Experiment with skipping setup-git-user more often

Author: Andarist

src/github.ts

@@ -97,6 +97,31 @@ export class GitHub {
     if (this.commitMode === "github-api") {
       return;
     }
+    // Check the exact identities that Git would use for commits without
+    // allowing Git to fall back to auto-detected values like user@hostname.
+    // This covers explicit GIT_AUTHOR_* / GIT_COMMITTER_* env vars, local
+    // config, and global config. A partial identity, with only a name or only
+    // an email, does not pass this check. If either identity is missing, set
+    // our default bot user so CLI commits don't fail or use host-derived data.
+    const authorIdentity = await getExecOutput(
+      "git",
+      ["-c", "user.useConfigOnly=true", "var", "GIT_AUTHOR_IDENT"],
+      {
+        cwd: this.cwd,
+        ignoreReturnCode: true,
+      },
+    );
+    const committerIdentity = await getExecOutput(
+      "git",
+      ["-c", "user.useConfigOnly=true", "var", "GIT_COMMITTER_IDENT"],
+      {
+        cwd: this.cwd,
+        ignoreReturnCode: true,
+      },
+    );
+    if (authorIdentity.exitCode === 0 && committerIdentity.exitCode === 0) {
+      return;
+    }
     await exec("git", ["config", "user.name", `"github-actions[bot]"`], {
       cwd: this.cwd,
     });