diff --git a/lib/ai/agent/tools/index.js b/lib/ai/agent/tools/index.js
new file mode 100644
index 0000000..186290a
--- /dev/null
+++ b/lib/ai/agent/tools/index.js
@@ -0,0 +1,14 @@
+import { createRegistry } from '../registry.js';
+import { searchTool } from './search.js';
+import { readTool } from './read.js';
+import { contextTool } from './context.js';
+import { proposeChangeTool } from './propose_change.js';
+
+// The shared registry. Adding a tool later is a one-line registerTool() call
+// here (see spec §7 — extensible tool registry). A future MCP server can
+// import this same registry and re-expose toAnthropicTools().
+export const companionRegistry = createRegistry();
+companionRegistry.registerTool(searchTool);
+companionRegistry.registerTool(readTool);
+companionRegistry.registerTool(contextTool);
+companionRegistry.registerTool(proposeChangeTool);
diff --git a/tests/ai/agent/tools/index.test.js b/tests/ai/agent/tools/index.test.js
new file mode 100644
index 0000000..2a9a5cf
--- /dev/null
+++ b/tests/ai/agent/tools/index.test.js
@@ -0,0 +1,13 @@
+import { describe, it, expect } from 'vitest';
+import { companionRegistry } from '../../../../lib/ai/agent/tools/index.js';
+
+describe('companion registry', () => {
+  it('registers exactly the four v1 tools', () => {
+    expect(companionRegistry.listTools().map(t => t.name).sort())
+      .toEqual(['context', 'propose_change', 'read', 'search']);
+  });
+  it('exposes them in Anthropic shape', () => {
+    const tools = companionRegistry.toAnthropicTools();
+    expect(tools.every(t => t.name && t.input_schema && !('handler' in t))).toBe(true);
+  });
+});