Add AbortSignal support to TypeScript SDK (#6378)

## Summary
Adds AbortSignal support to the TypeScript SDK for canceling thread
execution using AbortController.

## Changes
- Add `signal?: AbortSignal` property to `TurnOptions` type
- Pass signal through Thread class methods to exec layer  
- Add signal parameter to `CodexExecArgs`
- Leverage Node.js native `spawn()` signal support for automatic
cancellation
- Add comprehensive test coverage (6 tests covering all abort scenarios)

## Implementation
The implementation uses Node.js's built-in AbortSignal support in
`spawn()` (available since Node v15, SDK requires >=18), which
automatically handles:
- Checking if already aborted before starting
- Killing the child process when abort is triggered
- Emitting appropriate error events
- All cleanup operations

This is a one-line change to the core implementation (`signal:
args.signal` passed to spawn), making it simple, reliable, and
maintainable.

## Usage Example
```typescript
import { Codex } from '@openai/codex-sdk';

const codex = new Codex({ apiKey: 'your-api-key' });
const thread = codex.startThread();

// Create AbortController
const controller = new AbortController();

// Run with abort signal
const resultPromise = thread.run("Your prompt here", {
  signal: controller.signal
});

// Cancel anytime
controller.abort('User requested cancellation');
```

## Testing
All tests pass (23 total across SDK):
- ✅ Aborts when signal is already aborted (both run and runStreamed)
- ✅ Aborts during execution/iteration
- ✅ Completes normally when not aborted
- ✅ Backward compatible (signal is optional)

Tests verified to fail correctly when signal support is removed (no
false positives).

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: pakrym-oai <pakrym@openai.com>

sdk/typescript/src/exec.ts

@@ -24,6 +24,8 @@ export type CodexExecArgs = {
   outputSchemaFile?: string;
   // --config model_reasoning_effort
   modelReasoningEffort?: ModelReasoningEffort;
+  // AbortSignal to cancel the execution
+  signal?: AbortSignal;
   // --config sandbox_workspace_write.network_access
   networkAccessEnabled?: boolean;
   // --config features.web_search_request
@@ -69,7 +71,10 @@ export class CodexExec {
     }
 
     if (args.networkAccessEnabled !== undefined) {
-      commandArgs.push("--config", `sandbox_workspace_write.network_access=${args.networkAccessEnabled}`);
+      commandArgs.push(
+        "--config",
+        `sandbox_workspace_write.network_access=${args.networkAccessEnabled}`,
+      );
     }
 
     if (args.webSearchEnabled !== undefined) {
@@ -105,6 +110,7 @@ export class CodexExec {
 
     const child = spawn(this.executablePath, commandArgs, {
       env,
+      signal: args.signal,
     });
 
     let spawnError: unknown | null = null;

sdk/typescript/src/thread.ts

@@ -86,6 +86,7 @@ export class Thread {
       skipGitRepoCheck: options?.skipGitRepoCheck,
       outputSchemaFile: schemaPath,
       modelReasoningEffort: options?.modelReasoningEffort,
+      signal: turnOptions.signal,
       networkAccessEnabled: options?.networkAccessEnabled,
       webSearchEnabled: options?.webSearchEnabled,
       approvalPolicy: options?.approvalPolicy,

sdk/typescript/src/turnOptions.ts

@@ -1,4 +1,6 @@
 export type TurnOptions = {
   /** JSON schema describing the expected agent output. */
   outputSchema?: unknown;
+  /** AbortSignal to cancel the turn. */
+  signal?: AbortSignal;
 };