[BUG] Claude PowerPoint add-in: "Tool names must be unique" error on first message

Description

The Claude PowerPoint add-in returns "Tool names must be unique" when sending the first message. The add-in panel opens and loads normally, but any message typed into the chat window and submitted triggers this error.

Environment

• macOS: 26.3 (Build 25D125)
• Microsoft PowerPoint: 16.106.1
• Claude Plan: Pro
• Add-in source: pivot.claude.ai (hosted)

Steps to Reproduce

1. Open Microsoft PowerPoint
2. Open the Claude add-in panel (loads successfully)
3. Type any message into the chat input
4. Press Enter
5. Error appears: "Tool names must be unique"

What I've Tried

All of the following failed to resolve the issue:

1. Targeted Wef cache clearing — Deleted ~/Library/Containers/com.microsoft.Powerpoint/Data/Library/Microsoft/Office/16.0/Wef/
2. Nuclear cache clearing — Deleted Wef + WebKit + Caches/WebKit directories from the PowerPoint container
3. Restarting PowerPoint after each clearing attempt

None had any effect. This is expected — the error is an HTTP 400 from the Anthropic API rejecting duplicate tool definitions in the request payload, not a local caching issue.

Analysis

"Tool names must be unique" is a server-side API validation error that occurs when duplicate tool definitions are sent in a single API request. Since the add-in JavaScript is hosted at pivot.claude.ai and tool registration happens at runtime when a message is sent, this is either:

1. A code bug in the add-in that registers the same tool name twice in the API request, or
2. A server-side configuration issue with duplicate tool entries

This matches the pattern from Issue #25747 (closed Feb 16, 2026), where the add-in sent an invalid field (use_web_search_purpose) that the API rejected. That issue was also unfixable locally and required a server-side fix from Anthropic.

Possibly Related

• Active incident (Feb 17-20, 2026): "Intermittent errors in skills-related functionality" affecting claude.ai, Desktop, and API — https://status.claude.com
• Issue #25747: Similar add-in API validation failure, fixed server-side
• Issue #26385: PowerPoint MCP connector AppleScript syntax errors
• Issue #20473: Additional PowerPoint MCP connector failures

Expected Behavior

Message is sent to Claude and a response is returned.

Actual Behavior

Error "Tool names must be unique" is displayed instead of a response. The add-in is unusable.