Fix MP4 opts mutation, frame cleanup safety, silo skip warning

- Copy opts dict in render_mp4 to avoid mutating caller's dict
- Only delete generated frame files during cleanup, not all files
- Add missing-file warning in silo reader (consistent with binary reader)
- Fix render_mp4 comment and _resolve_path docstring accuracy

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: sbryngelson

toolchain/mfc/viz/renderer.py

@@ -156,7 +156,9 @@ def render_mp4(varname, steps, output, fps=10,  # pylint: disable=too-many-argum
     if not steps:
         raise ValueError("No timesteps provided for MP4 generation")
 
-    # Pre-compute vmin/vmax from first and last frames if not provided
+    opts = dict(opts)  # avoid mutating the caller's dict
+
+    # Pre-compute vmin/vmax from first, middle, and last frames if not provided
     auto_vmin = opts.get('vmin')
     auto_vmax = opts.get('vmax')
 
@@ -229,9 +231,14 @@ def render_mp4(varname, steps, output, fps=10,  # pylint: disable=too-many-argum
         if writer is not None:
             writer.close()
 
-    # Clean up frames
+    # Clean up only the frames we created
     if success:
-        for fname in os.listdir(viz_dir):
-            os.remove(os.path.join(viz_dir, fname))
-        os.rmdir(viz_dir)
+        for fname in frame_files:
+            fpath = os.path.join(viz_dir, fname)
+            if os.path.isfile(fpath):
+                os.remove(fpath)
+        try:
+            os.rmdir(viz_dir)
+        except OSError:
+            pass  # directory not empty (pre-existing files)
     return success

toolchain/mfc/viz/silo_reader.py

@@ -41,7 +41,7 @@ def _check_h5py():
 
 
 def _resolve_path(h5file, path_bytes):
-    """Resolve a silo internal path (e.g. b'/.silo/#000003') to a dataset."""
+    """Resolve a silo internal path (e.g. b'/.silo/#000003') and return its data as a numpy array."""
     path = path_bytes.decode() if isinstance(path_bytes, bytes) else str(path_bytes)
     return np.array(h5file[path])
 
@@ -160,6 +160,8 @@ def assemble_silo(
     for rank in ranks:
         silo_file = os.path.join(base, f"p{rank}", f"{step}.silo")
         if not os.path.isfile(silo_file):
+            import warnings  # pylint: disable=import-outside-toplevel
+            warnings.warn(f"Processor file not found, skipping: {silo_file}", stacklevel=2)
             continue
         pdata = read_silo_file(silo_file, var_filter=var)
         proc_data.append((rank, pdata))