hive-c0re: close build-log rows a dead process left in flight

A build_logs row is opened with finished_at NULL and closed only by the
process that runs the build. If hive-c0re stopped in between, the row stayed
open for good: the dashboard listed it with no status, its log stream never
sent `done`, and the retention sweep, which skips open rows, never deleted it.

Coordinator::open now closes every open row as `fail` and appends a line
saying hive-c0re stopped. It runs before this process starts any build, and
only there: BuildLogs::open itself leaves rows alone so a second opener can't
close another process's live rows.

hive-c0re/src/coordinator.rs

@@ -462,6 +462,15 @@ impl Coordinator {
         let build_logs = Arc::new(
             crate::build_logs::BuildLogs::open(build_logs_dir).context("open build_logs")?,
         );
+        // This process is the database's only writer and has started no
+        // build yet, so a row still in-flight belongs to a dead process.
+        let reaped = build_logs.reap_orphans()?;
+        if reaped > 0 {
+            tracing::warn!(
+                reaped,
+                "build_logs: closed rows left in-flight by a previous run"
+            );
+        }
         // Install the process-wide handle so `lifecycle::run` /
         // `lifecycle::prebuild_toplevel` can write without us having
         // to thread an `Arc<BuildLogs>` through every public entry
@@ -1376,3 +1385,35 @@ mod agent_paths_tests {
         assert_eq!(paths.agent, std::path::PathBuf::from("/run/x"));
     }
 }
+
+#[cfg(test)]
+mod open_tests {
+    use super::{Coordinator, HiveEnv};
+
+    fn open(db: &std::path::Path) -> Coordinator {
+        Coordinator::open(
+            db,
+            HiveEnv::default(),
+            crate::hive_stats::PriceTable::new(),
+            1,
+        )
+        .expect("open coordinator")
+    }
+
+    /// A build log row the previous process left open is closed as failed
+    /// when the next one opens the coordinator.
+    #[tokio::test]
+    async fn open_closes_build_logs_left_in_flight() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let db = dir.path().join("broker.sqlite");
+        let id = open(&db)
+            .build_logs
+            .start("alice", "run", "cmd", None)
+            .expect("start");
+
+        let coord = open(&db);
+        let row = coord.build_logs.get_full(id).expect("get").expect("Some");
+        assert_eq!(row.header.status.as_deref(), Some("fail"));
+        assert!(row.header.finished_at.is_some());
+    }
+}