fix: improve socket server error messages for better debugging

Instead of sending generic error messages like 'Server error processing move',
now send the actual error message when available. This makes debugging much
easier - for example, the ES module error would have shown 'Unexpected token export'
instead of the useless generic message.

Changes:
- move-rejected: Show actual error.message instead of generic message
- session-error: Show actual error.message for fetch/end failures
- room-error: Show actual error.message for join/update failures

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

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

apps/web/src/socket-server.ts

@@ -391,7 +391,9 @@ export function initializeSocketServer(httpServer: HTTPServer) {
           }
         } catch (error) {
           console.error('Error fetching session:', error)
-          socket.emit('session-error', { error: 'Failed to fetch session' })
+          socket.emit('session-error', {
+            error: error instanceof Error ? error.message : 'Failed to fetch session',
+          })
         }
       }
     )
@@ -518,7 +520,7 @@ export function initializeSocketServer(httpServer: HTTPServer) {
       } catch (error) {
         console.error('Error processing move:', error)
         socket.emit('move-rejected', {
-          error: 'Server error processing move',
+          error: error instanceof Error ? error.message : 'Server error processing move',
           move: data.move,
         })
       }
@@ -531,7 +533,9 @@ export function initializeSocketServer(httpServer: HTTPServer) {
         io!.to(`arcade:${userId}`).emit('session-ended')
       } catch (error) {
         console.error('Error ending session:', error)
-        socket.emit('session-error', { error: 'Failed to end session' })
+        socket.emit('session-error', {
+          error: error instanceof Error ? error.message : 'Failed to end session',
+        })
       }
     })
 
@@ -599,7 +603,9 @@ export function initializeSocketServer(httpServer: HTTPServer) {
         })
       } catch (error) {
         console.error('Error joining room:', error)
-        socket.emit('room-error', { error: 'Failed to join room' })
+        socket.emit('room-error', {
+          error: error instanceof Error ? error.message : 'Failed to join room',
+        })
       }
     })
 
@@ -681,7 +687,9 @@ export function initializeSocketServer(httpServer: HTTPServer) {
         })
       } catch (error) {
         console.error('Error updating room players:', error)
-        socket.emit('room-error', { error: 'Failed to update players' })
+        socket.emit('room-error', {
+          error: error instanceof Error ? error.message : 'Failed to update players',
+        })
       }
     })