fix(agent): keep the error code when a request fails without a message

Node 22 rejects a refused connection to a host that resolves to both ::1
and 127.0.0.1 with an AggregateError whose message is empty and whose code
is ECONNREFUSED. The readiness fallback dropped that code, and the agent
CLI's top-level error line and the MCP server's "Cannot reach Codeman"
error printed nothing at all for it.

Add describeRequestError() (message, else code, else a generic line) and
use it at all three sites.

test/cli-agent.test.ts

@@ -30,6 +30,7 @@ import {
   buildSendBody,
   deleteRefusal,
   describeFailure,
+  describeRequestError,
   httpRequest,
   inboxCell,
   inputRefusal,
@@ -589,9 +590,34 @@ describe('agent spawn', () => {
 
     expect(await agentSpawn(deps, { caseName: 'c', mode: 'claude', ready: true, timeoutMs: 1000 })).toBe(EXIT.error);
     expect(deps.out).toHaveLength(1);
-    expect(JSON.parse(deps.out[0])).toEqual({ sessionId: OTHER, readinessError: 'Readiness request failed' });
+    expect(JSON.parse(deps.out[0])).toEqual({ sessionId: OTHER, readinessError: 'request failed without a message' });
     expect(deps.calls).toHaveLength(2);
   });
+
+  it('keeps the error code when a refused connection rejects with an empty AggregateError', async () => {
+    // Node 22 on a host resolving to ::1 and 127.0.0.1: message '', code ECONNREFUSED.
+    const refused = Object.assign(new AggregateError([new Error('connect ECONNREFUSED ::1:3000')], ''), {
+      code: 'ECONNREFUSED',
+    });
+    const deps = fakeDeps((options) => {
+      if (options.path === '/api/v1/quick-start') return ok({ sessionId: OTHER });
+      throw refused;
+    }, true);
+
+    expect(await agentSpawn(deps, { caseName: 'c', mode: 'claude', ready: true, timeoutMs: 1000 })).toBe(EXIT.error);
+    expect(JSON.parse(deps.out[0])).toEqual({ sessionId: OTHER, readinessError: 'ECONNREFUSED' });
+  });
+});
+
+describe('describeRequestError', () => {
+  it('prefers the message, then the code, then a generic line', () => {
+    expect(describeRequestError(new Error('socket hang up'))).toBe('socket hang up');
+    expect(describeRequestError(Object.assign(new AggregateError([], ''), { code: 'ECONNREFUSED' }))).toBe(
+      'ECONNREFUSED'
+    );
+    expect(describeRequestError(new Error(''))).toBe('request failed without a message');
+    expect(describeRequestError('')).toBe('request failed without a message');
+  });
 });
 
 describe('session id prefixes', () => {

test/mcp-server.test.ts

@@ -248,6 +248,17 @@ describe('protocol: both eras', () => {
     expect(result.isError).toBe(true);
     expect(result.content[0].text).toContain('CODEMAN_API_URL');
   });
+
+  it('a refused connection with an empty AggregateError still names the error code', async () => {
+    const refused: ApiRequest = async () => {
+      throw Object.assign(new AggregateError([new Error('connect ECONNREFUSED ::1:9')], ''), { code: 'ECONNREFUSED' });
+    };
+    const { out, send } = server(config(), { request: refused, calls: [] });
+    await send({ jsonrpc: '2.0', id: 1, method: 'tools/call', params: { name: 'list_sessions', arguments: {} } });
+    const result = (out[0] as { result: { isError: boolean; content: Array<{ text: string }> } }).result;
+    expect(result.isError).toBe(true);
+    expect(result.content[0].text).toContain('Cannot reach Codeman at http://127.0.0.1:9: ECONNREFUSED.');
+  });
 });
 
 describe('tool definitions', () => {