commit_full_accept_test: a negative control, so the two runs cannot both take the same path (refs #1781)

npu/forward/include/q4nx_forward.h

@@ -204,6 +204,9 @@ class Q4nxNpuForward {
     // Public: a speculative driver outside this class begins a verify batch, then commits a prefix of it.
     void begin_verify(int rows, int start_pos);
     bool commit_verify_rows(int accepted);
+    // How many commits took the full-accept path (kept the batch's own state instead of restoring and replaying it).
+    // A test that compares the two paths reads it to know the path it meant to test is the one that ran.
+    long full_accepts_kept() const { return full_accepts_kept_; }
     bool gdn_apply_rows(int from, int to);      // recurrence-only replay of stored rows [from, to)
 
 
@@ -252,6 +255,7 @@ class Q4nxNpuForward {
     bool load_norms();
     std::vector<float> last_hidden_;  // last_hidden(): the post-final-norm state of the last position
     std::vector<float> last_residual_;  // and one norm earlier: the raw residual of the last position
+    long                full_accepts_kept_ = 0;   // commit_verify_rows(): see full_accepts_kept()
     std::vector<int>    tap_layers_;           // engine#1780: set_layer_taps()
     std::vector<float>* tap_sink_ = nullptr;
     size_t              tap_base_ = 0;         // where the current pass's rows start in *tap_sink_

npu/forward/src/q4nx_forward.cpp

@@ -2551,6 +2551,7 @@ bool Q4nxNpuForward::commit_verify_rows(int accepted) {
     // they are 11 ms + 7 ms per row, 67 ms of an 8-row round. NPU_COMMIT_FULL_REPLAY=1 keeps them, for an A/B.
     static const bool always_replay = std::getenv("NPU_COMMIT_FULL_REPLAY") != nullptr;
     const bool keep_batch_state = accepted == verify_rows_ && accepted > 0 && !always_replay && !replay_check;
+    if (keep_batch_state) full_accepts_kept_++;
     if (!keep_batch_state) {
         for (size_t l = 0; l < conv_state_.size(); l++) conv_state_[l] = snap_conv_[l];
         for (size_t l = 0; l < rec_state_.size(); l++) rec_state_[l] = snap_rec_[l];

tests/commit_full_accept_test.cpp

@@ -61,6 +61,14 @@ int run_once(const char* dir, const char* out) {
         if (!any) { std::printf("SKIP: the model has no recurrent (GDN) state\n"); return 77; }
     }
     if (!fwd.step(10, pos, logits)) { std::printf("FAIL step after the commit: %s\n", fwd.last_error()); return 1; }
+    // The negative control: each run must have taken the path it was started for, or the comparison below would
+    // compare a path with itself and pass while testing nothing.
+    const bool replay = std::getenv("NPU_COMMIT_FULL_REPLAY") != nullptr;
+    if (fwd.full_accepts_kept() != (replay ? 0 : 1)) {
+        std::printf("FAIL the %s run took the other commit path (%ld full accept(s) kept)\n", replay ? "replay" : "kept",
+                    fwd.full_accepts_kept());
+        return 1;
+    }
     FILE* f = std::fopen(out, "wb");   // file-create-ok: the test's own scratch file beside its build, removed below
     if (!f) return 1;
     auto put = [&](const std::vector<std::vector<float>>& vv) {