refactor(downloads): unify phase-2 dispatch in download_backends — A5 (plan #707)

Mirror verify_source_credential: download_backends.run_download is now the single
download entry, so that module is the ONE registry of how each platform both
downloads AND verifies — the seam that makes adding a platform a bounded job
(write its adapter construction next to its verify). The native-ingester
construction + campaign-id resolution moves out of download_service into
download_backends._run_native_ingester.

download_service.download_source drops its `if uses_native_ingester ... else
gdl.download` branch and calls one `self._run_download(...)` (a thin delegate to
run_download passing the service's gdl + sync sessionmaker). mode (tick/backfill/
recovery) is still chosen there from the backfill state machine and threaded
through. Removed the now-unused PatreonIngester / resolve_campaign_id_for_source
imports from download_service.

Tests: the phase-2 stub seam moves from svc._run_patreon_ingester to
svc._run_download (helper + the db-release test); the two native-construction
tests repoint to download_backends.run_download (patching
download_backends.resolve_campaign_id_for_source / PatreonIngester).

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

tests/test_download_service.py

@@ -89,7 +89,7 @@ def _make_fake_dl_result(
 def _fake_gdl_with_result(result):
     fake = MagicMock()
     fake.download = AsyncMock(return_value=result)
-    # Real values for the attrs _run_patreon_ingester reads off the gdl service
+    # Real values for the attrs run_download's native branch reads off the gdl
     # (the native pacing config, plan #703) — a MagicMock would break the
     # arithmetic (max(0.5, rate_limit/4)).
     fake._rate_limit = 3.0
@@ -105,19 +105,24 @@ def _fake_gdl_with_result(result):
 
 
 def _stub_patreon_ingester(svc, result, resolved_campaign_id=None):
-    """Route the Patreon phase-2 branch (plan #697 native ingester) to a canned
-    DownloadResult so these tests exercise download_service's
-    phase-2-result→phase-3 handling (status mapping, backfill lifecycle, health)
-    without the real ingester's network/DB. The ingester itself is covered by
-    test_patreon_ingester.py. Returns a list capturing (ctx, source_config, mode)
-    per call so a test can assert mode / resume_cursor threading."""
+    """Route the phase-2 dispatch (download_backends.run_download via
+    DownloadService._run_download, plan #707 A5) to a canned DownloadResult so
+    these tests exercise download_service's phase-2-result→phase-3 handling
+    (status mapping, backfill lifecycle, health) without the real ingester's
+    network/DB. The ingester itself is covered by test_patreon_ingester.py; the
+    native construction/resolution by the run_download tests below. Returns a list
+    capturing (ctx, source_config, skip_value, mode) per call so a test can assert
+    mode / resume_cursor threading."""
     calls = []
 
-    async def fake(ctx, source_config, mode):
-        calls.append({"ctx": ctx, "source_config": source_config, "mode": mode})
+    async def fake(*, ctx, source_config, skip_value, mode):
+        calls.append({
+            "ctx": ctx, "source_config": source_config,
+            "skip_value": skip_value, "mode": mode,
+        })
         return result, resolved_campaign_id
 
-    svc._run_patreon_ingester = fake
+    svc._run_download = fake
     return calls
 
 
@@ -285,20 +290,19 @@ async def test_patreon_resolved_campaign_id_is_cached(
 
 
 @pytest.mark.asyncio
-async def test_run_patreon_ingester_resolves_vanity_and_runs(
+async def test_run_download_native_resolves_vanity_and_runs(
     db, db_sync, tmp_path, seed_artist_and_source, monkeypatch,
 ):
-    """_run_patreon_ingester: with no cached campaign id, resolve the vanity and
-    pass the resolved id straight to the ingester; report it back so phase 3 can
-    cache it."""
-    from backend.app.services import download_service as dl_mod
-    from backend.app.services.download_service import DownloadService
+    """run_download (native branch, plan #707 A5): with no cached campaign id,
+    resolve the vanity and pass the resolved id straight to the ingester; report
+    it back so phase 3 can cache it."""
+    from backend.app.services import download_backends as db_mod
     from backend.app.services.gallery_dl import SourceConfig
 
