Making SolverGenericContact's contact_id public. (#888)

Author: dog-molecule

CHANGELOG.md

@@ -19,6 +19,7 @@
   `IntegrationParameters::softness` and `GenericJoint::softness` fields (#789).
 - Removed `IntegrationParameters::joint_natural_frequency` and `IntegrationParameters::joint_damping_ratio` in favor of
   per-joint softness coefficients `GenericJoint::softness` (#789).
+- Make `SolverContact::contact_id` public so that user code knows what geometric contact it originates from (#888).
 
 ## v0.30.1 (17 Oct. 2025)
 

src/geometry/contact_pair.rs

@@ -394,7 +394,7 @@ pub struct SolverContactGeneric<N: SimdRealCopy, const LANES: usize> {
     /// This isn’t a bool for optimizations purpose with SIMD.
     pub is_new: N, // 1/1
     /// The index of the manifold contact used to generate this solver contact.
-    pub(crate) contact_id: [u32; LANES], // 1/1
+    pub contact_id: [u32; LANES], // 1/1
     #[cfg(feature = "dim3")]
     pub(crate) padding: [N; 1],
 }