fix: _strip_reasoning_prose discards the answer when reasoning trails it (#1643)

tests/test_strip_reasoning_prose_dataloss.py

@@ -0,0 +1,25 @@
+"""Regression: _strip_reasoning_prose must not destroy the answer.
+
+It kept the text AFTER the *last* reasoning paragraph. When a reasoning-style
+sentence trailed the real answer, `keep` became empty and the function returned
+that trailing sentence (`paragraphs[-1]`), discarding the actual answer above
+it. It now strips only a leading contiguous run of reasoning paragraphs.
+"""
+from src.text_helpers import strip_think
+
+
+def test_leading_reasoning_is_stripped():
+    out = strip_think("I need to draft a reply.\n\nThe answer is 42.", prose=True)
+    assert out == "The answer is 42."
+
+
+def test_trailing_reasoning_does_not_destroy_answer():
+    text = ("Dear Alice,\n\nI will send the report by Friday.\n\nBest, Bob"
+            "\n\nI need to keep this reply concise and professional.")
+    out = strip_think(text, prose=True)
+    assert "send the report by Friday" in out
+    assert "Dear Alice" in out
+
+
+def test_plain_text_unchanged():
+    assert strip_think("Just a normal answer.", prose=True) == "Just a normal answer."