## What changed
Carry `ContextWindowId` through session metadata, compaction checkpoints, rollout recording, and thread creation instead of converting IDs to strings. Add deserialization and JSON schema support while preserving the serialized string format and legacy numeric compaction IDs.
Validate deserialized IDs as UUIDv7 values before restoring context windows, preserving the existing handling of unsupported IDs.
GitOrigin-RevId: fda329d0654f438171a955c9f75550817c32c047