fix(reports): auto-detect PoC language with Python fallback

tests/test_fenced_code.py

@@ -2,7 +2,13 @@
 
 from __future__ import annotations
 
-from strix.interface.tui.renderers.fenced import parse_fenced_code
+from pygments.lexers import BashLexer, PythonLexer
+
+from strix.interface.tui.renderers.fenced import (
+    guess_language_name,
+    parse_fenced_code,
+    resolve_lexer,
+)
 from strix.viewer.report_pdf import _strip_code_fence
 
 
@@ -43,3 +49,16 @@ def test_strip_code_fence_removes_fence() -> None:
 def test_strip_code_fence_passes_through_non_string_and_unfenced() -> None:
     assert _strip_code_fence(None) is None
     assert _strip_code_fence("x = 1") == "x = 1"
+
+
+def test_resolve_lexer_honors_explicit_language() -> None:
+    assert isinstance(resolve_lexer("bash", "echo hi"), BashLexer)
+
+
+def test_resolve_lexer_falls_back_to_python_when_unresolvable() -> None:
+    # Unknown language name and empty body -> nothing to auto-detect -> Python.
+    assert isinstance(resolve_lexer("not-a-language", ""), PythonLexer)
+
+
+def test_guess_language_name_defaults_to_python_when_inconclusive() -> None:
+    assert guess_language_name("") == "python"