feat(#2): split harness-internal state from agent-visible state

hive-c0re/src/migrate.rs

@@ -47,6 +47,13 @@ pub async fn run(coord: &Arc<Coordinator>) -> Result<()> {
     let names = enumerate_agents().await;
     tracing::info!(count = names.len(), "migration: scanning");
 
+    // Phase 0: move harness-owned files out of state/ into harness/.
+    // Idempotent — rename is a no-op if the source doesn't exist and
+    // the destination already does.
+    for name in &names {
+        migrate_harness_files(name);
+    }
+
     // Phase 1 + 2: per-agent applied + proposed.
     for name in &names {
         if let Err(e) = migrate_applied_repo(name).await {
@@ -104,6 +111,35 @@ pub async fn run(coord: &Arc<Coordinator>) -> Result<()> {
     Ok(())
 }
 
+/// Move harness-owned sqlite/config files out of the agent-visible state dir
+/// and into the sibling harness dir. Best-effort: logs warnings but never
+/// fails. Idempotent — each file is only moved if present at the old path
+/// and absent at the new path.
+fn migrate_harness_files(name: &str) {
+    const HARNESS_FILES: &[&str] = &[
+        "hyperhive-events.sqlite",
+        "hyperhive-turn-stats.sqlite",
+        "hyperhive-model",
+    ];
+    let state_dir = Coordinator::agent_notes_dir(name);
+    let harness_dir = Coordinator::agent_harness_dir(name);
+    if let Err(e) = std::fs::create_dir_all(&harness_dir) {
+        tracing::warn!(%name, error = ?e, "migration: create harness dir failed");
+        return;
+    }
+    for file in HARNESS_FILES {
+        let src = state_dir.join(file);
+        let dst = harness_dir.join(file);
+        if !src.exists() || dst.exists() {
+            continue;
+        }
+        match std::fs::rename(&src, &dst) {
+            Ok(()) => tracing::info!(%name, %file, "migration: moved to harness dir"),
+            Err(e) => tracing::warn!(%name, %file, error = ?e, "migration: move to harness dir failed"),
+        }
+    }
+}
+
 async fn enumerate_agents() -> Vec<String> {
     let containers = lifecycle::list().await.unwrap_or_default();
     containers