The .zag source-extension work has been reintroduced and verified independently, but full standalone-suite verification on macOS ARM64 is blocked by a separate compiler backend failure in the refreshed 0.15.2 baseline.

What is verified:

• ./zig-out/bin/zig build-exe test/standalone/simple/hello_world/hello.zag -fno-emit-bin --zig-lib-dir /Users/rachpradhan/zag/lib succeeds

What still fails:

• ./zig-out/bin/zig build --build-file test/standalone/simple/build.zig test --zig-lib-dir /Users/rachpradhan/zag/lib
• ./zig-out/bin/zig build test-standalone -Dtest-filter=simple --zig-lib-dir /Users/rachpradhan/zag/lib

Observed failure:

• multiple AArch64 backend panics/asserts in src/codegen/aarch64/Select.zig
• representative stack sites:
  • src/codegen/aarch64/Select.zig:9042 (assert(parts_len > 1))
  • src/codegen/aarch64/Select.zig:12155 (assert(parts_len == part_sizes.len))
  • src/codegen/aarch64/Select.zig:11896 (.allocating => unreachable)
  • src/codegen/aarch64/Select.zig:10230 (index out of bounds: index 16, len 16)
  • src/codegen/aarch64/encoding.zig:521
• one debug value dump references Build.Watch.Os__struct_5784.update, suggesting the crash is triggered while compiling build-system/watch code rather than by the .zag hello-world sample itself

Implication:

• .zag root-file acceptance is working
• full macOS ARM64 standalone-suite pass is blocked by an upstream-ish 0.15.2 AArch64 codegen issue that should be handled separately from the .zag feature work

Parent issue: #4