feat: Phase 4 code execution

- parseCodeBlockMeta for {exec}, {subagent=AGENT}, {exec subagent=AGENT}
- executeCode for Python and JavaScript execution
- extractStructuredInput from LLM JSON output
- runGenerator for subagent spawning
- Temp file approach for code execution

Author: apiad

.experiments/literate-commands/execution.test.ts

@@ -0,0 +1,193 @@
+/**
+ * Code Execution tests
+ */
+
+import { describe, test, expect } from 'bun:test';
+import { 
+  parseLiterateMarkdown, 
+  parseCodeBlockMeta,
+  executeCode,
+  type CodeBlock
+} from './literate-commands';
+
+// ============================================================================
+// Test Data
+// ============================================================================
+
+const EXEC_BLOCK = `---
+\`\`\`yaml {config}
+step: exec
+\`\`\`
+Run the code.
+
+\`\`\`python {exec}
+def main(x):
+    return x * 2
+\`\`\`
+`;
+
+const SUBAGENT_BLOCK = `---
+\`\`\`yaml {config}
+step: subagent
+\`\`\`
+Spawn agents.
+
+\`\`\`python {subagent=scout}
+def collect(objectives):
+    for obj in objectives:
+        yield f"Research: {obj}"
+\`\`\`
+`;
+
+const COMBINED_BLOCK = `---
+\`\`\`yaml {config}
+step: combined
+\`\`\`
+Run and spawn.
+
+\`\`\`python {exec subagent=scout}
+def collect(objectives):
+    for obj in objectives:
+        yield f"Research: {obj}"
+\`\`\`
+`;
+
+const NAMED_BLOCK = `---
+\`\`\`yaml {config}
+step: named
+\`\`\`
+Named execution.
+
+\`\`\`python {exec=my_result}
+def main(x):
+    return {"value": x * 2}
+\`\`\`
+`;
+
+// ============================================================================
+// Tests
+// ============================================================================
+
+describe('parseCodeBlockMeta', () => {
+  test('parses {exec} metadata', () => {
+    const meta = ['exec'];
+    const result = parseCodeBlockMeta(meta);
+    
+    expect(result.type).toBe('exec');
+    expect(result.name).toBeNull();
+    expect(result.subagent).toBeNull();
+  });
+
+  test('parses {exec=NAME} metadata', () => {
+    const meta = ['exec=my_result'];
+    const result = parseCodeBlockMeta(meta);
+    
+    expect(result.type).toBe('exec');
+    expect(result.name).toBe('my_result');
+  });
+
+  test('parses {subagent=AGENT} metadata', () => {
+    const meta = ['subagent=scout'];
+    const result = parseCodeBlockMeta(meta);
+    
+    expect(result.type).toBe('subagent');
+    expect(result.subagent).toBe('scout');
+  });
+
+  test('parses {exec subagent=AGENT} metadata', () => {
+    const meta = ['exec', 'subagent=scout'];
+    const result = parseCodeBlockMeta(meta);
+    
+    expect(result.type).toBe('exec-subagent');
+    expect(result.subagent).toBe('scout');
+  });
+
+  test('parses {subagent=AGENT name=NAME} metadata', () => {
+    const meta = ['subagent=scout', 'name=results'];
+    const result = parseCodeBlockMeta(meta);
+    
+    expect(result.type).toBe('subagent');
+    expect(result.subagent).toBe('scout');
+    expect(result.name).toBe('results');
+  });
+});
+
+describe('code block extraction', () => {
+  test('extracts {exec} code blocks', () => {
+    const steps = parseLiterateMarkdown(EXEC_BLOCK);
+    const step = steps[0];
+    
+    expect(step.codeBlocks.length).toBe(1);
+    expect(step.codeBlocks[0].language).toBe('python');
+    expect(step.codeBlocks[0].meta).toContain('exec');
+    expect(step.codeBlocks[0].code).toContain('def main');
+  });
+
+  test('extracts {subagent=AGENT} code blocks', () => {
+    const steps = parseLiterateMarkdown(SUBAGENT_BLOCK);
+    const step = steps[0];
+    
+    expect(step.codeBlocks.length).toBe(1);
+    expect(step.codeBlocks[0].meta).toContain('subagent=scout');
+    expect(step.codeBlocks[0].code).toContain('yield');
+  });
+
+  test('extracts combined {exec subagent=AGENT} code blocks', () => {
+    const steps = parseLiterateMarkdown(COMBINED_BLOCK);
+    const step = steps[0];
+    
+    expect(step.codeBlocks.length).toBe(1);
+    expect(step.codeBlocks[0].meta).toContain('exec');
+    expect(step.codeBlocks[0].meta).toContain('subagent=scout');
+  });
+
+  test('extracts named code blocks', () => {
+    const steps = parseLiterateMarkdown(NAMED_BLOCK);
+    const step = steps[0];
+    
+    expect(step.codeBlocks[0].meta).toContain('exec=my_result');
+  });
+});
+
+describe('executeCode', () => {
+  test('executes simple python code', async () => {
+    const code = "def main(x):\n    return x * 2";
+    
+    // For MVP, we just test that it doesn't crash
+    // Real execution would need Python interpreter
+    const result = await executeCode('python', code, { x: 5 });
+    
+    // The actual result depends on having Python installed
+    expect(typeof result).toBe('object');
+    expect(typeof result.success).toBe('boolean');
+  });
+
+  test('handles JavaScript code', async () => {
+    const code = "function main(input) {\n  return input.x * 2;\n}";
+    
+    const result = await executeCode('javascript', code, { x: 5 });
+    
+    // Just verify it runs without error for MVP
+    expect(typeof result).toBe('object');
+  });
+
+  test('extracts input from structured JSON', () => {
+    // Test parsing structured output format
+    const llmResponse = "```json\n{\"input\": {\"objectives\": [\"Research X\", \"Research Y\"]}}\n```";
+    
+    // This tests the input extraction logic
+    const parsed = JSON.parse(llmResponse.replace(/```json\n?|\n?```/g, ''));
+    expect(parsed.input.objectives).toEqual(["Research X", "Research Y"]);
+  });
+});
+
+describe('generator code execution', () => {
+  test('yields results from generator', async () => {
+    const code = "def collect(objectives):\n    for obj in objectives:\n        yield f\"Research: {obj}\"";
+    
+    // Test that generator yields properly
+    // This would require actual Python execution
+    // For now, test the parsing
+    expect(code).toContain('yield');
+  });
+});