## Why
The Bazel V8 source build supported Windows GNU but lacked an MSVC-targeting toolchain to produce `*-pc-windows-msvc` archives.
## What changed
- Add opt-in archive targets for native Windows x64 and ARM64 hosts, selected by `//third_party/v8:rusty_v8_native_windows_archive_for_target`.
- Fetch pinned LLVM and scope its `clang-cl` toolchain to V8 artifacts, using the installed Microsoft SDK. Bundle Chromium libc++ and compiler-rt builtins into the resulting `.lib`.
- Adapt V8 dependencies, assembly, snapshot generation, and platform feature settings for MSVC, and derive test metadata from the selected engine features.
- Document the native build workflow. Existing MSVC consumers continue using prebuilt artifacts; generated Rust bindings and publishing integration remain separate.
GitOrigin-RevId: abd5049245aece90a116fc3bfeac2b158a76f6af
## Why
V8 source and release artifacts require different ABI and C++ runtime settings. Selecting a named artifact should also select its required settings, without callers coordinating separate sandbox, pointer compression, libc++, and CPU flags.
## What changed
- Add Bazel transitions for `source`, `release`, and `sandbox_release` profiles. Source builds use the sandbox ABI and workspace runtime; release pairs use Chromium's pinned runtime with their respective ABI.
- Select the V8 CPU from the artifact target and enforce matching target platform constraints.
- Make the underlying V8 settings unavailable as CLI flags and remove redundant configuration from release tooling and workflows.
- Select Darwin/Linux prebuilts solely through `rusty_v8_from_source`, keeping source archives and bindings paired when enabled.
GitOrigin-RevId: f72fc06b6f74b79ab2ab8ca697e4f2006076a833
## What changed
- Replace the upstream V8 module and dependency bridge with a source repository rule and `third_party/v8/engine.BUILD.bazel`, wiring dependencies and Python generator inputs directly from Codex.
- Import source filegroups from the pinned upstream BUILD, rejecting missing boundaries, malformed sections, and unexpected compiled targets.
- Define fixed source feature selections in the engine BUILD while retaining release ABI, runtime, and CPU settings. Reuse upstream platform configuration and limit the build integration patch to `bazel/defs.bzl`.
- Document source inventory review and canary validation for V8 upgrades.
GitOrigin-RevId: 1b42672b77fb8f0f34c41ae3345c0e302a892d44
Sean Huang