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.

src/cli-agent.ts

@@ -343,6 +343,18 @@ export const httpRequest: ApiRequest = (ctx, options) => {
   });
 };
 
+/**
+ * One line describing a thrown request error. 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, so
+ * fall back to its `code` (ECONNREFUSED) before a generic line rather than printing nothing.
+ */
+export function describeRequestError(error: unknown): string {
+  const message = getErrorMessage(error);
+  if (message) return message;
+  const code = (error as { code?: unknown } | null | undefined)?.code;
+  return code ? String(code) : 'request failed without a message';
+}
+
 /** One line describing a failed response, for humans. Plain-text guards (401/403/429) have no envelope. */
 export function describeFailure(res: ApiResponse): string {
   if (res.json && !res.json.success) {
@@ -573,7 +585,7 @@ export async function agentSpawn(deps: AgentDeps, options: SpawnOptions): Promis
         ready = !dead && Boolean(result?.matched);
       }
     } catch (error) {
-      readinessError = getErrorMessage(error) || 'Readiness request failed';
+      readinessError = describeRequestError(error);
     }
   }
 
@@ -1042,7 +1054,7 @@ async function run(json: boolean, verb: (deps: AgentDeps) => Promise<number>): P
   try {
     process.exitCode = await verb(deps);
   } catch (err) {
-    console.error(palette.err(`${GLYPH.fail} ${getErrorMessage(err)}`));
+    console.error(palette.err(`${GLYPH.fail} ${describeRequestError(err)}`));
     process.exitCode = EXIT.error;
   }
 }

src/mcp-server.ts

@@ -38,6 +38,7 @@ import {
   buildSendBody,
   composerReadyMark,
   describeFailure,
+  describeRequestError,
   httpRequest,
   inputRefusal,
   isSelfSession,
@@ -497,7 +498,7 @@ export function createToolRunner(deps: ToolRunnerDeps) {
     } catch (err) {
       if (signal?.aborted) throw err;
       throw new ToolError(
-        `Cannot reach Codeman at ${ctx.apiUrl}: ${getErrorMessage(err)}. Check that it is running. If every call ` +
+        `Cannot reach Codeman at ${ctx.apiUrl}: ${describeRequestError(err)}. Check that it is running. If every call ` +
           'fails at once, a sandbox around this MCP server may be blocking network access to this machine.'
       );
     }