Avoid upstream tile-mode divide-by-zero on small inputs

app/runtime.py

@@ -145,7 +145,11 @@ class RealCuganRuntime:
         started = time.perf_counter()
         try:
             model = self._load_model(scale, variant)
-            tile_candidates = self._candidate_tile_modes(tile_mode)
+            tile_candidates = self._candidate_tile_modes(
+                tile_mode,
+                width=prepared.width,
+                height=prepared.height,
+            )
             cache_candidates = self._candidate_cache_modes(cache_mode)
             last_exc: Exception | None = None
             used_tile = tile_mode
@@ -336,9 +340,15 @@ class RealCuganRuntime:
         return digest.hexdigest()
 
     @staticmethod
-    def _candidate_tile_modes(tile_mode: int) -> list[int]:
+    def _candidate_tile_modes(tile_mode: int, *, width: int, height: int) -> list[int]:
+        short_edge = min(width, height)
+        safe_tile_mode = tile_mode
+        if tile_mode >= 2 and short_edge < 128:
+            safe_tile_mode = 1
         ordered: list[int] = []
-        for value in [tile_mode, 5, 4, 3, 2, 1, 0]:
+        for value in [safe_tile_mode, 5, 4, 3, 2, 1, 0]:
+            if value >= 2 and short_edge < 128:
+                continue
             if value not in ordered:
                 ordered.append(value)
         return ordered