docs: mark P5 as done in NEXT_PRIORITIES.md

NEXT_PRIORITIES.md

@@ -98,7 +98,11 @@ the prompt to apply doctrine rule 3, not to pick one.
   prefill / long-context throughput; "decode works without TMA" is true but
   doesn't generalize.
 
-### **P5 — In-kernel online softmax across KV tiles (the real P2)**
+### **P5 — Integrate multi-tile FMHA into production** ✅ DONE
+
+Shipped 2026-05-30. Wired the existing D1.5 kernel
+(fmha_6warp_tma_multirow_multitile.cuh) via fmha_multitile_capi.cu +
+fmha_multitile_op.py into production.py. 18 integration tests pass.
 
 After P3, the decode fast path bypasses the Python merge for `n_segments==1`.
 But CSA with `top_k=1024` always has `n_segments=8`, so the moment top_k > 128