fix(pathfinder): remove dead/misleading error handling in platform loaders (#2239)

* fix(pathfinder): remove dead/misleading error handling in platform loaders

Two dead error-handling paths in the dynamic-lib platform loaders:

- load_dl_linux.load_with_system_search guarded abs_path with
  'if abs_path is None: raise RuntimeError("No expected symbol ...")'.
  abs_path_for_dynamic_library never returns None (it returns a resolved
  path or raises OSError), so the branch is unreachable and its message is
  factually wrong (it concerns dlinfo path resolution, not symbols). Drop
  the dead branch and let the descriptive OSError surface, matching the
  deterministic-loader policy of not masking discovery/load failures.

- load_dl_windows.add_dll_directory had 'if not result: pass', a no-op; the
  PATH update below already runs unconditionally. Remove the dead branch and
  clarify the comment on why PATH is updated regardless.

No behavior change: both removed branches were unreachable or no-ops.

Signed-off-by: Aryan <aryansputta@gmail.com>

* fix(pathfinder): simplify loader review comments

---------

Signed-off-by: Aryan <aryansputta@gmail.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgkio@gmail.com>

Author: aryanputta

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_dl_linux.py

@@ -164,8 +164,6 @@ def load_with_system_search(desc: LibDescriptor) -> LoadedDL | None:
     Returns:
         A LoadedDL object if successful, None if the library cannot be loaded
 
-    Raises:
-        RuntimeError: If the library is loaded but no expected symbol is found
     """
     for soname in _candidate_sonames(desc):
         try:
@@ -174,8 +172,7 @@ def load_with_system_search(desc: LibDescriptor) -> LoadedDL | None:
             pass
         else:
             abs_path = abs_path_for_dynamic_library(desc.name, handle)
-            if abs_path is None:
-                raise RuntimeError(f"No expected symbol for libname={desc.name!r}")
+            assert abs_path
             return LoadedDL(abs_path, False, handle._handle, "system-search")
     return None
 

cuda_pathfinder/cuda/pathfinder/_dynamic_libs/load_dl_windows.py

@@ -69,11 +69,10 @@ def add_dll_directory(dll_abs_path: str) -> None:
     dirpath = os.path.dirname(dll_abs_path)
     assert os.path.isdir(dirpath), dll_abs_path
 
-    # Add the DLL directory to the search path
-    result = kernel32.AddDllDirectory(dirpath)
-    if not result:
-        # Fallback: just update PATH if AddDllDirectory fails
-        pass
+    # Add the DLL directory to the native search path. AddDllDirectory only
+    # affects the LOAD_LIBRARY_SEARCH_USER_DIRS search; PATH is updated
+    # unconditionally below to also cover legacy dependent-DLL resolution.
+    kernel32.AddDllDirectory(dirpath)
 
     # Update PATH as a fallback for dependent DLL resolution
     curr_path = os.environ.get("PATH")