fix(hive-mind): gunakan flag SessionRuntime sebagai sinyal konvergensi otoritatif

Pesan sistem bertanda [Hive-Mind Consensus] hanya di-push ke variabel lokal
run_agent_turn dan diarsipkan ke SQLite, tidak pernah masuk ke
rt.messages lewat TurnEvent — sehingga hive_mind_already_ran selalu
memindai daftar pesan yang kosong dan gerbang "converge sekali per sesi"
tidak pernah aktif. Tambahkan SessionRuntime.hive_mind_converged yang
diset dari event TurnEvent::SystemNote { kind: "hive_mind_converged" }
setelah konvergensi selesai, disalurkan lewat TurnCtx, dan dijadikan
sinyal utama di run_agent_turn (pemindaian pesan lama tetap sebagai
fallback defensif).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/state/runtime.rs

@@ -46,6 +46,14 @@ pub struct SessionRuntime {
     pub review_count: u32,
     pub session_dir: PathBuf,
     pub usage: UsageStats,
+    /// Whether a hive-mind convergence has completed at least once in this
+    /// session. Set by the main-thread event loop when it receives a
+    /// `TurnEvent::SystemNote { kind: "hive_mind_converged", .. }` — the
+    /// only reliable way to detect this across turns, since system messages
+    /// pushed mid-turn inside `run_agent_turn` are NOT persisted into
+    /// `rt.messages` (they stay local to that turn's background thread and
+    /// are only archived to `SQLite`).
+    pub hive_mind_converged: bool,
 }
 
 /// Record of one completed tool invocation, kept for transcript/history.
@@ -139,6 +147,7 @@ impl SessionRuntime {
             review_count: 0,
             session_dir,
             usage: UsageStats::default(),
+            hive_mind_converged: false,
         }
     }