Share the cloud conversation runtime adapter

[Neonforge98]

Problem

The shared-session React hook owned cloud token refresh, initial plane reconstruction, incremental plane loading, hidden-runner access settings, live overlay registration, cleanup, and signal bumps. A Work Item conversation bridge would have to copy all of that plumbing, which is the main reason the earlier #844 implementation grew large.

Solution

Move those I/O boundaries into one imperative cloudConversationRuntime adapter and make the existing hook call it. The adapter remains a thin layer over #944 conversation continuation primitives; it does not own dispatch, terminal state, cursors, or audience routing. Initial context loading keeps the same bounded 60-row window, current-intent exclusion, local-root merge, and author attribution.

This is a behavior-preserving extraction. Team Chat remains outside the Agent conversation plane, and no cloud API, schema, or capability behavior changes.

Potential risks

The adapter updates the same Jotai atoms through the instrumented store instead of hook-local setters. Those atoms use the same store and notify the same subscribers. Token refresh now goes through the existing imperative getFreshCloudAccessToken helper, which performs the same compare-and-set auth update.

Verification

• 22 focused runtime, continuation, cursor, and client tests pass
• TypeScript and modified-file ESLint pass
• Madge: 6462 files, no circular dependencies
• Prettier, diff check, and repository commit hooks pass

[Neonforge98]

Superseded by the final two-PR design: #844 removes the Work Item-specific remote continuation bridge, and stacked #939 keeps the reusable audience routing plus sender-local provider-native continuation. This dispatcher/store/handoff stack is intentionally retired.