feat(patreon): resolve the creator's campaign from a single-post URL

A source URL like https://www.patreon.com/posts/mimic-in-dungeon-158372536 is a
single-post permalink, not a creator page — the resolver grabbed "posts" as the
vanity and failed (operator-flagged 2026-06-07). Add a resolution path: extract
the trailing post id and follow it to the owning campaign via the Patreon post
API (/api/posts/<id>?include=campaign), so pasting any post URL subscribes to
that creator's whole feed. `posts/` is excluded from the vanity regex so it
can't masquerade as a creator slug.

Resolution order is now: cached override → id: URL → /posts/<id> → vanity
(campaigns API + creator-page scrape). Tests cover the post→campaign resolve
and that /posts/ URLs aren't treated as vanities.

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

backend/app/services/patreon_resolver.py

@@ -26,6 +26,7 @@ import requests
 log = logging.getLogger(__name__)
 
 _CAMPAIGNS_URL = "https://www.patreon.com/api/campaigns"
+_POSTS_API = "https://www.patreon.com/api/posts"
 
 # A source URL of the form `.../id:<digits>` already carries the campaign id
 # (no lookup needed). The vanity regex deliberately EXCLUDES the id: form so the
@@ -38,9 +39,15 @@ _CAMPAIGNS_URL = "https://www.patreon.com/api/campaigns"
 # `cw/Atole` matches the bare branch and yields vanity="cw" (operator-flagged
 # 2026-06-07: every `/cw/` source failed resolution on vanity="cw").
 _ID_URL_RE = re.compile(r"/id:(\d+)")
+# A single-post permalink — patreon.com/posts/<slug>-<post_id> (or bare
+# /posts/<post_id>). The trailing digits are the post id; the creator's
+# campaign is resolved from the post itself (operator-flagged 2026-06-07: a
+# /posts/ source resolved vanity="posts"). `posts/` is excluded from the vanity
+# regex so it never masquerades as a creator slug.
+_POST_URL_RE = re.compile(r"/posts/(?:[^/?#]*-)?(\d+)(?:[/?#]|$)")
 _VANITY_PREFIXES = ("cw/", "c/")
 _VANITY_RE = re.compile(
-    r"^https?://(?:www\.)?patreon\.com/(?:cw/|c/)?(?!id:)([^/?#]+)",
+    r"^https?://(?:www\.)?patreon\.com/(?:cw/|c/)?(?!(?:id:|posts/))([^/?#]+)",
     re.IGNORECASE,
 )
 _USER_AGENT = (
@@ -178,6 +185,41 @@ def _lookup_via_page(vanity: str, cookies_path: str | None) -> str | None:
     return None
 
 
+def _lookup_campaign_from_post(post_id: str, cookies_path: str | None) -> str | None:
+    """Resolve the owning campaign id from a single post id via the Patreon
+    post API (`/api/posts/<id>?include=campaign`). A `/posts/` source URL points
+    at one post, but a subscription walks the whole creator — so we follow the
+    post to its campaign. Never raises."""
+    jar = _load_cookie_jar(cookies_path)
+    headers = {"User-Agent": _USER_AGENT, "Accept": "application/vnd.api+json"}
+    params = {"include": "campaign", "fields[campaign]": "name"}
+    url = f"{_POSTS_API}/{post_id}"
+    try:
+        resp = requests.get(
+            url, params=params, headers=headers, cookies=jar,
+            timeout=_TIMEOUT_SECONDS,
+        )
+    except requests.RequestException as exc:
+        log.warning("Patreon post lookup failed for post=%s: %s", post_id, exc)
+        return None
+    if resp.status_code != 200:
+        log.warning("Patreon post API returned HTTP %d for post=%s", resp.status_code, post_id)
+        return None
+    try:
+        payload = resp.json()
+    except ValueError:
+        return None
+    data = payload.get("data") if isinstance(payload, dict) else None
+    if not isinstance(data, dict):
+        return None
+    campaign = ((data.get("relationships") or {}).get("campaign") or {}).get("data") or {}
+    campaign_id = campaign.get("id")
+    if isinstance(campaign_id, str) and campaign_id:
+        log.info("Resolved Patreon post=%s → campaign_id=%s", post_id, campaign_id)
+        return campaign_id
+    return None
+
+
 async def resolve_campaign_id(
     vanity: str,
     cookies_path: str | None,
@@ -188,6 +230,16 @@ async def resolve_campaign_id(
     return await loop.run_in_executor(None, _sync_lookup, vanity, cookies_path)
 
