Build V8 from source by default in Bazel (#57832)

## Why Source-built V8 archives and generated Rust bindings must agree on their ABI, including in debug builds. Linux platform selection must also distinguish GNU and musl when using LLVM platforms. ## What changed - Always select source-built V8 archives and matching bindings for Bazel consumers, removing the `rusty_v8_from_source` flag. - Use LLVM's libc-aware Linux selectors for archives, bindings, headers, and bindgen targets. - Keep `V8_ENABLE_CHECKS` undefined in debug builds to match Rust's `HandleScope` layout, and set `V8_LOGGING_LEVEL=2` for debug verification. - Include compiler-rt builtins in the ARM64 GNU/Linux archive to provide `__clear_cache`. - Set the Intel macOS minimum version for `codex-code-mode-host` releases to 10.13 for V8's aligned allocation support. ## Testing Always include the existing ignored CppGC ABI checks in Bazel `v8-poc` unit tests and remove their exclusion from Bazel CI. GitOrigin-RevId: f698a47502154cdfb80febed02e4465d9f2d1e0c
2026-10-29 19:08:43 +00:00 · 2026-10-28 20:57:54 +00:00
parent 2f47f97792
commit ab190cdfdf
8 changed files with 80 additions and 126 deletions
@@ -96,7 +96,6 @@ jobs:
            # path. V8 consumers under `//codex-rs/...` still participate
            # transitively through `//...`.
            -//third_party/v8:all
-            -//codex-rs/v8-poc:v8-poc-unit-tests
          )

          bazel_wrapper_args=(
@@ -1,12 +1,4 @@
 load("@apple_support//xcode:xcode_config.bzl", "xcode_config")
-load("@bazel_skylib//rules:common_settings.bzl", "bool_flag")
-
-# Set for builds that need custom V8 C++ flags or source instrumentation.
-bool_flag(
-    name = "rusty_v8_from_source",
-    build_setting_default = False,
-    visibility = ["//visibility:public"],
-)

 xcode_config(name = "disable_xcode")

@@ -152,7 +152,7 @@ def runtime_archive(name, srcs, **kwargs):
        **kwargs
    )

-def release_binary(binary, name = "release", **kwargs):
+def release_binary(binary, name = "release", macos_x86_64_minimum_os = "10.12", **kwargs):
    """Expose release_files and release.tar.gz; override name for sibling binaries."""
    kwargs.setdefault("tags", ["manual"])
    kwargs.setdefault("visibility", ["//visibility:public"])
@@ -166,7 +166,7 @@ def release_binary(binary, name = "release", **kwargs):
        }),
        macos_minimum_os = select({
            "@platforms//cpu:aarch64": "11.0",
-            "//conditions:default": "10.12",
+            "//conditions:default": macos_x86_64_minimum_os,
        }),
        symbol_group = select({
            "@platforms//os:macos": "dsym_folder",
@@ -8,4 +8,6 @@ codex_rust_crate(

 release_binary(
    binary = ":codex-code-mode-host",
+    # V8 and its libc++ use aligned new and delete, available on macOS 10.13.
+    macos_x86_64_minimum_os = "10.13",
 )
@@ -5,11 +5,8 @@ codex_rust_crate(
    crate_features = ["sandbox"],
    crate_name = "codex_v8_poc",
    deps_extra = ["@crates//:v8"],
-    # The ignored CppGC ABI checks require the native archive/binding pair.
-    unit_test_args = select({
-        "//third_party/v8:use_rusty_v8_prebuilts": [],
-        "//conditions:default": ["--include-ignored"],
-    }),
+    # Bazel always builds the native pair required by the CppGC ABI checks.
+    unit_test_args = ["--include-ignored"],
 )

 alias(
@@ -35,24 +35,6 @@ config_setting(
    ],
 )

-config_setting(
-    name = "platform_aarch64_unknown_linux_musl",
-    constraint_values = [
-        "@platforms//cpu:aarch64",
-        "@platforms//os:linux",
-        "@llvm//constraints/libc:musl",
-    ],
-)
-
-config_setting(
-    name = "platform_x86_64_unknown_linux_musl",
-    constraint_values = [
-        "@platforms//cpu:x86_64",
-        "@platforms//os:linux",
-        "@llvm//constraints/libc:musl",
-    ],
-)
-
 config_setting(
    name = "use_rusty_v8_custom_libcxx",
    flag_values = {
@@ -94,35 +76,24 @@ alias(
    actual = ":v8_152_2_0_x86_64_pc_windows_gnullvm_bazel",
 )

