Martin Au-Yeung ee46c5ba0e Negotiate MCP extensions per app-server session (#36910) ...

## Why

App-server clients need to advertise structured MCP extension settings, including supported MCP App UI MIME types, rather than only opting into OpenAI form elicitation with a boolean.

## What changed

- Add an `extensions` map to initialize capabilities and preserve `mcpServerOpenaiFormElicitation` as a legacy alias for `openai/form`.
- Capture the declared extension profile when a thread is started, resumed, or forked, propagate it to subagents, and advertise it to downstream MCP servers during initialization.
- Keep the profile stable for the lifetime of the loaded session instead of changing it on later turns or direct tool calls.

## Testing

- Cover extension conversion, downstream MCP initialization, session isolation, legacy form support, and subagent inheritance.

GitOrigin-RevId: fbcedbb74ce788e574b0f884a4c45c4cedb9de54

2026-08-04 15:23:43 +00:00

..

InitializeParams.json

Negotiate MCP extensions per app-server session (#36910)

2026-08-04 15:23:43 +00:00

InitializeResponse.json

app-server: Return codex home in initialize response (#15689)

2026-03-24 16:13:34 -07:00