FEATURE: disable rate limiting when skipping hyde (#793)

Embedding search is rate limited due to potentially expensive
hyde operation (which require LLM access).

Embedding generally is very cheap compared to it. (usually 100x cheaper)

This raises the limit to 100 per minute for embedding searches,
while keeping the old 4 per minute for HyDE powered search.

app/controllers/discourse_ai/embeddings/embeddings_controller.rb

@@ -7,6 +7,9 @@ module DiscourseAi
 
       SEMANTIC_SEARCH_TYPE = "semantic_search"
 
+      MAX_HYDE_SEARCHES_PER_MINUTE = 4
+      MAX_SEARCHES_PER_MINUTE = 100
+
       def search
         query = params[:q].to_s
         skip_hyde = params[:hyde].to_s.downcase == "false" || params[:hyde].to_s == "0"
@@ -26,8 +29,20 @@ module DiscourseAi
 
         semantic_search = DiscourseAi::Embeddings::SemanticSearch.new(guardian)
 
-        if !semantic_search.cached_query?(query)
-          RateLimiter.new(current_user, "semantic-search", 4, 1.minutes).performed!
+        if !skip_hyde && !semantic_search.cached_query?(query)
+          RateLimiter.new(
+            current_user,
+            "semantic-search",
+            MAX_HYDE_SEARCHES_PER_MINUTE,
+            1.minutes,
+          ).performed!
+        else
+          RateLimiter.new(
+            current_user,
+            "semantic-search-non-hyde",
+            MAX_SEARCHES_PER_MINUTE,
+            1.minutes,
+          ).performed!
         end
 
         hijack do

spec/requests/embeddings/embeddings_controller_spec.rb

@@ -60,6 +60,19 @@ describe DiscourseAi::Embeddings::EmbeddingsController do
       expect(response.parsed_body["topics"].map { |t| t["id"] }).to contain_exactly(topic.id)
     end
 
+    context "when rate limiting is enabled" do
+      before { RateLimiter.enable }
+
+      it "will not rate limit API for hyde search" do
+        10.times do |i|
+          query = "test #{SecureRandom.hex}"
+          stub_embedding(query)
+          get "/discourse-ai/embeddings/semantic-search.json?q=#{query}&hyde=false"
+          expect(response.status).to eq(200)
+        end
+      end
+    end
+
     it "returns results correctly when performing a non Hyde search" do
       index(topic)
       index(topic_in_subcategory)