test: docs contract merged-stream test pins its own ON FAILURE line (#146)

The comparison against render_failure_hint() alone passed unchanged if the
record lost its exit-1 cause, since both sides fell back to the same see: line.
CHANGES prose for 8d5fc6e corrected: three mismatches plus one #142 correction.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SnAJ7Z3CpVD3PRbN73QtU2

Files changed:
- CHANGES.md
- VERSION
- tools/chemenu/tests/test_cli.py

tools/chemenu/tests/test_cli.py

@@ -367,5 +367,10 @@ def test_stderr_hint_follows_the_error_line_when_streams_are_merged(tmp_path):
     assert result.returncode == 1
     lines = result.stdout.splitlines()
     assert lines[0] == "ERROR tools/CONTRACT.md is missing."
+    # Pinned literally, not only against `render_failure_hint`: that comparison
+    # alone would pass unchanged if the record lost its cause again, since both
+    # sides would then fall back to the same `see:` line.
+    assert lines[1] == "ON FAILURE (wikitool docs contract -h):"
+    assert lines[2].startswith("    `tools/CONTRACT.md` is missing -> Not transient - restore the file")
     hint = cli_contract.render_failure_hint(cli_contract.get("docs contract"))
     assert "\n".join(lines[1:]) == hint