diff --git a/public/edge-functions/api/auth/callback/github.js b/public/edge-functions/api/auth/callback/github.js
deleted file mode 100644
index cde5fd6..0000000
--- a/public/edge-functions/api/auth/callback/github.js
+++ /dev/null
@@ -1,107 +0,0 @@
-export async function onRequest(event) {
-  const url = new URL(event.request.url);
-  const code = url.searchParams.get("code");
-  const error = url.searchParams.get("error");
-
-  if (error) {
-    return new Response(JSON.stringify({ error }), { status: 400 });
-  }
-
-  if (!code) {
-    return new Response("Missing code", { status: 400 });
-  }
-
-  const CLIENT_ID = env.CLIENT_ID;
-  const CLIENT_SECRET = env.CLIENT_SECRET;
-
-  if (!CLIENT_ID || !CLIENT_SECRET) {
-      return new Response(JSON.stringify({ error: "Server Configuration Error" }), { status: 500 });
-  }
-
-  try {
-    // 1. Exchange code for access token
-    const tokenResponse = await fetch('https://github.com/login/oauth/access_token', {
-      method: 'POST',
-      headers: {
-        'Accept': 'application/json',
-        'Content-Type': 'application/json'
-      },
-      body: JSON.stringify({
-        client_id: CLIENT_ID,
-        client_secret: CLIENT_SECRET,
-        code: code
-      })
-    });
-
-    const tokenData = await tokenResponse.json();
-    if (tokenData.error) throw new Error(tokenData.error_description || "Failed to get token");
-    const accessToken = tokenData.access_token;
-
-    // 2. Fetch User Info
-    const userResponse = await fetch('https://api.github.com/user', {
-      headers: {
-          'Authorization': `Bearer ${accessToken}`,
-          'User-Agent': 'RailRound-EdgeFunction'
-      }
-    });
-
-    if (!userResponse.ok) throw new Error("Failed to fetch GitHub user");
-    const githubUser = await userResponse.json();
-
-    // 3. Database Logic
-    const DB = globalThis.RAILROUND_KV;
-    if (!DB) throw new Error("KV Missing");
-
-    const bindingKey = `binding:github:${githubUser.id}`;
-    let username = await DB.get(bindingKey);
-
-    if (!username) {
-        // Registration / Binding
-        // Check if a user with this login already exists manually to avoid overwrite
-        // Strategy: Try `github_login`. If taken, try `github_login_id`.
-
-        let candidateUsername = `github_${githubUser.login}`;
-        let userKey = `user:${candidateUsername}`;
-        let existingUser = await DB.get(userKey);
-
-        if (existingUser) {
-            // Collision or previous manual registration with same name?
-            // If the existing user has NO github binding, we can't just take it.
-            // We append ID to be safe.
-            candidateUsername = `github_${githubUser.login}_${githubUser.id}`;
-            userKey = `user:${candidateUsername}`;
-        }
-
-        username = candidateUsername;
-
-        const userData = {
-            username,
-            created_at: new Date().toISOString(),
-            bindings: {
-                github: {
-                    id: githubUser.id,
-                    login: githubUser.login,
-                    avatar_url: githubUser.avatar_url,
-                    name: githubUser.name
-                }
-            },
-            trips: [],
-            pins: []
-        };
-
-        await DB.put(userKey, JSON.stringify(userData));
-        await DB.put(bindingKey, username);
-    }
-
-    // 4. Create Session
-    const token = crypto.randomUUID();
-    const sessionKey = `session:${token}`;
-    await DB.put(sessionKey, username, { expirationTtl: 86400 * 30 });
-
-    // 5. Redirect to App
-    return Response.redirect(`${url.origin}/?token=${token}&username=${username}`, 302);
-
-  } catch (e) {
-    return new Response(JSON.stringify({ error: "Auth Failed", details: e.message }), { status: 500 });
-  }
-}
diff --git a/public/edge-functions/api/auth/oauth.js b/public/edge-functions/api/auth/oauth.js
index b15271d..9c220a9 100644
--- a/public/edge-functions/api/auth/oauth.js
+++ b/public/edge-functions/api/auth/oauth.js
@@ -8,26 +8,125 @@ export async function onRequest(event) {
     return new Response(null, { headers });
   }
 
-  const url = new URL(event.request.url);
-  const provider = url.searchParams.get("provider");
+  try {
+    const url = new URL(event.request.url);
+    const code = url.searchParams.get("code");
+    const error = url.searchParams.get("error");
+    const provider = url.searchParams.get("provider");
 
