feat(patreon): surface source URL + vanity in campaign-id resolution errors

Naming/lookup failures now report the source_url, the extracted vanity, and the
exact campaigns-API lookup URL attempted, so a "could not resolve campaign id"
error is diagnosable (wrong vanity? cookie/auth? creator renamed?) instead of
opaque. Applied to all three resolution surfaces: the native download event,
the dry-run preview, and the credential-verify probe.

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

backend/app/services/download_backends.py

@@ -25,7 +25,11 @@ from pathlib import Path
 
 from .gallery_dl import DownloadResult, ErrorType
 from .patreon_ingester import PatreonIngester
-from .patreon_resolver import resolve_campaign_id_for_source
+from .patreon_resolver import (
+    _CAMPAIGNS_URL as _CAMPAIGNS_API,
+    extract_vanity,
+    resolve_campaign_id_for_source,
+)
 
 # Platforms whose download + verify go through the native ingester rather than
 # gallery-dl. gallery-dl still serves every other platform (subscribestar,
@@ -93,15 +97,19 @@ async def _run_native_ingester(
         ctx["url"], ctx["cookies_path"], overrides
     )
     if not campaign_id:
+        url = ctx["url"]
+        vanity = extract_vanity(url)
         return (
             DownloadResult(
                 success=False,
-                url=ctx["url"],
+                url=url,
                 artist_slug=ctx["artist_slug"],
                 platform="patreon",
                 error_type=ErrorType.NOT_FOUND,
                 error_message=(
-                    "Could not resolve Patreon campaign id from the source URL "
+                    f"Could not resolve Patreon campaign id. source_url={url!r}; "
+                    f"vanity={vanity!r}; "
+                    f"lookup=GET {_CAMPAIGNS_API}?filter[vanity]={vanity or ''} "
                     "(vanity lookup failed — cookies expired or creator moved?)"
                 ),
             ),
@@ -172,9 +180,11 @@ async def preview_source(
         url, cookies_path, config_overrides or {}
     )
     if not campaign_id:
+        vanity = extract_vanity(url)
         return {
             "error": (
-                "Couldn't resolve the campaign id from the source URL "
+                f"Couldn't resolve the campaign id. source_url={url!r}; "
+                f"vanity={vanity!r}; lookup=GET {_CAMPAIGNS_API}?filter[vanity]={vanity or ''} "
                 "(cookies expired, or the creator moved/renamed?)."
             )
         }

backend/app/services/patreon_ingester.py

@@ -45,7 +45,7 @@ from .patreon_client import (
     PatreonDriftError,
 )
 from .patreon_downloader import PatreonDownloader
-from .patreon_resolver import resolve_campaign_id_for_source
+from .patreon_resolver import extract_vanity, resolve_campaign_id_for_source
 
 __all__ = [
     "DEAD_LETTER_THRESHOLD",
@@ -186,9 +186,11 @@ async def verify_patreon_credential(
     """
     campaign_id, _ = await resolve_campaign_id_for_source(url, cookies_path, overrides)
     if not campaign_id:
+        vanity = extract_vanity(url)
         return None, (
-            "Couldn't resolve the Patreon campaign id from the source URL — "
-            "can't verify (cookies expired, or the creator moved/renamed?)."
+            f"Couldn't resolve the Patreon campaign id — can't verify. "
+            f"source_url={url!r}; vanity={vanity!r} "
+            "(cookies expired, or the creator moved/renamed?)."
         )
     client = PatreonClient(cookies_path)
     loop = asyncio.get_running_loop()