fix: add TextFlush event so LLM response text renders before cost line

Agent loop collected streaming deltas but never flushed them before
emitting Cost/TurnComplete. TUI showed cost but no response text.
Added AgentEvent::TextFlush emitted after all deltas, before turn end.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Darth-Hidious

crates/agent/src/agent_loop.rs

@@ -432,10 +432,15 @@ pub async fn run_turn(
         }
 
         // ── 2e. Emit streamed text deltas ─────────────────────────
-        for delta in &streaming_deltas {
-            emit(AgentEvent::TextDelta {
-                text: delta.clone(),
-            });
+        if !streaming_deltas.is_empty() {
+            for delta in &streaming_deltas {
+                emit(AgentEvent::TextDelta {
+                    text: delta.clone(),
+                });
+            }
+            // Flush text so the TUI moves it from streaming buffer to chat history
+            // before cost/turn-complete events arrive.
+            emit(AgentEvent::TextFlush);
         }
 
         // ── 2f. Push assistant message ────────────────────────────

crates/agent/src/protocol.rs

@@ -3774,6 +3774,9 @@ fn emit_agent_event(event: AgentEvent) {
         AgentEvent::TextDelta { text } => {
             emit_notification("ui.text.delta", serde_json::json!({ "text": text }));
         }
+        AgentEvent::TextFlush => {
+            emit_notification("ui.text.flush", serde_json::json!({ "text": "" }));
+        }
         AgentEvent::ToolCallStart {
             tool_name,
             call_id,

crates/agent/src/types.rs

@@ -81,6 +81,8 @@ pub enum AgentEvent {
     TextDelta {
         text: String,
     },
+    /// Signal the frontend to flush accumulated streaming text into chat history.
+    TextFlush,
     ToolCallStart {
         tool_name: String,
         call_id: String,