Three gaps in the Planner → Journal → Planner roundtrip:
1. SaveToJournalButton: wasn't including isDayBreak when building
waypoints for GPX generation
2. PlannerMap GPX import: wasn't setting overnight on Y.Maps when
importing waypoints with isDayBreak
3. use-yjs initial waypoints: wasn't setting overnight from isDayBreak
Also widened the waypoint type throughout the chain (api.sessions,
session.$id, SessionView, extractWaypoints) to carry isDayBreak.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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