feat(downloads): bulk retry respects cooldown; single-source RETRY overrides

Today's platform-cooldown commit (61ce1ce) only filtered the scan tick
— manual /api/sources/<id>/check still bypassed it. Operator-flagged
2026-05-30: clicked "Retry failed" on a Patreon failure pile and saw
every one go 'queued' without realising the cooldown wasn't in the
loop. Bulk retry with N sources on a cooled-down platform bowls right
back into the rate limit the cooldown is trying to prevent.

**Backend (`/api/sources/<id>/check`):**
- Reads optional `?force=true` query flag.
- Without force: queries `active_platform_cooldowns` (renamed from the
  private `_platforms_in_cooldown` since it's now a cross-module API).
  If the source's platform is in cooldown, returns **202** with
  `{status: 'deferred', platform, cooldown_until}` — no event created,
  no dispatch.
- With force: cooldown skipped entirely.
- In-flight guard always applies (no point creating duplicate pendings).

**Frontend (`sourcesStore.checkNow(id, {force=false})`):** new optional
`force` flag → adds `?force=true` to the URL.

**Frontend (`DownloadsTab`):**
- `onRetrySource` (single-source RETRY click): passes `force: true` →
  explicit operator override, useful for rapid auth-fix testing.
- `onRetryAll` (RETRY ALL + MaintenanceMenu "Retry failed"): no force →
  cooldown respected. Tallies `deferred` alongside `queued` /
  `already_running`; toast reads e.g. *"5 queued, 12 deferred
  (cooldown), 3 already running"*. That count is the operator's
  diagnostic answer for "is rate-limit the cause of most failures?"
  (12-of-20 deferred → yes; 0 deferred → no).

**Auto-resume:** no new sweep needed. Deferred sources still have stale
`last_checked_at`, so the next scan tick after the cooldown AppSetting
expires picks them up via `select_due_sources` (which already filters
on `active_platform_cooldowns`).

Tests: two new — deferred-on-cooldown returns 202 with the right body
and no dispatch; force=true overrides the cooldown and creates the
event normally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_api_sources_check.py

@@ -63,3 +63,55 @@ async def test_check_409_when_already_running(client, db, seed, monkeypatch):
     assert resp.status_code == 409
     body = await resp.get_json()
     assert body["download_event_id"] == existing.id
+
+
+@pytest.mark.asyncio
+async def test_check_defers_when_platform_in_cooldown(client, db, seed, monkeypatch):
+    """Bulk retries land here without ?force — when the source's platform
+    has an active cooldown, return 202 with status='deferred' instead of
+    creating an event. Lets the bulk path tally deferred-vs-queued in
+    the toast so the operator can see rate-limit-induced failures at a
+    glance."""
+    from backend.app.services.scheduler_service import set_platform_cooldown
+
+    delays: list = []
+    monkeypatch.setattr(
+        "backend.app.tasks.download.download_source.delay",
+        lambda *a, **k: delays.append(a),
+    )
+
+    await set_platform_cooldown(db, seed.platform, seconds=900)
+    await db.commit()
+
+    resp = await client.post(f"/api/sources/{seed.id}/check")
+    assert resp.status_code == 202
+    body = await resp.get_json()
+    assert body["status"] == "deferred"
+    assert body["platform"] == seed.platform
+    assert body["cooldown_until"]
+    assert delays == []  # no dispatch when deferred
+
+
+@pytest.mark.asyncio
+async def test_check_force_overrides_cooldown(client, db, seed, monkeypatch):
+    """Single-source RETRY click sends ?force=true — explicit operator
+    override, used for rapid auth-fix testing without waiting on the
+    cooldown."""
+    from backend.app.services.scheduler_service import set_platform_cooldown
+
+    delays: list = []
+    monkeypatch.setattr(
+        "backend.app.tasks.download.download_source.delay",
+        lambda *a, **k: delays.append(a),
+    )
+
+    await set_platform_cooldown(db, seed.platform, seconds=900)
+    await db.commit()
+
+    resp = await client.post(f"/api/sources/{seed.id}/check?force=true")
+    assert resp.status_code == 202
+    body = await resp.get_json()
+    assert body["status"] == "pending"
+    assert isinstance(body["download_event_id"], int)
+    assert len(delays) == 1
+    assert delays[0] == (seed.id,)