refactor!: rename Capability::OUTPUT_STRUCTURED to STRUCTURED_OUTPUT

[OskarStark]

Summary

• Renamed the capability constant OUTPUT_STRUCTURED to STRUCTURED_OUTPUT for better naming consistency
• Changed the constant value from 'output-structured' to 'structured-output'
• Added UPGRADE.md documentation for the breaking change

Breaking Change

This is a breaking change that requires users to update their code:

• All references to Capability::OUTPUT_STRUCTURED must be changed to Capability::STRUCTURED_OUTPUT
• If storing or comparing capability strings directly, update from 'output-structured' to 'structured-output'

Test plan

• All tests pass with the renamed constant
• Updated all references in the codebase (6 files)
• Added upgrade documentation

🤖 Generated with Claude Code

[OskarStark]

It reads more natural to me

[chr-hertel]

i would for now favor to list the BC breaking PRs in the releases instead doing an upgrade guide - it's just additional work while a lot of stuff is still changing, sorry

[chr-hertel]

Yes, i had a hard time with this - my reasoning was that all capabilities where named INPUT_* and OUTPUT_* - so from a specific angle it is now less consistent 😆

If you feel like this is in conflict to the structured output feature - we could rename it to OUTPUT_JSON ?

[OskarStark]

To me structured output is the thing, people are talking about when talking about capabilities

[chr-hertel]

yea, i feel you - it's both inconsistent - what other options do we have 🤔

what do you think about splitting into three capability classes? like InputCapability::TEXT, OutputCapability::STRUCTURED and FeatureCapability::TOOL?

it will be important in the next steps to validate the models input and output capabilities while using the chain/platform - this is why i use those fixed categories in my head - what makes it easy?

another idea, next to OUTPUT_JSON would be OUTPUT_OBJECT - it's also called ObjectResponse and not StructuredResponse - i feel like OUTPUT_STRUCTURED_OUTPUT would be too much :D