feat(store): persist summary actions (watch/skip/save) — Stage-0 metric

The summary_actions table records the maintainer's act on a summary, the
column that makes the Stage-0 headline test ("acts on >=1 summary") queryable
(ui-spec.md §5, ADR-011). This is the gate lanes B/C build on.

- Migration 002: summary_actions (id, user_id, video_id TEXT, action, acted_at)
  with a CHECK on action IN ('watched','skipped','saved') and a UNIQUE
  (user_id, video_id, action). Per-user isolation: every row carries user_id.
- New actions.go: SetAction (idempotent, atomic watched<->skipped mutual
  exclusion in one tx; saved independent), ClearAction, ActionsFor for the list
  view, plus Go-side action validation.
- reads.go: additive SummaryRow.Actions, populated by composing ActionsFor
  (Go-side, not a SQL join — summaries.video_id is UUID, actions.video_id TEXT).
- embedded-postgres tests: set/clear, mutual exclusion, saved coexistence,
  idempotency, invalid rejection, user scoping, read-view surfacing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/adapters/store/actions_test.go

@@ -0,0 +1,161 @@
+package store_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSetActionThenActionsFor(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+
+	got, err := s.ActionsFor(ctx, userA, []string{videoX})
+	require.NoError(t, err)
+	require.Equal(t, map[string][]string{videoX: {"watched"}}, got)
+}
+
+func TestSetActionWatchedSkippedMutuallyExclusive(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	// Switching to skipped must clear watched (and vice versa).
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "skipped"))
+
+	got, err := s.ActionsFor(ctx, userA, []string{videoX})
+	require.NoError(t, err)
+	require.Equal(t, map[string][]string{videoX: {"skipped"}}, got, "skipped replaces watched")
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	got, err = s.ActionsFor(ctx, userA, []string{videoX})
+	require.NoError(t, err)
+	require.Equal(t, map[string][]string{videoX: {"watched"}}, got, "watched replaces skipped")
+}
+
+func TestSetActionSavedCoexists(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "saved"))
+
+	got, err := s.ActionsFor(ctx, userA, []string{videoX})
+	require.NoError(t, err)
+	// ActionsFor orders by action: saved, watched.
+	require.Equal(t, map[string][]string{videoX: {"saved", "watched"}}, got,
+		"saved is independent and coexists with watched")
+}
+
+func TestClearAction(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "saved"))
+	require.NoError(t, s.ClearAction(ctx, userA, videoX, "saved"))
+
+	got, err := s.ActionsFor(ctx, userA, []string{videoX})
+	require.NoError(t, err)
+	require.Empty(t, got, "cleared action no longer active")
+
+	// Clearing an action that was never set is a harmless no-op.
+	require.NoError(t, s.ClearAction(ctx, userA, videoX, "watched"))
+}
+
+func TestSetActionIsIdempotent(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	p := rawPool(t)
+	resetDB(t, p)
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+
+	var count int
+	require.NoError(t, p.QueryRow(ctx,
+		`SELECT count(*) FROM summary_actions
+		  WHERE user_id = $1 AND video_id = $2 AND action = 'watched'`,
+		userA, videoX).Scan(&count))
+	require.Equal(t, 1, count, "re-setting must refresh, not duplicate")
+}
+
+func TestSetActionRejectsInvalid(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.Error(t, s.SetAction(ctx, userA, videoX, "bookmarked"))
+	require.Error(t, s.ClearAction(ctx, userA, videoX, ""))
+}
+
+func TestActionsAreUserScoped(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+
+	got, err := s.ActionsFor(ctx, userB, []string{videoX})
+	require.NoError(t, err)
+	require.Empty(t, got, "user B must not see user A's actions")
+}
+
+func TestActionsForMultipleVideos(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	require.NoError(t, s.SetAction(ctx, userA, videoY, "saved"))
+
+	got, err := s.ActionsFor(ctx, userA, []string{videoX, videoY})
+	require.NoError(t, err)
+	require.Equal(t, map[string][]string{
+		videoX: {"watched"},
+		videoY: {"saved"},
+	}, got)
+
+	// Empty input -> empty (non-nil) map, no query.
+	empty, err := s.ActionsFor(ctx, userA, nil)
+	require.NoError(t, err)
+	require.Empty(t, empty)
+}
+
+func TestReadsSurfaceActions(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.Deliver(ctx, summary(userA, videoX, "body")))
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "watched"))
+	require.NoError(t, s.SetAction(ctx, userA, videoX, "saved"))
+
+	list, err := s.ListSummaries(ctx, userA, 50)
+	require.NoError(t, err)
+	require.Len(t, list, 1)
+	require.Equal(t, []string{"saved", "watched"}, list[0].Actions, "list view carries current actions")
+
+	detail, err := s.GetSummaryByVideo(ctx, userA, videoX)
+	require.NoError(t, err)
+	require.Equal(t, []string{"saved", "watched"}, detail.Actions, "detail view carries current actions")
+}
+
+func TestReadsSurfaceNoActionsAsNil(t *testing.T) {
+	ctx := context.Background()
+	s := newStore(t)
+	resetDB(t, rawPool(t))
+
+	require.NoError(t, s.Deliver(ctx, summary(userA, videoX, "body")))
+
+	list, err := s.ListSummaries(ctx, userA, 50)
+	require.NoError(t, err)
+	require.Len(t, list, 1)
+	require.Nil(t, list[0].Actions, "no actions -> nil slice")
+}