diff --git a/alembic/versions/0030_nullable_post_source_id_denorm_artist_id.py b/alembic/versions/0030_nullable_post_source_id_denorm_artist_id.py
new file mode 100644
index 0000000..c37e499
--- /dev/null
+++ b/alembic/versions/0030_nullable_post_source_id_denorm_artist_id.py
@@ -0,0 +1,145 @@
+"""nullable post.source_id + denormalized post.artist_id; retire sidecar synthetics
+
+Revision ID: 0030
+Revises: 0029
+Create Date: 2026-06-01
+
+Operator-asked 2026-06-01 after the Dymkens orphan investigation: the
+sidecar synthetic Source pattern (`sidecar:<platform>:<slug>` rows
+with enabled=false) was technically correct but misled the operator
+into thinking they had phantom subscriptions. The synthetics existed
+solely to satisfy `Post.source_id NOT NULL` for filesystem-imported
+content with no real subscription.
+
+This migration makes the data model honest:
+
+1. **Post gets a denormalized `artist_id` column** so artist filters
+   work without traversing `Post → Source.artist_id`. Backfilled from
+   the existing Source linkage, then NOT NULL'd.
+2. **`Post.source_id` becomes nullable**, FK ondelete `CASCADE` → `SET
+   NULL`. Deleting a Source detaches its Posts instead of destroying
+   imported content (semantically: subscription ends, archive stays).
+3. **`ImageProvenance.source_id` becomes nullable** with the same FK
+   semantic change.
+4. **Sidecar synthetic Sources are deleted** — first NULL out the
+   FKs from Post + ImageProvenance pointing at them (so the implicit
+   CASCADE doesn't fire), then delete. DownloadEvent FK is unchanged
+   (still CASCADE'd, NOT NULL'd) — synthetics have `enabled=false`
+   so no events exist for them.
+
+Uniqueness handling: the existing `uq_post_source_external_id`
+(source_id, external_post_id) keeps working for source-bound Posts
+(Postgres treats NULL != NULL so NULL-source rows aren't deduped by
+it). A second partial unique index covers the NULL-source case on
+(artist_id, external_post_id) so filesystem-imported posts still
+dedupe within an artist.
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+from sqlalchemy import text
+
+revision: str = "0030"
+down_revision: Union[str, None] = "0029"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    conn = op.get_bind()
+
+    # Step 1: add Post.artist_id, initially nullable for backfill.
+    # FK naming follows the Base.metadata naming_convention
+    # (fk_<table>_<column>_<referred_table>) — alembic 0001 set this up.
+    op.add_column(
+        "post",
+        sa.Column("artist_id", sa.Integer, nullable=True),
+    )
+    op.create_foreign_key(
+        "fk_post_artist_id_artist", "post", "artist",
+        ["artist_id"], ["id"], ondelete="CASCADE",
+    )
+
+    # Step 2: backfill from Source.artist_id (every existing Post has a
+    # Source today, so every row gets populated).
+    conn.execute(text("""
+        UPDATE post p
+        SET artist_id = s.artist_id
+        FROM source s
+        WHERE p.source_id = s.id AND p.artist_id IS NULL
+    """))
+
+    # Sanity: count any remaining NULLs. Should be zero pre-this-migration.
+    remaining = conn.execute(text(
+        "SELECT COUNT(*) FROM post WHERE artist_id IS NULL"
+    )).scalar_one()
+    if remaining:
+        raise RuntimeError(
+            f"alembic 0030: {remaining} post rows have no resolvable "
+            f"artist_id after backfill. Investigate before continuing."
+        )
+
+    # Step 3: enforce NOT NULL + add index for artist-filter queries.
+    op.alter_column("post", "artist_id", nullable=False)
+    op.create_index("ix_post_artist_id", "post", ["artist_id"])
+
+    # Step 4: relax post.source_id + flip FK to SET NULL. The original FK
+    # name from alembic 0001 is `fk_post_source_id_source` per the
+    # NAMING_CONVENTION in models/base.py.
+    op.alter_column("post", "source_id", nullable=True)
+    op.drop_constraint("fk_post_source_id_source", "post", type_="foreignkey")
+    op.create_foreign_key(
+        "fk_post_source_id_source", "post", "source",
+        ["source_id"], ["id"], ondelete="SET NULL",
+    )
+
+    # Step 5: relax image_provenance.source_id + flip FK to SET NULL.
+    op.alter_column("image_provenance", "source_id", nullable=True)
+    op.drop_constraint(
+        "fk_image_provenance_source_id_source", "image_provenance",
+        type_="foreignkey",
+    )
+    op.create_foreign_key(
+        "fk_image_provenance_source_id_source", "image_provenance", "source",
+        ["source_id"], ["id"], ondelete="SET NULL",
+    )
+
+    # Step 6: partial unique index on (artist_id, external_post_id) for
+    # NULL-source Posts. The existing uq_post_source_external_id keeps
+    # guarding source-bound rows; NULL-source rows now dedupe within
+    # an artist.
+    op.execute(
+        "CREATE UNIQUE INDEX uq_post_artist_external_id_null_source "
+        "ON post (artist_id, external_post_id) "
+        "WHERE source_id IS NULL"
+    )
+
+    # Step 7: retire sidecar synthetic Sources. NULL out the references
+    # FIRST (the new FK is SET NULL so CASCADE wouldn't fire anyway, but
+    # being explicit makes the intent clear). Then delete the synthetic
+    # source rows. Any DownloadEvent rows under synthetics CASCADE-die
+    # with the source — synthetics have enabled=false so there shouldn't
+    # be any in practice.
+    conn.execute(text("""
+        UPDATE post
+        SET source_id = NULL
+        WHERE source_id IN (SELECT id FROM source WHERE url LIKE 'sidecar:%')
+    """))
+    conn.execute(text("""
+        UPDATE image_provenance
+        SET source_id = NULL
+        WHERE source_id IN (SELECT id FROM source WHERE url LIKE 'sidecar:%')
+    """))
+    deleted = conn.execute(text(
+        "DELETE FROM source WHERE url LIKE 'sidecar:%' RETURNING id"
+    )).rowcount
+    print(f"alembic 0030: deleted {deleted} sidecar synthetic source rows")
+
+
+def downgrade() -> None:
+    # Lossy migration — the deleted sidecar synthetics can't be
+    # restored from the orphan post.source_id / image_provenance.source_id
+    # values, and the partial unique index encodes a constraint that
+    # NULL-source Posts may now exist. No safe downgrade.
+    pass
diff --git a/alembic/versions/0031_source_backfill_runs_remaining.py b/alembic/versions/0031_source_backfill_runs_remaining.py
new file mode 100644
index 0000000..ed140fc
--- /dev/null
+++ b/alembic/versions/0031_source_backfill_runs_remaining.py
@@ -0,0 +1,45 @@
+"""source.backfill_runs_remaining: sticky deep-scan mode
+
+Revision ID: 0031
+Revises: 0030
+Create Date: 2026-06-01
+
+Tick vs backfill mode for subscription downloads. When
+`backfill_runs_remaining > 0`, the next N download runs use
+`skip: True` + 30-min timeout (walk full history). When 0, runs use
+`skip: "exit:20"` + 14.5-min timeout (catch-up mode, exits early once
+20 contiguous archived items are seen).
+
+Operator-flagged 2026-06-01 (Knuxy run #38887): a creator with ~550
+archived posts saturates the 870s catch-up timeout even when there is
+no new content, because gallery-dl's default `skip: True` keeps walking.
+Tick mode short-circuits that; backfill mode is the explicit opt-in for
+deep history scans.
+
+Default 0 (all existing subscriptions start in tick mode).
+"""
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = "0031"
+down_revision: Union[str, None] = "0030"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "source",
+        sa.Column(
+            "backfill_runs_remaining",
+            sa.Integer,
+            nullable=False,
+            server_default="0",
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("source", "backfill_runs_remaining")
diff --git a/backend/app/api/sources.py b/backend/app/api/sources.py
index a1312ba..fe234ee 100644
--- a/backend/app/api/sources.py
+++ b/backend/app/api/sources.py
@@ -120,6 +120,31 @@ async def delete_source(source_id: int):
     return "", 204
 
