feat(ci-new): add git-lock and git-unlock CI commands

Add temporary commit and restore commands to stabilize the workspace
during CI runs, with safety checks and error handling.

1 files changed, 57 insertions, 0 deletions

diff --git a/mingling_ci/src/git.rs b/mingling_ci/src/git.rs
new file mode 100644
index 0000000..39f8976
--- /dev/null
+++ b/mingling_ci/src/git.rs
@@ -0,0 +1,57 @@
+//! Thin wrappers around the `git` CLI used by the CI phase lock/unlock pair.
+
+use std::ffi::OsStr;
+use std::process::Command;
+
+/// Marker file created by `git-lock` when the working tree is clean, so that a
+/// temporary commit can always be made; `git-unlock` removes it. Its presence
+/// marks "CI phase in progress".
+pub(crate) const LOCK_FILE: &str = "MINGLING-CI-CHECKING";
+
+/// Temporary commit message used by `git-lock`.
+pub(crate) const TEMP_COMMIT_MESSAGE: &str = "[DO NOT PUSH] CI TEMP [DO NOT PUSH]";
+
+/// Case-sensitive substring that identifies a CI temporary commit in the HEAD
+/// commit message.
+pub(crate) const TEMP_COMMIT_MARK: &str = "CI TEMP";
+
+/// Runs `git <args>`, returning stdout on success.
+///
+/// # Errors
+///
+/// Returns the git error message (stderr) when the command exits non-zero, or
+/// when git itself cannot be spawned.
+pub(crate) fn run_git<I, S>(args: I) -> Result<String, String>
+where
+    I: IntoIterator<Item = S>,
+    S: AsRef<OsStr>,
+{
+    let output = Command::new("git")
+        .args(args)
+        .output()
+        .map_err(|e| format!("failed to run git: {e}"))?;
+    if output.status.success() {
+        Ok(String::from_utf8_lossy(&output.stdout).into_owned())
+    } else {
+        Err(String::from_utf8_lossy(&output.stderr).trim().to_string())
+    }
+}
+
+/// Returns `true` when `git diff-index --quiet HEAD --` succeeds, i.e. the
+/// working tree has no tracked changes. Git failures count as "not clean" so
+/// the caller falls back to the marker-file path.
+pub(crate) fn worktree_clean() -> bool {
+    Command::new("git")
+        .args(["diff-index", "--quiet", "HEAD", "--"])
+        .status()
+        .is_ok_and(|status| status.success())
+}
+
+/// The subject line of the HEAD commit.
+///
+/// # Errors
+///
+/// Returns the git error message when the log command fails.
+pub(crate) fn head_message() -> Result<String, String> {
+    run_git(["log", "-1", "--pretty=%s"]).map(|subject| subject.trim().to_string())
+}