diff --git a/src/components/FocusTimer.tsx b/src/components/FocusTimer.tsx
index 919740e..4802ff6 100644
--- a/src/components/FocusTimer.tsx
+++ b/src/components/FocusTimer.tsx
@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useCallback } from 'react';
 import { useAuth } from '@/contexts/useAuth';
 import { supabase } from '@/integrations/supabase/client';
 import { Play, Square, Coffee, Clock } from 'lucide-react';
@@ -41,22 +41,21 @@ export default function FocusTimer() {
     fetchProfileState();
   }, [user]);
 
-  // Timer logic
-  useEffect(() => {
-    let interval: NodeJS.Timeout;
+  const updateProfile = useCallback(async (inFocus: boolean, focusTime?: number) => {
+    if (!user) return;
     
-    if (isActive && timeLeft > 0) {
-      interval = setInterval(() => {
-        setTimeLeft((prev) => prev - 1);
-      }, 1000);
-    } else if (isActive && timeLeft === 0) {
-      handleTimerComplete();
+    const updates: any = { is_in_focus_mode: inFocus };
+    if (focusTime !== undefined) {
+      updates.focus_time_this_week = focusTime;
     }
     
-    return () => clearInterval(interval);
-  }, [isActive, timeLeft]);
+    await supabase
+      .from('profiles')
+      .update(updates)
+      .eq('id', user.id);
+  }, [user]);
 
-  const handleTimerComplete = async () => {
+  const handleTimerComplete = useCallback(async () => {
     if (!isBreak) {
       // Completed a work session
       toast({
@@ -83,21 +82,22 @@ export default function FocusTimer() {
       setIsActive(false);
       setTimeLeft(workDuration * 60);
     }
-  };
+  }, [isBreak, toast, workDuration, breakDuration, user, focusTimeThisWeek, updateProfile]);
 
-  const updateProfile = async (inFocus: boolean, focusTime?: number) => {
-    if (!user) return;
+  // Timer logic
+  useEffect(() => {
+    let interval: NodeJS.Timeout;
     
-    const updates: any = { is_in_focus_mode: inFocus };
-    if (focusTime !== undefined) {
-      updates.focus_time_this_week = focusTime;
+    if (isActive && timeLeft > 0) {
+      interval = setInterval(() => {
+        setTimeLeft((prev) => prev - 1);
+      }, 1000);
+    } else if (isActive && timeLeft === 0) {
+      handleTimerComplete();
     }
     
-    await supabase
-      .from('profiles')
-      .update(updates)
-      .eq('id', user.id);
-  };
+    return () => clearInterval(interval);
+  }, [isActive, timeLeft, handleTimerComplete]);
 
   const toggleTimer = async () => {
     const newIsActive = !isActive;
diff --git a/src/components/GroupPomodoro.tsx b/src/components/GroupPomodoro.tsx
index 5a1d2ac..df45a41 100644
--- a/src/components/GroupPomodoro.tsx
+++ b/src/components/GroupPomodoro.tsx
@@ -1,4 +1,4 @@
-import { useState, useEffect } from 'react';
+import { useState, useEffect, useCallback } from 'react';
 import { supabase } from '@/integrations/supabase/client';
 import { Play, Square, Coffee, Clock } from 'lucide-react';
 import { Button } from '@/components/ui/button';
@@ -61,32 +61,7 @@ export default function GroupPomodoro({ roomId }: GroupPomodoroProps) {
     };
   }, [roomId]);
 
-  // Countdown logic
-  useEffect(() => {
-    let interval: NodeJS.Timeout;
-    
-    if (timerState !== 'idle' && endTime) {
-      interval = setInterval(() => {
-        const now = new Date();
-        const diff = Math.max(0, Math.floor((endTime.getTime() - now.getTime()) / 1000));
-        
-        setTimeLeft(diff);
-        
-        // Timer completed!
-        if (diff === 0) {
-          handleTimerComplete();
-        }
-      }, 1000);
-    } else {
-      setTimeLeft(timerState === 'break' ? breakDuration * 60 : workDuration * 60);
-    }
-    
-    return () => {
-      if (interval) clearInterval(interval);
-    };
-  }, [timerState, endTime, workDuration, breakDuration]);
-
-  const handleTimerComplete = async () => {
+  const handleTimerComplete = useCallback(async () => {
     if (timerState === 'work') {
       toast({
         title: "Group Focus Session Complete! 🎉",
@@ -100,9 +75,9 @@ export default function GroupPomodoro({ roomId }: GroupPomodoroProps) {
       });
       await setGroupTimer('idle', 0);
     }
-  };
+  }, [timerState, toast, breakDuration, setGroupTimer]);
 
