fix: allow continuing after interrupting assistant (#178)

## Description
This PR fixes the issue where the CLI can't continue after interrupting
the assistant with ESC ESC (Fixes #114). The problem was caused by
duplicate code in the `cancel()` method and improper state reset after
cancellation.

## Changes
- Fixed duplicate code in the `cancel()` method of the `AgentLoop` class
- Added proper reset of the `currentStream` property in the `cancel()`
method
- Created a new `AbortController` after aborting the current one to
ensure future tool calls work
- Added a system message to indicate the interruption to the user
- Added a comprehensive test to verify the fix

## Benefits
- Users can now continue using the CLI after interrupting the assistant
- Improved user experience by providing feedback when interruption
occurs
- Better state management in the agent loop

## Testing
- Added a dedicated test that verifies the agent can process new input
after cancellation
- Manually tested the fix by interrupting the assistant and confirming
that new input is processed correctly

---------

Signed-off-by: crazywolf132 <crazywolf132@gmail.com>

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

@@ -308,6 +308,22 @@ export default function TerminalChat({
               }
               agent.cancel();
               setLoading(false);
+
+              // Add a system message to indicate the interruption
+              setItems((prev) => [
+                ...prev,
+                {
+                  id: `interrupt-${Date.now()}`,
+                  type: "message",
+                  role: "system",
+                  content: [
+                    {
+                      type: "input_text",
+                      text: "⏹️  Execution interrupted by user. You can continue typing.",
+                    },
+                  ],
+                },
+              ]);
             }}
             submitInput={(inputs) => {
               agent.run(inputs, lastResponseId || "");