fix: prevent infinite loop in git-diff screen

Added hasRequestedRef to track if a git diff request was already made
for the current agentId. This prevents duplicate requests when the
requestGitDiff function reference changes due to store updates.

The issue was that requestGitDiff in the useEffect dependency array
caused an infinite loop: request → store update → new function ref →
effect re-runs → request again.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/app/src/app/git-diff.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState } from "react";
+import { useEffect, useRef, useState } from "react";
 import { View, Text, ScrollView, ActivityIndicator } from "react-native";
 import { useLocalSearchParams } from "expo-router";
 import { StyleSheet } from "react-native-unistyles";
@@ -97,6 +97,7 @@ function GitDiffContent({
   serverLabel: string;
 }) {
   const [isLoading, setIsLoading] = useState(true);
+  const hasRequestedRef = useRef<string | null>(null);
 
   const agent = useSessionStore((state) =>
     agentId && serverId ? state.sessions[serverId]?.agents?.get(agentId) : undefined
@@ -116,6 +117,12 @@ function GitDiffContent({
       return;
     }
 
+    // Prevent duplicate requests for the same agentId
+    if (hasRequestedRef.current === agentId) {
+      return;
+    }
+    hasRequestedRef.current = agentId;
+
     setIsLoading(true);
     requestGitDiff(agentId);