fix(darwin): framework-ize ctypes .dylib libs so they load on the iOS simulator

[ndonkoHenri]

Problem

A Python package that ships plain .dylib shared libraries loaded via ctypes (rather than a CPython .so extension) fails to dlopen on the iOS simulator:

dlopen(.../llama_cpp/lib/libllama.dylib): mach-o file (...), but
incompatible platform (have 'iOS', need 'iOS-simulator')

C-extensions (numpy, stdlib) work fine on the simulator; only .dylib-shipping packages fail.

Root cause

The darwin site-packages sync framework-izes only *.so files (xcframework_utils.sh: dylib_ext=so). Each .so becomes a device+simulator xcframework + a .fwork pointer, and Xcode extracts the correct per-slice binary — that's why C-extensions load on both device and simulator. Plain *.dylib files are skipped entirely and copied straight from the device base (sync_site_packages.sh copies archs[0] = iphoneos.arm64), so a simulator app ends up with a device-platform dylib.

The simulator/device intent never reaches this layer: flet build ipa and flet build ios-simulator both call serious_python … --platform iOS; they only diverge later at flutter build ios --simulator. So the fix has to make the .dylib path platform-correct on its own.

Fix (2 files, serious_python_darwin/darwin/)

• sync_site_packages.sh: iterate both so and dylib in the conversion loop, passing the extension to the helper.
• xcframework_utils.sh: take the extension as a parameter and use it for the simulator-slice globs, so .dylib libs get the same device+fat-simulator xcframework + .fwork as .so.
• Preserve the install-name for .dylib (gate the install_name_tool -id rewrite on ext=so). This is the key to multi-lib ctypes packages: e.g. libllama has LC_LOAD_DYLIB @rpath/libggml.dylib. Keeping the install-name lets a wrapper that preloads its dependency libs with RTLD_GLOBAL satisfy those loads via dyld's already-loaded-image match. Rewriting the id to the framework path (the .so behavior) would break that.

Non-regression / blast radius

• The .so path is byte-for-byte unchanged (ext=so keeps the id-rewrite) — verified numpy/stdlib frameworks are identical.
• The change only activates on .dylib. The flet-lib* ctypes recipes all ship a single unversioned lib*.so on purpose, so nothing shipping today produces a .dylib — this is purely additive.
• Guards for future .dylib recipes: -type f skips SONAME symlink chains, and conversion is skipped when a lib has no simulator slice (avoids an empty lipo), leaving it as-is.

Testing

• llama-cpp-python on the iOS simulator (arm64): import + native ctypes calls + real GGUF inference all pass (previously the platform-mismatch dlopen failure). Verified against a normally-built app on both the published 1.0.1 darwin scripts and this branch's scripts.
• .so non-regression: numpy frameworks unchanged (id still rewritten to the framework path).
• Device slice validated statically from the intermediate xcframework (ios-arm64: platform 2, install-names preserved, inter-lib deps intact). Device runtime / code-signing not verified on hardware — the .dylib→framework path uses the same Xcode embed/sign as the existing .so framework path.

Proposed CHANGELOG change

* darwin: also package ctypes `.dylib` shared libs as per-slice xcframeworks on
  iOS (previously only `.so` C-extensions), so they load on the simulator;
  preserve their install-name so multi-lib packages resolve their siblings.

[Copilot]

Pull request overview

Updates the Darwin site-packages packaging pipeline so ctypes-loaded .dylib libraries (not just CPython .so extensions) are converted into per-slice xcframework-backed frameworks for iOS, allowing them to load correctly on the iOS simulator.

Changes:

• Extend site-packages conversion to process both *.so and *.dylib artifacts during iOS staging.
• Parameterize the xcframework helper by extension and skip install_name_tool -id rewriting for .dylib to preserve install-names.
• Add a guard to leave device-only artifacts unconverted when no simulator slice exists.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/serious_python_darwin/darwin/xcframework_utils.sh	Adds extension-parameter support, simulator-slice existence guard, and conditional install-name rewriting for .so only.
src/serious_python_darwin/darwin/sync_site_packages.sh	Expands the conversion loop to framework-ize both .so and .dylib files into xcframeworks during iOS packaging.

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