refactor(rag_engine): narrow 'except Exception' in _get_sentence_transformers (Phase 13 site 1)

Site 1 (BC at L33) was:
    except Exception as e:
        sys.stderr.write(f'FAILED to import sentence_transformers: {e}')
        sys.stderr.flush()
        raise e

Per TIER1_REVIEW: catch + log + re-raise is Pattern 2 of the styleguide.
The fix is to narrow the except to specific exception types that
sentence_transformers could raise on import (ImportError, AttributeError).

Refactored to:
    except (ImportError, AttributeError) as e:
        sys.stderr.write(f'FAILED to import sentence_transformers: {e}')
        sys.stderr.flush()
        raise

The bare 'raise' re-raises the current exception being handled,
preserving the original type and traceback. (Replaces 'raise e' which
raised a specific value but lost the traceback context.)

Audit: rag_engine BC 5 -> 4. RETHROW +1 (the narrowed except is now
classified as Pattern 3 catch+re-raise; strict mode accepts).

src/rag_engine.py

@@ -30,10 +30,10 @@ def _get_sentence_transformers():
    if e.name == "sentence_transformers":
     raise ImportError(LOCAL_RAG_INSTALL_HINT) from e
    raise
-  except Exception as e:
+  except (ImportError, AttributeError) as e:
    sys.stderr.write(f"FAILED to import sentence_transformers: {e}\n")
    sys.stderr.flush()
-   raise e
+   raise
  return _SENTENCE_TRANSFORMERS
 
 def _get_google_genai():

tests/tier2/phase13_site1_test.py

@@ -0,0 +1,26 @@
+"""Phase 13 site 1: narrow 'except Exception' in _get_sentence_transformers.
+
+Site 1 (BC at L33): the second except in the try/except chain is broad:
+    except Exception as e:
+        sys.stderr.write(...)
+        sys.stderr.flush()
+        raise e
+
+Per TIER1_REVIEW: catch + log + re-raise is Pattern 2 of the styleguide.
+The fix is to narrow the except to specific exception types that
+sentence_transformers might raise on import (ImportError, AttributeError).
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase13_site1_get_sentence_transformers_narrow():
+    import inspect
+    import src.rag_engine
+    src_text = inspect.getsource(src.rag_engine._get_sentence_transformers)
+    # Must NOT have 'except Exception as e:' (broad catch)
+    assert "except Exception as e:" not in src_text, \
+        "_get_sentence_transformers must narrow 'except Exception'"
+    # Should have a narrow except for module-loading failures
+    assert "except ImportError" in src_text or "except (ImportError" in src_text, \
+        "_get_sentence_transformers should have narrow ImportError/AttributeError catch"