MCP Rust SDK stops treating a pointer found in a guessed .well-known response as an advertised resource

GitHub·low signalXBlueskyLinkedInCopy link

PR #1264, merged 2026-09-14, follows up #1204 on protected resource metadata discovery. A resource_metadata pointer found in a .well-known candidate's 401 response was being fetched as Advertised, which meant one bad document could end discovery before the remaining candidates were tried. It is now classified as a WellKnownGuess, and Advertised is reserved for the resource's own challenge. The distinction matters because a guess only rules itself out while an advertised URL reports the error, so misclassifying a guess turns a soft miss into a hard discovery failure.