refactor(rag_engine): migrate 3 index_file sites to Result[T] (Phase 13 sites 3+4+SS)

index_file had 3 try/except sites with similar patterns:

Site 3 (BC at L247): try: mtime = os.path.getmtime(full_path); except Exception: return
Site 4 (BC at L261): try: with open(full_path, ...) as f: content = f.read(); except Exception: return
Site 6 (SS at L255): try: res = self.collection.get(...); ...; except Exception: pass

Body: broad catch + early return/pass = SS-style violation.

New helpers:
- _get_file_mtime_result(full_path) -> Result[float]
  Catches OSError only (specific to file stat failures).
- _check_existing_index_result(file_path, mtime) -> Result[bool]
  Catches broad Exception (chromadb collection.get failures vary).
  Returns data=True if already indexed (skip), data=False if needs re-indexing.
- _read_file_content_result(full_path) -> Result[str]
  Catches (OSError, UnicodeDecodeError) (file I/O + encoding failures).

Legacy index_file calls each helper; on Result errors, returns early
(preserving the original behavior of skipping the file on failure).

Audit: rag_engine BC 3 -> 1 (L341 _async_search_mcp remaining).
SS: 1 -> 0.

src/rag_engine.py

@@ -241,6 +241,45 @@ class RAGEngine:
    return self._chunk_text(content)
   return chunks
 
+ def _get_file_mtime_result(self, full_path: str) -> Result[float]:
+  """Get file modification time. Returns Result[float]."""
+  try:
+   return Result(data=os.path.getmtime(full_path))
+  except OSError as e:
+   return Result(
+    data=None,
+    errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"failed to get mtime for {full_path}: {e}", source="rag_engine._get_file_mtime_result", original=e)],
+   )
+
+ def _check_existing_index_result(self, file_path: str, mtime: float) -> Result[bool]:
+  """Check if the file is already indexed at the current mtime.
+
+  Returns Result(data=True) if already indexed (skip), Result(data=False)
+  if needs re-indexing, Result(data=False, errors=[ErrorInfo]) on collection failure.
+  """
+  try:
+   res = self.collection.get(where={"path": file_path}, limit=1, include=["metadatas"])
+   if res and res["metadatas"] and res["metadatas"][0]:
+    if res["metadatas"][0].get("mtime") == mtime:
+     return Result(data=True)
+   return Result(data=False)
+  except Exception as e:
+   return Result(
+    data=False,
+    errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"failed to check existing index for {file_path}: {e}", source="rag_engine._check_existing_index_result", original=e)],
+   )
+
+ def _read_file_content_result(self, full_path: str) -> Result[str]:
+  """Read file contents. Returns Result[str]."""
+  try:
+   with open(full_path, "r", encoding="utf-8", errors="ignore") as f:
+    return Result(data=f.read())
+  except (OSError, UnicodeDecodeError) as e:
+   return Result(
+    data=None,
+    errors=[ErrorInfo(kind=ErrorKind.INTERNAL, message=f"failed to read {full_path}: {e}", source="rag_engine._read_file_content_result", original=e)],
+   )
+
  def index_file(self, file_path: str):
   """Reads, chunks, and indexes a file into the vector store."""
   if not self.config.enabled or self.collection == "mock":
@@ -259,24 +298,19 @@ class RAGEngine:
    else:
     return
 
-  try:
-   mtime = os.path.getmtime(full_path)
-  except Exception:
+  mtime_result = self._get_file_mtime_result(full_path)
+  if not mtime_result.ok:
+   return
+  mtime = mtime_result.data
+
+  existing_result = self._check_existing_index_result(file_path, mtime)
+  if existing_result.ok and existing_result.data:
    return
 
-  try:
-   res = self.collection.get(where={"path": file_path}, limit=1, include=["metadatas"])
-   if res and res["metadatas"] and res["metadatas"][0]:
-    if res["metadatas"][0].get("mtime") == mtime:
-     return
-  except Exception:
-   pass
-
-  try:
-   with open(full_path, "r", encoding="utf-8", errors="ignore") as f:
-    content = f.read()
-  except Exception:
+  content_result = self._read_file_content_result(full_path)
+  if not content_result.ok:
    return
+  content = content_result.data
 
   self.collection.delete(where={"path": file_path})
 

tests/tier2/phase13_sites346_test.py

@@ -0,0 +1,29 @@
+"""Phase 13 sites 3+4 + SS 6: index_file batched migration.
+
+index_file has 3 sites:
+- Site 3 (BC at L247): try: mtime = os.path.getmtime(full_path); except Exception: return
+- Site 4 (BC at L261): try: with open(full_path, ...) as f: content = f.read(); except Exception: return
+- Site 6 (SS at L255): try: res = self.collection.get(...); ...; except Exception: pass
+
+All 3 follow similar patterns: try/except + early return or pass.
+"""
+import sys
+sys.path.insert(0, ".")
+
+
+def test_phase13_sites346_index_file_no_broad_except():
+    """index_file must not have bare 'except Exception'."""
+    import inspect
+    import src.rag_engine
+    src_text = inspect.getsource(src.rag_engine.RAGEngine.index_file)
+    assert "except Exception:" not in src_text, \
+        "index_file must not have bare 'except Exception'"
+
+
+def test_phase13_sites346_index_file_helpers_exist():
+    """Helpers for getmtime, file_read, collection_get exist."""
+    import src.rag_engine
+    # Check via dir() of the class
+    members = [m for m in dir(src.rag_engine.RAGEngine) if 'result' in m.lower()]
+    # We expect 3 new _result helpers added to index_file
+    assert len(members) >= 3, f"Expected at least 3 _result helpers, got {members}"