feat: implement dynamic context compression for efficient memory usage

- Added Summary field to Session struct
- Implemented background summarization when history > 20 messages
- Included conversation summary in system prompt for long-term context
- Added thread-safety for concurrent summarization per session

pkg/agent/context.go

@@ -84,7 +84,7 @@ func (cb *ContextBuilder) LoadBootstrapFiles() string {
 	return result
 }
 
-func (cb *ContextBuilder) BuildMessages(history []providers.Message, currentMessage string, media []string) []providers.Message {
+func (cb *ContextBuilder) BuildMessages(history []providers.Message, summary string, currentMessage string, media []string) []providers.Message {
 	messages := []providers.Message{}
 
 	systemPrompt := cb.BuildSystemPrompt()
@@ -103,6 +103,10 @@ func (cb *ContextBuilder) BuildMessages(history []providers.Message, currentMess
 		systemPrompt += "\n\n" + skillsContent
 	}
 
+	if summary != "" {
+		systemPrompt += "\n\n## Summary of Previous Conversation\n\n" + summary
+	}
+
 	messages = append(messages, providers.Message{
 		Role:    "system",
 		Content: systemPrompt,