fix(mcpdo): fail connections/list and MRU inference on an over-limit socket path

clients/mcpdo/__tests__/mcp-coverage.test.ts

@@ -537,6 +537,48 @@ describe("mcp.ts coverage", () => {
     expect(unknown.stderr).toContain(`(config ${configPath}`);
   });
 
+  // Windows named pipes have no sun_path limit, so the check is a no-op there.
+  it.skipIf(process.platform === "win32")(
+    "an over-limit daemon socket path fails connections/list and MRU inference like connect does (#2823)",
+    async () => {
+      configPath = createSampleTestConfig();
+      const e = env();
+      // Never created: the point is that nothing could ever bind here.
+      const longDir = path.join(storageDir!, "d".repeat(120));
+      const longEnv = { ...e, MCP_INSPECTOR_DAEMON_DIR: longDir };
+
+      const listed = await runMcp(["connections/list", "--format", "json"], {
+        env: longEnv,
+      });
+      expectCliFailure(listed);
+      expect(listed.stdout).not.toMatch(/connections/);
+      expect(listed.stderr).toMatch(/socket path is too long/);
+      expect(listed.stderr).toContain(path.join(longDir, "mcpdod.sock"));
+
+      const noMru = await runMcp(["servers/show", "--config", configPath], {
+        env: longEnv,
+        timeout: 20000,
+      });
+      expectCliFailure(noMru);
+      expect(noMru.stderr).toMatch(/socket path is too long/);
+      expect(noMru.stderr).not.toMatch(/no most-recently-used connection/);
+
+      // Neither command starts the daemon, or even creates its directory.
+      expect(fs.existsSync(longDir)).toBe(false);
+
+      // Same error, same exit code as the command that would start it.
+      const connected = await runMcp(
+        ["connect", "test-stdio", "--config", configPath],
+        { env: longEnv, timeout: 20000 },
+      );
+      expectCliFailure(connected);
+      expect(connected.stderr).toMatch(/socket path is too long/);
+
+      expect(listed.exitCode).toBe(connected.exitCode);
+      expect(noMru.exitCode).toBe(connected.exitCode);
+    },
+  );
+
   it("connections/list and daemon status do not auto-spawn the daemon", async () => {
     const e = env();
     const listed = await runMcp(["connections/list", "--format", "json"], {

clients/mcpdo/src/connection/mcp.ts

@@ -31,7 +31,12 @@ import {
   getSecretStorageInfo,
   warnAboutSecretStorage,
 } from "@inspector/core/auth/node/secret-store-selection.js";
-import { callDaemon, ensureDaemon } from "../daemon/index.js";
+import {
+  assertSocketPathWithinLimit,
+  callDaemon,
+  ensureDaemon,
+  getDaemonSocketPath,
+} from "../daemon/index.js";
 import type {
   ConnectionInfo,
   ConnectionShowResult,
@@ -122,6 +127,19 @@ function isDaemonUnreachable(error: unknown): boolean {
   );
 }
 
+/**
+ * For commands that read "daemon unreachable" as "nothing is connected"
+ * without starting the daemon (`connections/list`, MRU name inference):
+ * rethrow anything that is not an unreachable daemon, and fail with
+ * `ensureDaemon()`'s own socket-path error when the daemon could never bind
+ * in this environment at all (#2823). Without the check, an over-limit
+ * socket path reads as a healthy empty machine while `connect` refuses.
+ */
+function assertNoDaemonMeansNothingConnected(error: unknown): void {
+  if (!isDaemonUnreachable(error)) throw error;
+  assertSocketPathWithinLimit(getDaemonSocketPath());
+}
+
 /**
  * `servers/show` with no name falls back to the MRU connection's entry name,
  * under the same non-interactive gate as MRU connection targeting: an agent
@@ -145,7 +163,7 @@ async function resolveMruEntryName(): Promise<string> {
     );
     connections = result.connections;
   } catch (error) {
-    if (!isDaemonUnreachable(error)) throw error;
+    assertNoDaemonMeansNothingConnected(error);
   }
   const mru = connections.find((c) => c.isMru);
   if (!mru) {
@@ -1062,14 +1080,11 @@ function registerConnectionAdmin(program: CommandType): void {
           connections: result.connections,
         });
       } catch (error) {
-        if (isDaemonUnreachable(error)) {
-          await writeConnectionOutput(outOpts(opts), {
-            kind: "connections/list",
-            connections: [],
-          });
-          return;
-        }
-        throw error;
+        assertNoDaemonMeansNothingConnected(error);
+        await writeConnectionOutput(outOpts(opts), {
+          kind: "connections/list",
+          connections: [],
+        });
       }
     });