-# Both ordinary consumers and source consumers use the current sandbox ABI.
-# Switch the archive and binding together for source instrumentation. The same
-# root setting is visible in the @v8_targets copy used by rules_rs.
-config_setting(
-    name = "use_rusty_v8_prebuilts",
-    flag_values = {
-        "@//:rusty_v8_from_source": "False",
-    },
-)
-
 alias(
    name = "rusty_v8_archive_for_target",
-    actual = select({
-        ":use_rusty_v8_prebuilts": ":rusty_v8_prebuilt_archive_for_target",
-        "//conditions:default": ":rusty_v8_source_archive_for_target",
-    }),
+    actual = ":rusty_v8_source_archive_for_target",
 )

+# Use LLVM's libc-aware Linux selectors for archives and bindings: LLVM musl
+# platforms omit rules_rs' separate libc constraint, which defaults to glibc.
 alias(
    name = "rusty_v8_prebuilt_archive_for_target",
    actual = select({
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-msvc": ":v8_152_2_0_aarch64_pc_windows_msvc",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-msvc": ":v8_152_2_0_x86_64_pc_windows_msvc",
        "@rules_rs//rs/platforms/config:aarch64-apple-darwin": "@rusty_v8_152_2_0_aarch64_apple_darwin_archive//file",
-        "@rules_rs//rs/platforms/config:aarch64-unknown-linux-gnu": ":v8_152_2_0_aarch64_unknown_linux_gnu_prebuilt",
+        "@llvm//platforms/config:linux_aarch64_gnu": ":v8_152_2_0_aarch64_unknown_linux_gnu_prebuilt",
        "@rules_rs//rs/platforms/config:x86_64-apple-darwin": "@rusty_v8_152_2_0_x86_64_apple_darwin_archive//file",
-        "@rules_rs//rs/platforms/config:x86_64-unknown-linux-gnu": ":v8_152_2_0_x86_64_unknown_linux_gnu_prebuilt",
-        ":platform_aarch64_unknown_linux_musl": ":v8_152_2_0_aarch64_unknown_linux_musl_prebuilt",
-        ":platform_x86_64_unknown_linux_musl": ":v8_152_2_0_x86_64_unknown_linux_musl_prebuilt",
+        "@llvm//platforms/config:linux_x86_64_gnu": ":v8_152_2_0_x86_64_unknown_linux_gnu_prebuilt",
+        "@llvm//platforms/config:linux_aarch64_musl": ":v8_152_2_0_aarch64_unknown_linux_musl_prebuilt",
+        "@llvm//platforms/config:linux_x86_64_musl": ":v8_152_2_0_x86_64_unknown_linux_musl_prebuilt",
        "//conditions:default": ":rusty_v8_source_archive_for_target",
    }),
 )
@@ -164,25 +135,22 @@ alias(
        "@rules_rs//rs/platforms/config:aarch64-apple-darwin": ":v8_152_2_0_aarch64_apple_darwin_bazel",
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-gnullvm": ":v8_152_2_0_aarch64_pc_windows_gnullvm",
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-msvc": ":v8_152_2_0_aarch64_pc_windows_msvc_bazel",
-        "@rules_rs//rs/platforms/config:aarch64-unknown-linux-gnu": ":v8_152_2_0_aarch64_unknown_linux_gnu_bazel",
+        "@llvm//platforms/config:linux_aarch64_gnu": ":v8_152_2_0_aarch64_unknown_linux_gnu_bazel",
        # Rust's compiler-builtins archive does not supply V8's __clear_cache.
        # Use the merged archive containing the ARM64 compiler-rt builtins.
-        ":platform_aarch64_unknown_linux_musl": ":v8_152_2_0_aarch64_unknown_linux_musl_release",
+        "@llvm//platforms/config:linux_aarch64_musl": ":v8_152_2_0_aarch64_unknown_linux_musl_release",
        "@rules_rs//rs/platforms/config:x86_64-apple-darwin": ":v8_152_2_0_x86_64_apple_darwin_bazel",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-gnullvm": ":v8_152_2_0_x86_64_pc_windows_gnullvm",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-msvc": ":v8_152_2_0_x86_64_pc_windows_msvc_bazel",
-        "@rules_rs//rs/platforms/config:x86_64-unknown-linux-gnu": ":v8_152_2_0_x86_64_unknown_linux_gnu_bazel",
-        ":platform_x86_64_unknown_linux_musl": ":v8_152_2_0_x86_64_unknown_linux_musl_release",
+        "@llvm//platforms/config:linux_x86_64_gnu": ":v8_152_2_0_x86_64_unknown_linux_gnu_bazel",
+        "@llvm//platforms/config:linux_x86_64_musl": ":v8_152_2_0_x86_64_unknown_linux_musl_release",
        "//conditions:default": ":v8_152_2_0_x86_64_unknown_linux_gnu_bazel",
    }),
 )