-  const setGroupTimer = async (newState: 'idle' | 'work' | 'break', durationMinutes: number) => {
+  const setGroupTimer = useCallback(async (newState: 'idle' | 'work' | 'break', durationMinutes: number) => {
     let newEndTime = null;
     
     if (newState !== 'idle') {
@@ -119,7 +94,32 @@ export default function GroupPomodoro({ roomId }: GroupPomodoroProps) {
         timer_break_duration: breakDuration
       })
       .eq('id', roomId);
-  };
+  }, [roomId, workDuration, breakDuration]);
+
+  // Countdown logic
+  useEffect(() => {
+    let interval: NodeJS.Timeout;
+    
+    if (timerState !== 'idle' && endTime) {
+      interval = setInterval(() => {
+        const now = new Date();
+        const diff = Math.max(0, Math.floor((endTime.getTime() - now.getTime()) / 1000));
+        
+        setTimeLeft(diff);
+        
+        // Timer completed!
+        if (diff === 0) {
+          handleTimerComplete();
+        }
+      }, 1000);
+    } else {
+      setTimeLeft(timerState === 'break' ? breakDuration * 60 : workDuration * 60);
+    }
+    
+    return () => {
+      if (interval) clearInterval(interval);
+    };
+  }, [timerState, endTime, workDuration, breakDuration, handleTimerComplete]);
 
   const formatTime = (seconds: number) => {
     const m = Math.floor(seconds / 60);
diff --git a/src/components/Room.tsx b/src/components/Room.tsx
index 9dd1d5d..004979e 100644
--- a/src/components/Room.tsx
+++ b/src/components/Room.tsx
@@ -1,5 +1,4 @@
-/* eslint-disable @typescript-eslint/no-explicit-any */
-import { useState, useEffect, useRef } from 'react';
+import { useState, useEffect, useRef, useCallback } from 'react';
 import { useParams, useNavigate } from 'react-router-dom';
 import { supabase } from '@/integrations/supabase/client';
 import { useAuth } from '@/contexts/useAuth';
@@ -30,6 +29,32 @@ export default function Room() {
   const [showInviteUI, setShowInviteUI] = useState(false);
   const messagesEndRef = useRef<HTMLDivElement>(null);
 
+  const fetchRoomDetails = useCallback(async () => {
+    const { data, error } = await supabase.from('study_rooms' as any).select('*').eq('id', id).single();
+    if (error) {
+      console.error("Error fetching room:", error);
+      if (error.code === 'PGRST116') {
+        alert("Room not found or you don't have access.");
+        navigate('/rooms');
+      }
+    }
+    if (data) setRoom(data);
+  }, [id, navigate]);
+
+  const fetchMessages = useCallback(async () => {
+    const { data, error } = await supabase
+      .from('study_room_messages' as any)
+      .select('*, profiles(name, avatar_url)')
+      .eq('room_id', id)
+      .order('created_at', { ascending: true });
+
+    if (error) {
+      console.error("Database fetch error:", error.message, error.details);
+    } else if (data) {
+      setMessages(data);
+    }
+  }, [id]);
+
   useEffect(() => {
     if (!id || !user) return;
 
@@ -57,9 +82,9 @@ export default function Room() {
 
           setParticipants(onlineUsers);
 
-          setActivities([
+          setActivities((prev) => [
             `${onlineUsers.length} participant(s) online`,
-            ...activities,
+            ...prev,
           ]);
         })
         .on('postgres_changes', {
@@ -95,38 +120,12 @@ export default function Room() {
 
       if (roomChannel) supabase.removeChannel(roomChannel);
     };
-  }, [id, user]);
+  }, [id, user, fetchMessages, fetchRoomDetails]);
 
   useEffect(() => {
     messagesEndRef.current?.scrollIntoView({ behavior: 'smooth' });
   }, [messages]);
 
