add flow-matching policy with factory integration

[DeepforThink]

Type / Scope

• Type: Feature
• Scope: policies.flow_matching

Summary / Motivation

This PR introduces a new flow_matching policy in LeRobot and integrates it into the policy factory and preprocessing pipeline.

Motivation:

• Add an alternative continuous-action objective with simple ODE-based sampling.
• Keep compatibility with existing LeRobot policy interfaces.

Related issues

• Fixes / Closes: N/A
• Related: N/A

What changed

• Added flow_matching policy module:
  • src/lerobot/policies/flow_matching/configuration_flow_matching.py
  • src/lerobot/policies/flow_matching/modeling_flow_matching.py
  • src/lerobot/policies/flow_matching/processor_flow_matching.py
  • src/lerobot/policies/flow_matching/README.md
• Exported FlowMatchingConfig in src/lerobot/policies/__init__.py
• Integrated flow_matching into src/lerobot/policies/factory.py (config + processor paths)
• Added tests:
  • tests/policies/flow_matching/test_flow_matching.py
• Follow-up style fix in modeling_flow_matching.py to satisfy ruff checks

How was this tested (or how to run locally)

• Ran pre-commit on changed flow-matching files in conda env lerobot (including gitleaks) — all checks passed.
• Ran:
  • PYTHONPATH= PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 conda run -n lerobot python -m pytest -q tests/policies/flow_matching/test_flow_matching.py
  • Result: 2 passed, 1 warning in 0.57s

Checklist (required before merge)

• Linting/formatting run (pre-commit)
• Relevant tests pass locally (pytest)
• Documentation updated
• CI is green

Reviewer notes

Please focus on:

1. src/lerobot/policies/flow_matching/modeling_flow_matching.py (objective + Euler sampling path)
2. src/lerobot/policies/factory.py (registration and processor integration)
3. tests/policies/flow_matching/test_flow_matching.py (targeted behavioral coverage)

[DeepforThink]

Thanks for reviewing! I can quickly address any CI or design feedback

[Copilot]

Pull request overview

This PR adds a new flow_matching policy implementation to LeRobot and wires it into the existing policy factory + processor pipeline so it can be instantiated via the standard configuration/factory entrypoints.

Changes:

• Added FlowMatchingConfig, FlowMatchingPolicy, and a flow-matching processor module under src/lerobot/policies/flow_matching/.
• Integrated flow_matching into make_policy_config and make_pre_post_processors in src/lerobot/policies/factory.py, and exported FlowMatchingConfig from src/lerobot/policies/__init__.py.
• Added targeted unit tests for config factory creation and a basic forward/select_action path.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 14 comments.

Show a summary per file

File	Description
src/lerobot/policies/flow_matching/configuration_flow_matching.py	Introduces the FlowMatchingConfig dataclass and feature validation/delta index definitions.
src/lerobot/policies/flow_matching/modeling_flow_matching.py	Implements the Flow Matching model (vector field net), Euler sampling, and PreTrainedPolicy interface.
src/lerobot/policies/flow_matching/processor_flow_matching.py	Adds pre/post-processing pipeline factory for Flow Matching integration with LeRobot processors.
src/lerobot/policies/flow_matching/README.md	Documents the new policy module layout.
src/lerobot/policies/factory.py	Registers the new config type and processor factory selection.
src/lerobot/policies/__init__.py	Exports FlowMatchingConfig in the public policies module.
tests/policies/flow_matching/test_flow_matching.py	Adds initial tests for config factory instantiation and basic policy behavior.

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[DeepforThink]

Thanks! All review threads are resolved on my side. Could a maintainer please approve workflows so required checks can run?

[DeepforThink]

Thanks for the follow-up review 🙏

I just pushed the latest updates, and the PR is currently blocked by branch protection:

• “New changes require approval from someone other than the last pusher”
• Workflow approval may also be required to run all required checks

Could a maintainer please help with:

1. approving the workflow run (if pending), and
2. providing an approval review from someone other than the last pusher?

All review comments have been addressed on my side. Thank you!