fix: one lapsed membership to a deleted creator no longer fails the Patreon roster

The first live sweep failed with "Patreon member resource has no campaign relationship". The operator ran FC's exact /api/members request in a browser and shared the response.
- It has 104 rows. The browser's settings page shows 43, because FC sends no membership-type filter and so also gets lapses back to 2016.
- Exactly one row has no `campaign` key at all: a former_patron whose membership ended in 2017. Its included reward has no campaign link either, so the creator's page is gone.
- Every other row, including the 4 is_active=false campaigns, has a campaign.

_membership returns None for a campaign-less row only when has_paid_access says it is definitely not paying (a known lapsed status, or a free member), and iter_memberships skips it. That changes no conclusion. A lapsed membership and an absent one both mean "not paying", and no Source can match a campaign with no id.

An active or unrecognised membership without a campaign still raises, because dropping a membership that might be paid would read downstream as a cancellation.

Paging still counts the rows the server sent, not the rows kept. A test pins that, so a skip can't re-read an offset or stop a page short.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SHQB1YukL3VyvMK8rcbmV9

backend/app/services/patreon_client.py

@@ -631,7 +631,27 @@ class PatreonClient:
                 "cannot tell a complete roster from a truncated one"
             )
 
-    def _membership(self, member: dict, index: dict) -> Membership:
+    def _membership(self, member: dict, index: dict) -> Membership | None:
+        """One member row as a Membership, or None for a row the roster can skip.
+
+        The one skippable row is a LAPSED membership whose creator no longer
+        exists. The live roster (note #3886, CORRECTION 3) returned 104 rows,
+        because FC sends no membership-type filter and so gets lapses going back
+        years. One of them, a membership that ended in 2017, carried no
+        `campaign` relationship at all: the key is absent, not null, and its
+        reward names no campaign either. The creator's page is gone.
+
+        Raising on that row made the whole roster unusable over one membership
+        nobody can act on. Skipping it changes no conclusion. A lapsed
+        membership already means "not paying", absence means the same, and no
+        Source can be matched to a campaign that no longer has an id.
+
+        The refusal stays for every other row. An active or unrecognised
+        membership without a creator is something FC cannot vouch for, and
+        dropping it would read downstream as a cancellation.
+        """
+        from .membership_roster import has_paid_access
+
         attrs = member.get("attributes") or {}
         if "patron_status" not in attrs:
             raise PatreonDriftError(
@@ -640,6 +660,17 @@ class PatreonClient:
 
         campaign_ids = self._related_ids(member, "campaign")
         if not campaign_ids:
+            paid = has_paid_access(
+                "patreon", attrs.get("patron_status"),
+                is_free_member=bool(attrs.get("is_free_member")),
+            )
+            if paid is False:
+                log.info(
+                    "Patreon roster: skipping a lapsed membership with no campaign "
+                    "(creator deleted); status=%s access_expires_at=%s",
+                    attrs.get("patron_status"), attrs.get("access_expires_at"),
+                )
+                return None
             raise PatreonDriftError(
                 "Patreon member resource has no campaign relationship — a "
                 "membership we cannot attribute to a creator is not usable"
@@ -700,7 +731,9 @@ class PatreonClient:
             index = self._transform(response)
             rows = [m for m in (response.get("data") or []) if isinstance(m, dict)]
             for member in rows:
-                yield self._membership(member, index)
+                membership = self._membership(member, index)
+                if membership is not None:
+                    yield membership
 
             seen += len(rows)
             total = int(response["meta"]["pagination"]["total"] or 0)