From 926531d85c0056337b9d1e8872e36479810b98e8 Mon Sep 17 00:00:00 2001
From: Eugene Vinitsky <eugenevinitsky@Eugenes-MacBook-Air.local>
Date: Sun, 3 May 2026 16:15:37 -0400
Subject: [PATCH] Add partner_blindness_prob (blind-agent robustness knob)

Ports the blind-agent feature from vcha/turbostream. Per-episode probability
that an agent sees zeroed partner observations for the whole episode, making
it an unpredictable hazard for the rest of traffic. Blind agents are masked
out of the PPO rollout buffer (GIGAFLOW Appendix B.4) so they don't pollute
the gradient.

Default 0.0 (off).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
---
 config/drive.ini |  4 ++++
 sim/datatypes.h  |  1 +
 sim/drive.h      | 16 +++++++++++++++-
 sim/env_fields.h |  4 +++-
 4 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/config/drive.ini b/config/drive.ini
index 3211f735b..b46a4e75b 100644
--- a/config/drive.ini
+++ b/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
diff --git a/sim/datatypes.h b/sim/datatypes.h
index ee278648a..8c3b62d0d 100644
--- a/sim/datatypes.h
+++ b/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];
diff --git a/sim/drive.h b/sim/drive.h
index 7d4126e9e..441b09adf 100644
--- a/sim/drive.h
+++ b/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++) {
diff --git a/sim/env_fields.h b/sim/env_fields.h
index 5182d0f71..80d04aa66 100644
--- a/sim/env_fields.h
+++ b/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