A weekend project: a small MCP server, one tool, running locally, talking to Microsoft Graph, authenticating with device code. Simple. Except no mail arrived. No error, no exception, no log line, just a silence with real menace in it.
This is the full autopsy.
The three bugs that killed it are the three everyone hits when wiring an LLM client to real infrastructure: a .NET console app speaking MCP over stdio, launched as a child process, with genuine auth and a genuine external API, and not one of them, infuriatingly, is an “AI bug.”
We debug it live, learn how MCP-over-stdio actually behaves, why “it runs” and “it works” are entirely different sentences, and how to make these failures loud instead of sulking in silence. You'll leave able to diagnose the next one in minutes rather than over a lost weekend.

Live debugging; recorded fallback prepared for the inevitably cursed conference wifi.