 
+@sources_bp.route("/<int:source_id>/backfill", methods=["POST"])
+async def set_backfill(source_id: int):
+    """Plan #544: arm a source for backfill mode for the next N download
+    runs. Body: `{"runs": int}` (1..10, default 3). Returns the updated
+    source dict. While backfill_runs_remaining > 0, downloads use
+    gallery-dl's full-walk config (skip: True + 30-min timeout) instead
+    of the catch-up default (skip: "exit:20" + 14.5-min timeout)."""
+    payload = await request.get_json(silent=True) or {}
+    runs = payload.get("runs", 3)
+    try:
+        runs = int(runs)
+    except (TypeError, ValueError):
+        return _bad("invalid_runs", detail="runs must be an integer")
+    async with get_session() as session:
+        try:
+            record = await SourceService(session).set_backfill_runs(
+                source_id, runs,
+            )
+        except LookupError:
+            return _bad("not_found", status=404)
+        except ValueError as exc:
+            return _bad("invalid_runs", detail=str(exc))
+    return jsonify(record.to_dict())
+
+
 @sources_bp.route("/<int:source_id>/check", methods=["POST"])
 async def check_source(source_id: int):
     """FC-3c: enqueue a download for this source.
diff --git a/backend/app/models/image_provenance.py b/backend/app/models/image_provenance.py
index ec3e756..eaa47df 100644
--- a/backend/app/models/image_provenance.py
+++ b/backend/app/models/image_provenance.py
@@ -34,8 +34,12 @@ class ImageProvenance(Base):
     post_id: Mapped[int] = mapped_column(
         ForeignKey("post.id", ondelete="CASCADE"), nullable=False, index=True
     )
-    source_id: Mapped[int] = mapped_column(
-        ForeignKey("source.id", ondelete="CASCADE"), nullable=False, index=True
+    # Nullable since alembic 0030 — provenance rows for filesystem-imported
+    # content with no subscription have NULL source_id. FK ondelete SET
+    # NULL so deleting a Source detaches its provenance rows instead of
+    # destroying the linkage between image and post.
+    source_id: Mapped[int | None] = mapped_column(
+        ForeignKey("source.id", ondelete="SET NULL"), nullable=True, index=True
     )
     captured_metadata: Mapped[dict | None] = mapped_column(JSON, nullable=True)
     captured_at: Mapped[datetime] = mapped_column(
diff --git a/backend/app/models/post.py b/backend/app/models/post.py
index d5263c9..d9830a2 100644
--- a/backend/app/models/post.py
+++ b/backend/app/models/post.py
@@ -1,6 +1,9 @@
-"""Post — provenance anchor for content downloaded from a Source.
+"""Post — provenance anchor for one creator post (may contain many images).
 
