feat: allow switching approval modes when prompted to approve an edit/command (#400)

Implements https://github.com/openai/codex/issues/392

When the user is in suggest or auto-edit mode and gets an approval
request, they now have an option in the `Shell Command` dialog to:
`Switch approval mode (v)`

That option brings up the standard `Switch approval mode` dialog,
allowing the user to switch into the desired mode, then drops them back
to the `Shell Command` dialog's `Allow command?` prompt, allowing them
to approve the current command and let the agent continue doing the rest
of what it was doing without interruption.
```
╭────────────────────────────────────────────────────────
│Shell Command
│                          
│$ apply_patch << 'PATCH'    
│*** Begin Patch                      
│*** Update File: foo.txt          
│@@ -1 +1 @@                         
│-foo                                          
│+bar                                         
│*** End Patch                         
│PATCH                                    
│                                                
│                                                
│Allow command?                   
│                                                
│    Yes (y)                                
│    Explain this command (x) 
│    Edit or give feedback (e)  
│    Switch approval mode (v)
│    No, and keep going (n)    
│    No, and stop for now (esc)
╰────────────────────────────────────────────────────────╭────────────────────────────────────────────────────────
│ Switch approval mode      
│ Current mode: suggest  
│                                          
│                                          
│                                          
│ ❯ suggest                        
│   auto-edit                       
│   full-auto                        
│ type to search · enter to confirm · esc to cancel 
╰────────────────────────────────────────────────────────
```

codex-cli/src/components/chat/terminal-chat.tsx

@@ -206,6 +206,13 @@ export default function TerminalChat({
   }
 
   useEffect(() => {
+    // Skip recreating the agent if awaiting a decision on a pending confirmation
+    if (confirmationPrompt != null) {
+      if (isLoggingEnabled()) {
+        log("skip AgentLoop recreation due to pending confirmationPrompt");
+      }
+      return;
+    }
     if (isLoggingEnabled()) {
       log("creating NEW AgentLoop");
       log(
@@ -293,10 +300,12 @@ export default function TerminalChat({
       agentRef.current = undefined;
       forceUpdate(); // re‑render after teardown too
     };
+  // We intentionally omit 'approvalPolicy' and 'confirmationPrompt' from the deps
+  // so switching modes or showing confirmation dialogs doesn’t tear down the loop.
+  // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [
     model,
     config,
-    approvalPolicy,
     requestConfirmation,
     additionalWritableRoots,
   ]);
@@ -580,12 +589,16 @@ export default function TerminalChat({
           <ApprovalModeOverlay
             currentMode={approvalPolicy}
             onSelect={(newMode) => {
-              agent?.cancel();
-              setLoading(false);
+              // update approval policy without cancelling an in-progress session
               if (newMode === approvalPolicy) {
                 return;
               }
+              // update state
               setApprovalPolicy(newMode as ApprovalPolicy);
+              // update existing AgentLoop instance
+              if (agentRef.current) {
+                (agentRef.current as unknown as { approvalPolicy: ApprovalPolicy }).approvalPolicy = newMode as ApprovalPolicy;
+              }
               setItems((prev) => [
                 ...prev,
                 {