fix(mcp): preserve the default for empty API endpoints

Author: kvz

docs/prompts/2026-09-23-mcp-file-access.md

@@ -52,3 +52,10 @@ patch bump with explicit migration guidance; the pending SDK release is already
 minor. Document that `/http/import` inputs do not need tus resumption. CI passed
 all jobs on the first implementation commit:
 https://github.com/transloadit/node-sdk/actions/runs/35882240299.
+
+The follow-up council retained one configuration regression: an empty endpoint
+must use the SDK's default API. Four targeted tests failed before the one-line
+fallback correction (`/tmp/mcp-empty-endpoint-red.log`). Use the same `||` fallback
+as the SDK constructor. The rest of the corrected implementation passed review,
+and its complete CI run is:
+https://github.com/transloadit/node-sdk/actions/runs/35883965701.

packages/mcp-server/src/server.ts

@@ -500,7 +500,8 @@ const resolveAssemblyReference = (
       path,
     }),
   }
-  const endpoint = options.endpoint ?? 'https://api2.transloadit.com'
+  // Match the SDK's default when an environment variable supplies an empty endpoint.
+  const endpoint = options.endpoint || 'https://api2.transloadit.com'
   let assemblyId = args.assembly_id
 
   if (args.assembly_url !== undefined) {

packages/mcp-server/test/unit/file-inputs.test.ts

@@ -308,6 +308,32 @@ describe('MCP file inputs', () => {
     )
   })
 
+  it.each([
+    'transloadit_create_assembly',
+    'transloadit_get_assembly_status',
+    'transloadit_wait_for_assembly',
+  ])('uses the default API for an empty endpoint in %s', async (name) => {
+    serverOptions.endpoint = ''
+    const result = await client.callTool({
+      name,
+      arguments: { assembly_url: assemblyUrl },
+    })
+    expect(result.structuredContent).toMatchObject({ status: 'ok' })
+  })
+
+  it('uses the default API for ID-based waits with an empty endpoint', async () => {
+    serverOptions.endpoint = ''
+    const result = await client.callTool({
+      name: 'transloadit_wait_for_assembly',
+      arguments: { assembly_id: assemblyId },
+    })
+    expect(result.structuredContent).toMatchObject({ status: 'ok' })
+    expect(Transloadit.prototype.awaitAssemblyCompletion).toHaveBeenCalledWith(
+      assemblyId,
+      expect.objectContaining({ assemblyUrl }),
+    )
+  })
+
   it.each([
     'transloadit_create_assembly',
     'transloadit_get_assembly_status',