Enable variable precision checkpoint-restart files

[iboutle]

PR Summary

Sci/Tech Reviewer: Harry Shepherd (@harry-shepherd)
Code Reviewer: Ricky Wong (@mo-rickywong)

Currently, checkpoint-restart files are forced to be double-precision, by the setting of prec="8" in various xml files. Typically, we run the model at single-precision, and therefore are writing checkpoint-restart files which are double the size they need to be.

These PRs fix this, by removing the precision from the xml file specification, and setting it instead via the model-xios interface depending on the precision of the model.

They also provide some preparatory work required for packing of diagnostics, namely removing the precision specification from diagnostic files, instead specifying the precision in the diagnostics definition. In future this will allow packed prec="2" diagnostics to be added, without their precision being over-ridden by the prec specification of the diagnostic files.

• linked Enable variable precision checkpoint-restart files lfric_apps#740

Code Quality Checklist

• I have performed a self-review of my own code
• My code follows the project's style guidelines
• Comments have been included that aid understanding and enhance the readability of the code
• My changes generate no new warnings
• All automated checks in the CI pipeline have completed successfully

Testing

• I have tested this change locally, using the LFRic Core rose-stem suite
• If required (e.g. API changes) I have also run the LFRic Apps test suite using this branch
• If any tests fail (rose-stem or CI) the reason is understood and acceptable (e.g. kgo changes)
• I have added tests to cover new functionality as appropriate (e.g. system tests, unit tests, etc.)
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trac.log

Test Suite Results - lfric_core - spdump_core/run1

Suite Information

Item	Value
Suite Name	spdump_core/run1
Suite User	ian.boutle
Workflow Start	2026-08-27T12:24:51
Groups Run	developer

Dependency	Reference	Main Like
lfric_core	iboutle/lfric_core@spdump_core	False
SimSys_Scripts	MetOffice/SimSys_Scripts@cab3315	True

Task Information

✅ succeeded tasks - 433

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Performance Impact

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AI Assistance and Attribution

• Some of the content of this change has been produced with the assistance of Generative AI tool name (e.g., Met Office Github Copilot Enterprise, Github Copilot Personal, ChatGPT GPT-4, etc) and I have followed the Simulation Systems AI policy (including attribution labels)

Documentation

• Where appropriate I have updated documentation related to this change and confirmed that it builds correctly

PSyclone Approval

• If you have edited any PSyclone-related code (e.g. PSyKAl-lite, Kernel interface, optimisation scripts, LFRic data structure code) then please contact the HPC Optimisation Team

Sci/Tech Review

• I understand this area of code and the changes being added
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• Sufficient testing has been completed

(Please alert the code reviewer via a tag when you have approved the SR)

Code Review

• All dependencies have been resolved
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• Documentation is complete and accurate
• Security considerations have been addressed
• Performance impact is acceptable