feat(openai-agents): Truncate long messages

[alexander-alderman-webb]

Description

Cherry-picked from #5049

Issues

Closes TET-1208

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[linear]

TET-1208 Python SDK: truncate gen_ai messages

[codecov]

Codecov Report

❌ Patch coverage is 77.77778% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.02%. Comparing base (80ba8fb) to head (e913b9e).
⚠️ Report is 18 commits behind head on master.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
...k/integrations/openai_agents/spans/invoke_agent.py	75.00%	0 Missing and 1 partial ⚠️
sentry_sdk/integrations/openai_agents/utils.py	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5141   +/-   ##
=======================================
  Coverage   84.02%   84.02%           
=======================================
  Files         180      180           
  Lines       18223    18230    +7     
  Branches     3233     3235    +2     
=======================================
+ Hits        15311    15317    +6     
  Misses       1922     1922           
- Partials      990      991    +1     

Files with missing lines	Coverage Δ
...k/integrations/openai_agents/spans/invoke_agent.py	86.11% <75.00%> (-1.77%)	⬇️
sentry_sdk/integrations/openai_agents/utils.py	89.77% <80.00%> (-0.71%)	⬇️

... and 1 file with indirect coverage changes

[cursor]

Bug: Empty messages no longer set span data

When request_messages is an empty list, truncate_and_annotate_messages returns None, causing the span data to not be set. Previously, the code would set SPANDATA.GEN_AI_REQUEST_MESSAGES to an empty JSON array even when request_messages was empty. This behavioral change could break code expecting this field to always exist when messages are processed.