MCP OAuth client-interop conformance: prove real clients can connect

Run five scripted client profiles encoding documented real-client OAuth behaviours (MCP Inspector, Claude Desktop, Cursor, Claude Code, VS Code) over real HTTP against an authorization-server fixture built to the server shape you describe, and get a perishable per-cell verdict — PASS, or FAIL with the exact failing step and a step-exact shim prescription. It reproduces the three documented breaks: Cursor x Cognito-like DCR, Claude Code x Cognito-like DCR-despite-client_id (#38102), VS Code x strict-loopback redirect port. Fixture shapes, not live tenants. Per-check $0.01 · Solo $9/mo per server · Fleet $29/mo (not self-serve).