sep-2164-error-code grades the resource-not-found code as SHOULD; 2026-07-28 makes it MUST #552

The released 2026-07-28 resources page says "If the requested resource does not exist, servers MUST return a JSON-RPC error with code -32602", and basic/index lists -32002 among the codes 2026-07-28 implementations MUST NOT emit. The wording changed from SHOULD in modelcontextprotocol/modelcontextprotocol#2863, after #246 set this check to WARNING. sep-2164-error-code still reports WARNING, so a server answering -32002 passes sep-2164-resource-not-found 3/3 (the server runner doesn't count warnings). Proposed: report FAILURE and update the yaml quote. Happy to send the PR.

AI disclosure per AI_POLICY.md: the investigation, code and tests were done primarily with Claude Code. The numbers above are from local runs.