Enforce min_res guarantee after nearest-multiple rounding

Nearest-multiple rounding could drop a dimension below min_res in
min-res mode (e.g. min_res=1100, multiple_of=256 -> 1024); bump such
dimensions to the next multiple instead.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nodes.py

@@ -245,6 +245,15 @@ class ConstrainResolution(io.ComfyNode):
         final_width = ConstrainResolution.round_to_multiple(int(new_width), multiple_of)
         final_height = ConstrainResolution.round_to_multiple(int(new_height), multiple_of)
 
+        # Nearest-multiple rounding can drop a dimension back below min_res
+        # (e.g. min_res=1100, multiple_of=256 -> 1024). In min-res mode, bump
+        # such a dimension up to the next multiple so the guarantee holds.
+        if constraint_mode == ConstraintMode.MIN_RES.value:
+            if final_width < min_res:
+                final_width = math.ceil(min_res / multiple_of) * multiple_of
+            if final_height < min_res:
+                final_height = math.ceil(min_res / multiple_of) * multiple_of
+
         # 4. In strict mode, rounding can exceed max_res (e.g. round_to_multiple(2160, 32) = 2176).
         #    Clamp to the largest valid multiple of multiple_of that is <= max_res.
         if constraint_mode == ConstraintMode.MAX_RES_STRICT.value:

tests/test_nodes.py

@@ -84,6 +84,17 @@ class TestMinRes:
         # The short dimension should be at least min_res
         assert min(w, h) >= 704
 
+    def test_rounding_never_drops_below_min_res(self):
+        """Nearest-multiple rounding must not violate the min_res guarantee.
+
+        min_res=1100 with multiple_of=256: 1100 would round to 1024 (< min_res);
+        it must be bumped up to 1280 instead.
+        """
+        w, h = calc(1000, 1000, 1100, 4096, 256, MIN)
+        assert min(w, h) >= 1100
+        assert w % 256 == 0
+        assert h % 256 == 0
+
     def test_min_res_normal_case(self):
         """In MIN_RES mode with no extreme ratio, both dims should stay within normal range."""
         w, h = calc(500, 333, 704, 2048, 32, MIN)