.

The app template now grants allow-jit instead of allow-unsigned-executable-memory. Only V8's JIT needs an exception, and libffi closures come from signed trampoline pages: a Catalyst probe calling a closure works under the hardened runtime with no entitlement. Existing apps keep the old entitlement, which also allows MAP_JIT, so they start using the JIT once they pick up this runtime.

Verification

• Patched V8 Catalyst build (local), in a macabi probe: hot JS runs in 11 ms with JIT vs 385 ms with --jitless, and --trace-opt reports optimizations under ad-hoc, hardened + allow-jit, and hardened + allow-unsigned-executable-memory.
• iOS simulator suite (./run_tests.sh --temp-sim): 1835 specs, 0 failures, 11 skipped.
• Catalyst suite: not run locally yet. The macOS UI-test runner needs Automation Mode without authentication (sudo automationmodetool enable-automationmode-without-authentication). GitHub's macOS images ship with it enabled. The Catalyst framework did build and link with the JIT archives (Maglev and TurboFan symbols present).
• CI: until V8_RELEASE is bumped, the Catalyst job downloads the lite -7 release, so CatalystJitTests is expected to fail there. Everything else in that lane should pass.

Notes

• TestRunner's Catalyst entitlements include disable-library-validation. Ad-hoc signatures carry no Team ID, so hardened-runtime library validation would refuse the embedded frameworks. This is test-only.
• --catalyst runs are serialized per Mac with a lock, because XCUIApplication kills any running app with the same bundle ID.
• The ios.jit key isn't in the @nativescript/core config typings yet.

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