[wangyinz]

Closes #848

Summary

• Reject incompatible time references, sample intervals, and non-integer grid offsets before waveform arithmetic mutates either operand.
• Apply arithmetic only on the physical overlap; never resample inside TimeSeries or Seismogram operators.
• In MCXcor's explicit alignment path, move each shifted start time to the nearest beam-grid sample without changing samples, dt, or npts.

Maintainer decision

Each TimeSeries remains a dense uniform series. Different sampling intervals must be resampled explicitly. MCXcor uses whole-trace nearest-grid placement as its default alignment policy; general waveform arithmetic remains strict. No interpolation is performed implicitly.

Validation

• Focused Python arithmetic and complete MCXcor regressions: 21 passed
• Full native CTest: 17 passed
• Black, Python byte compilation, and git diff --check: passed

[codecov]

Codecov Report

❌ Patch coverage is 95.39474% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.71%. Comparing base (70f40e8) to head (9c267f3).

Files with missing lines	Patch %	Lines
cxx/test/arithmetic/test_waveform_arithmetic.cc	97.52%	2 Missing and 1 partial ⚠️
cxx/src/lib/seismic/waveform_arithmetic.h	0.00%	2 Missing ⚠️
cxx/src/lib/seismic/CoreSeismogram.cc	93.75%	0 Missing and 1 partial ⚠️
cxx/src/lib/seismic/CoreTimeSeries.cc	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #899      +/-   ##
==========================================
+ Coverage   70.63%   70.71%   +0.07%     
==========================================
  Files         177      179       +2     
  Lines       35193    35262      +69     
  Branches     2503     2490      -13     
==========================================
+ Hits        24860    24936      +76     
  Misses       9430     9430              
+ Partials      903      896       -7     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[wangyinz]

Draft decision required (renewed review)

An MCXcor owner must choose how strict sampled-grid arithmetic handles the existing 0.312835-sample output-window mismatch: documented resampling, nearest-index accumulation with a justified tolerance, or rejection. Do not restore unconditional time-grid snapping; this PR stays draft until that algorithm decision is made.