Cherry-picked from PR #101542 by @sohomsahaun.
Two-step drill-down: provider static_select → model static_select,
with Back/Cancel buttons. Resolves through the same gateway callback
as Discord/Telegram, so persistence and failed-switch rollback
semantics come for free.
Changes:
- send_model_picker() posts Block Kit provider/model picker via chat_postMessage
- _handle_model_picker_action() dispatches provider/model/back/cancel actions
- _model_picker_state bounded dict (cap=100, workspace-scoped keys)
- Expired-state UX: missing state rewrites message to expiry notice
- Failure header: both exception and gateway error-prefix get 'Failed' header
- Index-based option values avoid Slack's 75-char value cap
- 21 tests covering send, action dispatch, gateway integration
Co-authored-by: Sohom Sahaun <ssahaun19@gmail.com>
1e69c12b64