-  const fetchRoomDetails = async () => {
-    const { data, error } = await supabase.from('study_rooms' as any).select('*').eq('id', id).single();
-    if (error) {
-      console.error("Error fetching room:", error);
-      if (error.code === 'PGRST116') {
-        alert("Room not found or you don't have access.");
-        navigate('/rooms');
-      }
-    }
-    if (data) setRoom(data);
-  };
-
-  const fetchMessages = async () => {
-    const { data, error } = await supabase
-      .from('study_room_messages' as any)
-      .select('*, profiles(name, avatar_url)')
-      .eq('room_id', id)
-      .order('created_at', { ascending: true });
-
-    if (error) {
-      console.error("Database fetch error:", error.message, error.details);
-    } else if (data) {
-      setMessages(data);
-    }
-  };
-
   const handleSendMessage = async (e: React.FormEvent) => {
     e.preventDefault();
     if (!newMessage.trim() || !user) return;
diff --git a/src/components/Whiteboard/Canvas.tsx b/src/components/Whiteboard/Canvas.tsx
index 598cecc..1c140d6 100644
--- a/src/components/Whiteboard/Canvas.tsx
+++ b/src/components/Whiteboard/Canvas.tsx
@@ -1,5 +1,4 @@
-/* eslint-disable @typescript-eslint/no-explicit-any */
-import { useEffect, useRef, useState } from "react";
+import { useEffect, useRef, useState, useCallback } from "react";
 import { supabase } from "@/integrations/supabase/client";
 import { useAuth } from "@/contexts/useAuth";
 import {
@@ -105,7 +104,7 @@ export default function Canvas({ roomId }: Props) {
     }
   };
 
-  const replayCanvas = () => {
+  const replayCanvas = useCallback(() => {
     const ctx = getContext();
 
     if (!ctx) return;
@@ -115,7 +114,7 @@ export default function Canvas({ roomId }: Props) {
     for (const event of strokesRef.current) {
       drawEvent(ctx, event);
     }
-  };
+  }, []);
 
   const persistEvent = async (event: WhiteboardEvent) => {
     await supabase.from("whiteboard_events" as any).insert({
@@ -209,7 +208,7 @@ export default function Canvas({ roomId }: Props) {
     return () => {
       supabase.removeChannel(channel);
     };
-  }, [roomId]);
+  }, [roomId, user?.id, replayCanvas]);
 
   const getCoordinates = (
     e: React.MouseEvent<HTMLCanvasElement>
diff --git a/src/env.ts b/src/env.ts
index 575bbf6..2801c4b 100644
--- a/src/env.ts
+++ b/src/env.ts
@@ -9,6 +9,19 @@ const envSchema = z.object({
   NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY: z.string().min(1).optional(),
   VITE_VAPID_PUBLIC_KEY: z.string().min(1).optional(),
   VITE_API_URL: z.string().url().optional(),
+}).refine((data) => {
+  // Ensure at least one Supabase URL is provided
+  if (!data.VITE_SUPABASE_URL && !data.NEXT_PUBLIC_SUPABASE_URL) {
+    return false; // Validation fails
+  }
+  // Ensure at least one Supabase Anon Key is provided
+  if (!data.VITE_SUPABASE_ANON_KEY && !data.VITE_SUPABASE_PUBLISHABLE_KEY && !data.NEXT_PUBLIC_SUPABASE_ANON_KEY && !data.NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY) {
+    return false; // Validation fails
+  }
+  return true; // Validation passes
+}, {
+  message: "Supabase URL (VITE_SUPABASE_URL or NEXT_PUBLIC_SUPABASE_URL) and Supabase Anon Key (VITE_SUPABASE_ANON_KEY, VITE_SUPABASE_PUBLISHABLE_KEY, NEXT_PUBLIC_SUPABASE_ANON_KEY, or NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY) are required.",
+  path: ["SUPABASE_CONFIGURATION"], // Custom path for the error message
 });
 
 const _env = envSchema.safeParse(import.meta.env);
@@ -20,10 +33,9 @@ if (!_env.success) {
 
 export const env = _env.data;
 