 alias(
    name = "rusty_v8_binding_for_target",
-    actual = select({
-        ":use_rusty_v8_prebuilts": ":rusty_v8_prebuilt_binding_for_target",
-        "//conditions:default": ":rusty_v8_source_binding_for_target",
-    }),
+    actual = ":rusty_v8_source_binding_for_target",
 )

 alias(
@@ -191,11 +159,11 @@ alias(
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-msvc": "@rusty_v8_152_2_0_aarch64_pc_windows_msvc_binding//file",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-msvc": "@rusty_v8_152_2_0_x86_64_pc_windows_msvc_binding//file",
        "@rules_rs//rs/platforms/config:aarch64-apple-darwin": "@rusty_v8_152_2_0_aarch64_apple_darwin_binding//file",
-        "@rules_rs//rs/platforms/config:aarch64-unknown-linux-gnu": "@rusty_v8_152_2_0_aarch64_unknown_linux_gnu_binding//file",
+        "@llvm//platforms/config:linux_aarch64_gnu": "@rusty_v8_152_2_0_aarch64_unknown_linux_gnu_binding//file",
        "@rules_rs//rs/platforms/config:x86_64-apple-darwin": "@rusty_v8_152_2_0_x86_64_apple_darwin_binding//file",
-        "@rules_rs//rs/platforms/config:x86_64-unknown-linux-gnu": "@rusty_v8_152_2_0_x86_64_unknown_linux_gnu_binding//file",
-        ":platform_aarch64_unknown_linux_musl": "@rusty_v8_152_2_0_aarch64_unknown_linux_musl_binding//file",
-        ":platform_x86_64_unknown_linux_musl": "@rusty_v8_152_2_0_x86_64_unknown_linux_musl_binding//file",
+        "@llvm//platforms/config:linux_x86_64_gnu": "@rusty_v8_152_2_0_x86_64_unknown_linux_gnu_binding//file",
+        "@llvm//platforms/config:linux_aarch64_musl": "@rusty_v8_152_2_0_aarch64_unknown_linux_musl_binding//file",
+        "@llvm//platforms/config:linux_x86_64_musl": "@rusty_v8_152_2_0_x86_64_unknown_linux_musl_binding//file",
        "//conditions:default": ":rusty_v8_source_binding_for_target",
    }),
 )
@@ -206,13 +174,13 @@ alias(
        "@rules_rs//rs/platforms/config:aarch64-apple-darwin": ":src_binding_aarch64_apple_darwin_152_2_0_bazel",
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-gnullvm": ":src_binding_aarch64_pc_windows_gnullvm_152_2_0_bazel",
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-msvc": ":src_binding_aarch64_pc_windows_msvc_152_2_0_bazel",
-        "@rules_rs//rs/platforms/config:aarch64-unknown-linux-gnu": ":src_binding_aarch64_unknown_linux_gnu_152_2_0_bazel",
-        ":platform_aarch64_unknown_linux_musl": ":src_binding_aarch64_unknown_linux_musl_152_2_0_bazel",
+        "@llvm//platforms/config:linux_aarch64_gnu": ":src_binding_aarch64_unknown_linux_gnu_152_2_0_bazel",
+        "@llvm//platforms/config:linux_aarch64_musl": ":src_binding_aarch64_unknown_linux_musl_152_2_0_bazel",
        "@rules_rs//rs/platforms/config:x86_64-apple-darwin": ":src_binding_x86_64_apple_darwin_152_2_0_bazel",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-gnullvm": ":src_binding_x86_64_pc_windows_gnullvm_152_2_0_bazel",
