[Bugs] Canvas fails to open custom extension canvas with RPC error -32603

[lauthieb]

Short summary

I created a custom canvas in user scope. The extension is present in ~/.copilot/extensions, and it is listed when I click + in the tab bar of a new agent session. However, selecting it always fails with: Failed to open canvas RPC error -32603

Affected version or release

v0.2.22

Installation context

Installed on my laptop, GitHub Copilot Business license

What happened?

Canvas does not open and shows:

Failed to open canvas RPC error -32603

Steps to reproduce

1. Create a canvas in user scope.
2. Confirm extension files exist under ~/.copilot/extensions.
3. Start a new agent session.
4. Click + in the tab bar and verify the canvas appears in the list.
5. Select the canvas.

Expected behavior

The selected canvas should open successfully.

Additional context

• Discovery/registration appears to work (canvas is listed).
• Failure happens specifically when opening the canvas.
• OS: macOS
• Scope: user scope (~/.copilot/extensions)

Thanks in advance for your help.