diff --git a/crates/ml-alpha/cuda/compute_advantage_return.cu b/crates/ml-alpha/cuda/compute_advantage_return.cu
index 45d016064..e850923ed 100644
--- a/crates/ml-alpha/cuda/compute_advantage_return.cu
+++ b/crates/ml-alpha/cuda/compute_advantage_return.cu
@@ -19,13 +19,26 @@ extern "C" __global__ void compute_advantage_return(
     const int b = blockIdx.x * blockDim.x + threadIdx.x;
     if (b >= b_size) return;
 
-    const float gamma = isv[RL_GAMMA_INDEX];
-    const float r     = rewards[b];
-    const float done  = dones[b];
-    const float vt    = v_t[b];
-    const float vtp1  = v_tp1[b];
+    const float gamma  = isv[RL_GAMMA_INDEX];
+    const float r      = rewards[b];
+    const float is_done = (dones[b] > 0.5f);
+    const float vt     = v_t[b];
+    const float vtp1   = v_tp1[b];
 
-    const float ret = r + gamma * (1.0f - done) * vtp1;
-    returns[b]    = ret;
-    advantages[b] = done * (ret - vt);
+    // 2026-05-29: branch-gate (not multiplication-gate) the V_tp1 term
+    // and the (ret - vt) advantage. Multiplication-gating fails on IEEE
+    // `0 * Inf = NaN`: if any batch's encoder produces a non-finite V
+    // prediction early in training (random init outliers), the prior
+    // `done * (ret - vt)` multiplication propagated NaN to ALL non-done
+    // batches' advantages, which then broke compute_advantage_rms (sum
+    // of A² → NaN) and PPO (A/RMS → NaN, ratio×A → NaN, l_pi → NaN).
+    // Branch-gating ensures non-finite vtp1/vt are NEVER mixed into a
+    // non-done batch's advantage. Validated by the smoke bisect at
+    // 10d4614fb (deterministic NaN at step 4 with l_v=6.329 stable —
+    // proving V REGRESSION is fine while V FORWARD has at least one
+    // non-finite output that the 0*Inf trick was promoting to NaN
+    // everywhere). Per `pearl_atomicadd_masks_v_instability`.
+    const float ret = is_done ? r : (r + gamma * vtp1);
+    returns[b]      = ret;
+    advantages[b]   = is_done ? (ret - vt) : 0.0f;
 }