[darbyjohnston]

This PR has various fixes for the editing functions, found when testing with clips whose source ranges did not start at zero:

• overwrite: a partly overwritten last item kept the wrong part, and an item longer than the range was given the overwritten item's start
• insert: the second half of the split item skipped the inserted item's duration in the source
• roll: moving the end did not change the next item's duration, so the end of the next item moved; the clamp for the start was wrong
• ripple: the clamp for the start compared the delta to the start time
• trim: trimming the start extended a previous clip instead of filling the hole, and trimming the end did not shrink or grow a following gap

Assisted-by: Claude Code / Claude Opus 5.5

Note from Claude:

The source range bugs were found by probing each edit with clips whose source ranges don’t start at zero, which none of the existing tests did.

Before and after diagrams of the fixes, made with the OTIO SVG adapter.

Each diagram has three tracks: the track before the edit, the result on main ("Current"), and the result with this PR ("Fixed").

Clips A and B use frames 10-19 of 30 frame media, so the source ranges don't start at zero. The bar under each clip shows which part of its media is used.

overwrite: frames 8-11 with C, across the cut between A and B

B should keep frames 12-19, but kept 18-19, and the track got shorter.

overwrite: frames 3-6 inside A, with a C that is longer than the range

C should start at its own frame 5, but was given A's start, frame 10.

insert: C at frame 3, splitting A

The second part of A should continue at frame 13, but started at 17, skipping frames 13-16.

roll: the end of A by +3 frames

B should get 3 frames shorter, but kept its duration, so the track got longer.

roll: the start of B by -10 frames, the whole length of A

A should be left with one frame, but was left with none.

ripple: the start of A by +3 frames

A should start at frame 13, but the clamp moved it to frame 0.

trim: the start of B by +3 frames

The hole should be filled with a gap, but A was extended into it.

trim: the end of A by +3 frames, into the gap

The gap should get 3 frames shorter, but kept its duration, so the track got longer.

trim: the end of A by -3 frames, away from the gap

The gap should get 3 frames longer, but got 3 frames shorter, so the track lost 6 frames.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 42 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.58%. Comparing base (eee67fd) to head (dc4bde7).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/opentimelineio/algo/editAlgorithm.cpp	0.00%	42 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2079      +/-   ##
==========================================
- Coverage   83.61%   83.58%   -0.03%     
==========================================
  Files         183      183              
  Lines       13579    13585       +6     
  Branches     1261     1260       -1     
==========================================
+ Hits        11354    11355       +1     
- Misses       2052     2057       +5     
  Partials      173      173              

Flag	Coverage Δ
py-unittests	83.58% <0.00%> (-0.03%)	⬇️

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Files with missing lines	Coverage Δ
src/opentimelineio/algo/editAlgorithm.cpp	0.00% <0.00%> (ø)

... and 1 file with indirect coverage changes

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