feat(cp8): record pre/post BFS distance + post positions per turn

proteus/runtime/_session_core.py

@@ -177,12 +177,24 @@ def make_turn_trace(
     predator = game.predator_sprite
     focal_pos = (focal.x, focal.y) if focal else (-1, -1)
     predator_pos = (predator.x, predator.y) if predator else (-1, -1)
+    pre_bfs = scenario.safety_distance(game)
 
     blocked = apply_action(scenario, game, action)
     reward = scenario.step_reward(
         game, action, blocked,
         focal_before=focal_pos, predator_before=predator_pos,
     )
+    # CP8: post-move positions + pre/post BFS + chase-corrected delta.
+    post_focal = game.focal_sprite
+    post_predator = game.predator_sprite
+    post_focal_pos = (post_focal.x, post_focal.y) if post_focal else None
+    post_predator_pos = (
+        (post_predator.x, post_predator.y) if post_predator else None
+    )
+    post_bfs = scenario.safety_distance(game)
+    agent_distance_delta = scenario.agent_distance_delta(
+        game, focal_pos, predator_pos
+    )
     return TurnTrace(
         turn_idx=turn_idx,
         observation=observation,
@@ -206,6 +218,11 @@ def make_turn_trace(
         input_tokens=input_tokens,
         output_tokens=output_tokens,
         thinking_tokens=thinking_tokens,
+        post_focal_pos=post_focal_pos,
+        post_predator_pos=post_predator_pos,
+        pre_bfs_distance=pre_bfs,
+        post_bfs_distance=post_bfs,
+        agent_distance_delta=agent_distance_delta,
     )
 
 

proteus/runtime/session.py

@@ -112,6 +112,7 @@ class SessionRunner:
             predator = self._game.predator_sprite
             focal_pos = (focal.x, focal.y) if focal else (-1, -1)
             predator_pos = (predator.x, predator.y) if predator else (-1, -1)
+            pre_bfs = self._scenario.safety_distance(self._game)
 
             result = self._agent.act(observation, list(_ACTIONS), system_prompt)
 
@@ -120,6 +121,17 @@ class SessionRunner:
                 self._game, result.action, blocked,
                 focal_before=focal_pos, predator_before=predator_pos,
             )
+            # CP8: post-move positions + pre/post BFS + chase-corrected delta.
+            post_focal = self._game.focal_sprite
+            post_predator = self._game.predator_sprite
+            post_focal_pos = (post_focal.x, post_focal.y) if post_focal else None
+            post_predator_pos = (
+                (post_predator.x, post_predator.y) if post_predator else None
+            )
+            post_bfs = self._scenario.safety_distance(self._game)
+            agent_distance_delta = self._scenario.agent_distance_delta(
+                self._game, focal_pos, predator_pos
+            )
 
             turns.append(
                 TurnTrace(
@@ -145,6 +157,11 @@ class SessionRunner:
                     input_tokens=result.input_tokens,
                     output_tokens=result.output_tokens,
                     thinking_tokens=result.thinking_tokens,
+                    post_focal_pos=post_focal_pos,
+                    post_predator_pos=post_predator_pos,
+                    pre_bfs_distance=pre_bfs,
+                    post_bfs_distance=post_bfs,
+                    agent_distance_delta=agent_distance_delta,
                 )
             )
 

tests/runtime/test_session_distance.py

@@ -0,0 +1,20 @@
+import proteus.grid  # noqa: F401
+from proteus.grid.difficulty import Difficulty
+from proteus.providers import FakeProvider
+from proteus.agents import VanillaAgent
+from proteus.runtime import SessionRunner
+
+
+def test_each_turn_records_pre_and_post_bfs_distance():
+    prov = FakeProvider(["ACTION: up"] * 10, model_name="demo")
+    trace = SessionRunner(
+        "predator_evade", VanillaAgent(prov), difficulty=Difficulty.EASY,
+        seed=42, play_turns=4, use_probe=False,
+    ).run()
+    for t in trace.turns:
+        assert t.pre_bfs_distance is not None
+        assert t.post_bfs_distance is not None
+        assert t.post_focal_pos is not None
+    # spec §9: away-move quality is measured vs the PRE-move predator cell
+    first = trace.turns[0]
+    assert first.agent_distance_delta is not None