Fix shm attachment support

[yellowhatter]

Fix SHM attachment support across all message types

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🏷️ Label-Based Checklist

Based on the labels applied to this PR, please complete these additional requirements:

Labels: bug, enhancement, breaking-change

🐛 Bug Fix Requirements

Since this PR is labeled as a bug fix, please ensure:

• Root cause documented - Explain what caused the bug in the PR description
• Reproduction test added - Test that fails on main branch without the fix
• Test passes with fix - The reproduction test passes with your changes
• Regression prevention - Test will catch if this bug reoccurs in the future
• Fix is minimal - Changes are focused only on fixing the bug
• Related bugs checked - Verified no similar bugs exist in related code

Why this matters: Bugs without tests often reoccur.

✨ Enhancement Requirements

Since this PR enhances existing functionality:

• Enhancement scope documented - Clear description of what is being improved
• Minimum necessary code - Implementation is as simple as possible, doesn't overcomplicate the system
• Backwards compatible - Existing code/APIs still work unchanged
• No new APIs added - Only improving existing functionality
• Tests updated - Existing tests pass, new test cases added if needed
• Performance improvement measured - If applicable, before/after metrics provided
• Documentation updated - Existing docs updated to reflect improvements
• User impact documented - How users benefit from this enhancement

Remember: Enhancements should not introduce new APIs or breaking changes.

💥 Breaking Change Requirements

Since this PR contains breaking changes:

• Breaking changes documented - Clear list of what breaks
• Migration guide provided - Step-by-step instructions for users
• Deprecation considered - Could this be done with deprecation warnings first?
• Version bump planned - Major or minor version bump needed
• Alternatives explored - Why is breaking change necessary?
• Impact assessed - How many users/use cases affected?

Note: Breaking changes should be discussed with maintainers before implementation.

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