Log avg_distance_per_infraction (port from emerge/temp_training)

Adds the metric:
  avg_distance_per_infraction = total_fleet_distance / max(1, total_fleet_infractions)
which tracks how far agents drive between offroad/collision/red-light
events — a useful single-scalar driving-quality signal for wandb.

The two underlying log fields already exist in puffer-4 and are already
aggregated per-step in add_log; only the binding-side ratio was missing.

my_log gains an `n` parameter and multiplies the per-agent-normalized
log->total_* fields by n to recover raw fleet totals. The ratio itself
is invariant to the 1/n scaling, but the un-normalization makes the
fmaxf(1.0f, total_infractions) clamp behave correctly: it floors the
denominator at "one infraction across the whole fleet", so a window
with zero infractions reports total fleet distance instead of
distance/epsilon. Both static_vec_log call sites in vecenv.h pass n.

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

Author: Eugene Vinitsky

sim/binding.c

@@ -182,7 +182,20 @@ void my_init(Env *env, Dict *kwargs) {
     }
 }
 
-void my_log(Log *log, Dict *out) {
+void my_log(Log *log, Dict *out, float n) {
+    // static_vec_aggregate_logs divides every Log field by total agent count n,
+    // so log->total_* are per-agent rates here. We want the fleet ratio
+    // sum_distance / sum_infractions; the n cancels in that ratio so we
+    // could compute it directly from the rates. We multiply by n anyway
+    // to recover the raw fleet totals: this makes the fmaxf(1.0f, ...)
+    // clamp meaningful (it floors the denominator at "1 infraction across
+    // the whole fleet"), so a zero-infraction window reports total fleet
+    // distance instead of distance / epsilon = absurd value.
+    float total_distance_travelled = log->total_distance_travelled * n;
+    float total_infractions = log->total_infractions * n;
+    float avg_distance_per_infraction =
+        total_distance_travelled / fmaxf(1.0f, total_infractions);
+
     dict_set(out, "score", log->score);
     dict_set(out, "episode_return", log->episode_return);
     dict_set(out, "episode_length", log->episode_length);
@@ -191,6 +204,7 @@ void my_log(Log *log, Dict *out) {
     dict_set(out, "num_goals_reached", log->num_goals_reached);
     dict_set(out, "avg_speed_per_agent", log->avg_speed_per_agent);
     dict_set(out, "dnf_rate", log->dnf_rate);
+    dict_set(out, "avg_distance_per_infraction", avg_distance_per_infraction);
     dict_set(out, "n", log->n);
 }
 

src/vecenv.h

@@ -238,7 +238,7 @@ extern const char* cudaGetErrorString(cudaError_t);
 
 // Forward declare env-provided functions (defined in binding.c after this include)
 void my_init(Env* env, Dict* kwargs);
-void my_log(Log* log, Dict* out);
+void my_log(Log* log, Dict* out, float n);
 void my_env_constants(void* env, Dict* out);
 
 struct StaticThreading {
@@ -643,7 +643,7 @@ void static_vec_log(StaticVec* vec, Dict* out) {
     for (int i = 0; i < vec->size; i++) {
         memset(&envs[i].log, 0, sizeof(Log));
     }
-    my_log(&aggregate, out);
+    my_log(&aggregate, out, n);
     dict_set(out, "n", n);
 }
 
@@ -653,7 +653,7 @@ void static_vec_eval_log(StaticVec* vec, Dict* out) {
     if (n == 0) {
         return;
     }
-    my_log(&aggregate, out);
+    my_log(&aggregate, out, n);
     dict_set(out, "n", n);
 }