fix: serve server/discover from the hand-rolled client-scenario mocks#347
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The SEP-2243, SEP-2322, and SEP-2106 client-direction scenarios build their own mock servers and did not answer server/discover, so a 2026-07-28 client that negotiates via discover before its scenario calls hit a -32601 or generic fallback and had to synthesize the response itself. The shared stateless mock and the request-metadata and auth scenarios already served it. BaseHttpScenario now answers server/discover with a valid DiscoverResult (supportedVersions, capabilities from an overridable discoverCapabilities(), serverInfo, plus the cacheable-result members) before delegating to handlePost; http-standard-headers overrides the capabilities to match the methods it serves. mrtr-client and json-schema-ref-no-deref answer it directly. New tests pin the response shape for all five scenarios.
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pcarleton
approved these changes
Jun 18, 2026
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The hand-rolled mock servers for the SEP-2243/2322/2106 client-direction scenarios now answer
server/discover, so a 2026-07-28 client that negotiates via discover before its scenario calls can proceed without intercepting the response at the transport layer.Motivation and Context
server/discoveris the recommended negotiation entry point at 2026-07-28 ("Clients MAY callserver/discover", server/discover); a client that does so against the suite's mocks should get a validDiscoverResult. The shared stateless mock (createServerStateless/validateStatelessRequest) and therequest-metadataand auth scenarios already serve it, but the hand-rolled servers used byhttp-standard-headers,http-custom-headers,http-invalid-tool-headers,sep-2322-client-request-state, andjson-schema-ref-no-derefdid not — discover hit their fallbacks (-32601for the MRTR mock, the generic empty result for the SEP-2243 scenarios, the bundled 1.x SDK's method-not-found for the SEP-2106 scenario). A client whose fixture negotiates via discover currently has to synthesize the response itself; the typescript-sdk's everythingClient carries exactly that workaround.Same family as #341: the mocks need to speak enough of the 2026-07-28 surface that a strictly-conforming client can connect and proceed.
What changed
BaseHttpScenarioanswersserver/discoveritself (before delegating tohandlePost) with a validDiscoverResult:supportedVersions: [DRAFT_PROTOCOL_VERSION],capabilitiesfrom a new overridablediscoverCapabilities()(default{ tools: {} }),serverInfo, and the requiredresultType/ttlMs/cacheScope.sendInitializedefaults its capabilities to the same hook so the legacy and modern paths advertise the same set.http-standard-headersoverridesdiscoverCapabilities()to{ tools: {}, resources: {}, prompts: {} }(the methods it actually serves).mrtr-clientadds aserver/discovercase to its method switch.json-schema-ref-no-derefanswersserver/discoverdirectly before handing the request to the bundled SDK transport (which predates the 2026-07-28 lifecycle).draft-result-fields.test.tsgains a parameterised test asserting each of the five scenarios returns a validDiscoverResultcarryingsupportedVersions: [draft], the expected capabilities, and the cacheable-result members.How Has This Been Tested?
npm run check,npm run build,npm test— all green (293 tests, including the 5 new discover assertions).node dist/index.js client --command "npx tsx examples/clients/typescript/everything-client.ts" --suite draftbefore and after the change: identical results (the bundled example client doesn't call discover on these scenarios, so this confirms no regression for clients that don't).Breaking Changes
None. The added
server/discoverhandling is purely additive; clients that don't call discover see no change.Types of changes
Checklist
Additional context
json-schema-ref-no-derefstill routes everything except discover through the bundled 1.x SDK transport (initialize handshake, no_metavalidation); fully reworking that scenario to a hand-rolled stateless server is a larger follow-up flagged in fix: include required result members in 2026-07-28 mock responses #341._metavalidation (unlike the shared stateless mock), so clients on either lifecycle can drive them; only the discover response was missing.BaseHttpScenarionow answers discover before delegating tohandlePost,http-standard-headersno longer emits its opportunisticMcp-Methodcheck forserver/discover(it was never in the scenario'sexpectedMethodslist, so no backfill or test changes). If we want SEP-2243 header coverage onserver/discover, the right place is the scenario's expected-methods list — separate question from this PR.