feat(pixiv): flip dispatch to the native ingester (#129 step 4)

pixiv joins NATIVE_INGESTER_PLATFORMS: download/verify/preview and the
recover/recapture UI actions now route through PixivIngester. Campaign id is
parsed straight from the source URL (numeric user id — no network resolver),
with a platform-aware resolution-failure message. auth_token now rides the
uniform adapter construction (token platforms use it, cookie platforms
accept-and-ignore), and the preview endpoint fetches/threads it. The legacy
gallery-dl pixiv path is fully removed (PLATFORM_DEFAULTS entry + the
refresh-token config branches in download/verify) per no-legacy policy;
gallery-dl keeps hentaifoundry/discord/deviantart until they migrate/retire.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

backend/app/services/download_backends.py

@@ -27,12 +27,15 @@ from .gallery_dl import DownloadResult, ErrorType
 from .native_ingest_common import NativeIngestError
 from .patreon_ingester import PatreonIngester
 from .patreon_resolver import extract_vanity, resolve_campaign_id_for_source
+from .pixiv_client import user_id_from_url
+from .pixiv_ingester import PixivIngester
 from .subscribestar_ingester import SubscribeStarIngester
 
 # Platforms whose download + verify go through the native ingester rather than
-# gallery-dl. gallery-dl still serves the rest (hentaifoundry, discord, pixiv,
-# deviantart) until they migrate too.
-NATIVE_INGESTER_PLATFORMS = frozenset({"patreon", "subscribestar"})
+# gallery-dl. gallery-dl still serves the rest (hentaifoundry, discord,
+# deviantart — the latter slated for retirement, not migration) until they
+# migrate too.
+NATIVE_INGESTER_PLATFORMS = frozenset({"patreon", "subscribestar", "pixiv"})
 
 # Mirrors patreon_resolver._CAMPAIGNS_URL — surfaced in resolution-failure
 # messages so the operator sees the exact lookup endpoint that was hit.
@@ -46,6 +49,7 @@ def _native_ingester_cls(platform: str):
     dispatch pick up the replacement."""
     return {
         "patreon": PatreonIngester,
+        "pixiv": PixivIngester,
         "subscribestar": SubscribeStarIngester,
     }[platform]
 
@@ -98,14 +102,34 @@ async def _resolve_native_campaign_id(
     platform: str, url: str, cookies_path: str | None, overrides: dict,
 ) -> tuple[str | None, str | None]:
     """`(campaign_id, resolved_campaign_id)` for a native source. SubscribeStar's
-    feed id IS the creator URL (no lookup → resolved None). Patreon resolves the
+    feed id IS the creator URL; Pixiv's is the numeric user id parsed straight
+    from it (no lookup → resolved None either way). Patreon resolves the
     campaign id from the vanity URL (resolved non-None when a lookup actually ran,
     so phase 3 caches it)."""
     if platform == "subscribestar":
         return url, None
+    if platform == "pixiv":
+        return user_id_from_url(url), None
     return await resolve_campaign_id_for_source(url, cookies_path, overrides)
 
 
+def _campaign_resolution_error(platform: str, url: str) -> str:
+    """Operator-facing message for a native source whose campaign id could not
+    be resolved — names the platform's own lookup mechanism."""
+    if platform == "pixiv":
+        return (
+            f"Could not extract a pixiv user id. source_url={url!r} — expected "
+            "a URL like https://www.pixiv.net/users/<id>."
+        )
+    vanity = extract_vanity(url)
+    return (
+        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?)"
+    )
+
+
 async def _run_native_ingester(
     ctx: dict, source_config, mode: str | None, gdl, sync_session_factory,
 ) -> tuple[DownloadResult, str | None]:
@@ -123,9 +147,9 @@ async def _run_native_ingester(
         platform, ctx["url"], ctx["cookies_path"], overrides
     )
     if not campaign_id:
-        # Only reachable for Patreon (SubscribeStar's campaign id is the URL).
+        # Patreon: vanity lookup failed. Pixiv: no numeric user id in the URL.
+        # (SubscribeStar's campaign id is the URL itself — never lands here.)
         url = ctx["url"]
-        vanity = extract_vanity(url)
         return (
             DownloadResult(
                 success=False,
@@ -133,12 +157,7 @@ async def _run_native_ingester(
                 artist_slug=ctx["artist_slug"],
                 platform=platform,
                 error_type=ErrorType.NOT_FOUND,
-                error_message=(
-                    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?)"
-                ),
+                error_message=_campaign_resolution_error(platform, url),
             ),
             None,
         )
@@ -161,6 +180,10 @@ async def _run_native_ingester(
         validate=gdl._validate_files,
         rate_limit=rate_limit,
         request_sleep=request_sleep,
+        # Uniform across adapters: token platforms (pixiv) authenticate with
+        # it, cookie platforms accept-and-ignore — so this construction stays
+        # platform-agnostic.
+        auth_token=ctx["auth_token"],
     )
     loop = asyncio.get_running_loop()
     dl_result = await loop.run_in_executor(
@@ -190,6 +213,7 @@ async def preview_source(
     cookies_path: str | None,
     images_root: Path,
     sync_session_factory,
+    auth_token: str | None = None,
     page_limit: int = 3,
 ) -> dict:
     """Dry-run preview for a native platform (plan #708 B4): resolve the campaign
@@ -205,18 +229,12 @@ async def preview_source(
         platform, url, cookies_path, config_overrides or {}
     )
     if not campaign_id:
-        vanity = extract_vanity(url)
-        return {
-            "error": (
-                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?)."
-            )
-        }
+        return {"error": _campaign_resolution_error(platform, url)}
     ingester = _native_ingester_cls(platform)(
         images_root=images_root,
         cookies_path=cookies_path,
         session_factory=sync_session_factory,
+        auth_token=auth_token,
     )
     loop = asyncio.get_running_loop()
     try:
@@ -245,13 +263,18 @@ async def verify_source_credential(
     this and render the result.
     """
     if uses_native_ingester(platform):
-        # Native ingester platforms verify via their own lightweight auth probe
-        # (one authenticated feed fetch). SubscribeStar's probe takes the creator
-        # URL directly; Patreon's resolves the campaign id first.
+        # Native ingester platforms verify via their own lightweight auth probe.
+        # SubscribeStar's probe takes the creator URL directly; Patreon's
+        # resolves the campaign id first; Pixiv's is one OAuth refresh (the
+        # exact call that fails when the token is bad — no feed walk).
         if platform == "subscribestar":
             from .subscribestar_ingester import verify_subscribestar_credential
 
             return await verify_subscribestar_credential(url, cookies_path, config_overrides)
+        if platform == "pixiv":
+            from .pixiv_ingester import verify_pixiv_credential
+
+            return await verify_pixiv_credential(auth_token)
         from .patreon_ingester import verify_patreon_credential
 
         return await verify_patreon_credential(url, cookies_path, config_overrides)