-A Post is one creator post; it may contain many images/videos.
+`source_id` is nullable since alembic 0030 — filesystem-imported posts
+with no live subscription have NULL source_id. `artist_id` is the
+denormalized always-present link to the creator (added in 0030 so
+artist-filter queries don't depend on the Source detour).
 """
 
 from datetime import datetime
@@ -14,12 +17,25 @@ from .base import Base
 class Post(Base):
     __tablename__ = "post"
     __table_args__ = (
+        # Source-bound dedup. Postgres treats NULL != NULL so rows
+        # with source_id IS NULL aren't deduped by this constraint;
+        # the partial unique index `uq_post_artist_external_id_null_source`
+        # (created in alembic 0030) covers that case via
+        # (artist_id, external_post_id).
         UniqueConstraint("source_id", "external_post_id", name="uq_post_source_external_id"),
     )
 
     id: Mapped[int] = mapped_column(Integer, primary_key=True)
-    source_id: Mapped[int] = mapped_column(
-        ForeignKey("source.id", ondelete="CASCADE"), nullable=False, index=True
+    source_id: Mapped[int | None] = mapped_column(
+        ForeignKey("source.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    # Denormalized; always equals source.artist_id when source_id is set
+    # (the importer is responsible for keeping them consistent on insert).
+    # Filter queries (artist detail, artist-scoped posts feed) use this
+    # directly instead of joining through Source.
+    artist_id: Mapped[int] = mapped_column(
+        ForeignKey("artist.id", ondelete="CASCADE"),
+        nullable=False, index=True,
     )
     external_post_id: Mapped[str] = mapped_column(String(128), nullable=False)
     post_url: Mapped[str | None] = mapped_column(Text, nullable=True)
diff --git a/backend/app/models/source.py b/backend/app/models/source.py
index 9c90e81..407227e 100644
--- a/backend/app/models/source.py
+++ b/backend/app/models/source.py
@@ -29,4 +29,13 @@ class Source(Base):
     check_interval_override: Mapped[int | None] = mapped_column(Integer, nullable=True)
     consecutive_failures: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
 
+    # alembic 0031: sticky deep-scan budget. When > 0, the next N download
+    # runs use gallery-dl's full-walk config (skip: True + 1800s timeout);
+    # when 0, runs use tick mode (skip: "exit:20" + 870s, exits early once
+    # 20 contiguous archived items are seen). Auto-decrements per run, with
+    # an auto-reset to 0 on clean exit + zero downloads (queue drained).
+    backfill_runs_remaining: Mapped[int] = mapped_column(
+        Integer, nullable=False, default=0, server_default="0",
+    )
+
     artist = relationship("Artist", back_populates="sources")
diff --git a/backend/app/services/artist_service.py b/backend/app/services/artist_service.py
index 56f19ff..0947411 100644
--- a/backend/app/services/artist_service.py
+++ b/backend/app/services/artist_service.py
@@ -58,13 +58,17 @@ class ArtistService:
             )
         ).scalar_one()
 
+        # Posts under this artist that have at least one image attached.
+        # Use Post.artist_id (alembic 0030) for the artist filter; keep
+        # the ImageProvenance JOIN so date bounds reflect only image-
+        # bearing posts (matches the original semantic). NULL-source
+        # posts now surface too.
         date_row = (
             await self.session.execute(
                 select(func.min(Post.post_date), func.max(Post.post_date))
                 .select_from(Post)
                 .join(ImageProvenance, ImageProvenance.post_id == Post.id)
-                .join(Source, Source.id == ImageProvenance.source_id)
-                .where(Source.artist_id == aid)
+                .where(Post.artist_id == aid)
             )
         ).first()
         dmin, dmax = date_row if date_row else (None, None)
@@ -98,14 +102,14 @@ class ArtistService:
             )
         ).all()
 
