Remove collision filter deprecation scaffolding

Replace finalized model collision filters with a compact read-only set
view and remove the expired mutation compatibility path.

Remove the deprecated contact-pair rebuilding API and update docs,
serialization handling, and regression coverage.

Author: eric-heiden

changelog/+model-collision-filters-2f6c8a1d.removed.md

@@ -0,0 +1 @@
+Remove `ModelBuilder.find_shape_contact_pairs()` and support for mutating `Model.shape_collision_filter_pairs`; update `ModelBuilder.shape_collision_filter_pairs` before calling `finalize()` and rebuild the model instead.

docs/concepts/collisions.rst

@@ -708,14 +708,10 @@ Filter pairs are automatically populated in several cases:
 - **USD filtered pairs**: Pairs defined by ``physics:filteredPairs`` relationships in USD files
 - **USD collision disabled**: Shapes with ``physics:collisionEnabled=false`` (filtered against all other shapes)
 
-The resulting filter pairs are stored in :attr:`~Model.shape_collision_filter_pairs` as a set of
-``(shape_index_a, shape_index_b)`` tuples (canonical order: ``a < b``).
-
-.. deprecated:: 1.4
-   Mutating this finalized-model set is deprecated; update
-   :attr:`~ModelBuilder.shape_collision_filter_pairs` before calling ``finalize()`` and rebuild the
-   model instead, because the precomputed :attr:`~Model.shape_contact_pairs` array is not rebuilt by
-   post-finalize filter edits.
+The resulting filter pairs are stored in :attr:`~Model.shape_collision_filter_pairs` as a read-only
+set of ``(shape_index_a, shape_index_b)`` tuples (canonical order: ``a < b``). Update
+:attr:`~ModelBuilder.shape_collision_filter_pairs` before calling ``finalize()`` and rebuild the
+model to change collision filters.
 
 **USD Import Example**
 

newton/_src/sim/builder.py

@@ -13197,9 +13197,7 @@ def _to_wp_array(data, dtype, requires_grad):
             m.mujoco.equality_constraint_world_start = wp.array(self._equality_constraint_world_start, dtype=wp.int32)
             m.constraint_mimic_count = len(self.constraint_mimic_joint0)
 
-            # The packed array was just installed on the model, so builder and
-            # model filters are known to match without rebuilding it.
-            self._find_shape_contact_pairs(m, allow_filter_blocks=True)
+            self._find_shape_contact_pairs(m)
 
             # enable ground plane
             m.up_axis = self.up_axis
@@ -13511,43 +13509,7 @@ def _validate_compact_shape_collision_filter_blocks(self, compact_filter_blocks)
                     )
             validated_templates.add(template_key)
 
-    def find_shape_contact_pairs(self, model: Model):
-        """Deprecated method for rebuilding explicit shape contact pairs.
-
-        .. deprecated:: 1.4
-            Shape contact pairs are generated automatically by :meth:`finalize`.
-            Configure collision filters before finalization instead of rebuilding
-            contact pairs manually.
-
-        Identifies and stores all potential shape contact pairs for collision detection.
-
-        This method examines the collision groups and collision masks of all shapes in the model
-        to determine which pairs of shapes should be considered for contact generation. It respects
-        any user-specified collision filter pairs to avoid redundant or undesired contacts.
-
-        The resulting contact pairs are stored in the model as a 2D array of shape indices.
-
-        Uses the exact same filtering logic as the broad phase kernels (test_world_and_group_pair)
-        to ensure consistency between EXPLICIT mode (precomputed pairs) and NXN/SAP modes.
-
-        Args:
-            model: The simulation model to which the contact pairs will be assigned.
-
-        Side Effects:
-            - Sets `model.shape_contact_pairs` to a wp.array of shape pairs (wp.vec2i).
-            - Sets `model.shape_contact_pair_count` to the number of contact pairs found.
-        """
-        warnings.warn(
-            "ModelBuilder.find_shape_contact_pairs() is deprecated; shape contact pairs are generated "
-            + "automatically by ModelBuilder.finalize(). Configure collision filters before finalization instead.",
-            DeprecationWarning,
-            stacklevel=2,
-        )
-        # Deprecated calls may supply an unrelated model or a builder that has
-        # changed since finalization, so always query filters from the model.
-        self._find_shape_contact_pairs(model, allow_filter_blocks=False)
-
-    def _find_shape_contact_pairs(self, model: Model, *, allow_filter_blocks: bool) -> None:
+    def _find_shape_contact_pairs(self, model: Model) -> None:
         filter_pairs = self._shape_collision_filter_pairs
         world_filter_blocks: tuple[_ShapeCollisionFilterBlock, ...] = ()
         explicit_filter_pairs: tuple[tuple[int, int], ...] = ()
@@ -13570,11 +13532,7 @@ def _find_shape_contact_pairs(self, model: Model, *, allow_filter_blocks: bool)
                 self._iter_validated_shape_collision_filter_pairs((*filter_pairs.explicit_pairs, *floating_block_pairs))
             )
 
-        # Builder-side storage is valid only while it describes the model's
-        # filters exactly; otherwise the general path queries the model.
-        use_world_templates = (
-            allow_filter_blocks and self.world_count > 0 and isinstance(filter_pairs, _BuilderShapeCollisionFilterPairs)
-        )
+        use_world_templates = self.world_count > 0 and isinstance(filter_pairs, _BuilderShapeCollisionFilterPairs)
         if use_world_templates:
             shape_world_np = np.asarray(self.shape_world, dtype=np.int32)
             starts = self.shape_world_start