## Motivation and Context
SEP-2322 (merged for the 2026-07-28 spec release) makes `resultType` a REQUIRED member of every result
a 2026-07-28 server returns: "Servers implementing this protocol version MUST include this field",
with absence tolerated only when the result comes FROM an earlier protocol version.
The client-side vocabulary landed earlier (`MCP::ResultType`, treating an absent value as `"complete"`),
but every ordinary modern result the server returns is unstamped, which violates the MUST for `tools/list`,
`tools/call`, `ping`, and every other standard result on the modern wire.
The conformance suite's 2026-07-28 requirements fail each of those scenarios on wire-schema validation
(`CallToolResult: must have required property 'resultType'`).
The dispatch path now stamps `resultType: "complete"` centrally: any Hash result of a request carrying
the SEP-2575 `_meta` envelope that does not already carry a `resultType` gets the standard value merged in.
Results that already carry a discriminator keep it, notifications and cancellation-suppressed responses
are untouched, and legacy results stay unstamped because pre-2026 clients do not know the field.
`server/discover`, which is exempt from the `_meta` envelope (pre-version discovery),
stamps its `DiscoverResult` at its construction site instead.
## How Has This Been Tested?
`bundle exec rake test` passes with zero failures. New tests in `test/mcp/server_test.rb`: `tools/list`,
`ping`, and `tools/call` results carry `resultType: "complete"` on modern requests and no `resultType`
on legacy requests; `server/discover` carries the stamp. The conformance scenarios previously failing
on the missing property (`tools-call-simple-text`, `prompts-get-simple`, `completion-complete`, and
the other tools/prompts scenarios) pass at `--spec-version 2026-07-28` against the conformance fixture server.
## Breaking Changes
None. The stamp applies only to results of requests carrying the SEP-2575 modern `_meta` envelope;
results on stable protocol versions through 2025-11-25 are byte-for-byte unchanged.
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