     _artist, source = seed_artist_and_source
 
     monkeypatch.setattr(
-        dl_mod, "resolve_campaign_id_for_source",
+        db_mod, "resolve_campaign_id_for_source",
         AsyncMock(return_value=("4242", "4242")),
     )
     run_kwargs = {}
@@ -311,21 +315,19 @@ async def test_run_patreon_ingester_resolves_vanity_and_runs(
             run_kwargs.update(kw)
             return _make_fake_dl_result(success=True, written_paths=[])
 
-    monkeypatch.setattr(dl_mod, "PatreonIngester", _FakeIngester)
+    monkeypatch.setattr(db_mod, "PatreonIngester", _FakeIngester)
 
-    svc = DownloadService(
-        async_session=db, sync_session=db_sync,
-        gdl=_fake_gdl_with_result(_make_fake_dl_result(success=True)),
-        importer=MagicMock(), cred_service=MagicMock(),
-        sync_session_factory=MagicMock(),
-    )
     ctx = {
+        "platform": "patreon",
         "source_id": source.id, "url": "https://patreon.com/alice",
         "artist_slug": "alice", "cookies_path": None,
         "config_overrides": {},
     }
-    result, resolved = await svc._run_patreon_ingester(
-        ctx, SourceConfig.from_dict({}), "tick",
+    result, resolved = await db_mod.run_download(
+        ctx=ctx, source_config=SourceConfig.from_dict({}), skip_value=True,
+        mode="tick",
+        gdl=_fake_gdl_with_result(_make_fake_dl_result(success=True)),
+        sync_session_factory=MagicMock(),
     )
     assert result.success is True
     assert resolved == "4242"
@@ -334,33 +336,29 @@ async def test_run_patreon_ingester_resolves_vanity_and_runs(
 
 
 @pytest.mark.asyncio
-async def test_run_patreon_ingester_unresolvable_fails_loud(
+async def test_run_download_native_unresolvable_fails_loud(
     db, db_sync, tmp_path, seed_artist_and_source, monkeypatch,
 ):
     """A campaign id we can't resolve is a loud NOT_FOUND failure, never a
     silent empty success."""
-    from backend.app.services import download_service as dl_mod
-    from backend.app.services.download_service import DownloadService
+    from backend.app.services import download_backends as db_mod
     from backend.app.services.gallery_dl import ErrorType, SourceConfig
 
     _artist, source = seed_artist_and_source
 
     monkeypatch.setattr(
-        dl_mod, "resolve_campaign_id_for_source",
+        db_mod, "resolve_campaign_id_for_source",
         AsyncMock(return_value=(None, None)),
     )
-    svc = DownloadService(
-        async_session=db, sync_session=db_sync,
-        gdl=MagicMock(), importer=MagicMock(), cred_service=MagicMock(),
-        sync_session_factory=MagicMock(),
-    )
     ctx = {
+        "platform": "patreon",
         "source_id": source.id, "url": "https://patreon.com/alice",
         "artist_slug": "alice", "cookies_path": None,
         "config_overrides": {},
     }
-    result, resolved = await svc._run_patreon_ingester(
-        ctx, SourceConfig.from_dict({}), "tick",
+    result, resolved = await db_mod.run_download(
+        ctx=ctx, source_config=SourceConfig.from_dict({}), skip_value=True,
+        mode="tick", gdl=MagicMock(), sync_session_factory=MagicMock(),
     )
     assert result.success is False
     assert result.error_type == ErrorType.NOT_FOUND
@@ -926,11 +924,11 @@ async def test_releases_db_connections_before_subprocess(
         gdl=fake_gdl, importer=importer, cred_service=cred_service,
     )
 
-    async def fake_ingest(ctx, source_config, mode):
+    async def fake_ingest(*, ctx, source_config, skip_value, mode):
         seen["closed_before_phase2"] = closed["async"]
         return _make_fake_dl_result(success=True, written_paths=[], stdout=""), None
 
-    svc._run_patreon_ingester = fake_ingest
+    svc._run_download = fake_ingest
     event_id = await svc.download_source(source.id)
 
     assert seen["closed_before_phase2"] is True