+        # Same Post.artist_id direct filter — counts NULL-source posts too.
         month = func.date_trunc("month", Post.post_date).label("m")
         activity = (
             await self.session.execute(
                 select(month, func.count(func.distinct(ImageProvenance.image_record_id)))
                 .select_from(Post)
                 .join(ImageProvenance, ImageProvenance.post_id == Post.id)
-                .join(Source, Source.id == ImageProvenance.source_id)
-                .where(and_(Source.artist_id == aid, Post.post_date.isnot(None)))
+                .where(and_(Post.artist_id == aid, Post.post_date.isnot(None)))
                 .group_by(month)
                 .order_by(month)
             )
@@ -114,9 +118,7 @@ class ArtistService:
         post_count = (
             await self.session.execute(
                 select(func.count(func.distinct(Post.id)))
-                .select_from(Post)
-                .join(Source, Source.id == Post.source_id)
-                .where(Source.artist_id == aid)
+                .where(Post.artist_id == aid)
             )
         ).scalar_one()
 
diff --git a/backend/app/services/download_service.py b/backend/app/services/download_service.py
index 6e917c3..529da83 100644
--- a/backend/app/services/download_service.py
+++ b/backend/app/services/download_service.py
@@ -25,7 +25,14 @@ from sqlalchemy.orm import joinedload
 
 from ..models import Artist, DownloadEvent, Source
 from .credential_service import CredentialService
-from .gallery_dl import GalleryDLService, SourceConfig
+from .gallery_dl import (
+    BACKFILL_SKIP_VALUE,
+    BACKFILL_TIMEOUT_SECONDS,
+    TICK_SKIP_VALUE,
+    ErrorType,
+    GalleryDLService,
+    SourceConfig,
+)
 from .importer import Importer
 from .patreon_resolver import resolve_campaign_id
 from .scheduler_service import set_platform_cooldown
@@ -84,6 +91,18 @@ class DownloadService:
         ctx = setup
 
         source_config = SourceConfig.from_dict(ctx["config_overrides"] or {})
+        # alembic 0031 / plan #544: derive skip_value + timeout from the
+        # source's backfill_runs_remaining counter. When > 0, walk the full
+        # post history (skip: True + 1800s); when 0, exit gallery-dl after
+        # 20 contiguous archived items (skip: "exit:20" + the default
+        # 870s). Operator sets backfill via POST /api/sources/{id}/backfill.
+        backfill_remaining = ctx.get("backfill_runs_remaining", 0) or 0
+        if backfill_remaining > 0:
+            skip_value: bool | str = BACKFILL_SKIP_VALUE
+            source_config.timeout = BACKFILL_TIMEOUT_SECONDS
+        else:
+            skip_value = TICK_SKIP_VALUE
+
         effective_url = _effective_url(
             ctx["platform"], ctx["url"], ctx["config_overrides"] or {}
         )
@@ -95,6 +114,7 @@ class DownloadService:
             source_config=source_config,
             cookies_path=ctx["cookies_path"],
             auth_token=ctx["auth_token"],
+            skip_value=skip_value,
         )
 
         resolved_campaign_id: str | None = None
@@ -121,6 +141,7 @@ class DownloadService:
                         source_config=source_config,
                         cookies_path=ctx["cookies_path"],
                         auth_token=ctx["auth_token"],
+                        skip_value=skip_value,
                     )
 
         return await self._phase3_persist(
@@ -185,6 +206,7 @@ class DownloadService:
             "config_overrides": dict(source.config_overrides or {}),
             "cookies_path": cookies_path,
             "auth_token": auth_token,
+            "backfill_runs_remaining": source.backfill_runs_remaining or 0,
         }
 
     async def _phase3_persist(
@@ -259,12 +281,21 @@ class DownloadService:
         run_stats["quarantined_count"] = dl_result.files_quarantined
         stderr_summary = self.gdl._extract_errors_warnings(dl_result.stderr)
 
-        status = "ok" if (dl_result.success and import_summary["errors"] == 0) else "error"
+        # Plan #544: PARTIAL means the run downloaded ≥1 file but the
+        # subprocess didn't finish in budget (typically wall-clock timeout
+        # mid-walk). Real work happened; the next tick continues via
+        # gallery-dl's archive. NOT a failure for status purposes.
+        if dl_result.success and import_summary["errors"] == 0:
+            status = "ok"
+        elif dl_result.error_type == ErrorType.PARTIAL and import_summary["errors"] == 0:
+            status = "ok"
+        else:
+            status = "error"
         ev.status = status
         ev.finished_at = datetime.now(UTC)
         ev.files_count = import_summary["attached"]
         ev.bytes_downloaded = bytes_downloaded
-        ev.error = dl_result.error_message if not dl_result.success else None
+        ev.error = dl_result.error_message if status == "error" else None
         ev.metadata_ = {
             "run_stats": run_stats,
             "error_type": dl_result.error_type.value if dl_result.error_type else None,
@@ -279,6 +310,19 @@ class DownloadService:
             source_id=ctx["source_id"], status=status, error_message=ev.error,
             error_type=dl_result.error_type.value if dl_result.error_type else None,
         )
+        # Plan #544: backfill lifecycle — auto-complete when a clean
+        # backfill run drained the queue (gallery-dl exited 0 + zero files
+        # downloaded means there was nothing to fetch); otherwise decrement
+        # the counter. Next tick falls back to tick mode once it hits 0.
+        backfill_remaining = ctx.get("backfill_runs_remaining", 0) or 0
+        if backfill_remaining > 0:
+            src = (await self.async_session.execute(
+                select(Source).where(Source.id == ctx["source_id"])
+            )).scalar_one()
+            if dl_result.return_code == 0 and dl_result.files_downloaded == 0:
+                src.backfill_runs_remaining = 0
+            else:
+                src.backfill_runs_remaining = max(0, backfill_remaining - 1)
         await self.async_session.commit()
         return event_id
 
