fix(flowchat): prevent pet session history from loading indefinitely

[bobleer]

Summary

Fix pet bubble navigation leaving an uncached historical session permanently loading. Programmatic opens restore history before selecting the session, but the active-only hydration guard discarded the returned records while the session was still inactive. Allow these restores to commit before activation and upgrade any weaker in-flight preload.

Type and Areas

Type: Bug fix

Areas: Web UI, desktop pet session navigation, historical session hydration

Motivation / Impact

Clicking a pet bubble for an inactive, uncached local session could select a metadata-only session after its history request had already settled, with no remaining request to populate the chat. The session now receives its restored messages before selection. Existing activate-first navigation retains its active-only hydration guard.

Verification

• Added a regression at the real SessionModule/FlowChatStore boundary. Confirmed the original code fails with empty turns and metadata-only; the fix passes both direct-open and concurrent-preload cases.
• Passed 268 tests with:

  pnpm --dir src/web-ui run test:run src/flow_chat/store/FlowChatStore.test.ts src/flow_chat/services/flow-chat-manager/SessionModule.test.ts src/app/services/openAgentCompanionSession.test.ts src/app/services/sessionSceneLifecycle.test.ts src/flow_chat/services/sessionActivation.test.ts src/flow_chat/services/storeSync.test.ts src/app/stores/sceneStore.test.ts

• Passed pnpm run check:web and git diff --check.
• No desktop manual click test or live remote end-to-end test was performed. Existing mocked coverage exercises remote workspace, Peer Device surface isolation, and Dispatch ownership; Remote Control was not exercised end to end.

Reviewer Notes

AI-assisted implementation and review. Validation consists of automated tests and frontend checks; desktop and remote manual validation remains outstanding. No persisted schema, protocol, user-facing copy, or styling changes.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable (not applicable).