Cloud Sandbox creation fails immediately with `-32601: Unhandled method session.create` using bundled CLI

[trask]

Short summary

Creating a Cloud session from GitHub Copilot Desktop fails immediately because the session runtime returns RPC error -32601: Unhandled method session.create.

The failure occurs before a remote sandbox or Agent Task is created. Local sessions continue to work with the same app, bundled SDK, and bundled CLI.

Affected version or release

• GitHub Copilot app 1.1.20
• Bundled Copilot CLI 1.0.84-5
• Windows 11, x86_64

The same error also occurred with GitHub Copilot app 1.1.17 and bundled Copilot CLI 1.0.83.

Installation context

GitHub Copilot Desktop installed through WinGet. No COPILOT_CLI_PATH override is configured for these attempts. The app uses its matched bundled Copilot SDK and CLI.

I reproduced the failure against both:

• trask/copilot-plugins
• open-telemetry/opentelemetry-java-instrumentation

The current app release is 1.1.20 according to WinGet.

What happened?

Starting a Cloud session from the Desktop session-creation UI fails almost immediately:

Session creation failed
Failed to create session: RPC error -32601: Unhandled method session.create

A sanitized app-log sequence shows that Desktop uses the bundled SDK and CLI, then receives the missing-method response:

GitHub Copilot app started version=1.1.20 platform=windows arch=x86_64
Detected Copilot CLI version at startup version=1.0.84-5 source=Bundled
Wiring bundled copilot-sdk path for session.create
session creation failed error=RPC error -32601: Unhandled method session.create
cloud kickoff: session creation failed error=RPC error -32601: Unhandled method session.create

The RPC fails within milliseconds. No remote task ID, session URL, or provisioning event is produced.

Local project sessions created by the same app and CLI successfully complete session.create, generally in two to three seconds. The failure appears specific to Cloud session creation rather than the base session RPC or repository configuration.

Steps to reproduce

1. Install GitHub Copilot Desktop 1.1.20 on Windows 11.
2. Open a configured GitHub repository project.
3. Create a new session and select Cloud as the execution location.
4. Enter a kickoff prompt and start the session.
5. Observe the immediate -32601: Unhandled method session.create error.
6. Create a local worktree session for the same repository and observe that it starts successfully.

The failure can also be reproduced through the Copilot SDK:

import { CopilotClient } from "@github/copilot-sdk";

const client = new CopilotClient();
await client.start();

await client.createSession({
  enableExperimentalMode: true,
  cloud: {
    repository: {
      owner: "open-telemetry",
      name: "opentelemetry-java-instrumentation",
      branch: "main",
    },
  },
  onPermissionRequest: async () => ({ kind: "approve-once" }),
});

The createSession call returns:

Error: Unhandled method session.create
code: -32601

I reproduced the SDK failure with:

• @github/copilot-sdk 1.0.13, using its pinned CLI 1.0.83
• @github/copilot-sdk 1.0.14-preview.0, using its pinned CLI 1.0.84-5

Expected behavior

Desktop or the SDK should create a remote Linux Cloud Sandbox and return a usable Cloud session.

If the account or runtime does not support Cloud sessions, the app should reject the request with a clear entitlement or compatibility error rather than exposing the Cloud option and calling an unavailable RPC method.

Additional context

The immediate session.create method error does not match the following reports:

• Cloud session create times out waiting for remote sandbox CLI host #3137 creates a remote task, then times out waiting for the sandbox CLI host. The -32601 error reported here occurs before Desktop creates a remote task.
• Desktop-created cloud sessions never receive their kickoff prompt: session.remote.notifySteerableChanged unsupported by the native session bridge #2865 creates the remote session, then fails to deliver its kickoff prompt because another bridge method is unsupported. The -32601 error reported here prevents Desktop from creating the remote session.
• Desktop cannot resume sessions with newer CLI via COPILOT_CLI_PATH (missing session.permissions.getAllowAll) #3284 requires an external CLI override and fails on session.permissions.getAllowAll. The -32601 error reported here occurs with Desktop's matched bundled SDK and CLI.
• [Bugs] cloud sanboxes are failing RPC requests #646 is a general report of Cloud Sandbox RPC failures from app 0.2.22, but it does not identify session.create or provide a matching reproduction.

Copilot CLI 1.0.84-6 was published after these tests. Its release notes do not mention a fix for Cloud session.create or this RPC error.

I can provide additional sanitized log context if needed.