diff --git a/backend/app/services/gallery_dl.py b/backend/app/services/gallery_dl.py
index 3e19a69..0f19793 100644
--- a/backend/app/services/gallery_dl.py
+++ b/backend/app/services/gallery_dl.py
@@ -39,9 +39,29 @@ class ErrorType(StrEnum):
     HTTP_ERROR = "http_error"
     UNSUPPORTED_URL = "unsupported_url"
     VALIDATION_FAILED = "validation_failed"
+    # Run made real progress (downloaded ≥1 file) but did not finish in the
+    # subprocess budget. Distinct from UNKNOWN_ERROR — the downstream status
+    # mapping classifies this as "ok" because the next tick continues.
+    PARTIAL = "partial"
     UNKNOWN_ERROR = "unknown_error"
 
 
+# Tick mode (routine cron polls): skip ≤20 contiguous already-archived
+# items, then exit gallery-dl. Established subscription with zero new
+# content exits in ~30s of HEAD requests instead of walking to the bottom
+# of the post history (which can be hours for prolific creators). 20 (not
+# 5) is operator-set headroom against any edge case where paywalled or
+# otherwise-non-downloadable items might interleave with archived ones —
+# 20 contiguous HEADs is still negligible.
+TICK_SKIP_VALUE = "exit:20"
+
+# Backfill mode (operator-triggered deep scan): walk the full history.
+# Source.backfill_runs_remaining > 0 selects this mode; the longer
+# timeout below absorbs creators with thousands of posts.
+BACKFILL_SKIP_VALUE = True
+BACKFILL_TIMEOUT_SECONDS = 1800
+
+
 # 30 seconds shy of download_source's Celery soft_time_limit (900s, see
 # tasks/download.py:32). subprocess.run MUST raise TimeoutExpired before
 # Celery raises SoftTimeLimitExceeded — otherwise Celery wins the race,
@@ -56,12 +76,19 @@ _DEFAULT_GDL_TIMEOUT_SECONDS = 870
 
 @dataclass
 class SourceConfig:
+    """Per-source overrides loaded from Source.config_overrides JSON.
+
+    Note: the gallery-dl `skip` value (tick vs backfill, see TICK_SKIP_VALUE /
+    BACKFILL_SKIP_VALUE) is NOT carried here — it derives from the
+    Source.backfill_runs_remaining column at the download_service layer
+    and is passed to _build_config_for_source as `skip_value`. Same for
+    the per-run subprocess timeout.
+    """
     content_types: list[str] = field(default_factory=lambda: ["all"])
     sleep: float | None = None
     sleep_request: float | None = None
     directory_pattern: str | None = None
     filename_pattern: str | None = None
-    skip_existing: bool = True
     save_metadata: bool = True
     timeout: int = _DEFAULT_GDL_TIMEOUT_SECONDS
 
@@ -73,7 +100,6 @@ class SourceConfig:
             sleep_request=data.get("sleep_request"),
             directory_pattern=data.get("directory_pattern"),
             filename_pattern=data.get("filename_pattern"),
-            skip_existing=data.get("skip_existing", True),
             save_metadata=data.get("save_metadata", True),
             timeout=data.get("timeout", _DEFAULT_GDL_TIMEOUT_SECONDS),
         )
@@ -231,6 +257,25 @@ class GalleryDLService:
                 "part-directory": str(self._config_dir / "temp"),
                 "retries": 3,
                 "timeout": 120.0,
+                # Forward Patreon as Referer/Origin to yt-dlp when it
+                # fetches video manifests. Operator-flagged 2026-06-01
+                # (DaferQ patreon): video posts hosted on Mux carry a JWT
+                # playback restriction that checks Referer/Origin on every
+                # request — not just the token signature. gallery-dl's
+                # HEAD probe to stream.mux.com returns 200 (the token is
+                # valid), but yt-dlp's actual GET-with-Range to fetch the
+                # m3u8 manifest 403s because yt-dlp sends its own default
+                # Referer, which Mux's policy rejects. Forcing the right
+                # headers fixes the headers-only case; Mux IP-range
+                # restrictions are unfixable from here.
+                "ytdl": {
+                    "raw-options": {
+                        "http_headers": {
+                            "Referer": "https://www.patreon.com/",
+                            "Origin": "https://www.patreon.com",
+                        },
+                    },
+                },
             },
             "output": {"progress": True},
         }
@@ -245,7 +290,18 @@ class GalleryDLService:
         platform: str,
         source_config: SourceConfig,
         artist_slug: str,
+        skip_value: bool | str = BACKFILL_SKIP_VALUE,
     ) -> dict:
+        """`skip_value` controls gallery-dl's archive-walk behavior:
+            - True (BACKFILL_SKIP_VALUE): walk full post history, skipping
+              archived items but continuing past them. Used in backfill mode.
+            - "exit:20" (TICK_SKIP_VALUE): exit gallery-dl after 20
+              contiguous archived items. Used in tick (routine catch-up)
+              mode for fast no-op syncs on creators with deep history.
+            - False: don't skip — redownload everything (not used in FC).
+        The caller (download_service) chooses based on
+        Source.backfill_runs_remaining.
+        """
         config = json.loads(json.dumps(self._get_default_config()))  # deep copy
 
