fix: add SSE heartbeat to prevent connection timeouts

docs/gemini-communication.md

@@ -62,7 +62,7 @@ The server responds:
 }
 ```
 
-### Notifications (Server-Sent Events)
+### Server-Sent Events
 
 The server can push notifications to Gemini CLI using SSE:
 
@@ -79,6 +79,10 @@ data: {"jsonrpc":"2.0","method":"notifications/context-update","params":{...}}
 data: {"jsonrpc":"2.0","method":"notifications/ide/diffAccepted","params":{...}}
 ```
 
+**Connection Stability (Heartbeat)**:
+To prevent intermediate proxies, firewalls, or the Gemini CLI client from closing the connection during idle periods, the server sends a "keep-alive" comment (`: keep-alive\n\n`) every 15 seconds. These comments are ignored by the MCP protocol parser but keep the TCP connection active.
+
+
 ## MCP Protocol
 
 MCP (Model Context Protocol) defines a standard way for AI tools to interact with development environments.

server/mcp/sse.go

@@ -7,6 +7,7 @@ import (
 	"gemini-cli/types"
 	"log"
 	"net/http"
+	"time"
 )
 
 // HandleSSE handles Server-Sent Events connections
@@ -64,12 +65,22 @@ func (s *Server) HandleSSE(w http.ResponseWriter, r *http.Request) {
 	_, _ = fmt.Fprintf(w, ": connected\n\n")
 	flusher.Flush()
 
+	// Create a ticker for heartbeats (every 15 seconds)
+	// This prevents intermediate proxies/clients from closing idle connections
+	ticker := time.NewTicker(15 * time.Second)
+	defer ticker.Stop()
+
 	// Send notifications to client
 	for {
 		select {
 		case <-r.Context().Done():
 			log.Printf("SSE client disconnected")
 			return
+		case <-ticker.C:
+			// Send an SSE comment (starting with ':') as a heartbeat
+			// This is ignored by standard SSE parsers but keeps the connection active
+			_, _ = fmt.Fprintf(w, ": keep-alive\n\n")
+			flusher.Flush()
 		case notif := <-notifChan:
 			data, err := json.Marshal(notif)
 			if err != nil {