fix(mcp): advertise no elicitation capability when no handler is configured#1910
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…igured Connections without an elicitation handler advertised form-mode elicitation while rejecting every request that arrived, so spec- compliant servers chose elicitation over their fallback flows and the tool call failed mid-flight. The capability is now advertised only when it can be handled; without a handler, servers see no elicitation capability and fall back gracefully. Handler registration is gated on the advertisement because the SDK client throws when registering a handler for an undeclared capability. The deprecated instance-patch of handleElicitationRequest no longer receives requests unless the capability is declared explicitly; RPC tests migrated to the elicitationHandler option.
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This was referenced Jul 9, 2026
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Follow-up to #1903.
Problem
A connection without an elicitation handler advertised form-mode elicitation (
elicitation: {}) while rejecting every elicitation request that arrived — a leftover from before #1903, when the capability was hardcoded. Spec-compliant servers gate on client capabilities, so the false advertisement made them choose elicitation over their non-elicitation fallback flows, and the tool call then failed mid-flight with an opaque error.Fix
Complete the "capabilities follow the handler" rule from #1903: the elicitation capability is advertised only when it can be handled.
Agent.onElicitRequestoverride or theelicitationHandleroption):{ form: {}, url: {} }, unchanged.client.capabilities.elicitationdeclaration still wins wholesale.Handler registration is now gated on the advertisement — the MCP SDK client throws when registering a request handler for an undeclared capability.
Behavior change
Code relying on the deprecated pattern of instance-patching
handleElicitationRequeston a connection stops receiving elicitation requests (the capability is no longer advertised). That path was undocumented, broke across hibernation, and the client elicitation scenario was baselined as a known conformance failure until #1903 — migration isAgent.onElicitRequest, theelicitationHandleroption, or an explicit capability declaration. Called out in the changeset.Tests
elicitationHandleroption (which also exercises the new gate end-to-end — without the advertised capability the server refuses to elicit).npm run checkgreen.