fix: preserve tool failures under noisy output

tests/test_text.py

@@ -0,0 +1,26 @@
+from __future__ import annotations
+
+from agent_platform.text import truncate_middle
+
+
+def test_truncate_middle_preserves_error_at_end() -> None:
+    text = "stdout:" + ("x" * 1000) + "\nNameError: start is not defined"
+
+    truncated = truncate_middle(text, 120)
+
+    assert len(truncated) == 120
+    assert truncated.startswith("stdout:")
+    assert "middle omitted" in truncated
+    assert truncated.endswith("NameError: start is not defined")
+
+
+def test_truncate_middle_leaves_short_text_unchanged() -> None:
+    assert truncate_middle("short", 20) == "short"
+
+
+def test_truncate_middle_honors_tiny_limits() -> None:
+    marker = "<omitted>"
+
+    assert truncate_middle("abcdef", 0, marker) == ""
+    assert truncate_middle("abcdef", 3, marker) == "abc"
+    assert truncate_middle("abcdefghijklmnopqrstuvwxyz", len(marker) + 1, marker) == "a<omitted>"