MCP OAuth Debug

An MCP server that uses OAuth can look perfectly healthy and still leave you with no token: the client reports "connected", `tools/list` works, and every account-scoped tool returns 401 forever. There is no obvious error to search for — this skill is that missing error message. Any of these, all with the same cause: - `mcp login <server>` (or the client's "connect / authenticate" button) finishes with a message like `Server responded, but no OAuth token was obtained — authentication did not complete.` - No browser window, no consent URL, no device code is ever shown. - The token file for the server is missing, or only the *client registration* file exists (e.g. `*.client.json` present, `*.json` with `access_token` absent). - The server is listed as connected, discovery lists its tools, but every tool call returns `401 Unauthorized` — sometimes only for account-scoped tools (profile, library, orders, credits) while public tools (search, catalog, docs) work fine. The MCP authorization spec makes the **client** start the OAuth flow reactively: it only begins discovery and authorization when the server answers a request with