A county GIS assistant must show progressive map-description text while tools fetch parcel attributes. Which approach fits?

County GIS assistants that must show progressive map-description text while tools fetch parcel attributes should stream progressive description text while those tools return. Combining Messages API streaming with tool use fits because clerks and planners get immediate narrative feedback about the map context instead of staring at a blocked UI, while parcel attribute tools continue to resolve in parallel or interleaved fashion according to the client design. Progressive text improves perceived performance without inventing parcel facts that tools have not yet returned. Batching map-description text with parcel attributes in a combined response after tool calls fails by concept: it serializes the entire wait into a frozen screen and withholds useful interim description. Streaming tool status updates for parcel lookup while holding description text for response fails by concept: it withholds the progressive map narrative while lookups run, so users get status pings but no interim description as parcel attributes resolve. Refusing streaming whenever any tool might run fails by concept: tool use and streaming are complementary capabilities; forbidding the combination discards responsiveness for geospatial workflows that need both. Exam caveat: streamed text must not present unverified parcel attributes as final—clients should mark pending tool results and reconcile the narrative once tool payloads arrive—and public GIS answers must respect suppression rules for sensitive parcels. Operational check: in a county GIS staging client, start a parcel question that triggers a tool call, observe that streamed map-description tokens appear before tool completion, and assert the UI labels attribute fields as pending until the tool response is merged.