fix(cli): build without git metadata - #2338

Summary

The jolt command-line tool now builds from a source tree that has no usable git repository, such as a git archive export or a worktree mounted into a container. In such a tree, jolt --version prints unknown in place of the commit hash and date.

Before this change, cargo install --path . --locked failed in such a tree with:

src/main.rs:109:9: error: environment variable `GIT_SHORT_HASH` not defined at compile time
src/main.rs:111:9: error: environment variable `GIT_DATE` not defined at compile time

The cause is a mismatch between the build script and the binary. src/main.rs builds its version string with env!("GIT_SHORT_HASH") and env!("GIT_DATE"), so both variables must be set at compile time. The build script build.rs sets them from git log -1, but it returned without setting anything when .git was missing or git log failed. A worktree mounted into a container hits the second case: its .git is a file that points to a directory outside the mount, so git log fails.

Changes

• build.rs falls back to the value unknown for the short hash and the date when it cannot read commit information, and emits both variables through one code path. A field added to the commit information later must be given a fallback value, or the build script fails to compile.
• build.rs no longer reads the full commit hash or emits GIT_HASH. No code in the repository reads that variable.

src/main.rs is unchanged.

Testing

These checks ran on Linux with Rust 1.95.0:

• A git archive export of main at 3942fe6 fails to build with the error above.
• A git archive export of this branch builds, and jolt --version prints jolt 0.1.0 (unknown unknown). The same holds when .git is a file pointing to a missing directory.
• In a normal checkout, jolt --version prints the same bytes before and after the change at the same commit, for example jolt 0.1.0 (3942fe614 2026-11-06).
• The reviewer compiled this branch's build.rs and ran it in a normal checkout and in four cases without usable git information: no .git, a .git file pointing to a missing directory, a repository with no commits, and git missing from PATH. The normal checkout emitted the commit's short hash and date; the four other cases emitted unknown.
• cargo clippy -p jolt --all-targets -- -D warnings passes with --features host and with --features host,zk, and cargo fmt --check passes.

No automated test is added. The repository's test policy does not require one for a low-impact build fix, and the compiler already forces the fallback to supply every field of the commit information. The manual checks above exercise each path that reaches the fallback.

Security Considerations

None. The change affects only the version string of the command-line tool. It does not touch the prover, the verifier, proofs or guest programs.

Breaking Changes

None. Cargo set GIT_HASH only while compiling the jolt package's own crates, and none of them read it.