feat(sp22-vNext): Phase A2 — trade-outcome label producer kernel

First foundation kernel for the H6 vNext trade-outcome aux head.

Per-env classification at trade-close events into K=3 outcomes:
- 0 = Profit (pnl_vs_target >= 1.0)
- 1 = Stop (pnl_vs_stop >= 1.0)
- 2 = Timeout (neither threshold hit)

Sparse labels — most bars get -1 mask. Priority: Profit > Stop > Timeout.

Pure per-env map; no atomicAdd, no reduction. Launch: grid(ceil(N/256)),
block(256).

Registered in build.rs. Cubin compiles clean. Currently dead code —
launcher wireup comes in Phase A3+ commits.

See docs/plans/2026-05-14-sp22-h6-vNext-trade-outcome-aux.md for the
full vNext architecture.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/ml/build.rs

@@ -792,6 +792,16 @@ fn main() {
         // producer chain has fresh labels every rollout step. Same per-thread
         // O(1) map; same lookahead window semantics; same skip sentinel.
         "aux_sign_label_per_step_kernel.cu",
+        // SP22 H6 vNext (2026-05-13): trade-outcome label producer kernel.
+        // Replaces the per-bar binary direction label with a per-trade-close
+        // 3-way outcome label {Profit, Stop, Timeout}. Sparse labels
+        // (only at trade-close events) but aligned with the system's
+        // actual multi-bar trade decision horizon. See
+        // `docs/plans/2026-05-14-sp22-h6-vNext-trade-outcome-aux.md` for
+        // the full vNext architecture spec. This kernel is the FOUNDATION
+        // (Phase A2) — additional kernels for aux forward / loss /
+        // backward + 12-weight W atom-shift land in subsequent commits.
+        "trade_outcome_label_kernel.cu",
         // SP22 H6 (2026-05-12): per-env p_up extractor that copies
         // `aux_softmax[env, 1]` → `prev_aux_dir_prob[env]` after each aux
         // forward. The cache buffer is read by `experience_state_gather`