         destination = str(self.images_root / artist_slug / platform)
@@ -255,7 +311,7 @@ class GalleryDLService:
             config["extractor"]["sleep"] = source_config.sleep
         if source_config.sleep_request is not None:
             config["extractor"]["sleep-request"] = source_config.sleep_request
-        config["extractor"]["skip"] = source_config.skip_existing
+        config["extractor"]["skip"] = skip_value
 
         if source_config.save_metadata:
             config["extractor"]["postprocessors"] = [
@@ -394,6 +450,22 @@ class GalleryDLService:
                     f"Subscription tier does not grant access to {count} post{'s' if count != 1 else ''}",
                 )
 
+        # Partial-success: the subprocess exited non-zero (typically because
+        # the wall-clock timeout fired mid-walk), but it had downloaded ≥1
+        # file by then and no source-level error category fired. The work
+        # the run DID do is real; gallery-dl's archive will pick up where
+        # it left off on the next tick. Mapped to status="ok" downstream
+        # (download_service.py) so this doesn't flag the source as
+        # "needs attention." Operator-flagged 2026-06-01 after a Knuxy
+        # patreon run downloaded hundreds of files then ran red on timeout.
+        files_downloaded = self._count_downloaded_files(stdout)
+        if not has_actual_error and files_downloaded > 0:
+            return (
+                ErrorType.PARTIAL,
+                f"Downloaded {files_downloaded} file{'s' if files_downloaded != 1 else ''}; "
+                "run did not complete in budget — next tick will continue",
+            )
+
         return ErrorType.UNKNOWN_ERROR, f"Unknown error (return code: {return_code})"
 
     def _count_downloaded_files(self, stdout: str) -> int:
@@ -545,6 +617,7 @@ class GalleryDLService:
         source_config: SourceConfig | None = None,
         cookies_path: str | None = None,
         auth_token: str | None = None,
+        skip_value: bool | str = BACKFILL_SKIP_VALUE,
     ) -> DownloadResult:
         start_time = time.time()
         started_at = datetime.now(UTC).isoformat()
@@ -552,7 +625,9 @@ class GalleryDLService:
         if source_config is None:
             source_config = SourceConfig()
 
-        config = self._build_config_for_source(platform, source_config, artist_slug)
+        config = self._build_config_for_source(
+            platform, source_config, artist_slug, skip_value=skip_value,
+        )
 
         if cookies_path:
             config["extractor"]["cookies"] = cookies_path
diff --git a/backend/app/services/gallery_service.py b/backend/app/services/gallery_service.py
index 095890d..3331510 100644
--- a/backend/app/services/gallery_service.py
+++ b/backend/app/services/gallery_service.py
@@ -20,8 +20,9 @@ from datetime import datetime
 
 from sqlalchemy import Select, and_, exists, func, or_, select
 from sqlalchemy.ext.asyncio import AsyncSession
+from sqlalchemy.orm import aliased
 
-from ..models import Artist, ImageProvenance, ImageRecord, Post, Source, Tag
+from ..models import Artist, ImageProvenance, ImageRecord, Post, Tag
 from ..models.tag import image_tag
 
 CURSOR_SEPARATOR = "|"
@@ -133,10 +134,23 @@ def _provenance_clause(post_id, artist_id):
             ImageProvenance.post_id == post_id,
         )
     if artist_id is not None:
+        # Use Post.artist_id (alembic 0030 denormalized column) instead
+        # of joining through ImageProvenance.source_id → Source.artist_id.
+        # The denormalization is the always-present linkage; the source
+        # path now drops NULL-source provenance rows (filesystem-imported
+        # content) which would otherwise vanish from artist-filtered
+        # gallery views.
+        # ALIAS Post: the gallery query outer-joins Post on
+        # ImageRecord.primary_post_id (`_outer_join_primary_post`).
+        # SQLAlchemy would otherwise correlate a bare `Post` reference
+        # in this EXISTS subquery to that outer Post (which is NULL for
+        # images with no primary post), and the filter would silently
+        # match nothing.
+        post_inner = aliased(Post)
         return exists().where(
             ImageProvenance.image_record_id == ImageRecord.id,
-            ImageProvenance.source_id == Source.id,
-            Source.artist_id == artist_id,
+            ImageProvenance.post_id == post_inner.id,
+            post_inner.artist_id == artist_id,
         )
     return None
 
diff --git a/backend/app/services/importer.py b/backend/app/services/importer.py
index c66caa8..6e3ed23 100644
--- a/backend/app/services/importer.py
+++ b/backend/app/services/importer.py
@@ -212,10 +212,10 @@ class Importer:
         which would lose the surrounding scan's progress — and re-run `stmt`
         (scalar_one) to return the row the other worker created.
 
