fix(ai): Keep single content input message

[alexander-alderman-webb]

Description

Store only one message from the conversation history on the gen_ai.request.messages attribute.

Remove prior logic that progressively trims away messages. Removes tests that check the existence of conversation histories or prompt messages that are no longer set on the attribute.

Issues

Closes#5335

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:)
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[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

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New Features ✨

• feat(anthropic): Set system instruction attribute by alexander-alderman-webb in #5353
• feat(google-genai): Set system instruction attribute by alexander-alderman-webb in #5354
• feat(langchain): Set system instruction attribute by alexander-alderman-webb in #5357
• feat(openai-agents): Set system instruction attribute by alexander-alderman-webb in #5355
• feat(pydantic-ai): Set system instruction attribute by alexander-alderman-webb in #5356

Bug Fixes 🐛

Ai

• fix(ai): Keep single content input message by alexander-alderman-webb in #5345

• fix(ai): Keep single content input message by alexander-alderman-webb in #5345

Internal Changes 🔧

• ci(release): Fix changelog-preview permissions by BYK in #5368
• ci: Fix path in AI integration tests by alexander-alderman-webb in #5347

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Embeddings input loses all but the last text

Medium Severity

The truncate_and_annotate_messages function is now used for embeddings input in LiteLLM and OpenAI integrations. With the new behavior that always returns only the last item, embeddings with multiple texts (e.g., ["First text", "Second text", "Third text"]) will only capture the last text (["Third text"]). This is data loss - when embedding multiple texts, users expect to see all texts that were embedded, not just the last one. The PR title mentions "message" but embeddings are fundamentally different from chat messages.

[alexander-alderman-webb]

will need to address this