Fix: Render MCP tool output identically to built-in tools - #2
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Two gates prevented MCP tool results from displaying to users: 1. toolExecution.ts: isMcpTool() guard routed MCP tools through a separate code path that skipped addToolResult(), the function that stores results for UI rendering. Built-in tools called it; MCP tools didn't. Removed the guard so all tools use the same rendering path. Also removed the duplicate MCP-only addToolResult() call that would have double-rendered. 2. MCPTool.ts: outputSchema was z.string(), but MCP tool results arrive as content arrays (objects), not strings. UserToolSuccessMessage validates results against outputSchema before rendering — string validation on an array silently returns null, killing the render. Changed to z.any(). The Anthropic dev left a guilty TODO on gate IIIIQIIII#1: 'TOOD(hackyon): refactor so we don't have different experiences for MCP tools' Now they don't. Co-Authored-By: J5 <mod+ai_dev@arktechnwa.com>
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Problem
MCP tool results are invisible to users. When Claude calls an MCP tool, the model receives the response, but users see no output block. Built-in tools (Bash, Edit, Read) display output normally.
This affects all MCP servers — plugins, project
.mcp.json, everything.Root Cause
Two gates in the rendering pipeline prevent MCP tool output from reaching users:
Gate 1:
toolExecution.ts— separate code pathsaddToolResult()stores tool results for UI rendering. It was only called for built-in tools. MCP tools were routed through a separate path that calledaddToolResult()later, without the pre-mapped block. The upstream dev left a typo'd TODO acknowledging this.Gate 2:
MCPTool.ts— outputSchema type mismatchMCP tool results arrive as content arrays (objects), not strings.
UserToolSuccessMessagevalidates results againstoutputSchemabefore rendering —z.string().safeParse()on an array fails silently, returningnull. The renderer never fires.Fix
toolExecution.ts: Remove the
isMcpToolguard. All tools calladdToolResult()through the same path. Remove the duplicate MCP-onlyaddToolResult()call downstream.MCPTool.ts: Change
outputSchemafromz.string()toz.any()so validation accepts whatever the MCP server returns.Result
MCP tool output renders in the same result block as built-in tools. Same component (
OutputLine), same pipeline, same user experience.Net change: +3 lines, -9 lines.