[WIP] Fix BatchNormalization layer export issue in ONNX model

[Copilot]

• Verify final name-fixing behavior and optimizer test conventions
• Add a focused regression test for unnamed optional outputs
• Remove the optimizer step that reassigns cleared output names
• Run targeted tests, lintrunner, secret scan, and security validation

• Fixes BatchNormalization layer with training_mode=1 results in incorrect ONNX model #2969

[Justin Chu (justinchuby)]

Copilot name fix pass is still needed. Let me know if onnx-ir needs updating or if there is another way to fix it

[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 72.65%. Comparing base (457a260) to head (a7ec3f0).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
onnxscript/optimizer/_optimizer.py	94.11%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2988      +/-   ##
==========================================
+ Coverage   72.63%   72.65%   +0.01%     
==========================================
  Files         265      265              
  Lines       32205    32231      +26     
  Branches     3041     3047       +6     
==========================================
+ Hits        23392    23417      +25     
  Misses       7779     7779              
- Partials     1034     1035       +1     

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[Bas Aarts (bas-aarts)]

Copilot, adding a call to RemoveUnusedNodesPass (the pass that started this issue to begin with) for the sole purpose of clearing the output names of unused inference BatchNormalization layers, is a heavy handed and lazy way to circumvent the issue.

Apologies for speaking out of turn Justin Chu (@justinchuby). I just had to.

[Justin Chu (justinchuby)]

Copilot please update as commented

[Copilot]

Copilot please update as commented

Updated in a7ec3f0. The second RemoveUnusedNodesPass is replaced by a BatchNormalization-only output-slot cleanup before NameFixPass; the regression now validates the serialized model with the ONNX checker. Current onnx-ir releases still need an upstream general fix.