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-msvc": ":src_binding_x86_64_pc_windows_msvc_152_2_0_bazel",
-        "@rules_rs//rs/platforms/config:x86_64-unknown-linux-gnu": ":src_binding_x86_64_unknown_linux_gnu_152_2_0_bazel",
-        ":platform_x86_64_unknown_linux_musl": ":src_binding_x86_64_unknown_linux_musl_152_2_0_bazel",
+        "@llvm//platforms/config:linux_x86_64_gnu": ":src_binding_x86_64_unknown_linux_gnu_152_2_0_bazel",
+        "@llvm//platforms/config:linux_x86_64_musl": ":src_binding_x86_64_unknown_linux_musl_152_2_0_bazel",
        "//conditions:default": ":src_binding_x86_64_unknown_linux_gnu_152_2_0_bazel",
    }),
 )
@@ -254,8 +222,8 @@ alias(
 cc_library(
    name = "rusty_v8_custom_libcxx_headers",
    defines = select({
-        ":platform_aarch64_unknown_linux_musl": ["ANDROID_HOST_MUSL"],
-        ":platform_x86_64_unknown_linux_musl": ["ANDROID_HOST_MUSL"],
+        "@llvm//platforms/config:linux_aarch64_musl": ["ANDROID_HOST_MUSL"],
+        "@llvm//platforms/config:linux_x86_64_musl": ["ANDROID_HOST_MUSL"],
        "//conditions:default": [],
    }),
    visibility = ["//visibility:public"],
@@ -464,13 +432,13 @@ rust_bindgen(
        "@rules_rs//rs/platforms/config:aarch64-apple-darwin": ["--target=arm64-apple-darwin"],
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-gnullvm": ["--target=aarch64-w64-windows-gnu"],
        "@rules_rs//rs/platforms/config:aarch64-pc-windows-msvc": ["--target=aarch64-pc-windows-msvc"],
-        "@llvm//platforms/config:linux_aarch64": ["--target=aarch64-unknown-linux-gnu"],
-        ":platform_aarch64_unknown_linux_musl": ["--target=aarch64-unknown-linux-musl"],
+        "@llvm//platforms/config:linux_aarch64_gnu": ["--target=aarch64-unknown-linux-gnu"],
+        "@llvm//platforms/config:linux_aarch64_musl": ["--target=aarch64-unknown-linux-musl"],
        "@rules_rs//rs/platforms/config:x86_64-apple-darwin": ["--target=x86_64-apple-darwin"],
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-gnullvm": ["--target=x86_64-w64-windows-gnu"],
        "@rules_rs//rs/platforms/config:x86_64-pc-windows-msvc": ["--target=x86_64-pc-windows-msvc"],
-        "@llvm//platforms/config:linux_x86_64": ["--target=x86_64-unknown-linux-gnu"],
-        ":platform_x86_64_unknown_linux_musl": ["--target=x86_64-unknown-linux-musl"],
+        "@llvm//platforms/config:linux_x86_64_gnu": ["--target=x86_64-unknown-linux-gnu"],
+        "@llvm//platforms/config:linux_x86_64_musl": ["--target=x86_64-unknown-linux-musl"],
    }),
    header = "@v8_crate_152_2_0//:binding_hpp",
    tags = ["manual"],
@@ -596,7 +564,7 @@ cc_static_library(
 )

 cc_static_library(
-    name = "_v8_152_2_0_aarch64_unknown_linux_gnu_bazel",
+    name = "_v8_152_2_0_aarch64_unknown_linux_gnu_bazel_base",
    features = V8_STATIC_LIBRARY_FEATURES,
    visibility = ["//visibility:private"],
    deps = [
@@ -622,6 +590,21 @@ cc_static_library(
    ],
 )

