simplify complete model runs

[tomjemmett]

the logic for the step counts and aggregations is identical, it makes sense to combine into one single step.

fixes #288 - at least, this doesn't appear to be an issue anymore. rather than just deleting the groupby/sum, added in a check to ensure there are no duplicated rows in the series. if there are then we will raise an assertion error.

this also simplifies the model iteration, instead of returning a tuple of the aggregated results and the step counts, the step counts are added to the results dictionary

[github-actions]

✅ A new build is available.

You can use the following to use pull the image into your local environment:

docker pull ghcr.io/the-strategy-unit/nhp_model:pr-620

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (65bc79c) to head (7f469b5).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #620   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           20        20           
  Lines         1130      1134    +4     
  Branches        56        58    +2     
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+ Hits          1130      1134    +4     

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[Copilot]

Pull request overview

Simplifies result aggregation by merging step counts handling into the standard model results combination flow. Previously, get_aggregate_results returned a tuple of (aggregated_results, step_counts) requiring a separate _combine_step_counts function; now step counts are an entry in the same dictionary, eliminating duplicate logic. As part of this, the historical "duplicate rows" workaround (issue #288) is replaced with a defensive _check_for_duplicates assertion.

Changes:

• Replace ModelRunResult tuple type with a plain dict[str, pd.Series] and place step_counts into the aggregations dict.
• Remove _combine_step_counts and route step counts through _combine_model_results, adding a _check_for_duplicates guard.
• Update unit/integration tests to match the new return shape and add coverage for the duplicate check.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/nhp/model/model_iteration.py	Change ModelRunResult to a dict and add step counts into the aggregations dict.
src/nhp/model/results.py	Remove _combine_step_counts; add _check_for_duplicates; reroute step counts through unified combine path.
src/nhp/model/run.py	Adjust unpacking of get_aggregate_results and read step counts from results dict.
tests/unit/nhp/model/test_results.py	Replace _combine_step_counts tests with _check_for_duplicates tests and update combine tests.
tests/unit/nhp/model/test_model_iteration.py	Update assertions; add test for None step counts.
tests/unit/nhp/model/test_run.py	Update mock side effects to new return shape.
tests/integration/nhp/model/test_single_model_run.py	Stop unpacking tuple; remove redundant step_counts assignment.