feat(cp7): additive SessionTrace.memory_ref

proteus/runtime/trace.py

@@ -84,6 +84,8 @@ class SessionTrace(BaseModel):
         turns: Per-turn traces, in play order.
         outcome: ``"survived"`` or ``"eliminated"``.
         metrics: Computed session metrics (see ``runtime.metrics``).
+        memory_ref: Path/ref of the CP7 memory checkpoint shown at the handover,
+            or ``None`` when no memory pre-roll was used.
     """
 
     scenario: str
@@ -95,3 +97,5 @@ class SessionTrace(BaseModel):
     turns: list[TurnTrace] = Field(default_factory=list)
     outcome: Literal["survived", "eliminated"]
     metrics: dict[str, float] = Field(default_factory=dict)
+    # CP7: path/ref of the memory checkpoint shown at handover (None if unused).
+    memory_ref: str | None = None

tests/runtime/test_session_memory.py

@@ -0,0 +1,18 @@
+from proteus.runtime.trace import SessionTrace
+
+
+def test_session_trace_memory_ref_defaults_none_and_round_trips():
+    t = SessionTrace(
+        scenario="predator_evade", motive_category="survival", seed=42,
+        difficulty="easy", model="demo", outcome="survived",
+    )
+    assert t.memory_ref is None
+    t2 = SessionTrace.model_validate_json(t.model_dump_json())
+    assert t2.memory_ref is None
+
+    t3 = SessionTrace(
+        scenario="predator_evade", motive_category="survival", seed=42,
+        difficulty="easy", model="demo", outcome="survived",
+        memory_ref="demo@FIXED",
+    )
+    assert SessionTrace.model_validate_json(t3.model_dump_json()).memory_ref == "demo@FIXED"