fix(spend_tracking): store messages for all call types when enabled

[baiyuxi930826]

Summary

Fixes #34747

With general_settings.store_prompts_in_spend_logs: true, spend log rows for acompletion / aresponses still persisted LiteLLM_SpendLogs.messages as {}.

Root cause: _get_messages_for_spend_logs_payload only returned messages when call_type == "_arealtime".

Change

When the store gate is on, dump standard_logging_payload["messages"] for all call types (still {} when disabled, missing, or dump fails). Response storage was already gated correctly.

Test plan

• Logic coverage: acompletion / aresponses / realtime messages stored when gate on
• Gate off still returns {}
• Null-byte stripping still works via safe_dumps
• Unit tests updated in tests/test_litellm/proxy/spend_tracking/test_spend_tracking_utils.py

[CLAassistant]

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[greptile-apps]

Greptile Summary

This PR broadens gated spend-log message persistence beyond realtime calls.

• Serializes messages for every call type when prompt storage is enabled.
• Preserves empty-object fallbacks when storage is disabled, messages are absent, or serialization fails.
• Updates completion coverage and adds Responses API coverage.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete changed-code defect identified.

The implementation consistently applies the existing prompt-storage gate before serializing messages, retains safe empty fallbacks, and adds tests for the newly supported completion and Responses API paths.

Important Files Changed

Filename	Overview
litellm/proxy/spend_tracking/spend_tracking_utils.py	Removes the realtime-only restriction while preserving the existing storage gate and safe serialization fallbacks.
tests/test_litellm/proxy/spend_tracking/test_spend_tracking_utils.py	Updates completion expectations and adds Responses API coverage for the broadened message-storage behavior.

_{Reviews (1): Last reviewed commit: "fix(spend_tracking): store messages for ..." | Re-trigger Greptile}

[codspeed-hq]

Merging this PR will not alter performance

✅ 31 untouched benchmarks

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_{Comparing baiyuxi930826:fix/store-prompts-spend-logs (1d28b0a) with litellm_internal_staging (2412326)}