fix(desktop): refresh active session for external messages

[yungchentang]

Summary

Fixes #53563.

Hermes Desktop now reacts when the currently open persisted session row is refreshed with additional externally appended messages. This covers Signal/gateway sessions whose sidebar metadata updates while the active chat timeline still has an older transcript loaded.

Root cause

The messaging sidebar slice used an id/title-only equality check, so Signal rows whose last_active, message_count, or preview changed could keep the same atom reference. Even when the session list refreshed, the active chat state did not observe that metadata change and did not rehydrate the open transcript.

Changes

• Add useActiveSessionExternalRefresh to watch the selected stored session row across recents and messaging slices.
• Hydrate the active runtime session when the refreshed persisted row has more messages than the in-memory transcript and the runtime is idle.
• Use a fuller messaging row signature so external metadata changes update the messaging session atom.
• Let stored-session hydration resolve profile metadata from messaging sessions as well as local recents.
• Add focused jsdom regression coverage for external Signal-style row updates, busy-runtime skips, and metadata-only updates.

Validation

• npm run test:ui -- use-active-session-external-refresh.test.tsx use-session-state-cache.test.tsx
• npm run typecheck
• npx eslint src/app/desktop-controller.tsx src/app/session/hooks/use-active-session-external-refresh.ts src/app/session/hooks/use-active-session-external-refresh.test.tsx
• npx prettier --check src/app/desktop-controller.tsx src/app/session/hooks/use-active-session-external-refresh.ts src/app/session/hooks/use-active-session-external-refresh.test.tsx
• git diff --cached --check

[teknium1]

Thanks for the focused Desktop investigation and regression coverage.

Automated hermes-sweeper review found that the requested behavior is already implemented on current main:

• 52d0d671e79ec1d5727881a6e8519332d04c1a07 (fix(desktop): poll messaging sessions so platform traffic appears live) updates messaging row comparison to include preview, message_count, and last_active, and is included in v2026.7.7.
• apps/desktop/src/app/desktop-controller.tsx:547 reloads persisted messages for the active messaging session and publishes them only when the transcript signature changed.
• apps/desktop/src/app/desktop-controller.tsx:926 polls the visible active messaging transcript every five seconds and refreshes immediately on activation/visibility changes.

This satisfies the Signal/gateway externally appended-message case described here, without needing the PR's older hook-based implementation.