[BUG] visualize:read_me and visualize:show_widget return 400 in Claude Desktop (Windows) and don’t register in tool context

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?

Severity: Medium — feature completely non-functional
Environment:

Client: Claude Desktop app (Windows)
Plan: [your plan — /Max]
App version: [Help → About]
Date/time: April 23, 2026

What happened:
Both visualize:read_me and visualize:show_widget tool calls return Tool call failed: 400 in every attempt within this session. Running tool_search for "visualize" returns no results, indicating the tools are not registering in the active tool context despite being defined in the system prompt.
Steps to reproduce:

Open Claude Desktop
Start a conversation in a Project with a large system prompt
Ask Claude to render an inline HTML widget or diagram
Claude calls visualize:read_me → returns Tool call failed: 400
Claude calls visualize:show_widget → returns Tool call failed: 400

Expected behavior:
Inline rendered widget appears in chat, as it has worked previously in Claude Desktop.
Actual behavior:
400 error on both tool calls. Tools do not appear in tool_search results.
Additional context:

status.anthropic.com showed All Systems Operational at time of failure
The issue appears session or project-specific — not a platform-wide outage
Previously worked in Claude Desktop (user confirmed)

What Should Happen?

Claude should render inline editable HTML in the chat not on side pane that I can copy paste. IT USED TO WORK GREAT. SOMETHING BROKE IT

Error Messages/Logs

Steps to Reproduce

Just ask claude to generate a inline editable HTML for any content

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

n/a this is on the claude desktop chat

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_