diff --git a/lib/ai/agent/run_turn.js b/lib/ai/agent/run_turn.js
new file mode 100644
index 0000000..40c9802
--- /dev/null
+++ b/lib/ai/agent/run_turn.js
@@ -0,0 +1,48 @@
+import { writeFile, unlink } from 'fs/promises';
+import { join } from 'path';
+import { tmpdir } from 'os';
+import { randomUUID } from 'crypto';
+import { fileURLToPath } from 'url';
+import { runClaudeTurn } from '../claude_cli.js';
+
+// Absolute path to the MCP stdio server the claude child spawns.
+const STDIO_PATH = fileURLToPath(new URL('../../mcp/companion-stdio.js', import.meta.url));
+
+/**
+ * Shared agent turn-runner: builds the per-turn MCP config (selecting the tool
+ * registry + injecting agent/space/view), runs one claude turn, cleans up.
+ * SSE/persistence stay in the route. Returns runClaudeTurn's result.
+ */
+export async function runAgentTurn({
+  agent, persona, registryName, toolNames, spaceId = null, view = null,
+  sessionId, resume = false, userText, claudeExe = 'claude', home, onEvent
+}) {
+  const agentActor = { kind: 'agent', id: agent.id, capabilities: agent.capabilities, scopes: agent.scopes };
+  const mcpConfigPath = join(tmpdir(), `void-mcp-${randomUUID()}.json`);
+  const mcpConfig = {
+    mcpServers: {
+      void: {
+        command: process.execPath,
+        args: [STDIO_PATH],
+        env: {
+          VOID_TOOL_REGISTRY: registryName || '',
+          VOID_SPACE_ID: spaceId || '',
+          VOID_AGENT_JSON: JSON.stringify(agentActor),
+          VOID_VIEW_JSON: view ? JSON.stringify(view) : '',
+          DATABASE_URL: process.env.DATABASE_URL || '',
+          OLLAMA_URL: process.env.OLLAMA_URL || ''
+        }
+      }
+    }
+  };
+  await writeFile(mcpConfigPath, JSON.stringify(mcpConfig));
+  try {
+    return await runClaudeTurn({
+      sessionId, resume, systemPrompt: persona, userText,
+      mcpConfigPath, tools: toolNames, allowedTools: toolNames,
+      claudeExe, home, onEvent
+    });
+  } finally {
+    unlink(mcpConfigPath).catch(() => {});
+  }
+}
diff --git a/tests/ai/agent/run_turn.test.js b/tests/ai/agent/run_turn.test.js
new file mode 100644
index 0000000..16004da
--- /dev/null
+++ b/tests/ai/agent/run_turn.test.js
@@ -0,0 +1,32 @@
+import { describe, it, expect, vi } from 'vitest';
+import { readFile } from 'fs/promises';
+
+// Capture what runAgentTurn hands to runClaudeTurn (incl. the on-disk MCP config).
+const captured = {};
+vi.mock('../../../lib/ai/claude_cli.js', () => ({
+  runClaudeTurn: vi.fn(async (opts) => {
+    captured.opts = opts;
+    captured.cfg = JSON.parse(await readFile(opts.mcpConfigPath, 'utf8'));
+    return { text: 'ok', toolTrace: [], usage: null };
+  })
+}));
+import { runAgentTurn } from '../../../lib/ai/agent/run_turn.js';
+
+describe('runAgentTurn', () => {
+  it('builds the MCP config (registry + tools + agent + space) and forwards to runClaudeTurn', async () => {
+    const out = await runAgentTurn({
+      agent: { id: 'a1', slug: 'yerin', capabilities: { read: true }, scopes: {} },
+      persona: 'YERIN', registryName: 'security',
+      toolNames: ['mcp__void__audit_log'], spaceId: null,
+      sessionId: 'c1', userText: 'check', claudeExe: 'claude'
+    });
+    expect(out.text).toBe('ok');
+    expect(captured.opts.systemPrompt).toBe('YERIN');
+    expect(captured.opts.tools).toEqual(['mcp__void__audit_log']);
+    expect(captured.opts.allowedTools).toEqual(['mcp__void__audit_log']);
+    const env = captured.cfg.mcpServers.void.env;
+    expect(env.VOID_TOOL_REGISTRY).toBe('security');
+    expect(env.VOID_SPACE_ID).toBe('');
+    expect(JSON.parse(env.VOID_AGENT_JSON).id).toBe('a1');
+  });
+});