feat(pi05): add training-time RTC

Extend trained RTC conditioning and postfix-only flow loss to plain PI05 so single-task checkpoints can use the same real-time chunking path as PI052.

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/policies/pi0_pi05/test_pi05_training_time_rtc.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+
+# Copyright 2026 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+
+import pytest
+import torch
+
+pytest.importorskip("transformers")
+
+from lerobot.policies.pi05.configuration_pi05 import PI05Config  # noqa: E402
+from lerobot.policies.pi05.modeling_pi05 import (  # noqa: E402
+    _build_flow_matching_inputs,
+    _reduce_training_rtc_loss,
+)
+
+
+def test_pi05_training_rtc_uses_clean_prefix_and_per_token_time():
+    actions = torch.tensor([[[1.0], [2.0], [3.0], [4.0]]])
+    noise = torch.tensor([[[10.0], [20.0], [30.0], [40.0]]])
+    time = torch.tensor([0.25])
+    prefix_mask = torch.tensor([[True, True, False, False]])
+
+    x_t, model_time = _build_flow_matching_inputs(actions, noise, time, prefix_mask)
+
+    assert model_time.tolist() == [[0.0, 0.0, 0.25, 0.25]]
+    assert torch.equal(x_t[:, :2], actions[:, :2])
+    assert torch.equal(x_t[:, 2:], 0.25 * noise[:, 2:] + 0.75 * actions[:, 2:])
+
+
+def test_pi05_training_rtc_loss_excludes_clean_prefix():
+    losses = torch.tensor([[[100.0], [100.0], [2.0], [4.0]]])
+    prefix_mask = torch.tensor([[True, True, False, False]])
+
+    loss = _reduce_training_rtc_loss(losses, prefix_mask, reduction="mean")
+
+    assert loss.item() == pytest.approx(3.0)
+
+
+@pytest.mark.parametrize("max_delay", [-1, 5])
+def test_pi05_config_rejects_invalid_training_rtc_delay(max_delay):
+    with pytest.raises(ValueError, match="rtc_training_max_delay"):
+        PI05Config(chunk_size=5, n_action_steps=5, rtc_training_max_delay=max_delay)

tests/policies/rtc/test_modeling_rtc.py

@@ -96,7 +96,7 @@ def test_rtc_processor_initialization_without_debug(rtc_config_debug_disabled):
 def test_rtc_processor_rejects_trained_mode_when_policy_does_not_support_it():
     config = RTCConfig(mode="trained")
 
-    with pytest.raises(ValueError, match="requires a Pi052 checkpoint"):
+    with pytest.raises(ValueError, match="requires a PI05-compatible checkpoint"):
         RTCProcessor(config)
 
     processor = RTCProcessor(config, trained_mode_supported=True)