diff --git a/internal/adapters/store/videos.go b/internal/adapters/store/videos.go
new file mode 100644
index 0000000..64e63a5
--- /dev/null
+++ b/internal/adapters/store/videos.go
@@ -0,0 +1,77 @@
+package store
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"gitea.d-ma.be/mathias/tapir/internal/domain"
+)
+
+// UpsertVideo persists a video's metadata and returns its durable store id (the
+// videos.id UUID). It is idempotent on (user_id, provider, provider_video_id):
+// the same provider video for a user always resolves to the same row and the
+// same returned id, so the run loop can use that id as the stable dedup key
+// across restarts (it matches summaries.video_id once a summary exists).
+//
+// This lives in a separate file from store.go on purpose: the Sink port only
+// carries a domain.Summary (no title/channel), so video metadata is persisted
+// here, out of the delivery path, to keep the reader's rows readable.
+//
+// subscription_id is intentionally left NULL at Stage 0: the YouTube
+// Subscription.ID is a provider resource id, not the UUID that column expects,
+// and the subscriptions table is not part of this slice (data-model.md).
+func (s *Store) UpsertVideo(ctx context.Context, v domain.Video) (string, error) {
+	if v.UserID == "" {
+		return "", fmt.Errorf("store: upsert video: empty user id")
+	}
+	if v.ProviderVideoID == "" {
+		return "", fmt.Errorf("store: upsert video: empty provider video id")
+	}
+
+	tx, err := s.pool.Begin(ctx)
+	if err != nil {
+		return "", fmt.Errorf("store: begin: %w", err)
+	}
+	defer tx.Rollback(ctx) //nolint:errcheck // no-op after Commit
+
+	// Ensure the owning user exists (FK target) — same as the Deliver path.
+	if _, err := tx.Exec(ctx,
+		`INSERT INTO users (id) VALUES ($1) ON CONFLICT (id) DO NOTHING`,
+		v.UserID); err != nil {
+		return "", fmt.Errorf("store: upsert user: %w", err)
+	}
+
+	provider := string(v.Provider)
+	if provider == "" {
+		provider = string(domain.ProviderYouTube)
+	}
+
+	var id string
+	if err := tx.QueryRow(ctx,
+		`INSERT INTO videos (user_id, provider, provider_video_id, title, url, published_at)
+		 VALUES ($1, $2, $3, $4, $5, $6)
+		 ON CONFLICT (user_id, provider, provider_video_id) DO UPDATE SET
+		     title        = EXCLUDED.title,
+		     url          = EXCLUDED.url,
+		     published_at = EXCLUDED.published_at
+		 RETURNING id`,
+		v.UserID, provider, v.ProviderVideoID, v.Title, v.URL, nullTime(v.PublishedAt),
+	).Scan(&id); err != nil {
+		return "", fmt.Errorf("store: upsert video: %w", err)
+	}
+
+	if err := tx.Commit(ctx); err != nil {
+		return "", fmt.Errorf("store: commit: %w", err)
+	}
+	return id, nil
+}
+
+// nullTime maps the zero time to NULL so an unknown published_at is stored as
+// SQL NULL rather than year 0001.
+func nullTime(t time.Time) *time.Time {
+	if t.IsZero() {
+		return nil
+	}
+	return &t
+}
diff --git a/internal/adapters/store/videos_test.go b/internal/adapters/store/videos_test.go
new file mode 100644
index 0000000..a30d383
--- /dev/null
+++ b/internal/adapters/store/videos_test.go
@@ -0,0 +1,83 @@
+package store_test
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+
+	"gitea.d-ma.be/mathias/tapir/internal/domain"
+)
+
+func ytVideo(userID, provVideoID, title string) domain.Video {
+	return domain.Video{
+		UserID:          userID,
+		Provider:        domain.ProviderYouTube,
+		ProviderVideoID: provVideoID,
+		Title:           title,
+		URL:             "https://www.youtube.com/watch?v=" + provVideoID,
+		PublishedAt:     time.Date(2026, 6, 1, 12, 0, 0, 0, time.UTC),
+		// SubscriptionID is a provider resource id, not a UUID — must not be
+		// written to the UUID column. Set it to prove UpsertVideo ignores it.
+		SubscriptionID: "yt-subscription-resource-id",
+	}
+}
+
+func TestUpsertVideo_ReturnsStableID(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	id1, err := s.UpsertVideo(ctx, ytVideo(userA, "dQw4w9WgXcQ", "first title"))
+	require.NoError(t, err)
+	require.NotEmpty(t, id1)
+
+	// Same (user, provider, provider_video_id) -> same row, same id, updated meta.
+	id2, err := s.UpsertVideo(ctx, ytVideo(userA, "dQw4w9WgXcQ", "updated title"))
+	require.NoError(t, err)
+	require.Equal(t, id1, id2, "idempotent upsert must return the same durable id")
+
+	p := rawPool(t)
+	var (
+		title string
+		count int
+	)
+	require.NoError(t, p.QueryRow(ctx,
+		`SELECT title FROM videos WHERE id = $1`, id1).Scan(&title))
+	require.Equal(t, "updated title", title, "second upsert must update metadata in place")
+
+	require.NoError(t, p.QueryRow(ctx,
+		`SELECT count(*) FROM videos WHERE user_id = $1`, userA).Scan(&count))
+	require.Equal(t, 1, count, "must not duplicate the row")
+}
+
+func TestUpsertVideo_IDMatchesSummaryDedup(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	// Upsert assigns the durable video id; a summary delivered under that id
+	// must then show up in SeenVideoIDs — this is the cross-restart dedup chain.
+	id, err := s.UpsertVideo(ctx, ytVideo(userA, "abc123", "t"))
+	require.NoError(t, err)
+
+	require.NoError(t, s.Deliver(ctx, summary(userA, id, "the summary")))
+
+	seen, err := s.SeenVideoIDs(ctx, userA)
+	require.NoError(t, err)
+	require.True(t, seen[id], "the upserted video id must match the summary dedup key")
+}
+
+func TestUpsertVideo_PerUserIsolation(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	idA, err := s.UpsertVideo(ctx, ytVideo(userA, "same-provider-id", "a"))
+	require.NoError(t, err)
+	idB, err := s.UpsertVideo(ctx, ytVideo(userB, "same-provider-id", "b"))
+	require.NoError(t, err)
+
+	require.NotEqual(t, idA, idB, "same provider video for two users must be two distinct rows")
+}