MCP tools don't populate output.output in the tool.execute.after hook —
the MCP content flows through OpenCode's internal parts pipeline instead.
This caused a crash: undefined is not an object (evaluating 'text.length')
in the truncate function.
The MCP server requires @modelcontextprotocol/sdk and zod which are not
globally installed. Added .agents/mcp/package.json and updated install.sh
to run 'npm install --prefix' on first setup.
