Implements ports.Sink over Postgres (pgx/v5 + pgxpool, DSN from env per estate convention). This is the primary sink (ADR-003) and the source of the engine's durable, cross-restart dedup — the in-engine processed map is process-lifetime only. - Migrations (golang-migrate, NNN_name.up/down.sql per estate convention, applied from an embedded FS on New): users, videos, transcripts, summaries, sink_deliveries. Every user-owned table carries user_id (Stage-0 per-user isolation promise, data-model.md). summaries has UNIQUE(user_id, video_id) — at most one summary per video; highlights / takeaways are jsonb. - Deliver upserts the summary idempotently on (user_id, video_id) (ON CONFLICT DO UPDATE) inside one tx with its sink_delivery row. Re- delivering the same summary updates in place, never duplicates or errors. - Dedup reads (store methods, not a new port): HasSummary(ctx,userID, videoID) and SeenVideoIDs(ctx,userID) — both user_id-scoped, so one user never sees another's videos. summaries.video_id is intentionally not FK-constrained to videos at Stage 0: the sink receives only a Summary, so the dedup key stands alone; video-row persistence is the engine/source's concern, deferred. Tested against a real in-process Postgres via embedded-postgres (real SQL: constraints, ON CONFLICT, jsonb, user_id scoping) — no docker, no live cluster, no creds, fully offline. Deps: golang-migrate/migrate/v4 and jackc/pgx/v5 (runtime), fergusstrange/embedded-postgres + stretchr/testify (test-only). go mod tidy raised the go directive to 1.25.0 (minimum required by the dep graph; estate elsewhere already runs 1.26.1). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>