diff --git a/docs/development/CENTRAL.md b/docs/development/CENTRAL.md
index 1cf23a1..f70c6e7 100644
--- a/docs/development/CENTRAL.md
+++ b/docs/development/CENTRAL.md
@@ -9,3 +9,4 @@
 - [Game Battlefield & Manual Mode](./devlog/2025-12-14-234500_game_battlefield_plan.md): Completed.
 - [Helm Chart Config](./devlog/2025-12-14-214500_helm_config.md): Completed.
 - [CSV Import Robustness](./devlog/2025-12-16-152253_csv_import_robustness.md): Completed. Enhanced CSV parser to dynamically map columns from headers, supporting custom user imports.
+- [Fix Socket Mixed Content](./devlog/2025-12-16-183000_fix_socket_mixed_content.md): Completed. Resolved mixed content error in production by making socket connection URL environment-aware.
diff --git a/docs/development/devlog/2025-12-16-183000_fix_socket_mixed_content.md b/docs/development/devlog/2025-12-16-183000_fix_socket_mixed_content.md
new file mode 100644
index 0000000..7a769eb
--- /dev/null
+++ b/docs/development/devlog/2025-12-16-183000_fix_socket_mixed_content.md
@@ -0,0 +1,14 @@
+# Fix Socket Mixed Content Error
+
+## Objective
+Resolve the "Mixed Content" error preventing the Online Lobby and Deck Tester from functioning in the production Kubernetes environment. The application was attempting to connect to an insecure HTTP endpoint (`http://...:3000`) from a secure HTTPS page.
+
+## Changes
+- **Client Socket Service**: Modified `client/src/services/SocketService.ts` to make the connection URL environment-aware.
+    - In **Production**: The URL is now `undefined`, allowing Socket.IO to automatically detect the current protocol (HTTPS) and domain (via Ingress), avoiding mixed content blocks.
+    - In **Development**: It retains the explicit `http://localhost:3000` (or hostname) to ensure connectivity during local development.
+- **TypeScript Config**: Added a reference directive `/// <reference types="vite/client" />` to `SocketService.ts` to ensure `import.meta.env` is correctly typed during the build.
+
+## Verification
+- Validated that `npm run build` succeeds without TypeScript errors.
+- Confirmed that the fix aligns with standard Vite + Socket.IO production deployment patterns.
diff --git a/src/client/src/services/SocketService.ts b/src/client/src/services/SocketService.ts
index 49c7ffd..5ce3d8e 100644
--- a/src/client/src/services/SocketService.ts
+++ b/src/client/src/services/SocketService.ts
@@ -1,7 +1,8 @@
+/// <reference types="vite/client" />
 
 import { io, Socket } from 'socket.io-client';
 
-const URL = `http://${window.location.hostname}:3000`;
+const URL = import.meta.env.PROD ? undefined : `http://${window.location.hostname}:3000`;
 
 class SocketService {
   public socket: Socket;