POST misses sessionId?

[ronsmits]

Hi I am trying to get this project to work I have added the example to a simple ktor server:

fun Application.module() {

    install(SSE)
    routing {
        get("/") {
            call.respondText("Ktor: ${Greeting().greet()}")
        }

        mcp("/mcp") {
            name = "my-server"
            version = "1.0.0"

            tool("greet", "Greets the user") {
                val name = args["name"] ?: "World"
                textResult("Hello, $name!")
            }
        }
    }
}

When I start this and link it to lm-studio like this:

{
  "mcpServers": {
    "nestor-hub": {
      "url": "http://localhost:8080/mcp"
    }
  }
}

The tool/list is successfully called but calling the actual tool gets a "no response"

greet
({"name":"ron"}…})

mcp/nestor-hub

Arguments: {"name":"ron"}

Result: [{"type":"text","text":"No response"}]

The lm-studio log shows:

2026-01-02 21:58:57 [ERROR]
 [Plugin(mcp/nestor-hub)] stderr: Failed to connect to MCP server using Streamable HTTP transport: Error: Error POSTing to endpoint (HTTP 400): sessionId required
    at _0x387670.<computed>.send (/tmp/.mount_LM-StuSPhgS1/resources/app/.webpack/lib/mcpbridgeworker.js:1:806989)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
Try to fallback to SSE now.

Also tested this in gemini cli with the same result:

 ✓  greet (test MCP Server) {}                                                                                                                                                               │
│                                                                                                                                                                                             │
│ No response