test(tui): freeze clock in thinking-preview cache equivalence test

The output-equivalence test compared full Console.export_text() across two
compose() calls, whose status line embeds elapsed time and token rate. Freeze
time.monotonic so the two renders are deterministic and only the cached preview
governs the comparison; guards against a rare timing-boundary flake.

Author: elkaix

tests/ui_and_conv/test_streaming_content_block.py

@@ -697,9 +697,16 @@ def counting(preview: str):
         block.compose()  # pending changed -> recompute
         assert len(calls) == 2
 
-    def test_stream_mode_cached_preview_matches_uncached_render(self):
+    def test_stream_mode_cached_preview_matches_uncached_render(self, monkeypatch):
         """Caching is behavior-preserving: composed output is byte-identical to a
         fresh (uncached) render of the same reasoning content across ticks."""
+        from pythinker_code.ui.shell.visualize import _blocks
+
+        # Freeze the clock so the elapsed/token-rate status line is identical
+        # across both compose() calls — the comparison targets the cached preview,
+        # not wall-clock timing.
+        monkeypatch.setattr(_blocks.time, "monotonic", lambda: 100.0)
+
         block = _ContentBlock(is_think=True, show_thinking_stream=True)
         block.append("**Preparing report generation**")