Registers modelcontextprotocol/ruby-sdk in KNOWN_SDKS so `tier-check --sdk-path` and `sdk ruby-sdk` manage
the build and per-revision runs themselves, instead of requiring the --conformance-server-url/--client-cmd
fallback for unknown SDKs. This is the registry path the Ruby SDK's SEP-1730 Tier 1 application
(modelcontextprotocol/modelcontextprotocol#3247) was scored through: with the entry in place, reviewers can
reproduce the submission with a single `tier-check --sdk-path <checkout> --requirements 2025-11-25,2026-07-28`,
the same way every other registered SDK is checked.
The entry drives the same fixtures the SDK's own CI runs through `rake conformance`: `conformance/server.rb`
behind the `conformance:server` rake task (PORT from the environment; PORT=3000 matches the registry's port convention)
and `conformance/client.rb`, which reads MCP_CONFORMANCE_SCENARIO from the environment and the server URL from argv,
per the runner's contract. The baseline is `conformance/expected_failures.yml`. One dual-era server serves every revision
from the same /mcp endpoint (stateful dated-spec handshake and the SEP-2575 stateless lifecycle side by side),
so the entry needs no specOverrides.
Testing: `npm test` (525 passing, including a new known-sdks entry test), `npm run check`, and `npm run build` pass.
The entry has already carried four full end-to-end audit runs: the 2026-08-14 and 2026-08-15 tier-check runs against
a local ruby-sdk checkout (`--sdk-path` with `--requirements 2025-11-25,2026-07-28`) each built the SDK, started the
server on PORT=3000, and completed both legs at both revisions, producing the 67/67 server and 50/50 client results
submitted in modelcontextprotocol/modelcontextprotocol#3247. Individually, `sdk ruby-sdk --path <checkout> --mode
server --requirements 2025-11-25` exits 0 with 78/78 checks, and `--mode client --requirements 2025-11-25` exits 0
with every scored scenario passing (failures confined to not_scored extensions).
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