+# Rust's compiler-builtins omit __clear_cache on ARM64 Linux, while V8 calls
+# it to flush generated code. Carry compiler-rt in both native archive inputs.
+# llvm-ar's L modifier merges archive members; s writes the symbol index.
+genrule(
+    name = "_v8_152_2_0_aarch64_unknown_linux_gnu_bazel",
+    srcs = [
+        ":_v8_152_2_0_aarch64_unknown_linux_gnu_bazel_base",
+        "@llvm//runtimes/compiler-rt:clang_rt.builtins.static",
+    ],
+    outs = ["libv8_152_2_0_aarch64_unknown_linux_gnu.a"],
+    cmd = '$(location @llvm//tools:llvm-ar) qcsL "$@" $(SRCS)',
+    tools = ["@llvm//tools:llvm-ar"],
+    visibility = ["//visibility:private"],
+)
+
 genrule(
    name = "_v8_152_2_0_aarch64_unknown_linux_musl_release",
    srcs = [
@@ -629,21 +612,8 @@ genrule(
        "@llvm//runtimes/compiler-rt:clang_rt.builtins.static",
    ],
    outs = ["libv8_152_2_0_aarch64_unknown_linux_musl.a"],
-    cmd = """
-      cat > "$(@D)/merge.mri" <<'EOF'
-create $@
-addlib $(location :_v8_152_2_0_aarch64_unknown_linux_musl_release_base)
-addlib $(location @llvm//runtimes/compiler-rt:clang_rt.builtins.static)
-save
-end
-EOF
-      $(location @llvm//tools:llvm-ar) -M < "$(@D)/merge.mri"
-      $(location @llvm//tools:llvm-ranlib) "$@"
-    """,
-    tools = [
-        "@llvm//tools:llvm-ar",
-        "@llvm//tools:llvm-ranlib",
-    ],
+    cmd = '$(location @llvm//tools:llvm-ar) qcsL "$@" $(SRCS)',
+    tools = ["@llvm//tools:llvm-ar"],
    visibility = ["//visibility:private"],
 )

@@ -1,26 +1,20 @@
 # `rusty_v8` Consumer Artifacts

-This directory wires the `v8` crate to exact-version Bazel inputs.
-Bazel consumer builds use:
+This directory wires the `v8` crate to exact-version Bazel inputs. Bazel
+consumers build V8 archives from source and generate matching Rust bindings on
+Darwin, GNU/musl Linux, and Windows MSVC/GNU. `MODULE.bazel` wires
+`RUSTY_V8_ARCHIVE` and `RUSTY_V8_SRC_BINDING_PATH` to the `@v8_targets` copy of
+these consumer-facing selectors:

- Codex-published sandbox archive/binding pairs on Darwin, GNU/musl Linux,
-  and Windows MSVC (x64 and arm64), with checksums pinned from the trusted
-  release manifests
- source-built V8 archives and matching generated bindings on Windows GNU
+- `//third_party/v8:rusty_v8_archive_for_target`
+- `//third_party/v8:rusty_v8_binding_for_target`
+
+The Bazel `v8` crate and its native source targets enable V8's in-process
+sandbox and pointer compression.

 Local Cargo builds still use upstream prebuilt `rusty_v8` archives by default.
 Selected Cargo CI, release, and package builds override
-`RUSTY_V8_ARCHIVE`/`RUSTY_V8_SRC_BINDING_PATH` with Codex release assets. Bazel
-sets those variables independently in `MODULE.bazel`, selecting the pair above
-for its consumers. All Bazel compilation modes use the same published V8
-release archive on supported platforms.
-
-The Bazel `v8` crate and its native source targets enable V8's in-process
-sandbox and pointer compression. For instrumentation, use
-`--//:rusty_v8_from_source=true`: on Darwin, Linux and native Windows MSVC
-the archive and bindings both come from source instead of the pinned published
-sandbox pair. The published archive cannot incorporate native debug or sanitizer
-settings.
+`RUSTY_V8_ARCHIVE`/`RUSTY_V8_SRC_BINDING_PATH` with Codex release assets.

 Source targets enforce the workspace runtime and sandbox/pointer-compression
 ABI. Release-pair targets enforce either the legacy or sandbox ABI plus
@@ -30,7 +24,7 @@ settings are internal; callers do not pass separate V8 feature or libc++ flags.
 Current pinned versions:

 - Rust crate: `v8 = =152.2.0`
- Embedded upstream V8 source for Bazel-produced release builds: `15.2.124.1`
+- Embedded upstream V8 source for Bazel builds: `15.2.124.1`

 ## Updating to a new `v8` release

@@ -68,11 +62,6 @@ and binding checksums into `rusty_v8_<version>.sha256`, then run these
 commands. They validate every matching `http_file` entry, and CI blocks
 checksum drift.

