[RFC PATCH 13/13] review_tui: guard against unmounted diff-viewer In certain asynchronous contexts or during rapid UI transitions, _show_content may be invoked before the diff-viewer widget has been fully mounted in the DOM. This is particularly reproducible in headless test environments and on platforms with slower console I/O initialization.

[Adrian Neftali Sanchez <lutgaru@gmail.com>]

Add a defensive try-except block to catch NoMatches when querying for
'#diff-viewer'. If the widget is not yet available, log a debug message
and return early to prevent an application crash.

Signed-off-by: Adrian Neftali Sanchez <lutgaru@gmail.com>
---
 src/b4/review_tui/_review_app.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/src/b4/review_tui/_review_app.py b/src/b4/review_tui/_review_app.py
index 8786fbb..e6d6e4e 100644
--- a/src/b4/review_tui/_review_app.py
+++ b/src/b4/review_tui/_review_app.py
@@ -18,6 +18,7 @@ from rich.text import Text
 from textual.app import App, ComposeResult
 from textual.binding import Binding
 from textual.containers import Horizontal, Vertical
+from textual.css.query import NoMatches
 from textual.events import Click
 from textual.widgets import Label, ListItem, ListView, RichLog, Static
 
@@ -458,7 +459,12 @@ class ReviewApp(CheckRunnerMixin, App[None]):
         total = len(self._commit_shas)
         if display_idx < 0 or display_idx > total:
             return
-        viewer = self.query_one('#diff-viewer', RichLog)
+        # Defensive: widget may not be mounted yet in headless/async tests
+        try:
+            viewer = self.query_one('#diff-viewer', RichLog)
+        except NoMatches:
+            self.log.debug("diff-viewer not ready for patch %s", display_idx)
+            return
         viewer.clear()
         self._comment_positions = []
         self._followup_positions = {}
-- 
2.45.0.windows.1