-        Centralizes the pattern shared by _find_or_create_source,
-        _source_for_sidecar, and _find_or_create_post. The plain
-        SELECT-then-INSERT version lost races under the 5-min recovery sweep
-        (operator-flagged 2026-05-26)."""
+        Centralizes the pattern shared by _find_or_create_source and
+        _find_or_create_post. The plain SELECT-then-INSERT version lost
+        races under the 5-min recovery sweep (operator-flagged
+        2026-05-26)."""
         existing = self.session.execute(stmt).scalar_one_or_none()
         if existing is not None:
             return existing
@@ -258,47 +258,25 @@ class Importer:
             lambda: Source(artist_id=artist_id, platform=platform, url=url),
         )
 
-    def _source_for_sidecar(
-        self, *, artist_id: int, platform: str, artist_slug: str,
-    ) -> Source:
-        """Sidecar-import Source resolver. Used by both filesystem imports
-        and gallery-dl downloads (both write sidecar JSON, both flow through
-        _apply_sidecar / _capture_attachment).
+    def _lookup_source_for_sidecar(
+        self, *, artist_id: int, platform: str,
+    ) -> Source | None:
+        """Find the real subscription Source for (artist, platform), or
+        None if no subscription exists.
 
-        Source represents a subscription feed (one per artist+platform — the
-        URL polled by the FC-3 downloader). The filesystem importer used to
-        call _find_or_create_source(url=sd.post_url), creating one Source
-        row per post URL — 100s of junk Sources per artist, all with
-        enabled=True, polluting the artist detail page and tricking the
-        subscription checker into trying to poll patreon post URLs as feeds.
-        Operator-flagged 2026-05-26; consolidated via alembic 0022.
-
-        Resolution order: prefer a real (non-sidecar) Source over a
-        synthetic anchor. When alembic 0022 ran, it may have rewritten
-        per-post Sources into `sidecar:<platform>:<slug>` synthetic
-        anchors. If the operator later added the real subscription, both
-        rows now coexist. A naive `ORDER BY id ASC LIMIT 1` lookup would
-        pick the older synthetic and silently attach every gallery-dl
-        download to the wrong Source — operator-flagged 2026-05-31 after
-        the Subscriptions UI surfaced the phantom anchors. Pick the real
-        one when one exists; fall back to the synthetic; only create a
-        new synthetic when nothing exists for (artist, platform).
+        Pre-alembic-0030 this method would CREATE a synthetic
+        `sidecar:<platform>:<slug>` Source when no real one existed —
+        because `Post.source_id` was NOT NULL and the importer needed
+        something to attach Posts to. Alembic 0030 relaxed both
+        `Post.source_id` and `ImageProvenance.source_id` to nullable, so
+        synthetic anchors are obsolete; the importer now leaves
+        source_id as None when no subscription exists for the (artist,
+        platform). Operator-asked 2026-06-01: synthetic Sources had
+        leaked into the Subscriptions UI as phantom subscriptions and
+        the operator wanted the data model to truthfully say "this
+        content has no live subscription."
         """
-        real_stmt = (
-            select(Source)
-            .where(
-                Source.artist_id == artist_id,
-                Source.platform == platform,
-                ~Source.url.like("sidecar:%"),
-            )
-            .order_by(Source.id.asc())
-            .limit(1)
-        )
-        real = self.session.execute(real_stmt).scalar_one_or_none()
-        if real is not None:
-            return real
-
-        any_stmt = (
+        stmt = (
             select(Source)
             .where(
                 Source.artist_id == artist_id,
@@ -307,29 +285,37 @@ class Importer:
             .order_by(Source.id.asc())
             .limit(1)
         )
-        return self._get_or_create(
-            any_stmt,
-            lambda: Source(
-                artist_id=artist_id,
-                platform=platform,
-                url=f"sidecar:{platform}:{artist_slug}",
-                enabled=False,
-            ),
-        )
+        return self.session.execute(stmt).scalar_one_or_none()
 
