rtx-cfd legacy GPU: buffers re-borrowed after nested device calls; writing and delegating methods take &mut self

crates/specialized/rtx-cfd/src/solvers/lbm/d2q9_gpu.rs

@@ -256,11 +256,15 @@ impl D2Q9GpuSolver {
     fn gpu_collision_step(&mut self) -> CfdResult<()> {
         let buffers = self
             .gpu_buffers
-            .as_mut()
+            .as_ref()
             .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;
 
         // First compute equilibrium distributions
         self.gpu_compute_equilibrium()?;
+        let buffers = self
+            .gpu_buffers
+            .as_mut()
+            .ok_or_else(|| CfdError::gpu_error("GPU buffers not initialized"))?;
 
         // Then perform collision: f = f + omega * (f_eq - f)
         let module = self
@@ -476,7 +480,7 @@ impl D2Q9GpuSolver {
     }
 
     /// Complete GPU LBM time step
-    pub fn gpu_step(&self) -> CfdResult<()> {
+    pub fn gpu_step(&mut self) -> CfdResult<()> {
         self.gpu_collision_step()?;
         self.gpu_streaming_step()?;
         self.gpu_apply_bounce_back_boundaries()?;
@@ -575,7 +579,7 @@ impl D2Q9GpuSolver {
     }
 
     /// Apply boundary conditions
-    fn gpu_apply_boundaries(&self, _boundary_conditions: &BoundaryConditions) -> CfdResult<()> {
+    fn gpu_apply_boundaries(&mut self, _boundary_conditions: &BoundaryConditions) -> CfdResult<()> {
         // For now, just apply bounce-back
         self.gpu_apply_bounce_back_boundaries()?;
         Ok(())