add client query to retrieve pending nudge

Rather than only delivering pending nudges from dispatch on Linux, which rules out a client in a clean call from receiving them, we should add a client query to retrieve any pending nudges.

The issue identifies Linux dispatch and the client as the relevant entry points, but names no files or tests. Start by tracing how pending nudges are delivered during dispatch and how clients make clean calls. Done means a client can query and receive any pending nudges rather than relying only on dispatch delivery.

Written by the indexing model from the issue text.