Python: [BREAKING] Review preview behavioral ABCs for Protocol-compatible contracts #9626

Maintainer-owned issue. Community contributors: please do not pick up or start implementing this issue. This issue covers alpha and beta package extension points.

Problem

Several preview packages expose ABCs that appear to define behavioral contracts without substantial shared implementation. These should be reviewed before the packages stabilize.

Use Case and Evidence

Examples include FileSearchBackend in Azure Content Understanding, ConversationStore in DevUI, and store-provider contracts in Foundry Hosting. The audit found about 31 ABC/abstractmethod matches across six non-core runtime files.

Desired Outcome

Use Protocol-compatible structural contracts where appropriate while retaining inheritance where lifecycle or shared implementation justifies it.

Alternatives Considered

Converting every ABC would erase useful semantics; retaining every ABC would make simple integrations inherit framework classes unnecessarily.

Proposed Direction

Review each exported preview contract, document why it is an ABC or Protocol, and make any breaking cleanup before package release.

Scope and Non-Goals

Released contracts and Core middleware are excluded and tracked separately.

Language

Python

Contribution Intent

Maintainer-owned; implementation must wait for maintainer design agreement.

Acknowledgements

• I searched existing issues and did not find a duplicate.
• I will wait for explicit maintainer agreement before starting implementation of a non-trivial change.

Ownership: Core maintainers only; not available for community pickup.