feat(perception): enforce six-layer freshness through receipt

src/k1link/perception/realtime_contract.py

@@ -181,6 +181,9 @@ class LayerEvidence:
     source_time_ns: int | None
     state: str
     payload_sha256: str | None
+    # Old callers omit this field. New layered results require it explicitly:
+    # recomputing a derived layer cannot refresh the age of its required inputs.
+    oldest_required_input_time_ns: int | None = None
 
     def __post_init__(self) -> None:
         if self.layer not in REQUIRED_LAYERS:
@@ -191,13 +194,22 @@ class LayerEvidence:
         if self.state == "unavailable":
             if any(
                 x is not None
-                for x in (self.source_sequence, self.source_time_ns, self.payload_sha256)
+                for x in (
+                    self.source_sequence,
+                    self.source_time_ns,
+                    self.payload_sha256,
+                    self.oldest_required_input_time_ns,
+                )
             ):
                 raise RealtimeContractError("unavailable evidence cannot claim a payload")
         else:
             _integer(self.source_sequence, "source_sequence")
             _integer(self.source_time_ns, "source_time_ns")
             _digest(self.payload_sha256, "payload_sha256")
+            if self.oldest_required_input_time_ns is not None:
+                _integer(self.oldest_required_input_time_ns, "oldest_required_input_time_ns")
+                if self.oldest_required_input_time_ns > cast(int, self.source_time_ns):
+                    raise RealtimeContractError("required input is newer than its layer")
 
 
 def validate_scene_layers(
@@ -223,7 +235,10 @@ def validate_scene_layers(
             raise RealtimeContractError("layer belongs to another stream epoch")
         if layer.source_time_ns is None:
             continue
-        age_ns = source_time_ns - layer.source_time_ns
+        if layer.source_time_ns > source_time_ns:
+            raise RealtimeContractError("future observations are not causal input")
+        stamp = layer.oldest_required_input_time_ns
+        age_ns = source_time_ns - (layer.source_time_ns if stamp is None else stamp)
         if age_ns < 0:
             raise RealtimeContractError("future observations are not causal input")
         if age_ns > maximum_layer_age_ms * 1_000_000 and layer.state in ("current", "held"):