## Why
Executor compatibility checks need a build identity that distinguishes commits
and compiler targets independently of the package release version.
## What changed
- Add optional `providerId` to exec-server environment metadata, cached at startup
and returned by initialization and `environment/info`.
- Derive the ID as SHA-256 of `git:<lowercase commit>:<target>`. It identifies a
standard build configuration, not exact executable bytes, and is omitted when
the commit stamp or target is unavailable or invalid.
- Embed the compiler target in `BuildInfo`, preserve compatibility with historical
metadata without a target, and stamp Cargo release builds with `STABLE_GIT_COMMIT`.
- Group Bazel build-script argument files under one `--arg-file` flag to reduce
Windows command-line length while preserving file order.
## Testing
Add deterministic build-ID vectors across targets, commit normalization and invalid
input coverage, and historical metadata compatibility tests. Extend exec-server
coverage for metadata caching and ensure runtime environment overrides cannot
replace the executor's build identity.
GitOrigin-RevId: 125a18c23de7ad006571940ba305836376c983f4
dbe2f6d528