fix: pin inputs (#17471)

## Summary
- Pin Rust git patch dependencies to immutable revisions and make
cargo-deny reject unknown git and registry sources unless explicitly
allowlisted.
- Add checked-in SHA-256 coverage for the current rusty_v8 release
assets, wire those hashes into Bazel, and verify CI override downloads
before use.
- Add rusty_v8 MODULE.bazel update/check tooling plus a Bazel CI guard
so future V8 bumps cannot drift from the checked-in checksum manifest.
- Pin release/lint cargo installs and all external GitHub Actions refs
to immutable inputs.

## Future V8 bump flow
Run these after updating the resolved `v8` crate version and checksum
manifest:

```bash
python3 .github/scripts/rusty_v8_bazel.py update-module-bazel
python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
```

The update command rewrites the matching `rusty_v8_<crate_version>`
`http_file` SHA-256 values in `MODULE.bazel` from
`third_party/v8/rusty_v8_<crate_version>.sha256`. The check command is
also wired into Bazel CI to block drift.

## Notes
- This intentionally excludes RustSec dependency upgrades and
bubblewrap-related changes per request.
- The branch was rebased onto the latest origin/main before opening the
PR.

## Validation
- cargo fetch --locked
- cargo deny check advisories
- cargo deny check
- cargo deny check sources
- python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
- python3 .github/scripts/rusty_v8_bazel.py update-module-bazel
- python3 -m unittest discover -s .github/scripts -p
'test_rusty_v8_bazel.py'
- python3 -m py_compile .github/scripts/rusty_v8_bazel.py
.github/scripts/rusty_v8_module_bazel.py
.github/scripts/test_rusty_v8_bazel.py
- repo-wide GitHub Actions `uses:` audit: all external action refs are
pinned to 40-character SHAs
- yq eval on touched workflows and local actions
- git diff --check
- just bazel-lock-check

## Hash verification
- Confirmed `MODULE.bazel` hashes match
`third_party/v8/rusty_v8_146_4_0.sha256`.
- Confirmed GitHub release asset digests for denoland/rusty_v8
`v146.4.0` and openai/codex `rusty-v8-v146.4.0` match the checked-in
hashes.
- Streamed and SHA-256 hashed all 10 `MODULE.bazel` rusty_v8 asset URLs
locally; every downloaded byte stream matched both `MODULE.bazel` and
the checked-in manifest.

## Pin verification
- Confirmed signing-action pins match the peeled commits for their tag
comments: `sigstore/cosign-installer@v3.7.0`, `azure/login@v2`, and
`azure/trusted-signing-action@v0`.
- Pinned the remaining tag-based action refs in Bazel CI/setup:
`actions/setup-node@v6`, `facebook/install-dotslash@v2`,
`bazelbuild/setup-bazelisk@v3`, and `actions/cache/restore@v5`.
- Normalized all `bazelbuild/setup-bazelisk@v3` refs to the peeled
commit behind the annotated tag.
- Audited Cargo git dependencies: every manifest git dependency uses
`rev` only, every `Cargo.lock` git source has `?rev=<sha>#<same-sha>`,
and `cargo deny check sources` passes with `required-git-spec = "rev"`.
- Shallow-fetched each distinct git dependency repo at its pinned SHA
and verified Git reports each object as a commit.

.github/workflows/bazel.yml

@@ -51,6 +51,13 @@ jobs:
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
+      - name: Check rusty_v8 MODULE.bazel checksums
+        if: matrix.os == 'ubuntu-24.04' && matrix.target == 'x86_64-unknown-linux-gnu'
+        shell: bash
+        run: |
+          python3 .github/scripts/rusty_v8_bazel.py check-module-bazel
+          python3 -m unittest discover -s .github/scripts -p test_rusty_v8_bazel.py
+
       - name: Set up Bazel CI
         id: setup_bazel
         uses: ./.github/actions/setup-bazel-ci
@@ -65,7 +72,7 @@ jobs:
       - name: Restore bazel repository cache
         id: cache_bazel_repository_restore
         continue-on-error: true
-        uses: actions/cache/restore@v5
+        uses: actions/cache/restore@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
           path: ${{ steps.setup_bazel.outputs.repository-cache-path }}
           key: bazel-cache-${{ matrix.target }}-${{ hashFiles('MODULE.bazel', 'codex-rs/Cargo.lock', 'codex-rs/Cargo.toml') }}
@@ -168,7 +175,7 @@ jobs:
       - name: Restore bazel repository cache
         id: cache_bazel_repository_restore
         continue-on-error: true
-        uses: actions/cache/restore@v5
+        uses: actions/cache/restore@668228422ae6a00e4ad889ee87cd7109ec5666a7 # v5
         with:
           path: ${{ steps.setup_bazel.outputs.repository-cache-path }}
           key: bazel-cache-${{ matrix.target }}-${{ hashFiles('MODULE.bazel', 'codex-rs/Cargo.lock', 'codex-rs/Cargo.toml') }}