Harden readers and CLI error handling

- Validate Fortran record length is non-negative
- Clip searchsorted indices to prevent out-of-bounds in assembly
- Check silo_hdf5 directory exists before listing
- Catch discover_format FileNotFoundError for clean CLI output

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

Author: sbryngelson

toolchain/mfc/viz/reader.py

@@ -73,6 +73,8 @@ def _read_record_endian(f, endian: str) -> bytes:
     if len(raw) < 4:
         raise EOFError("Unexpected end of file reading record marker")
     rec_len = struct.unpack(f'{endian}i', raw)[0]
+    if rec_len < 0:
+        raise ValueError(f"Invalid Fortran record length: {rec_len}")
     payload = f.read(rec_len)
     if len(payload) < rec_len:
         raise EOFError("Unexpected end of file reading record payload")
@@ -316,9 +318,9 @@ def assemble_from_proc_data(  # pylint: disable=too-many-locals
 
     # Place each processor's data using per-cell coordinate lookup
     for _rank, pd, x_cc, y_cc, z_cc in proc_centers:
-        xi = np.searchsorted(global_x, np.round(x_cc, 12))
-        yi = np.searchsorted(global_y, np.round(y_cc, 12)) if ndim >= 2 else np.array([0])
-        zi = np.searchsorted(global_z, np.round(z_cc, 12)) if ndim >= 3 else np.array([0])
+        xi = np.clip(np.searchsorted(global_x, np.round(x_cc, 12)), 0, nx - 1)
+        yi = np.clip(np.searchsorted(global_y, np.round(y_cc, 12)), 0, ny - 1) if ndim >= 2 else np.array([0])
+        zi = np.clip(np.searchsorted(global_z, np.round(z_cc, 12)), 0, nz - 1) if ndim >= 3 else np.array([0])
 
         for vn, data in pd.variables.items():
             if vn not in global_vars:

toolchain/mfc/viz/silo_reader.py

@@ -145,6 +145,8 @@ def assemble_silo(
     _check_h5py()
 
     base = os.path.join(case_dir, "silo_hdf5")
+    if not os.path.isdir(base):
+        raise FileNotFoundError(f"Silo-HDF5 directory not found: {base}")
     ranks: List[int] = []
     for entry in os.listdir(base):
         if entry.startswith("p") and entry[1:].isdigit():

toolchain/mfc/viz/viz.py

@@ -63,7 +63,11 @@ def viz():  # pylint: disable=too-many-locals,too-many-statements,too-many-branc
     if fmt_arg:
         fmt = fmt_arg
     else:
-        fmt = discover_format(case_dir)
+        try:
+            fmt = discover_format(case_dir)
+        except FileNotFoundError as exc:
+            cons.print(f"[bold red]Error:[/bold red] {exc}")
+            sys.exit(1)
 
     cons.print(f"[bold]Format:[/bold] {fmt}")