fix(patreon): full-fetch fallback when sparse fieldset returns null content (#842)

Operator-flagged: 9 StickySpoodge posts had empty bodies in FC despite the body
plainly existing + being accessible (creds refresh didn't help). All 9 are
body-only / poll / embed / announcement posts with no downloadable gallery
media — Patreon's detail endpoint returns content:null for these under the
sparse fields[post]=content request even though the body exists.

fetch_post_detail_content now re-fetches the FULL post resource once when the
sparse request comes back empty: recovers the body when the sparse fieldset was
the cause, and logs post_type when even the full resource is empty (body lives
elsewhere). Only the empty cases pay the extra GET; the 126 already-working
posts keep the fast sparse path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/app/services/patreon_client.py

@@ -612,12 +612,39 @@ class PatreonClient:
         if isinstance(content, str) and content.strip():
             log.info("post-detail: fetched %d chars (post %s)", len(content), post_id)
             return content
-        # 200 OK but content is null/empty — the common silent case (a tier-gated
-        # post serves content:null, or the post genuinely has no text body). Logged
-        # so a recapture that "caught nothing" is diagnosable, not invisible.
+        # Sparse `fields[post]=content` came back null/empty. Patreon serves null
+        # under the sparse fieldset for some post types (polls, embeds/films,
+        # body-only announcements) even when the body plainly exists. Re-fetch the
+        # FULL post resource ONCE — only the empty cases pay this extra GET — which
+        # both DIAGNOSES (logs post_type) and RECOVERS the body when the sparse
+        # fieldset was the cause (#842).
+        try:
+            full = self._session.get(
+                url, params={"json-api-version": "1.0"}, timeout=_TIMEOUT_SECONDS,
+            )
+        except requests.RequestException as exc:
+            log.warning("post-detail full re-fetch failed (post %s): %s", post_id, exc)
+            return None
+        fa = None
+        if full.status_code == 200:
+            try:
+                fp = full.json()
+            except ValueError:
+                fp = None
+            fdata = fp.get("data") if isinstance(fp, dict) else None
+            fa = fdata.get("attributes") if isinstance(fdata, dict) else None
+        fcontent = fa.get("content") if isinstance(fa, dict) else None
+        ptype = fa.get("post_type") if isinstance(fa, dict) else None
+        if isinstance(fcontent, str) and fcontent.strip():
+            log.warning(
+                "post-detail: sparse fieldset gave null but FULL fetch has %d chars "
+                "(post %s, post_type=%s) — using full body",
+                len(fcontent), post_id, ptype,
+            )
+            return fcontent
         log.info(
-            "post-detail: empty/null content (post %s) — body unavailable "
-            "(tier-gated, or post has no text)", post_id,
+            "post-detail: empty/null content (post %s, post_type=%s) even on full "
+            "fetch — body not in the post resource", post_id, ptype,
         )
         return None