Add partner_blindness_prob (blind-agent robustness knob)

config/drive.ini

@@ -81,6 +81,10 @@ obs_slots_lane = 40
 obs_slots_boundary = 40
 obs_slots_partners = 16
 obs_slots_traffic_controls = 4
+; --- Robustness features ---
+; Per-episode probability that an agent is blind to other agents for the whole episode.
+; Blind agents see zeroed partner observations and are masked out of the PPO rollout buffer.
+partner_blindness_prob = 0.0
 ; --- Observation normalization (meters) ---
 norm_goal_offset_m = 100.0
 norm_xy_offset_m = 100.0

sim/datatypes.h

@@ -181,6 +181,7 @@ struct Agent {
     float distance_since_spawn;
     int stopped;
     int removed;
+    int is_blind_partner; // Episode-level flag: agent sees no other agents
     // Goal positions
     float goal_positions_x[MAX_TARGET_POINTS];
     float goal_positions_y[MAX_TARGET_POINTS];

sim/drive.h

@@ -236,6 +236,8 @@ struct Drive {
     float obs_range_partner_m;
     float obs_range_traffic_control_m;
     int obs_size;
+    // Robustness features
+    float partner_blindness_prob;
 };
 
 #include "dataloader.h"
@@ -2520,6 +2522,11 @@ static int write_reward_target_obs(Drive *env, Agent *ego, float *obs, int obs_i
 }
 
 static int write_partner_obs(Drive *env, Agent *ego, int agent_idx, float *obs, int obs_idx, int *partner_count) {
+    if (ego->is_blind_partner) {
+        // Partner slots stay zero (compute_observations memset's the buffer).
+        *partner_count = 0;
+        return obs_idx + env->obs_slots_partners * PARTNER_FEATURES;
+    }
     typedef struct {
         int index;
         float dist_sq;
@@ -2884,6 +2891,11 @@ void c_reset(Drive *env) {
         env->logs[i] = (Log) {0};
         Agent *agent = &env->agents[i];
 
+        // Sample episode-level erratic flags before any continue, so every
+        // agent (including those that fail to spawn) gets a fresh value.
+        agent->is_blind_partner =
+            (env->partner_blindness_prob > 0.0f && random_uniform(0.0f, 1.0f) < env->partner_blindness_prob) ? 1 : 0;
+
         if (env->simulation_mode == SIMULATION_GIGAFLOW && agent->removed) {
             continue;
         }
@@ -2904,9 +2916,11 @@ void c_step(Drive *env) {
     memset(env->masks, 0, env->num_agents * sizeof(unsigned char));
     env->timestep++;
 
+    // Erratic-driver flags (e.g. blind partners) act in the world but their
+    // transitions are excluded from the PPO rollout buffer per GIGAFLOW Appendix B.4.
     for (int i = 0; i < env->num_agents; i++) {
         Agent *a = &env->agents[i];
-        env->masks[i] = !(a->stopped || a->removed);
+        env->masks[i] = !(a->stopped || a->removed || a->is_blind_partner);
     }
 
     for (int i = 0; i < env->num_moving_log_agents; i++) {

sim/env_fields.h

@@ -63,6 +63,8 @@
     F(float, obs_range_road_behind_m)                                                                                  \
     F(float, obs_range_road_side_m)                                                                                    \
     F(float, obs_range_partner_m)                                                                                      \
-    F(float, obs_range_traffic_control_m)
+    F(float, obs_range_traffic_control_m)                                                                              \
+    /* Robustness features */                                                                                          \
+    F(float, partner_blindness_prob)
 
 #endif