Bug: Built-in Canva MCP `start-editing-transaction` hangs indefinitely

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

The built-in Canva MCP start-editing-transaction tool
hangs indefinitely — no response, no error, no timeout. The
only way to stop it is pressing Escape to cancel. Other
Canva MCP tools (get-design, get-design-content) work
instantly on the same design.

Reproduced 3+ times across 2 different sessions. Once left
running for over an hour with no response.

What Should Happen?

start-editing-transaction should return a transaction_id
and the design's richtexts/fills within a few seconds, as
documented in the tool's description.

Error Messages/Logs

Steps to Reproduce

No error is returned. The tool call simply never completes.

After manual cancellation (Escape), Claude Code reports:
"The user doesn't want to proceed with this tool use. The
tool use was rejected."

Tool call that hangs:
mcp__claude_ai_Canva__start-editing-transaction
design_id: "DAGtz8HKlfg" (valid: 11 chars, starts with D,
passes regex)

Tools that work instantly on the same design:
mcp__claude_ai_Canva__get-design → responds with metadata

• thumbnail

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.72 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Cursor

Additional Information

The issue is specifically with the built-in Claude.ai Canva
MCP integration
(mcp__claude_ai_Canva), not a locally configured MCP server.

All other built-in Canva tools work fine:

• get-design: responds instantly
• get-design-content: responds instantly
• get-design-pages: responds instantly

Only start-editing-transaction hangs. The design tested has
20 pages
(8.5x11 in pattern PDF), which may be relevant.

Permission mode: bypassPermissions (so it's not a
user-approval issue).