MaterializeDelta

The materialize delta for a cognitive map since its last materialize — the trigger signal the
region-materialize cron pulls. formation_events is the gated metric (a structural-drift count);
exceeds_threshold is the "should this re-materialize" answer.

{
    "cogmap_id": "b2008c45-9f31-4aae-8f49-0cadcb6ad25e",
    "exceeds_threshold": true,
    "formation_events": 0,
    "threshold": 0,
    "watermark": "ea4f9af3-b7e1-487b-b9a4-cd5c1b8015d5"
}