Use URL run IDs for shareable flight booking sessions

[pranaygp]

Summary

• store the flight booking workflow run ID in the runId URL query param instead of localStorage
• keep stream reconnection wired through the existing /api/chat/[id]/stream path without changing startIndex handling
• clear the runId query param when the workflow ends or the user starts a new chat

Testing

• pnpm build

Screenshot

• No visual UI changes. Local verification screenshot captured from the running app: .codex-artifacts/flight-booking-home.png

[Copilot]

Pull request overview

This PR makes multi-turn flight booking chat sessions shareable by persisting the workflow run ID in the page URL (runId query param) instead of localStorage, while keeping stream reconnection behavior on /api/chat/[id]/stream intact.

Changes:

• Added helpers to read/write the workflow run ID to the runId URL query parameter.
• Updated session initialization/resume to derive the run ID from the URL (and clear it when the session ends).
• Updated stream reconnection logic to use the current run ID (via a ref/URL fallback) without altering SDK reconnect request data like startIndex.

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