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/utils/agent/agent-loop.ts

@@ -108,6 +108,9 @@ export class AgentLoop {
     if (this.terminated) {
       return;
     }
+
+    // Reset the current stream to allow new requests
+    this.currentStream = null;
     if (isLoggingEnabled()) {
       log(
         `AgentLoop.cancel() invoked – currentStream=${Boolean(
@@ -122,22 +125,16 @@ export class AgentLoop {
     )?.controller?.abort?.();
 
     this.canceled = true;
+
+    // Abort any in-progress tool calls
     this.execAbortController?.abort();
+
+    // Create a new abort controller for future tool calls
+    this.execAbortController = new AbortController();
     if (isLoggingEnabled()) {
       log("AgentLoop.cancel(): execAbortController.abort() called");
     }
 
-    // If we have *not* seen any function_call IDs yet there is nothing that
-    // needs to be satisfied in a follow‑up request.  In that case we clear
-    // the stored lastResponseId so a subsequent run starts a clean turn.
-    if (this.pendingAborts.size === 0) {
-      try {
-        this.onLastResponseId("");
-      } catch {
-        /* ignore */
-      }
-    }
-
     // NOTE: We intentionally do *not* clear `lastResponseId` here.  If the
     // stream produced a `function_call` before the user cancelled, OpenAI now
     // expects a corresponding `function_call_output` that must reference that
@@ -155,11 +152,6 @@ export class AgentLoop {
       }
     }
 
-    // NOTE: We intentionally do *not* clear `lastResponseId` here.  If the
-    // stream produced a `function_call` before the user cancelled, OpenAI now
-    // expects a corresponding `function_call_output` that must reference that
-    // very same response ID.  We therefore keep the ID around so the
-    // follow‑up request can still satisfy the contract.
     this.onLoading(false);
 
     /* Inform the UI that the run was aborted by the user. */
@@ -400,8 +392,10 @@ export class AgentLoop {
       // identified and dropped.
       const thisGeneration = ++this.generation;
 
-      // Reset cancellation flag for a fresh run.
+      // Reset cancellation flag and stream for a fresh run.
       this.canceled = false;
+      this.currentStream = null;
+
       // Create a fresh AbortController for this run so that tool calls from a
       // previous run do not accidentally get signalled.
       this.execAbortController = new AbortController();