The hard-constraint-first then vector similarity ranking order is the right call, and most demos do it backwards. Embedding everything and ranking by similarity before filtering on capacity or dates is how you end up confidently recommending venues that don't exist or can't fit the group. Applying hard constraints as a pre-filter is basic production hygiene but it's skipped constantly.

The piece I'd probe: what happens when a vendor replies asynchronously after the conversation has moved on? You're correctly framing this as a stateful coordination problem, but vendor responses are inherently slow and async. If the user has already selected venue B while venue A's quote is still in flight, do you have a reconciliation layer for that dangling thread, or does it just get dropped?

The split UI (chat left, structured results right) is a pattern that works well for this kind of agentic workflow - it stops the user treating the agent like a search engine while still giving them the structured view they need to make actual decisions. Good call.