Resolver dependency injection: a tool parameter annotated Annotated[T, Resolve(fn)] is filled by running the resolver fn before the tool body, instead of from the LLM-supplied arguments. Here refund_order(order_id, reason) refunds what the order record says — cents is resolver-computed and does not appear in the input schema at all, so the model cannot supply or inflate the amount. Resolvers form a DAG (load_order → refund_scope → refund_amount / ask_restock), may return Elicit[...] to ask the human, and ask each question at most once per call. A resolver's own plain parameters are filled from the tool's arguments by name — load_order(order_id) receives the order_id the model passed to refund_order.

Run it

# stdio (default — the client spawns the server as a subprocess)
uv run python -m stories.refund_desk.client

# HTTP — the client self-hosts the server on a free port, runs, then tears it
# down (2026 protocol: the questions ride embedded input_required round-trips;
# add --legacy to ride synchronous push elicitation instead)
uv run python -m stories.refund_desk.client --http

What to look at

server.py refund_order — the signature is the whole story: order_id and reason are model-facing; cents and restock carry Resolve(...) markers and never reach the input schema. client.py asserts properties and required are exactly {order_id, reason}. At 2026 the resolver's elicited answers ride between rounds inside a requestState the SDK seals by default; see mrtr/ for the full security walk-through.
server.py refund_scope — the no-round-trip fast path: a one-line order returns Scope(full=True) directly; only a multi-line order returns Elicit(...). The ORD-7001 call completes with zero elicitations.
server.py _scoped — the elicited SKU is human-typed free text; it is validated against the order (ToolError on a miss) before any amount is computed.
The decline contrast: refund_amount takes scope unwrapped, so declining the scope question aborts the whole cents chain with an error containing the framework's Resolver for parameter 'scope' could not resolve: elicitation was decline (the client sees it behind the usual Error executing tool refund_order: prefix); restock keeps the ElicitationResult union, so declining restock still refunds — just with restocked: false.
client.py — the scope counter proves memoization from outside: one call consumes refund_scope from two resolvers but the question fires once.

Caveats

Transport per era. The framework picks the elicitation transport from the negotiated protocol: at >= 2026-07-28 the questions ride embedded input_required round-trips (a resolver that depends on another's answer is asked in a later round); at <= 2025-11-25 each is a synchronous elicitation/create push request mid-call. Author code is identical on both — this client runs unchanged on either era.
Decline order. A declined unwrapped dependency aborts resolution in tool-signature order — cents resolves before restock, so ask_restock never runs. Don't rely on a later resolver's side effects after an earlier consumer can abort.
Memoization scope. Each question is asked at most once per call, and within a round each resolver runs at most once, keyed by function identity. Across 2026 rounds only elicited outcomes persist (in requestState); any resolver's body may run again on each round the call passes through. A recorded answer is consulted only when the resolver asks its question again: it satisfies the question without re-prompting the user, and it never stands in for a value the resolver computes itself. An answer is matched back to its question when the call resumes, so an eliciting resolver must derive its question deterministically from the tool's arguments and earlier answers; a per-call generated value (a default_factory id, a timestamp) is re-derived each round and must not appear in a question the answer is meant to bind to. Nothing is cached across calls or connections.
Validate elicited values. Elicited answers are human-typed; check them against your records (as _scoped does) before acting on them.

Spec

Elicitation — client features, Input required tool results — server features

README.md

refund-desk

Run it

What to look at

Caveats

Spec

See also