bug: GetWorkspaceByAgentID is called over a million times a day on dogfood

[spikecurtis]

https://console.cloud.google.com/sql/instances/dogfood-v2/insights;database=coder;start=2025-06-12T05:55:18.232Z;end=2025-06-19T05:55:18.232Z;trace=ac9bc1c4b501d64bb6ad790ae5a8633a;span=c6909b51da0c6db3;query_hash=3814061901782322789;sort_by=TOTAL_EXEC_TIME?inv=1&invt=Ab0giQ&project=coder-dogfood-v2