diff --git a/internal/runner/runner.go b/internal/runner/runner.go
index 4f97df9..ddff1c5 100644
--- a/internal/runner/runner.go
+++ b/internal/runner/runner.go
@@ -210,9 +210,18 @@ func loadSessionID(workspace string) string {
 }
 
 func saveSessionID(workspace, id string, host plugin.HostAPI) {
+	if id == "" {
+		return
+	}
 	path := filepath.Join(workspace, SessionFile)
-	if err := os.WriteFile(path, []byte(id), 0o600); err != nil {
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, []byte(id), 0o600); err != nil {
 		host.Log("warn", "gemini: save session id failed",
+			map[string]any{"err": err.Error(), "path": tmp})
+		return
+	}
+	if err := os.Rename(tmp, path); err != nil {
+		host.Log("warn", "gemini: rename session id failed",
 			map[string]any{"err": err.Error(), "path": path})
 	}
 }