fix(tui): only show 'Worked for' separator when actual work was performed (#8958)

Fixes #7919.

This PR addresses a TUI display bug where the "Worked for" separator
would appear prematurely during the planning stage.

**Changes:**
- Added `had_work_activity` flag to `ChatWidget` to track if actual work
(exec commands, MCP tool calls, patches) was performed in the current
turn.
- Updated `handle_streaming_delta` to only display the
`FinalMessageSeparator` if both `needs_final_message_separator` AND
`had_work_activity` are true.
- Updated `handle_exec_end_now`, `handle_patch_apply_end_now`, and
`handle_mcp_end_now` to set `had_work_activity = true`.

**Verification:**
- Ran `cargo test -p codex-tui` to ensure no regressions.
- Manual verification confirms the separator now only appears after
actual work is completed.

---------

Co-authored-by: Josh McKinney <joshka@openai.com>

codex-rs/tui/src/chatwidget.rs

@@ -462,8 +462,17 @@ pub(crate) struct ChatWidget {
     is_review_mode: bool,
     // Snapshot of token usage to restore after review mode exits.
     pre_review_token_info: Option<Option<TokenUsageInfo>>,
-    // Whether to add a final message separator after the last message
+    // Whether the next streamed assistant content should be preceded by a final message separator.
+    //
+    // This is set whenever we insert a visible history cell that conceptually belongs to a turn.
+    // The separator itself is only rendered if the turn recorded "work" activity (see
+    // `had_work_activity`).
     needs_final_message_separator: bool,
+    // Whether the current turn performed "work" (exec commands, MCP tool calls, patch applications).
+    //
+    // This gates rendering of the "Worked for …" separator so purely conversational turns don't
+    // show an empty divider. It is reset when the separator is emitted.
+    had_work_activity: bool,
 
     last_rendered_width: std::cell::Cell<Option<usize>>,
     // Feedback sink for /feedback
@@ -1348,13 +1357,19 @@ impl ChatWidget {
         self.flush_active_cell();
 
         if self.stream_controller.is_none() {
-            if self.needs_final_message_separator {
+            // If the previous turn inserted non-stream history (exec output, patch status, MCP
+            // calls), render a separator before starting the next streamed assistant message.
+            if self.needs_final_message_separator && self.had_work_activity {
                 let elapsed_seconds = self
                     .bottom_pane
                     .status_widget()
                     .map(super::status_indicator_widget::StatusIndicatorWidget::elapsed_seconds);
                 self.add_to_history(history_cell::FinalMessageSeparator::new(elapsed_seconds));
                 self.needs_final_message_separator = false;
+                self.had_work_activity = false;
+            } else if self.needs_final_message_separator {
+                // Reset the flag even if we don't show separator (no work was done)
+                self.needs_final_message_separator = false;
             }
             self.stream_controller = Some(StreamController::new(
                 self.last_rendered_width.get().map(|w| w.saturating_sub(2)),
@@ -1423,6 +1438,8 @@ impl ChatWidget {
                 self.request_redraw();
             }
         }
+        // Mark that actual work was done (command executed)
+        self.had_work_activity = true;
     }
 
     pub(crate) fn handle_patch_apply_end_now(
@@ -1434,6 +1451,8 @@ impl ChatWidget {
         if !event.success {
             self.add_to_history(history_cell::new_patch_apply_failure(event.stderr));
         }
+        // Mark that actual work was done (patch applied)
+        self.had_work_activity = true;
     }
 
     pub(crate) fn handle_exec_approval_now(&mut self, id: String, ev: ExecApprovalRequestEvent) {
@@ -1599,6 +1618,8 @@ impl ChatWidget {
         if let Some(extra) = extra_cell {
             self.add_boxed_history(extra);
         }
+        // Mark that actual work was done (MCP tool call)
+        self.had_work_activity = true;
     }
 
     pub(crate) fn new(common: ChatWidgetInit, thread_manager: Arc<ThreadManager>) -> Self {
@@ -1687,6 +1708,7 @@ impl ChatWidget {
             is_review_mode: false,
             pre_review_token_info: None,
             needs_final_message_separator: false,
+            had_work_activity: false,
             last_rendered_width: std::cell::Cell::new(None),
             feedback,
             current_rollout_path: None,
@@ -1784,6 +1806,7 @@ impl ChatWidget {
             is_review_mode: false,
             pre_review_token_info: None,
             needs_final_message_separator: false,
+            had_work_activity: false,
             last_rendered_width: std::cell::Cell::new(None),
             feedback,
             current_rollout_path: None,