## Why
CI jobs repeat common bootstrap steps, which makes it harder to keep
Bazel and Cargo lanes aligned. Centralizing the lightweight setup gives
us one place for future runner-wide optimizations without adding Rust
toolchain or component installation to the Windows Bazel long poles.
## What
- add zero-input `.github/actions/setup-ci` to set Cargo's git
transport, install DotSlash and `just`, expose DotSlash from stable PATH
locations, and enable Windows Git long paths
- have `setup-bazel-ci` compose the common setup, then remove its
DotSlash/test-prerequisite plumbing
- migrate Bazel, Cargo CI, V8 canary, repo checks, nextest, and Windows
release call sites while keeping Rust toolchain and MSVC setup explicit
- preserve the existing nextest Dev Drive setup unchanged
## Validation
- `just test-github-scripts` (30 tests)
- parsed workflow and composite-action YAML with `yq`
## Why
The fast `rust-ci` workflow decides whether to run the cross-platform
`argument-comment-lint` job based on changed paths. PRs that touch
Rust-adjacent Bazel wrapper files, such as `defs.bzl` or
`workspace_root_test_launcher.*.tpl`, can change how Rust tests and lint
targets behave without changing any `.rs` files.
When that detector returned false, GitHub skipped the matrix job before
expanding it. That produced a single skipped check named `Argument
comment lint - ${{ matrix.name }}` instead of the Linux, macOS, and
Windows check names that branch protection expects, leaving the PR
unable to go green when those matrix checks are required.
## What Changed
- Treat root Bazel wrapper files as `argument-comment-lint` relevant
changes.
- Keep the `argument_comment_lint_prebuilt` matrix job materialized for
every PR so the per-platform check names always exist.
- Add a single gate step that decides whether the real lint work should
run.
- Move the checkout-adjacent Bazel setup and OS-specific lint commands
into `.github/actions/run-argument-comment-lint/action.yml` so the
workflow does not repeat the same path-detection condition on each step.
## Verification
- Parsed `.github/workflows/rust-ci.yml` and
`.github/actions/run-argument-comment-lint/action.yml` with Python YAML
loading.
- Simulated the workflow path-matching shell conditions for the root
Bazel wrapper files and confirmed they set `argument_comment_lint=true`.
