Refactor chat session boundaries and host hook layout

[roackb2]

Summary

• move chat host orchestration toward the documented hook/controller layout
• split chat session persistence into a file-backed repository and separate session record helpers
• make the TUI session hook call core session services instead of touching storage directly
• update boundary docs/comments and add coverage for the session service changes

Verification

• yarn eslint
• yarn typecheck
• focused vitest coverage for chat/session/control-plane paths
• npx tsx scripts/verify-tui-session-switch.tsx
• real ask-mode smoke checks with --new-session and --latest

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Keep chat session storage path configurable

The session hook no longer accepts sessionCatalogFile and now always builds its service config from stateRoot, which hardwires persistence to stateRoot/chat-sessions.catalog.json. This breaks callers that provide a non-default catalog path (for example embedding runtimes), and it can desynchronize state because turn execution still reads from runtime.sessionCatalogFile in the run controller path. Please thread the runtime-provided session catalog path through useChatSessions so both session CRUD and turn execution target the same file.

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