Use long text columns for conversation payloads

[gracjankubicki]

Summary

This updates the default database conversation storage schema to use longText columns for conversation message payloads.

The following agent_conversation_messages columns now use longText:

• content
• attachments
• tool_calls
• tool_results
• usage
• meta

Motivation

Agent conversation messages may contain large payloads, including long assistant responses, attachment metadata, tool calls, tool results, usage information, and provider metadata.

On MySQL-compatible databases, regular text columns can be too small for these payloads. Using longText gives the default conversation storage schema more room for larger AI conversation data without changing the public API.

Upgrade note

New installations will receive longText payload columns from the default conversation migration.

Applications that have already published and run the previous conversation migration should update their published migration or add an application-level migration to alter the existing agent_conversation_messages payload columns from text to longText.

Tests

• composer test -- tests/Feature/Storage/DatabaseConversationStoreTest.php
• composer test:lint
• vendor/bin/phpstan --memory-limit=-1
• composer test

[pushpak1300]

hey migration provided by the sdk should be forward looking. we probably don't need this migration. we can add it in release notes though.

[gracjankubicki]

Sounds good, removed the follow-up migration and left the upgrade path as a release note in the PR description.