Auto-set ZARR3 and OCDBT to False for Pathways in config

[igorts-git]

Description

Address b/490520104: ZARR3 and OCDBT flags must be manually set to False for Pathways (should be default).

When enable_single_controller==True we automatically set ZARR3 and OCDBT flags to False.

One potentially controversial change as part of this PR is that the checkpoint conversion script to_maxtext now needs to be explicitly told enable_single_controller=True. I did not see a way around it.

FIXES: b/490520104

Pair-programmed with Gemini-CLI.

Tests

Added a unit test. Manually ran a tiny Pathways workload.

Checklist

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• I have performed a self-review of my code. For an optional AI review, add the gemini-review label.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[github-actions]

🤖 Hi @igorts-git, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[github-actions]

## 📋 Review Summary

This pull request correctly centralizes the logic for disabling ZARR3 and OCDBT when using Pathways (enable_single_controller=True) into the configuration system. This simplifies command-line invocations by removing the need to manually set these flags and ensures consistent default behavior across the codebase.

🔍 General Feedback

• The architectural choice to move the configuration overrides to a single source of truth in types.py is sound and enhances maintainability.
• The unit tests clearly and effectively verify that the overridden defaults behave as expected, covering both the default scenario and the edge case where colocated_python_checkpointing is set to True.
• Good job updating the documentation and standalone scripts to reflect the new unified approach.

[github-actions]

🟢 The path to the config file might need to be prefixed with `src/` to match the Python script execution path, assuming the user is running this from the repository root.

Suggested change

	# maxtext/configs/base.yml \
	# src/maxtext/configs/base.yml \