Feat/pipeline add feature contract (#1637)

* Add feature contract to pipelinestep and pipeline

* Add tests

* Add processor tests

* PR feedback

* encorperate pr feedback

* type in doc

* oops

tests/processor/test_rename_processor.py

@@ -19,7 +19,9 @@ from pathlib import Path
 import numpy as np
 import torch
 
+from lerobot.configs.types import FeatureType
 from lerobot.processor import ProcessorStepRegistry, RenameProcessor, RobotProcessor, TransitionKey
+from tests.conftest import assert_contract_is_typed
 
 
 def create_transition(
@@ -406,3 +408,60 @@ def test_value_types_preserved():
     assert processed_obs["old_string"] == "hello"
     assert processed_obs["old_dict"] == {"nested": "value"}
     assert processed_obs["old_list"] == [1, 2, 3]
+
+
+def test_feature_contract_basic_renaming(policy_feature_factory):
+    processor = RenameProcessor(rename_map={"a": "x", "b": "y"})
+    features = {
+        "a": policy_feature_factory(FeatureType.STATE, (2,)),
+        "b": policy_feature_factory(FeatureType.ACTION, (3,)),
+        "c": policy_feature_factory(FeatureType.ENV, (1,)),
+    }
+
+    out = processor.feature_contract(features.copy())
+
+    # Values preserved and typed
+    assert out["x"] == features["a"]
+    assert out["y"] == features["b"]
+    assert out["c"] == features["c"]
+
+    assert_contract_is_typed(out)
+    # Input not mutated
+    assert set(features) == {"a", "b", "c"}
+
+
+def test_feature_contract_overlapping_keys(policy_feature_factory):
+    # Overlapping renames: both 'a' and 'b' exist. 'a'->'b', 'b'->'c'
+    processor = RenameProcessor(rename_map={"a": "b", "b": "c"})
+    features = {
+        "a": policy_feature_factory(FeatureType.STATE, (1,)),
+        "b": policy_feature_factory(FeatureType.STATE, (2,)),
+    }
+    out = processor.feature_contract(features)
+
+    assert set(out) == {"b", "c"}
+    assert out["b"] == features["a"]  # 'a' renamed to'b'
+    assert out["c"] == features["b"]  # 'b' renamed to 'c'
+    assert_contract_is_typed(out)
+
+
+def test_feature_contract_chained_processors(policy_feature_factory):
+    # Chain two rename processors at the contract level
+    processor1 = RenameProcessor(rename_map={"pos": "agent_position", "img": "camera_image"})
+    processor2 = RenameProcessor(
+        rename_map={"agent_position": "observation.state", "camera_image": "observation.image"}
+    )
+    pipeline = RobotProcessor([processor1, processor2])
+
+    spec = {
+        "pos": policy_feature_factory(FeatureType.STATE, (7,)),
+        "img": policy_feature_factory(FeatureType.VISUAL, (3, 64, 64)),
+        "extra": policy_feature_factory(FeatureType.ENV, (1,)),
+    }
+    out = pipeline.feature_contract(initial_features=spec)
+
+    assert set(out) == {"observation.state", "observation.image", "extra"}
+    assert out["observation.state"] == spec["pos"]
+    assert out["observation.image"] == spec["img"]
+    assert out["extra"] == spec["extra"]
+    assert_contract_is_typed(out)