 
+async def resolve_campaign_from_post(
+    post_id: str, cookies_path: str | None,
+) -> str | None:
+    """Async wrapper around _lookup_campaign_from_post. Never raises."""
+    loop = asyncio.get_running_loop()
+    return await loop.run_in_executor(
+        None, _lookup_campaign_from_post, post_id, cookies_path
+    )
+
+
 def extract_vanity(url: str) -> str | None:
     """The vanity slug from a Patreon creator URL, or None for an `id:` URL."""
     m = _VANITY_RE.match(url or "")
@@ -203,10 +255,11 @@ async def resolve_campaign_id_for_source(
     shared by the download ingester and the credential-verify probe.
 
     Order: cached `patreon_campaign_id` override → an `id:<digits>` URL → a
+    `/posts/<id>` permalink (resolve the owning campaign from the post) → a
     vanity lookup against the campaigns API. Returns
-    `(campaign_id, newly_resolved_id)`: `newly_resolved_id` is non-None ONLY when
-    a vanity lookup actually ran, so the caller knows to cache it on the source
-    (the override/id: paths needed no lookup). `(None, None)` when unresolvable.
+    `(campaign_id, newly_resolved_id)`: `newly_resolved_id` is non-None whenever
+    a lookup actually ran, so the caller caches it on the source (the
+    override/id: paths needed no lookup). `(None, None)` when unresolvable.
     Never raises.
     """
     overrides = overrides or {}
@@ -216,6 +269,12 @@ async def resolve_campaign_id_for_source(
     id_match = _ID_URL_RE.search(url or "")
     if id_match:
         return id_match.group(1), None
+    # A single-post URL → follow the post to its creator's campaign so the
+    # source subscribes to the whole feed (a subscription isn't one post).
+    post_match = _POST_URL_RE.search(url or "")
+    if post_match:
+        resolved = await resolve_campaign_from_post(post_match.group(1), cookies_path)
+        return resolved, resolved
     vanity = extract_vanity(url)
     if vanity:
         resolved = await resolve_campaign_id(vanity, cookies_path)

tests/test_patreon_resolver.py

@@ -183,3 +183,35 @@ def test_extract_vanity_handles_all_path_prefixes():
     assert extract_vanity("https://patreon.com/cw/Atole") == "Atole"
     # id: URLs are NOT vanities (handled by the id path).
     assert extract_vanity("https://www.patreon.com/id:123") is None
+    # /posts/ permalinks are NOT vanities (handled by the post path) — must not
+    # masquerade as a creator slug named "posts".
+    assert extract_vanity(
+        "https://www.patreon.com/posts/mimic-in-dungeon-158372536"
+    ) is None
+
+
+@pytest.mark.asyncio
+async def test_for_source_resolves_post_url_to_campaign():
+    """A /posts/<slug>-<id> permalink resolves to the OWNING creator's campaign
+    (a subscription walks the whole feed, not one post)."""
+    post_resp = MagicMock()
+    post_resp.status_code = 200
+    post_resp.json.return_value = {
+        "data": {
+            "id": "158372536", "type": "post",
+            "relationships": {"campaign": {"data": {"id": "9988", "type": "campaign"}}},
+        }
+    }
+    calls = []
+
+    def _get(url, **kwargs):
+        calls.append(url)
+        return post_resp
+
+    with patch("backend.app.services.patreon_resolver.requests.get", side_effect=_get):
+        cid, resolved = await resolve_campaign_id_for_source(
+            "https://www.patreon.com/posts/mimic-in-dungeon-158372536", None, {},
+        )
+    assert cid == "9988"
+    assert resolved == "9988"  # newly resolved → caller caches it
+    assert calls and "/api/posts/158372536" in calls[0]