Building a multi-agent document-search copilot — Part 2: adaptive Hybrid, and a permission gate after the rank
This is Part 2 of two. Part 1 opened on a document-search copilot whose v1 produced muddy results — two retrieval lanes fused into one rerank, where metadata rows that carry no text corrupted the relevance scores. The fix was two reframes: collapse the router into one structured Bedrock call (with a deterministic fallback), and pick exactly one retrieval strategy per query — MetadataOnly, ContentOnly, or Hybrid — instead of fusing the lanes. We left off at the one strategy that refuses to be tidy: Hybrid, where the user wants a topic and filters at the same time.
Picking up where Part 1 stopped, we're now in the back half of the same pipeline — the direct_search → rerank → permission_filter → finalize_results tail of the search graph. Two decisions left: how Hybrid actually retrieves, and where permissions get enforced.
3️⃣ Adaptive Hybrid: peek once, then pick filter-first or rank-then-filter
Hybrid is the interesting one, because "topic + filters" is genuinely a tradeoff and not a single right answer. There was a real debate about it — the kind that goes a few rounds on a whiteboard: run the filter and the rank in parallel (fast, but you have to reconcile two sets), or in sequence (precise, but slower)? We resolved it by refusing to pick — and routing on selectivity instead.
