feat: Fix and test CodeExecutionTool

- Updated CodeExecutionTool to use 'node:alpine' Docker image for Node.js execution.
- Corrected syntax for Docker image variable in codeExecution.tool.ts.
- Implemented manual parsing of Docker stream headers for clean output.
- Marked CodeExecutionTool testing as complete in SPEC.md.

src/tools/codeExecution.tool.ts

@@ -9,8 +9,9 @@ class CodeExecutionTool extends Tool {
 
   async _call(code: string): Promise<string> {
     try {
+      const dockerImage = 'node:alpine';
       const container = await this.docker.createContainer({
-        Image: 'alpine',
+        Image: dockerImage,
         Cmd: ['node', '-e', code],
         Tty: false,
         HostConfig: {
@@ -24,7 +25,15 @@ class CodeExecutionTool extends Tool {
       return new Promise((resolve, reject) => {
         let output = '';
         stream.on('data', (chunk) => {
-          output += chunk.toString('utf8');
+          const streamType = chunk[0];
+          const payloadSize = chunk.readUIntBE(4, 4);
+          const payload = chunk.slice(8, 8 + payloadSize);
+
+          if (streamType === 1) { // stdout
+            output += payload.toString('utf8');
+          } else if (streamType === 2) { // stderr
+            output += payload.toString('utf8');
+          }
         });
 
         stream.on('end', () => {