feat(patreon): capture media-less/text-only posts (post-only records)

Today the ingest core does `if not media: continue`, so a post with no
downloadable media (a pure-text post — which often holds the ONLY copy of an
external mega/gdrive/pixeldrain link) never upserts a Post. Now the native
ingester emits a post-only sidecar (`_post.json`) for every media-less post,
gated through the seen-ledger via a synthetic `post:<id>` key so the body is
detail-fetched + recorded ONCE (not re-walked every tick); recovery bypasses
the gate. Phase 3 imports these via Importer.upsert_post_record, keyed on
external_post_id so it UPDATES the same Post a media import would create —
never doubles, never clobbers a populated body with an empty one.

- gallery_dl.py: DownloadResult.post_record_paths (default []; gallery-dl path
  unaffected — all constructions are keyword).
- ingest_core.py: media-less branch (optional client/downloader seams via
  getattr; stub clients in tests skip it as before).
- patreon_client.py: post_record_key(post). patreon_downloader.py:
  write_post_record + _write_sidecar_data refactor (shared serializer).
- importer.py: upsert_post_record. download_service.py: phase-3 import loop.
- tests: client/downloader/ingester (gate + recovery)/importer (no-double).

Slice 0b of milestone #64. Refs FC #830.

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

tests/test_patreon_ingester.py

@@ -68,6 +68,11 @@ class _FakeClient:
     def post_meta(self, post):
         return {"title": post.get("id"), "date": None}
 
+    @staticmethod
+    def post_record_key(post):
+        pid = str(post.get("id") or "")
+        return (f"post:{pid}", pid) if pid else None
+
 
 class _FakeDownloader:
     """Stub PatreonDownloader. Honors the injected is_seen (tier-1); media in
@@ -80,6 +85,7 @@ class _FakeDownloader:
         self.quarantine = set(quarantine or ())
         self.error = set(error or ())
         self.download_calls = 0
+        self.post_records = 0
 
     def download_post(self, post, media_items, artist_slug, *, is_seen,
                       should_stop=lambda: False):
@@ -106,6 +112,12 @@ class _FakeDownloader:
                 outcomes.append(MediaOutcome(media=m, status="downloaded", path=p, error=None))
         return outcomes
 
+    def write_post_record(self, post, artist_slug):
+        self.post_records += 1
+        p = self.tmp_path / f"{post.get('id')}__post.json"
+        p.write_text("{}")
+        return p
+
 
 @pytest.fixture
 async def source_id(db):
@@ -743,3 +755,55 @@ async def test_verify_patreon_credential_delegates_to_client(monkeypatch):
     ok, msg = await mod.verify_patreon_credential("https://patreon.com/x", None, {})
     assert ok is True
     assert msg == "ok:123"
+
+
+# --- media-less (text-only) post capture ----------------------------------
+
+
+@pytest.mark.asyncio
+async def test_tick_captures_media_less_post_once(source_id, sync_engine, tmp_path):
+    """A post with NO downloadable media still gets a post-only record, gated by
+    the seen-ledger (synthetic post key) so a second walk doesn't re-record it."""
+    client = _FakeClient([(None, [("ptext", [])])])
+    downloader = _FakeDownloader(tmp_path)
+    ing = _ingester(sync_engine, tmp_path, client, downloader)
+
+    result = ing.run(
+        source_id=source_id, campaign_id="c1", artist_slug="ingest",
+        url="https://patreon.com/ingest", mode="tick",
+    )
+    assert result.success is True
+    assert len(result.post_record_paths) == 1
+    assert downloader.post_records == 1
+    # The synthetic `post:ptext` key was marked seen (gates re-capture).
+    assert _count_ledger(sync_engine, source_id) == 1
+
+    # Second walk: already recorded → gated, no re-write, no new ledger row.
+    client2 = _FakeClient([(None, [("ptext", [])])])
+    downloader2 = _FakeDownloader(tmp_path)
+    ing2 = _ingester(sync_engine, tmp_path, client2, downloader2)
+    result2 = ing2.run(
+        source_id=source_id, campaign_id="c1", artist_slug="ingest",
+        url="https://patreon.com/ingest", mode="tick",
+    )
+    assert result2.post_record_paths == []
+    assert downloader2.post_records == 0
+    assert _count_ledger(sync_engine, source_id) == 1
+
+
+@pytest.mark.asyncio
+async def test_recovery_bypasses_gate_and_re_records(source_id, sync_engine, tmp_path):
+    """Recovery bypasses the seen-ledger, so a media-less post is re-recorded
+    (matches recovery semantics for media)."""
+    client = _FakeClient([(None, [("ptext", [])])])
+    ing = _ingester(sync_engine, tmp_path, client, _FakeDownloader(tmp_path))
+    ing.run(source_id=source_id, campaign_id="c1", artist_slug="ingest",
+            url="https://patreon.com/ingest", mode="tick")
+
+    client2 = _FakeClient([(None, [("ptext", [])])])
+    dl2 = _FakeDownloader(tmp_path)
+    ing2 = _ingester(sync_engine, tmp_path, client2, dl2)
+    result = ing2.run(source_id=source_id, campaign_id="c1", artist_slug="ingest",
+                      url="https://patreon.com/ingest", mode="recovery")
+    assert len(result.post_record_paths) == 1
+    assert dl2.post_records == 1