1. Watermark Messages: - Nov 16: Simple - single my_state_watermark,
single state_watermark in response - Main: Complex - per-resource
my_resource_watermarks HashMap, resource counts, content hashes 2.
DataAvailableNotification: - Nov 16: Doesn't exist - Main: New message
type that triggers watermark exchanges 3. FK Mapper: - Nov 16: Sets
missing FKs to NULL, applies all records - Main: Marks records with
missing FKs as failed, filters them out 4. Watermark Storage (internal,
not in messages): - Nov 16: Single last_watermark per resource - Main:
Dual watermarks - cursor_watermark and
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