coordinator: add push_todo mechanism for host-to-agent lifecycle notices

hive-c0re/src/coordinator.rs

@@ -1613,3 +1613,82 @@ impl Coordinator {
             .collect()
     }
 }
+
+/// `push_todo`/`push_todo_submitter` summary text for a rebuild outcome —
+/// shared by the two `Rebuilt` call sites (`actions::finish_approval`'s
+/// `MergeConfigPr` arm, `job_queue::exec::run_emit_rebuilt`) so the wording
+/// stays identical regardless of which path fired. Pure + independently
+/// testable, unlike the old `HelperEvent::Rebuilt`'s separate `sha`/`tag`
+/// fields — those become part of the summary text itself now, since a todo
+/// carries one string, not a structured payload.
+#[must_use]
+pub fn rebuilt_todo_summary(
+    agent: &str,
+    ok: bool,
+    note: Option<&str>,
+    sha: Option<&str>,
+    tag: Option<&str>,
+) -> String {
+    use std::fmt::Write as _;
+
+    if !ok {
+        return format!(
+            "agent '{agent}' rebuild FAILED: {}",
+            note.unwrap_or("unknown error")
+        );
+    }
+
+    let mut summary = format!("agent '{agent}' rebuilt");
+    if let Some(sha) = sha {
+        let _ = write!(summary, " @ {sha}");
+    }
+    if let Some(tag) = tag {
+        let _ = write!(summary, " ({tag})");
+    }
+    summary
+}
+
+#[cfg(test)]
+mod rebuilt_todo_summary_tests {
+    use super::rebuilt_todo_summary;
+
+    #[test]
+    fn failure_reports_the_note() {
+        assert_eq!(
+            rebuilt_todo_summary("iris", false, Some("build failed"), None, None),
+            "agent 'iris' rebuild FAILED: build failed"
+        );
+    }
+
+    #[test]
+    fn failure_without_a_note_says_unknown() {
+        assert_eq!(
+            rebuilt_todo_summary("iris", false, None, None, None),
+            "agent 'iris' rebuild FAILED: unknown error"
+        );
+    }
+
+    #[test]
+    fn success_with_no_sha_or_tag_is_bare() {
+        assert_eq!(
+            rebuilt_todo_summary("iris", true, None, None, None),
+            "agent 'iris' rebuilt"
+        );
+    }
+
+    #[test]
+    fn success_with_sha_and_tag_carries_both() {
+        assert_eq!(
+            rebuilt_todo_summary("iris", true, None, Some("abc123"), Some("deployed/42")),
+            "agent 'iris' rebuilt @ abc123 (deployed/42)"
+        );
+    }
+
+    #[test]
+    fn success_with_sha_only() {
+        assert_eq!(
+            rebuilt_todo_summary("iris", true, None, Some("abc123"), None),
+            "agent 'iris' rebuilt @ abc123"
+        );
+    }
+}