MCP Router: protocol versions

The final property name versions is used by both protocol profiles.

protocols.legacy.versions

• Default: [2025-11-25, 2025-06-18, 2025-03-26, 2024-11-05]
• The list must be non-empty and contain no duplicates.
• Only those four versions are supported by the legacy adapter.

protocols.stateless.versions

• Shipped default: [2026-07-28]
• When stateless is enabled, the list must be non-empty.
• The current stateless adapter accepts only 2026-07-28, without duplicates.

protocols:
  legacy:
    versions: [2025-11-25, 2025-06-18, 2025-03-26, 2024-11-05]
  stateless:
    versions: [2026-07-28]

The stateless classifier requires the request header version and the params._meta["io.modelcontextprotocol/protocolVersion"] value to agree. Unsupported, duplicated, or cross-profile versions reject configuration or the request, depending on where the mismatch is found.