client: persist interactive conversation state across navigation and restarts

[ananmouaz]

Problem / motivation

The new AiQuestion and part-action APIs enable interactive conversations, but host apps must retain accepted answers and pending state when transcript rows are evicted, screens are recreated, or the process restarts. A reliable recipe and explicit lifecycle contracts are needed beyond the happy path.

Proposed solution

Demonstrate durable restoration of messages, question answers, and pending actions using a pluggable application-owned store. Design correlated approval requests/responses as a separate, reviewable engine slice where needed. Coordinate in-flight reconnect with #98 rather than introduce another reconnect mechanism.

Acceptance criteria

• Define ownership and serialization of settled answers and pending/failed actions, including migration/versioning expectations for stored application state.
• Demonstrate restoring AiQuestion answers after lazy-list eviction, navigation, and process recreation without re-submitting accepted actions.
• Define action identity and how the current message ID + original part index contract remains valid across restoration; do not silently rely on reordered parts keeping the same identity.
• Specify pending/approved/denied/expired approval behavior, correlated responses, and retry handling before implementing public engine changes.
• Cover duplicate responses, stale/late events, superseded turns, denial, disconnection, foreground/background transitions and explicit stop with lifecycle tests.
• Coordinate server-side deduplication for side effects; document that client persistence alone cannot guarantee exactly-once execution.
• Provide a runnable persistence recipe and document which restoration works offline versus requires a resumable backend.

Dependencies / boundaries

Build on the hosted-agent adapter #153 for remote run/session identities. Extend the reconnect design in #98. Keep the durable store pluggable and preserve current saved-message compatibility unless an explicit migration is designed.

Background

October 3 library review and interactive foundation release PR #152.