Constant GDN_TC_SPINE_ENTRY 

pub const GDN_TC_SPINE_ENTRY: &str = "gated_delta_rule_chunk_delta_h_tcfuse_x2";

2026-09-25: The spine entry the gdn_prefill_tc lever launches: two bf16 limbs of S_c. Both entries take the same arguments, grid, block and shared memory, so nothing downstream depends on which one is bound.