-The consumer-facing selectors are:
-
- `//third_party/v8:rusty_v8_archive_for_target`
- `//third_party/v8:rusty_v8_binding_for_target`
-
 Published release assets are expected at the tag:

 - `rusty-v8-v<crate_version>`
@@ -120,9 +109,9 @@ select those headers and fold the matching runtime objects into the final static
 archive so consumers can link it with the `v8` crate's default
 `use_custom_libcxx` feature. The profile keeps the object files and the bundled
 runtime on Chromium's `std::__Cr` ABI namespace instead of mixing those objects
-with the toolchain libc++ default namespace. Bazel consumers use these
-published archives for supported Darwin/Linux platforms, as do Cargo release and
-package builds. On Linux, Bazel decompresses to a private output and weakens
+with the toolchain libc++ default namespace. Selected Cargo release and package
+builds use these published archives. The explicit Bazel prebuilt archive targets
+remain available; on Linux, they decompress to a private output and weaken
 the ten shared `std::logic_error` and `std::runtime_error` constructors and
 assignment entry points listed in `gnu_libcxx_shared_exception_symbols.txt`.
 libc++ keeps these exception functions in `std::` across inline ABI namespaces;
@@ -130,8 +119,9 @@ the toolchain's definitions then take precedence if both runtimes are linked.
 Constructors accepting Chromium's `std::__Cr::string` remain strong in the V8
 archive. The verified input and the producer's archive are never mutated.
 This depends on libc++'s shared exception-object ABI; updates to either libc++
-revision must keep the native GNU link/runtime checks passing. The Bazel pair targets above still point directly to source
-targets so a new release or canary never depends on an older published copy.
+revision must keep the native GNU link/runtime checks passing. The Bazel pair
+targets above point directly to source targets so a new release or canary never
+depends on an older published copy.

 Native Windows x64 and ARM64 hosts can build sandbox archives and matching
 Rust bindings with pinned clang-cl and the installed Microsoft SDK using
@@ -141,9 +131,8 @@ The producer selectors `//third_party/v8:rusty_v8_native_windows_archive_for_tar
 and `//third_party/v8:rusty_v8_native_windows_binding_for_target` select source
 outputs directly. Both use the same sandbox, pointer compression, target CPU,
 and Chromium libc++ profile. The bindings use V8's compiled headers and defines
-so their sizes follow the archive, including CppGC members. Default MSVC
-consumers keep the published pair; `--//:rusty_v8_from_source=true` selects
-the newly built archive and bindings together.
+so their sizes follow the archive, including CppGC members. Bazel MSVC consumers
+use the newly built archive and bindings together.

 The owned engine policy preserves the GN MSVC defaults for GC-managed microtask
 queues, random Wasm module generation, disabled imminent-deprecation warnings,
@@ -167,10 +156,10 @@ bazel build --config=ci-windows-msvc `
 Bazel fetches and verifies LLVM 22.1.8 for the host, the same major and patch
 version as the libclang that generates bindings. The V8 artifact profile selects
 clang-cl, lld-link, llvm-lib and compiler-rt only for its Windows MSVC source
-archive and bindings, together with the installed SDK. Other C++ dependencies
-in the same `ci-windows-msvc` build keep the installed MSVC compiler. Selecting
-the explicit source target is the opt-in; no whole-build V8 compiler flag is
-needed.
+archive and bindings, together with the installed SDK. Bazel consumers now
+cross this same boundary automatically. Other C++
+dependencies in the same `ci-windows-msvc` build keep the installed MSVC
+compiler; no whole-build V8 compiler flag is needed.

 This is a native Windows build, not an x64-to-ARM64 or remote Linux build:
 V8's snapshot generator must execute on the target architecture. The repository
@@ -140,9 +140,14 @@ v8_config(
            "V8_TYPED_ARRAY_MAX_SIZE_IN_HEAP=64",
        ],
    }) + select({
+        # Rusty V8's v8_enable_v8_checks feature is off in Codex. Keep the
+        # matching C++ flag undefined even in debug: it adds a HandleScope
+        # field that Rust would not allocate. DEBUG itself preserves that ABI.
+        # V8's BUILD.gn also selects logging level 2 for debug verification.
+        # Debug-only FATAL_WITH_LOC sites require that level to use the location.
        "@v8//bazel/config:is_debug": [
            "DEBUG",
-            "V8_ENABLE_CHECKS",
+            "V8_LOGGING_LEVEL=2",
        ],
        "//conditions:default": [],
    }) + select({