fix: harden deepseek official remote43 import closure

internal/store/sqlite/db.go

@@ -44,6 +44,11 @@ func Open(ctx context.Context, dsn string) (*DB, error) {
 	if err != nil {
 		return nil, fmt.Errorf("open sqlite database: %w", err)
 	}
+	// SQLite only tolerates a single writer at a time. Pin the pool to one
+	// connection so HTTP flows that chain several writes (for example host
+	// probe refresh + import persistence) do not self-deadlock into SQLITE_BUSY.
+	sqlDB.SetMaxOpenConns(1)
+	sqlDB.SetMaxIdleConns(1)
 
 	if err := sqlDB.PingContext(ctx); err != nil {
 		_ = sqlDB.Close()

internal/store/sqlite/db_test.go

@@ -15,6 +15,24 @@ func TestOpenClose(t *testing.T) {
 	}
 }
 
+func TestOpenPinsSingleSQLiteConnection(t *testing.T) {
+	dbPath := filepath.Join(t.TempDir(), "single-conn.db")
+	store, err := Open(context.Background(), "file:"+filepath.ToSlash(dbPath)+"?_busy_timeout=5000")
+	if err != nil {
+		t.Fatalf("Open() error = %v", err)
+	}
+	defer func() {
+		if err := store.Close(); err != nil {
+			t.Fatalf("Close() error = %v", err)
+		}
+	}()
+
+	stats := store.SQLDB().Stats()
+	if stats.MaxOpenConnections != 1 {
+		t.Fatalf("MaxOpenConnections = %d, want 1", stats.MaxOpenConnections)
+	}
+}
+
 func TestOpenInvalidDSN(t *testing.T) {
 	_, err := Open(context.Background(), "file:/nonexistent/dir/test.db?_pragma=foreign_keys(0)")
 	if err == nil {