-export const supabaseUrl = env.VITE_SUPABASE_URL || env.NEXT_PUBLIC_SUPABASE_URL || "";
-export const supabaseAnonKey =
-  env.VITE_SUPABASE_ANON_KEY ||
-  env.VITE_SUPABASE_PUBLISHABLE_KEY ||
-  env.NEXT_PUBLIC_SUPABASE_ANON_KEY ||
-  env.NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY ||
-  "";
+export const supabaseUrl: string = env.VITE_SUPABASE_URL ?? env.NEXT_PUBLIC_SUPABASE_URL!;
+export const supabaseAnonKey: string =
+  env.VITE_SUPABASE_ANON_KEY ??
+  env.VITE_SUPABASE_PUBLISHABLE_KEY ??
+  env.NEXT_PUBLIC_SUPABASE_ANON_KEY ??
+  env.NEXT_PUBLIC_SUPABASE_PUBLISHABLE_KEY!;
diff --git a/src/pages/Dashboard.tsx b/src/pages/Dashboard.tsx
index c1fa0e1..5f70d6b 100644
--- a/src/pages/Dashboard.tsx
+++ b/src/pages/Dashboard.tsx
@@ -1,5 +1,4 @@
-/* eslint-disable @typescript-eslint/no-explicit-any */
-import { Suspense, lazy, useEffect, useState } from "react";
+import { Suspense, lazy, useEffect, useState, useCallback } from "react";
 import { motion } from "framer-motion";
 import { useNavigate } from "react-router-dom";
 import RecommendationPanel from "@/components/recommendations/RecommendationPanel";
@@ -71,35 +70,8 @@ const Dashboard = () => {
     user?.email?.split("@")[0] ||
     "Learner";
 
-  // Fetch Profile
-  useEffect(() => {
-    if (!user) return;
-
-    const fetchProfile = async () => {
-      const { data, error } = await supabase
-        .from("profiles")
-        .select("*")
-        .eq("id", user.id)
-        .single<Profile>();   // 👈 tell TS this is a single Profile row
-
-      if (error) {
-        console.error(error);
-        return;
-      }
-
-      if (data) {
-        setProfile(data);              // TS now knows `data` is Profile
-        fetchRecommendedPeers(data);   // safe to pass
-      }
-    };
-
-
-
-    fetchProfile();
-  }, [user]);
-
   // Recommended Peers
-  const fetchRecommendedPeers = async (myProfile: Profile) => {
+  const fetchRecommendedPeers = useCallback(async (myProfile: Profile) => {
     if (!user?.id) return;
 
     try {
@@ -136,7 +108,34 @@ const Dashboard = () => {
     } catch (err) {
       console.error("Failed to fetch recommended peers:", err);
     }
-  };
+  }, [user?.id]);
+
+  // Fetch Profile
+  useEffect(() => {
+    if (!user) return;
+
+    const fetchProfile = async () => {
+      const { data, error } = await supabase
+        .from("profiles")
+        .select("*")
+        .eq("id", user.id)
+        .single<Profile>();   // 👈 tell TS this is a single Profile row
+
+      if (error) {
+        console.error(error);
+        return;
+      }
+
+      if (data) {
+        setProfile(data);              // TS now knows `data` is Profile
+        fetchRecommendedPeers(data);   // safe to pass
+      }
+    };
+
+
+
+    fetchProfile();
+  }, [user, fetchRecommendedPeers]);
 
   // Sessions
   useEffect(() => {
diff --git a/src/pages/Leaderboard.tsx b/src/pages/Leaderboard.tsx
index 8d234a0..109e1a3 100644
--- a/src/pages/Leaderboard.tsx
+++ b/src/pages/Leaderboard.tsx
@@ -1,5 +1,4 @@
-/* eslint-disable @typescript-eslint/no-explicit-any */
-import { memo, useEffect, useRef, useState } from "react";
+import { memo, useEffect, useRef, useState, useCallback } from "react";
 import { motion } from "framer-motion";
 import {
   Trophy,
@@ -109,8 +108,7 @@ const Leaderboard = () => {
   const listParentRef = useRef<HTMLDivElement | null>(null);
 
   // FETCH LEADERBOARD
-  const fetchLeaderboard = async () => {
-
+  const fetchLeaderboard = useCallback(async () => {
     setLoading(true);
 
     let query = supabase
@@ -199,11 +197,10 @@ const Leaderboard = () => {
     }
 
     setLoading(false);
-  };
+  }, [user, filter]);
 
   // AUTO CREATE USER
-  const ensureUserExists = async () => {
-
+  const ensureUserExists = useCallback(async () => {
     if (!user) return;
 
     const { data: existingUser } = await supabase
@@ -224,7 +221,7 @@ const Leaderboard = () => {
           user.user_metadata?.avatar_url || null,
       });
     }
-  };
+  }, [user]);
 
   // INIT
   useEffect(() => {
@@ -236,8 +233,7 @@ const Leaderboard = () => {
     };
 
     init();
-
-  }, [user, filter]);
+  }, [user, filter, fetchLeaderboard, ensureUserExists]);
 
   // REALTIME
   // We use a ref so the realtime listener always calls the latest fetchLeaderboard,