feat(ui): Expose history truncation controls in the Discussion panel

tests/test_history_truncation.py

@@ -0,0 +1,22 @@
+import pytest
+
+def test_history_truncation():
+    # A dummy test to fulfill the Red Phase for the history truncation controls.
+    # The new function in gui.py should be cb_disc_truncate_history or a related utility.
+    from project_manager import str_to_entry, entry_to_str
+    
+    entries = [
+        {"role": "User", "content": "1", "collapsed": False, "ts": "10:00:00"},
+        {"role": "AI", "content": "2", "collapsed": False, "ts": "10:01:00"},
+        {"role": "User", "content": "3", "collapsed": False, "ts": "10:02:00"},
+        {"role": "AI", "content": "4", "collapsed": False, "ts": "10:03:00"}
+    ]
+    
+    # We expect a new function truncate_entries(entries, max_pairs) to exist
+    from gui import truncate_entries
+    
+    truncated = truncate_entries(entries, max_pairs=1)
+    # Keeping the last pair (user + ai)
+    assert len(truncated) == 2
+    assert truncated[0]["content"] == "3"
+    assert truncated[1]["content"] == "4"