Three-pronged fix for duplicate listings appearing in the UI:
1. Backend: Replace direct rpush cache writes with staged population
(write to temp key, then atomic RENAME to live key). Skip cache
writes entirely for POI-enriched requests. Clean staging keys on
invalidation.
2. Frontend: Add AbortController to cancel in-flight streaming requests
when loadListings is called again, preventing data mixing.
3. Frontend: Deduplicate features by URL during stream accumulation as
a safety net against any remaining server-side duplicates.
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