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The PCF tap jitter was keyed on the receiver's 1/8-texel cell in the shadow map. The GPU computes the receiver's map position with last-bit differences from the CPU, so a receiver next to a cell line could take another cell's jitter on one backend, and every tap moved. In a wide penumbra that changed the coverage by several 8-bit levels: gpu_matches_cpu_wide_penumbrae failed on Windows with 15 of 4159 shadowed pixels on an NVIDIA RTX 5080 and 22 on an AMD Radeon iGPU, against a budget of 8. tap_jitter now blends the hashes at the four corners of the cell by the receiver's position in it, in shade.rs and in advanced3d.wgsl. At the lattice points the jitter is the per-cell hash it was before. A CPU test checks that the coverage does not jump at a lattice line.