fix: prevent tool-pair summarization from being silently undone (#7413)

Two changes that fix a conversation state desync between server and UI:

1. Emit HistoryReplaced at end of agent loop iterations where conversation
   was mutated, so the UI stays in sync with server-side metadata changes
   (e.g. tool-pair summarization marking messages agent-invisible).

2. Stop sending conversation_so_far on normal chat turns. The server
   already has the authoritative conversation in its DB. Sending it back
   from the UI created a window where stale client state could overwrite
   server-side changes. Edit-in-place flow (onMessageUpdate) is unchanged.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: bzqzheng

crates/goose/src/agents/agent.rs

@@ -1617,10 +1617,20 @@ impl Agent {
                     }
                 }
 
+                let conversation_mutated = !messages_to_add.is_empty();
                 for msg in &messages_to_add {
                     session_manager.add_message(&session_config.id, msg).await?;
                 }
                 conversation.extend(messages_to_add);
+
+                // Notify the UI of conversation changes so its local state stays
+                // in sync with the server. Without this, the client may send back
+                // stale conversation_so_far on the next turn, overwriting server-side
+                // metadata mutations (e.g. from tool-pair summarization).
+                if conversation_mutated && !did_recovery_compact_this_iteration {
+                    yield AgentEvent::HistoryReplaced(conversation.clone());
+                }
+
                 if exit_chat {
                     break;
                 }

ui/desktop/src/hooks/useChatStream.ts

@@ -590,7 +590,6 @@ export function useChatStream({
           body: {
             session_id: sessionId,
             user_message: newMessage,
-            ...(hasExistingMessages && { conversation_so_far: currentState.messages }),
           },
           throwOnError: true,
           signal: abortControllerRef.current.signal,