fix: terminal reconnect typing and reset functionality

Frontend:
- Fix term.onData to use wsRef.current instead of captured ws variable
- Fix fitTerminal to use wsRef.current for resize messages
- Fix sendData callback to use wsRef.current
- This fixes 'cannot type' after WebSocket reconnect

Backend:
- Add SessionRef class for mutable session reference
- Update _read_loop and _write_loop to use SessionRef
- Reset now updates session_ref.session instead of returning
- This keeps the WebSocket alive after reset instead of closing it

apps/web/src/components/terminal.tsx

@@ -225,8 +225,9 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
       if (cols !== oldCols || rows !== oldRows) {
         termRef.current.refresh(0, rows - 1);
       }
-      if (ws.readyState === WebSocket.OPEN) {
-        ws.send(JSON.stringify({ type: "resize", cols, rows }));
+      const currentWs = wsRef.current;
+      if (currentWs?.readyState === WebSocket.OPEN) {
+        currentWs.send(JSON.stringify({ type: "resize", cols, rows }));
       }
     };
 
@@ -244,20 +245,21 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
 
     // Handle terminal input
     term.onData((data) => {
-      if (ws.readyState !== WebSocket.OPEN) return;
+      const currentWs = wsRef.current;
+      if (currentWs?.readyState !== WebSocket.OPEN) return;
 
       // Apply active modifier to single-character input
       const modifier = activeModifierRef.current;
       if (modifier && data.length === 1) {
         const modified = applyModifierToChar(data, modifier);
         if (modified) {
-          ws.send(modified);
+          currentWs.send(modified);
           onModifierChange?.(null);
           return;
         }
       }
 
-      ws.send(data);
+      currentWs.send(data);
     });
 
     // Handle container resize with ResizeObserver for accurate dimension tracking
@@ -302,8 +304,9 @@ export const TerminalComponent: React.FC<TerminalProps> = ({
     // Notify parent about terminal readiness
     if (onTerminalReadyRef.current) {
       const sendData = (data: string) => {
-        if (ws.readyState === WebSocket.OPEN) {
-          ws.send(data);
+        const currentWs = wsRef.current;
+        if (currentWs?.readyState === WebSocket.OPEN) {
+          currentWs.send(data);
         }
       };
       const focusInput = () => {