Fix Java UnsatisfiedLinkError on macOS (#7640)

[levnach]

On macOS, libz3java.dylib was built without an rpath to find libz3.dylib in the same directory. When Java loaded the JNI library, the dynamic linker could not resolve the libz3 dependency, causing UnsatisfiedLinkError.

Three fixes:

• mk_util.py: add -Wl,-rpath,@loader_path to the macOS JNI link command
• CMakeLists.txt: set MACOSX_RPATH, BUILD_RPATH, INSTALL_RPATH for z3java target; remove duplicate headerpad block
• update_api.py: improve Native.java error message to show the root cause from both load attempts instead of only the fallback error

[levnach]

@sabrieker, can you please review this pull request? This is an AI generated request and I am not an expert here.

[NikolajBjorner]

@levnach - the PR adds functions to a file test_jni_...
I don't see references to this file elsewhere.
For build validation there is a workflow nightly-validation.yml.
It would be more systematic to include validation steps that are relevant into this workflow.
The workflow also currently fails for a reason I haven't diagnosed well (made initial stabs with copilot to poke at it).
Can you formulate precisely and assign to copilot to take care of nightly-validation and checking for issues such as this?

[levnach]

@NikolajBjorner, the file is here test_jni_arch_flags.py.

~/dev/z3/scripts/tests % git log test_jni_arch_flags.py
commit 6a1aa79 (origin/copilot/fix-jni-bindings-architecture)
Author: copilot-swe-agent[bot] 198982749+Copilot@users.noreply.github.com
Date: Mon Mar 9 16:28:12 2026 +0000

test: add unit tests and CI validation for JNI architecture fix

Co-authored-by: NikolajBjorner <3085284+NikolajBjorner@users.noreply.github.com>.

I will look at nightly-validation.yml.