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Server scenarios fail servers for capabilities they never declared #516

Description

@sebastienrousseau

The same minimal server as above declares only tools. Against it, server mode reports 6 passed, 24 failed. Nearly all of the 24 are not conformance failures:

Cause Scenarios
Capability not declared; -32601 Method not found is the correct answer prompts-* (5), resources-* (6), logging-set-level, tools-call-with-logging, completion-complete
Fixture tool not present (test_image_content, test_tool_with_progress, …) tools-call-image, -audio, -embedded-resource, -mixed-content, -with-progress, -sampling, -elicitation, elicitation-sep1034-defaults, elicitation-sep1330-enums
Genuine dns-rebinding-protection (served a foreign Host/Origin with 200)

For comparison, @modelcontextprotocol/server-everything 2026.8.31 scores 13 passed, 19 failed on 0.1.16.

This is expected for a suite built to test SDKs against the everything-server. The result is still that the suite cannot be pointed at a production server to answer "is this server conformant?", which is the question most operators and registries are asking. A correct server scores 6/30, and its only real defect is buried among 23 false ones.

Suggestions, cheapest first:

  1. Gate on declared capabilities. Read capabilities from initialize and report prompts, resources, logging and completions scenarios as not applicable when the capability is absent. Answering -32601 for an undeclared capability is what the spec says to do.
  2. Mark fixture-dependent scenarios (those that call test_* tools or test:// resources) as needing the fixture, and report them as not applicable when the tool is missing from tools/list, rather than failing them.
  3. A capability-agnostic suite (e.g. --suite production) holding only the scenarios that apply to any server: initialize, ping, tools/list shape, unknown-method and invalid-params handling, session handling, protocol-version header validation, and DNS-rebinding protection. That would let registries and operators cite the official suite for a real server.

Happy to contribute scenarios for (3) if that direction is welcome.

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