feat(runner): bound auto-summarize to a recency window

In automatic mode the scheduler now only summarizes videos published within
TAPIR_AUTO_SUMMARIZE_WINDOW (default ~7d). Older videos are still discovered
and listed — they keep the manual "Summarize" affordance — but are not
auto-processed, so a large back-catalogue (the maintainer's ~256-deep queue)
stops self-inflicting 429s against the per-IP caption gate each cycle (UX
review B1, recency design).

- runner.WithAutoWindow + Stats.SkippedTooOld; tooOld() treats a zero window
  as disabled and an undated video as never-aged-out (processed, not stranded).
- An explicit manual request bypasses the bound even in auto mode (requested
  videos are loaded in auto mode when a window is active).
- Wired through cmdRun, the scheduler's per-user runner, sumStats, and pass
  logging. config: TAPIR_AUTO_SUMMARIZE_WINDOW (default 168h), .env.example.
- Account copy (A7) updated to match: "Automatic summarizes new videos from
  about the last week; older videos stay browsable — summarize on demand."

The rate gate is untouched; the manual path still serialises through it. This
bounds auto LOAD, it does not fetch harder.

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

internal/runner/runner_test.go

@@ -234,6 +234,96 @@ func TestRunOnce_ManualMode_ProcessesRequested(t *testing.T) {
 	require.Equal(t, []string{"id-v1"}, st.cleared, "the queue flag is cleared after summarizing")
 }
 
+// --- recency window (B1) ---------------------------------------------------
+
+// TestRunOnce_AutoMode_SkipsOldVideos: with a recency window set, auto mode
+// summarizes only videos published within the window; older ones are discovered
+// (upserted) but not auto-summarized — they wait for a manual request.
+func TestRunOnce_AutoMode_SkipsOldVideos(t *testing.T) {
+	base := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	src := &fakeSource{
+		subs: []domain.Subscription{sub("chan1", "Channel One")},
+		videos: map[string][]domain.Video{"chan1": {
+			vidAt("recent", "Recent", base.Add(-24*time.Hour)), // 1d old → in window
+			vidAt("old", "Old", base.Add(-30*24*time.Hour)),    // 30d old → out of window
+		}},
+	}
+	st := &fakeStore{seen: map[string]bool{}, auto: true}
+	sink := &recordingSink{}
+	eng := usecase.NewEngine(src, fakeSummarizer{}, sink)
+	r := runner.New(src, st, eng, testUser, quietLogger(),
+		runner.WithAutoWindow(7*24*time.Hour), runner.WithClock(func() time.Time { return base }))
+
+	stats, err := r.RunOnce(context.Background())
+	require.NoError(t, err)
+	require.Equal(t, 1, stats.Summarized, "only the recent video is auto-summarized")
+	require.Equal(t, 1, stats.SkippedTooOld, "the old video is skipped by the recency bound")
+	require.Len(t, sink.delivered, 1)
+	require.Equal(t, "id-recent", sink.delivered[0].VideoID)
+	require.Len(t, st.upserted, 2, "both videos are still discovered and listed")
+}
+
+// TestRunOnce_AutoMode_OldVideoRequestedBypassesWindow: an explicit manual
+// request (summarize_requested) overrides the recency bound even in auto mode.
+func TestRunOnce_AutoMode_OldVideoRequestedBypassesWindow(t *testing.T) {
+	base := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	src := &fakeSource{
+		subs:   []domain.Subscription{sub("chan1", "Channel One")},
+		videos: map[string][]domain.Video{"chan1": {vidAt("old", "Old", base.Add(-30*24*time.Hour))}},
+	}
+	st := &fakeStore{seen: map[string]bool{}, auto: true, requested: map[string]bool{"id-old": true}}
+	sink := &recordingSink{}
+	eng := usecase.NewEngine(src, fakeSummarizer{}, sink)
+	r := runner.New(src, st, eng, testUser, quietLogger(),
+		runner.WithAutoWindow(7*24*time.Hour), runner.WithClock(func() time.Time { return base }))
+
+	stats, err := r.RunOnce(context.Background())
+	require.NoError(t, err)
+	require.Equal(t, 1, stats.Summarized, "a requested old video is summarized despite the window")
+	require.Equal(t, 0, stats.SkippedTooOld)
+	require.Len(t, sink.delivered, 1)
+}
+
+// TestRunOnce_AutoWindowZero_SummarizesOld: a zero window disables the bound —
+// the pre-recency behaviour (summarize every unseen video) is preserved.
+func TestRunOnce_AutoWindowZero_SummarizesOld(t *testing.T) {
+	base := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	src := &fakeSource{
+		subs:   []domain.Subscription{sub("chan1", "Channel One")},
+		videos: map[string][]domain.Video{"chan1": {vidAt("old", "Old", base.Add(-365*24*time.Hour))}},
+	}
+	st := &fakeStore{seen: map[string]bool{}, auto: true}
+	sink := &recordingSink{}
+	eng := usecase.NewEngine(src, fakeSummarizer{}, sink)
+	r := runner.New(src, st, eng, testUser, quietLogger(),
+		runner.WithClock(func() time.Time { return base })) // no WithAutoWindow → 0
+
+	stats, err := r.RunOnce(context.Background())
+	require.NoError(t, err)
+	require.Equal(t, 1, stats.Summarized, "window disabled → old video summarized")
+	require.Equal(t, 0, stats.SkippedTooOld)
+}
+
+// TestRunOnce_AutoMode_UndatedVideoSummarized: a video with no published_at
+// cannot be aged out — it is processed, not silently stranded.
+func TestRunOnce_AutoMode_UndatedVideoSummarized(t *testing.T) {
+	base := time.Date(2026, 6, 8, 12, 0, 0, 0, time.UTC)
+	src := &fakeSource{
+		subs:   []domain.Subscription{sub("chan1", "Channel One")},
+		videos: map[string][]domain.Video{"chan1": {vid("undated", "Undated")}}, // zero PublishedAt
+	}
+	st := &fakeStore{seen: map[string]bool{}, auto: true}
+	sink := &recordingSink{}
+	eng := usecase.NewEngine(src, fakeSummarizer{}, sink)
+	r := runner.New(src, st, eng, testUser, quietLogger(),
+		runner.WithAutoWindow(7*24*time.Hour), runner.WithClock(func() time.Time { return base }))
+
+	stats, err := r.RunOnce(context.Background())
+	require.NoError(t, err)
+	require.Equal(t, 1, stats.Summarized, "an undated video is processed, not aged out")
+	require.Equal(t, 0, stats.SkippedTooOld)
+}
+
 // noFetchSource fails the test if a transcript fetch happens — used to prove the
 // runner skips a rate-limited video before touching the caption endpoint.
 type noFetchSource struct{ *fakeSource }