fix: clone prototype-less metadata objects in shallowClone

[DylanPiercey]

shallowClone dispatched on v.constructor with a case null: arm for prototype-less objects — but Object.create(null).constructor is undefined, so the arm was dead and such metadata crashed the compile with Cannot read properties of undefined (reading 'name'). The case now matches undefined and the default's message survives falsy constructors.

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🦋 Changeset detected

Latest commit: e48fa00

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@marko/compiler	Patch

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📥 Commits

Reviewing files that changed from the base of the PR and between de8fb5f and e48fa00.

📒 Files selected for processing (3)

• .changeset/shallow-clone-null-proto.md
• agent-feedback/bugs.md
• packages/compiler/src/babel-plugin/index.js

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[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 90.64%. Comparing base (de8fb5f) to head (e48fa00).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/compiler/src/babel-plugin/index.js	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3846   +/-   ##
=======================================
  Coverage   90.64%   90.64%           
=======================================
  Files         421      421           
  Lines       19953    19953           
  Branches     3705     3705           
=======================================
  Hits        18087    18087           
  Misses       1322     1322           
  Partials      544      544           

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