Elicit structured user input mid-tool from a Python MCP server (accept/decline/cancel, schema limits)

Documented steps

1. Two forms: (1) resolver — Annotated[T, Resolve(fn)] where fn returns Elicit(...) — works on every connection era; (2) direct await ctx.elicit(...) in the tool body — server-initiated, works only on legacy connections (spec 2025-11-25 or earlier) and fails outright on a 2026-07-28 connection. Prefer the resolver. Docs: https://py.sdk.modelcontextprotocol.io/handlers/elicitation/
2. Resolver form: from mcp.server.mcpserver import AcceptedElicitation, CancelledElicitation, DeclinedElicitation, Elicit, ElicitationResult, Resolve. The resolver returns the value directly when already known (no round trip) or Elicit(message, Model) to ask. Annotate the tool param confirm: Annotated[ElicitationResult[Confirm], Resolve(confirm_delete)] and match on AcceptedElicitation(data=...), DeclinedElicitation(), CancelledElicitation().
3. Annotate with the bare model type instead of ElicitationResult[...] when you don't need to branch — decline/cancel then aborts the tool with an error automatically.
4. Direct form (legacy connections): result = await ctx.elicit(message="...", schema=SomePydanticModel) inside an async def tool; branch on result.action: 'accept' (result.data is a validated schema instance — .data exists only in this branch), 'decline', 'cancel'.
5. For flows that must bypass the model entirely (OAuth consent, payments, credentials) use await ctx.elicit_url(message=..., url=..., elicitation_id="deposit-123"), then await ctx.session.send_elicit_complete("deposit-123") when the out-of-band flow finishes.
6. Client-side testing: pass elicitation_callback= to Client(..., mode="legacy", elicitation_callback=handle) returning an ElicitResult(action=..., content={...}); mode="legacy" is required for direct elicitation.