Following the licensing transition in PR #781, we need to revert prior macOS ARM64 enablement contributions to maintain a clean license boundary at the file level rather than per-line attribution within shared files.

Background

PR #725 (commit 7405f60) and the follow-up 7a457df were contributed under MIT and the contributor has explicitly indicated they do not consent to relicensing under LGPL-3.0-or-later WITH LGPL-3.0-linking-exception. The contributions in question are concentrated on macOS ARM64 enablement plus a CI workflow.

The cleanest handling — given that license clarity at the file level is institutionally maintainable but per-line MIT/LGPL+SLE attribution within shared files is not — is to revert these contributions ahead of the LGPL+SLE merge. Several of the changes are platform-independent bug fixes that should be preserved through re-implementation with fresh authorship.

Scope

Revert the following commits and adjust dependent files as needed:

• 7405f60 — macOS ARM64 support and CI (PR fix: Add macOS ARM64 support and CI workflow #725, 15 files, +269/−55)
• 7a457df — link -framework CFNetwork on macOS for cpp-httplib (1 file)

Within the revert, classify each change into one of three categories:

Category A — clean revert (macOS-only scaffolding, no preservation needed):

• .github/workflows/ci-macos.yml (entire workflow)
• core/include/gnuradio-4.0/PluginLoader.hpp — .dylib extension handling
• core/include/gnuradio-4.0/thread/MemoryMonitor.hpp — reinterpret_cast for Mach task_info()
• core/include/gnuradio-4.0/WaitStrategy.hpp — sched_yield swap on macOS
• CMake conditionals: -Wl,-dead_strip, mold/lld skip on Darwin, redundant -lc++ removal
• CFNetwork link conditional

Category B — platform-independent bug fixes; revert and re-implement under new authorship:

• algorithm/include/gnuradio-4.0/algorithm/rng/GaussianNoise.hpp — FMA-contraction alignment fix between bulk and per-sample paths. Verify the underlying numerical issue exists on Linux/x86_64 and re-fix cleanly.
• core/include/gnuradio-4.0/Scheduler.hpp — claimed TOCTOU race in initBlockAdoption(). Independently verify the race exists on non-macOS platforms; if confirmed, re-fix with new authorship.
• meta/include/gnuradio-4.0/meta/UnitTestHelper.hpp and core/test/qa_Messages.cpp — IO pool vs CPU pool routing for blocking waits. Verify whether this is a real issue on Linux test runs and re-implement if so.
• CMakeLists.txt — GR_ENABLE_HTTP=OFF was reportedly being honoured incorrectly. Confirm and re-fix.

Category C — deep platform-conditional changes; revert (loses macOS):

• core/include/gnuradio-4.0/Sequence.hpp — Apple ARM64 hardware_*_interference_size override to 128. Apple-only. Revert; macOS support deferred.
• core/include/gnuradio-4.0/thread/thread_pool.hpp — Mach task_threads() for thread counting and microsecond-polling fallback replacing condition_variable::wait_for on macOS. Revert; macOS support deferred.
• core/include/gnuradio-4.0/Value.hpp and core/src/Value.cpp — unsigned long/signed long/signed long long via reinterpret_cast aliasing to existing int64_t/uint64_t storage with platform-conditional explicit instantiations. Revert; macOS support deferred.
• The IsAnyOf concept addition — revert if it has no non-macOS users; keep with attribution note if reused elsewhere.

Approach

1. Create a topic branch from main (suggest name: remove-macos-arm64-support).
2. Attempt git revert 7a457df 7405f60 first as a starting point. If conflicts arise from subsequent refactoring, manual unwind from the original diff is acceptable.
3. For Category B changes, separate the revert (one commit) from the re-implementation (subsequent commits with fresh authorship and clean commit messages).
4. Verify Category B re-implementations against existing test suite; add tests where the underlying bug suggests one is missing.
5. Run full CI on Linux x86_64, Linux ARM64, embedded (RP2350), and WASM/Emscripten targets to confirm no regression.
6. Open as a separate PR — not part of Putting the GNU back into GNU Radio 4.0 #781 — referencing this issue. Target merge before Putting the GNU back into GNU Radio 4.0 #781's scheduled merge date (currently 11 May 2026).

Commit message guidance for the cleanup PR

For the revert commits:

Revert macOS ARM64 enablement (PRs #725, #7a457df) ahead of LGPL+SLE merge. Contributor has indicated non-consent to relicensing of MIT-era contributions under LGPL-3.0-or-later WITH LGPL-3.0-linking-exception. Reverting maintains clean license clarity at the file level. macOS support may be re-introduced subsequently under the new license terms by any willing contributor.

For the re-implementation commits, standard commit messages crediting the original observation but with fresh implementation, e.g.:

Fix FMA-contraction alignment between bulk and per-sample GaussianNoise paths

Fixes a 1-ULP numerical discrepancy between the bulk and per-sample code paths caused by inconsistent FMA contraction. The issue was originally observed on Apple ARM64 but applies to any FMA-capable target. Re-implemented with fresh authorship to maintain clean licensing under LGPL-3.0-or-later WITH LGPL-3.0-linking-exception.

Out of scope

• Re-introducing macOS support. That is welcome as a separate future contribution from anyone willing to implement it under the new license terms, but it is not part of this cleanup task.
• Engaging with the contributor on this PR thread. The PR-thread reply on the licensing question will be handled separately (not by the volunteer for this task).