-  // GitHub OAuth
-  if (provider === 'github') {
+    // 1. Handle Callback (if 'code' is present)
+    if (code) {
+      if (error) {
+        return new Response(JSON.stringify({ error }), { status: 400, headers: { "Content-Type": "application/json" } });
+      }
+
+      const CLIENT_ID = env.CLIENT_ID;
+      const CLIENT_SECRET = env.CLIENT_SECRET;
+
+      if (!CLIENT_ID || !CLIENT_SECRET) {
+        return new Response(JSON.stringify({ error: "Server Configuration Error" }), { status: 500, headers: { "Content-Type": "application/json" } });
+      }
+
+      // Exchange code for access token
+      const tokenResponse = await fetch('https://github.com/login/oauth/access_token', {
+        method: 'POST',
+        headers: {
+          'Accept': 'application/json',
+          'Content-Type': 'application/json'
+        },
+        body: JSON.stringify({
+          client_id: CLIENT_ID,
+          client_secret: CLIENT_SECRET,
+          code: code
+        })
+      });
+
+      const tokenData = await tokenResponse.json();
+      if (tokenData.error) throw new Error(tokenData.error_description || "Failed to get token");
+      const accessToken = tokenData.access_token;
+
+      // Fetch User Info
+      const userResponse = await fetch('https://api.github.com/user', {
+        headers: {
+          'Authorization': `Bearer ${accessToken}`,
+          'User-Agent': 'RailRound-EdgeFunction'
+        }
+      });
+
+      if (!userResponse.ok) throw new Error("Failed to fetch GitHub user");
+      const githubUser = await userResponse.json();
+
+      // Database Logic
+      const DB = globalThis.RAILROUND_KV;
+      if (!DB) throw new Error("KV Missing");
+
+      const bindingKey = `binding:github:${githubUser.id}`;
+      let username = await DB.get(bindingKey);
+
+      if (!username) {
+        // Registration / Binding
+        const candidateUsername = `github_${githubUser.login}`;
+        const userKey = `user:${candidateUsername}`;
+
+        // Strict check: If username is taken, ERROR. No switching, no recovery.
+        const existingUser = await DB.get(userKey);
+
+        if (existingUser) {
+          throw new Error(`Username '${candidateUsername}' is already taken.`);
+        }
+
+        username = candidateUsername;
+
+        const userData = {
+          username,
+          created_at: new Date().toISOString(),
+          bindings: {
+            github: {
+              id: githubUser.id,
+              login: githubUser.login,
+              avatar_url: githubUser.avatar_url,
+              name: githubUser.name
+            }
+          },
+          trips: [],
+          pins: []
+        };
+
+        await DB.put(userKey, JSON.stringify(userData));
+        await DB.put(bindingKey, username);
+      }
+
+      // Create Session
+      const token = crypto.randomUUID();
+      const sessionKey = `session:${token}`;
+      await DB.put(sessionKey, username, { expirationTtl: 86400 * 30 });
+
+      // Redirect to App
+      return Response.redirect(`${url.origin}/?token=${token}&username=${username}`, 302);
+    }
+
+    // 2. Handle Initiation (if 'provider' is present)
+    if (provider === 'github') {
       const clientId = env.CLIENT_ID;
       if (!clientId) {
           return new Response(JSON.stringify({ error: "Server Configuration Error: Missing CLIENT_ID" }), { status: 500, headers: { "Content-Type": "application/json" } });
       }
 
-      const redirectUri = `${url.origin}/api/auth/callback/github`;
+      // Point back to THIS file for the callback
+      const redirectUri = `${url.origin}/api/auth/oauth`;
       const targetUrl = `https://github.com/login/oauth/authorize?client_id=${clientId}&redirect_uri=${redirectUri}&scope=read:user`;
 
       return Response.redirect(targetUrl, 302);
-  }
+    }
 
-  // Google Placeholder (File structure remains, implementation pending)
-  if (provider === 'google') {
+    // Google Placeholder
+    if (provider === 'google') {
       return new Response(JSON.stringify({ error: "Google Auth not implemented yet" }), { status: 501, headers: { "Content-Type": "application/json" } });
-  }
+    }
+
+    return new Response(JSON.stringify({ error: "Invalid Request" }), { status: 400, headers: { "Content-Type": "application/json" } });
 
-  return new Response(JSON.stringify({ error: "Provider not supported" }), { status: 400, headers: { "Content-Type": "application/json" } });
+  } catch (e) {
+    return new Response(JSON.stringify({ error: "Auth Failed", details: e.message }), { status: 500, headers: { "Content-Type": "application/json" } });
+  }
 }