tui: separator above final agent message (#4324)

Adds a separator line before the final agent message

<img width="1011" height="884" alt="Screenshot 2025-09-26 at 4 55 01 PM"
src="https://github.com/user-attachments/assets/7c91adbf-6035-4578-8b88-a6921f11bcbc"
/>

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__binary_size_ideal_response.snap

@@ -1,5 +1,6 @@
 ---
 source: tui/src/chatwidget/tests.rs
+assertion_line: 1152
 expression: "lines[start_idx..].join(\"\\n\")"
 ---
 • I need to check the codex-rs repository to explain why the project's binaries
@@ -9,6 +10,8 @@ expression: "lines[start_idx..].join(\"\\n\")"
   is set up. I should look into the Cargo.toml file to confirm features and
   profiles without needing to edit any code. Let's get started on this!
 
+─ Worked for 0s ────────────────────────────────────────────────────────────────
+
 • I’m going to scan the workspace and Cargo manifests to see build profiles and
   dependencies that impact binary size. Then I’ll summarize the main causes.
 
@@ -110,6 +113,8 @@ expression: "lines[start_idx..].join(\"\\n\")"
   "Main Causes" and "Build-Mode Notes." I can also include brief suggestions for
   reducing size, but I want to stay focused on answering the user's question.
 
+─ Worked for 0s ────────────────────────────────────────────────────────────────
+
 • Here’s what’s driving size in this workspace’s binaries.
 
   Main Causes

codex-rs/tui/src/chatwidget/tests.rs

@@ -340,6 +340,7 @@ fn make_chatwidget_manual() -> (
         is_review_mode: false,
         ghost_snapshots: Vec::new(),
         ghost_snapshots_disabled: false,
+        needs_final_message_separator: false,
     };
     (widget, rx, op_rx)
 }