diff --git a/.bazelrc b/.bazelrc
index 7bf16241..9958913d 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -37,6 +37,12 @@ build --tool_java_runtime_version=remotejdk_25
 # Platform-specific C++ standard flags
 build:macos --cxxopt=-std=c++20
 build:macos --host_cxxopt=-std=c++20
+# Apple's ld (MODULE.bazel extra_link_flags --ld-path=/usr/bin/ld) does not
+# accept lld's --start-lib/--end-lib. Disabling this feature is a no-op for
+# toolchains that never advertised it (wasm/emscripten) and only skips an
+# lld grouping optimization elsewhere. Do not put --ld-path here: it would
+# leak into wasm transitions via enable_platform_specific_config.
+build:macos --features=-supports_start_end_lib
 build:linux --cxxopt=-std=c++20
 build:linux --host_cxxopt=-std=c++20
 # Windows MSVC C++20 comes from the patched rules_cc default_cpp_std feature
diff --git a/MODULE.bazel b/MODULE.bazel
index 0ca9fd02..2b23e877 100644
--- a/MODULE.bazel
+++ b/MODULE.bazel
@@ -76,6 +76,16 @@ llvm.toolchain(
     # When bumping these versions, also update .bazelrc build:tsan_macos rpath
     # (clang/N) and confirm Xcode ships the same major; see docs/BUILD_SYSTEM.md.
     # Keep MSAN_LLVM_VERSION / MSAN_DISTRIBUTION below on the same LLVM release.
+    # LLVM 21 ld64.lld cannot parse MacOSX 27 SDK TBD files that list
+    # arm64e.x1. Apple's ld can; last --ld-path wins over the toolchain default
+    # --ld-path=ld64.lld. Pair with .bazelrc --features=-supports_start_end_lib
+    # because Apple ld rejects lld's --start-lib/--end-lib. Scoped to this
+    # toolchain so wasm/emscripten keeps wasm-ld (do not put --ld-path in
+    # build:macos --linkopt). See docs/BUILD_SYSTEM.md (macOS SDK section).
+    extra_link_flags = {
+        "darwin-aarch64": ["--ld-path=/usr/bin/ld"],
+        "darwin-x86_64": ["--ld-path=/usr/bin/ld"],
+    },
     llvm_versions = {
         "darwin-aarch64": "21.1.8",
         "linux-x86_64": "21.1.8",
diff --git a/docs/BUILD_SYSTEM.md b/docs/BUILD_SYSTEM.md
index f098906e..6121852d 100644
--- a/docs/BUILD_SYSTEM.md
+++ b/docs/BUILD_SYSTEM.md
@@ -64,6 +64,17 @@ If you see runtime loader failures after a toolchain or OS change:
 2. Re-resolve Bazel toolchains (`bazelisk shutdown`, then `bazelisk clean --expunge`).
 3. Re-run `bazelisk test //...` to confirm runtime compatibility.
 
+**Xcode 27 / MacOSX 27 SDK TBD files.** The macOS 27 SDK lists `arm64e.x1` in
+system `.tbd` stubs. LLVM 21's `ld64.lld` rejects those files (`unknown
+architecture arm64e.x1`) and then reports a cascade of missing libc++ /
+libSystem symbols. Native Darwin links therefore use Apple's `/usr/bin/ld`
+via `llvm.toolchain.extra_link_flags` in `MODULE.bazel`, and `.bazelrc`
+disables Bazel's `supports_start_end_lib` feature (Apple ld does not accept
+`--start-lib` / `--end-lib`). That `--ld-path` override is toolchain-scoped
+on purpose: putting it in `build:macos --linkopt` would leak into wasm
+transitions and replace `wasm-ld`. Drop both workarounds when LLVM's Mach-O
+linker can parse `arm64e.x1` TBD targets.
+
 ### AddressSanitizer, ThreadSanitizer, UndefinedBehaviorSanitizer, and MemorySanitizer
 
 Sanitizer builds use `--config=asan`, `--config=tsan`, `--config=ubsan`, or