feat(schema): optimize agent message format

[meguminnnnnnnnn]

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[codecov]

Codecov Report

❌ Patch coverage is 64.70588% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.74%. Comparing base (c12678a) to head (b53ee53).
⚠️ Report is 1 commits behind head on release/agentic_model.

Files with missing lines	Patch %	Lines
schema/agentic_message.go	64.70%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@                    Coverage Diff                    @@
##           release/agentic_model     #671      +/-   ##
=========================================================
- Coverage                  78.81%   78.74%   -0.07%     
=========================================================
  Files                        132      132              
  Lines                      13248    13252       +4     
=========================================================
- Hits                       10441    10435       -6     
- Misses                      1936     1945       +9     
- Partials                     871      872       +1     

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