What problems was I solving

Four props on the internal FieldAgentFocusCanvasProps interface (topic, hasResponseContent, onSelectTopic, onBack) and the parent FieldAgentSurface pass-through plumbing were left orphaned after an earlier rewrite of the Field Agent canvas body removed the suggested-topics grid and topic header UI that used them.

What user-facing changes did I ship

No user-facing changes. The topic header and suggested-topic grid were already absent; this change only removes the leftover declarations and state that previously fed them.

How I implemented it

I removed the dead props from FieldAgentFocusCanvasProps, deleted the now-write-only fieldCanvasTopic state in FieldAgentSurface, stripped the unused canvas prop pass-through expressions, and simplified onUserQuestion so it no longer captures and stores the question text.

Description for the changelog

Removed orphaned topic, hasResponseContent, onSelectTopic, and onBack props from the internal FieldAgentFocusCanvasProps interface and cleaned up the stale pass-through logic and write-only fieldCanvasTopic state in FieldAgentSurface. This is a non-breaking dead-code cleanup with no customer-visible behavior change.