fix: implement Speakeasy hook to fix multipart file field names

[chris-freeman-glean]

Fix multipart file field names with Speakeasy SDK hook

Problem

Speakeasy generates incorrect code that adds "[]" suffix to file field names in multipart forms:

# Generated (incorrect):
files.append((f_name + "[]", (file_name, content, content_type)))

# Expected:
files.append((f_name, (file_name, content, content_type)))

The "[]" suffix should only apply to regular form field arrays, not file fields.

Solution

Implemented an SDKInitHook that patches serialize_multipart_form at runtime:

1. Wraps the original function during SDK initialization
2. Post-processes the files list to remove "[]" suffix from file fields only
3. Identifies file fields by their tuple structure: (filename, content, [content_type])
4. Preserves "[]" suffix for regular form field arrays

Files Changed

• src/glean/api_client/_hooks/multipart_fix_hook.py - Hook implementation
• src/glean/api_client/_hooks/registration.py - Hook registration
• tests/test_multipart_fix_hook.py - Test coverage

Testing

Run python -m pytest tests/test_multipart_fix_hook.py -v

Notes

• Hook runs automatically on SDK initialization
• Generated code in forms.py still contains the original bug
• Fix applies at runtime during multipart serialization
• No breaking changes to public APIs