Introduce signals change (#655)

* adding support for signals

* reducing false positives for signals like positive interaction

* adding docs. Still need to fix the messages list, but waiting on PR #621

* Improve frustration detection: normalize contractions and refine punctuation

* Further refine test cases with longer messages

* minor doc changes

* fixing echo statement for build

* fixing the messages construction and using the trait for signals

* update signals docs

* fixed some minor doc changes

* added more tests and fixed docuemtnation. PR 100% ready

* made fixes based on PR comments

* Optimize latency

1. replace sliding window approach with trigram containment check
2. add code to pre-compute ngrams for patterns

* removed some debug statements to make tests easier to read

* PR comments to make ObservableStreamProcessor accept optonal Vec<Messagges>

* fixed PR comments

---------

Co-authored-by: Salman Paracha <salmanparacha@MacBook-Pro-342.local>
Co-authored-by: MeiyuZhong <mariazhong9612@gmail.com>
Co-authored-by: nehcgs <54548843+nehcgs@users.noreply.github.com>

crates/brightstaff/src/handlers/llm.rs

@@ -111,6 +111,9 @@ pub async fn llm_chat(
         .get_recent_user_message()
         .map(|msg| truncate_message(&msg, 50));
 
+    // Extract messages for signal analysis (clone before moving client_request)
+    let messages_for_signals = client_request.get_messages();
+
     client_request.set_model(resolved_model.clone());
     if client_request.remove_metadata_key("archgw_preference_config") {
         debug!(
@@ -292,6 +295,7 @@ pub async fn llm_chat(
         operation_component::LLM,
         llm_span,
         request_start_time,
+        Some(messages_for_signals),
     );
 
     // === v1/responses state management: Wrap with ResponsesStateProcessor ===