If you've built an MCP App — the HTML widget an MCP server hands a host to render inline — you may have hit this: the tool call succeeds, structuredContent comes back fine, the model announces that a widget rendered, and the user sees nothing. No error. No console output. Just a gap in the conversation. There's a long issue full of people with this exact symptom, all of them (me included) posting variations of "my server is spec-correct and nothing renders." That's a hard thing to act on....