[anishmehta24]

Fixes #40504

agg with a list combines the per-partition count/size results with s.agg(['sum']), so the row came back labelled sum. This combines them with {base_func: 'sum'} instead, which keeps the count/size label. Added a test to frames_test.py and a CHANGES.md entry.

Written with help from Claude.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 56.24%. Comparing base (76f6e6d) to head (93827f0).
⚠️ Report is 111 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #40506      +/-   ##
============================================
+ Coverage     56.16%   56.24%   +0.07%     
  Complexity     2288     2288              
============================================
  Files          1124     1124              
  Lines        178336   178361      +25     
  Branches       1489     1489              
============================================
+ Hits         100170   100316     +146     
+ Misses        75645    75524     -121     
  Partials       2521     2521              

Flag	Coverage Δ
python	79.70% <100.00%> (+0.15%)	⬆️

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[github-actions]

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R: @damccorm for label python.

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[damccorm]

Thanks!