     def _find_or_create_post(
-        self, *, source_id: int, external_post_id: str,
+        self, *, source_id: int | None, external_post_id: str,
+        artist_id: int,
     ) -> Post:
-        """Race-safe find-or-create on `post` keyed by
-        (source_id, external_post_id). Mirrors `_find_or_create_source`
-        — same savepoint + IntegrityError-recovery pattern."""
-        stmt = select(Post).where(
-            Post.source_id == source_id,
-            Post.external_post_id == external_post_id,
-        )
+        """Race-safe find-or-create on `post`. Keyed by
+        (source_id, external_post_id) when source_id is set — the
+        `uq_post_source_external_id` constraint guards. For NULL-source
+        posts the existence check matches on (artist_id, external_post_id),
+        which the partial unique index `uq_post_artist_external_id_null_source`
+        (alembic 0030) guards. Same savepoint + IntegrityError-recovery
+        pattern as the rest of the helpers."""
+        if source_id is not None:
+            stmt = select(Post).where(
+                Post.source_id == source_id,
+                Post.external_post_id == external_post_id,
+            )
+        else:
+            stmt = select(Post).where(
+                Post.source_id.is_(None),
+                Post.artist_id == artist_id,
+                Post.external_post_id == external_post_id,
+            )
         return self._get_or_create(
             stmt,
-            lambda: Post(source_id=source_id, external_post_id=external_post_id),
+            lambda: Post(
+                source_id=source_id,
+                artist_id=artist_id,
+                external_post_id=external_post_id,
+            ),
         )
 
     def import_one(self, source: Path) -> ImportResult:
@@ -370,12 +356,14 @@ class Importer:
             return None
         sd = parse_sidecar(data)
         platform = sd.platform or "unknown"
-        src = self._source_for_sidecar(
-            artist_id=artist.id, platform=platform, artist_slug=artist.slug,
+        src = self._lookup_source_for_sidecar(
+            artist_id=artist.id, platform=platform,
         )
         epid = sd.external_post_id or sc.stem
         return self._find_or_create_post(
-            source_id=src.id, external_post_id=epid,
+            source_id=src.id if src else None,
+            external_post_id=epid,
+            artist_id=artist.id,
         )
 
     def _capture_attachment(
@@ -858,14 +846,15 @@ class Importer:
             src = explicit_source
         else:
             platform = sd.platform or "unknown"
-            src = self._source_for_sidecar(
+            src = self._lookup_source_for_sidecar(
                 artist_id=artist.id, platform=platform,
-                artist_slug=artist.slug,
             )
 
         epid = sd.external_post_id or sc.stem
         post = self._find_or_create_post(
-            source_id=src.id, external_post_id=epid,
+            source_id=src.id if src else None,
+            external_post_id=epid,
+            artist_id=artist.id,
         )
         if sd.post_url is not None:
             post.post_url = sd.post_url
@@ -901,7 +890,7 @@ class Importer:
                     ImageProvenance(
                         image_record_id=record.id,
                         post_id=post.id,
-                        source_id=src.id,
+                        source_id=src.id if src else None,
                         captured_metadata=sd.raw,
                     )
                 )
diff --git a/backend/app/services/platforms/base.py b/backend/app/services/platforms/base.py
index 8a626b7..737b529 100644
--- a/backend/app/services/platforms/base.py
+++ b/backend/app/services/platforms/base.py
@@ -96,10 +96,12 @@ def str_field(v) -> str | None:
 # Shared gallery-dl invocation defaults. Embedded in each platform's
 # default_config (with platform-specific overrides) so per-platform
 # choices stay explicit.
+# Note: the gallery-dl `skip` value (tick "exit:20" vs backfill True) is
+# NOT here — it's derived from Source.backfill_runs_remaining at download
+# time. See plan #544 / gallery_dl.TICK_SKIP_VALUE,BACKFILL_SKIP_VALUE.
 GD_DEFAULTS = {
     "sleep": 3.0,
     "sleep_request": 1.5,
-    "skip_existing": True,
     "save_metadata": True,
     "timeout": 3600,
 }
diff --git a/backend/app/services/post_feed_service.py b/backend/app/services/post_feed_service.py
index 634cfd3..66d2745 100644
--- a/backend/app/services/post_feed_service.py
+++ b/backend/app/services/post_feed_service.py
@@ -69,13 +69,19 @@ class PostFeedService:
             raise ValueError("direction must be 'older' or 'newer'")
 
         sort_key = _sort_key()
+        # Artist via the denormalized Post.artist_id (alembic 0030);
+        # Source via LEFT JOIN since post.source_id can now be NULL for
+        # filesystem-imported posts with no live subscription. A
+        # platform= filter implicitly excludes NULL-source posts (they
+        # have no platform); an artist_id= filter still surfaces them
+        # because Post.artist_id is always set.
         stmt = (
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
         )
         if artist_id is not None:
-            stmt = stmt.where(Source.artist_id == artist_id)
+            stmt = stmt.where(Post.artist_id == artist_id)
         if platform is not None:
             stmt = stmt.where(Source.platform == platform)
         if cursor:
@@ -135,8 +141,8 @@ class PostFeedService:
         cursor for each end. Returns None if the post doesn't exist."""
         anchor = (await self.session.execute(
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
             .where(Post.id == post_id)
         )).one_or_none()
         if anchor is None:
@@ -168,8 +174,8 @@ class PostFeedService:
     async def get_post(self, post_id: int) -> dict | None:
         row = (await self.session.execute(
             select(Post, Artist, Source)
-            .join(Source, Post.source_id == Source.id)
-            .join(Artist, Source.artist_id == Artist.id)
+            .join(Artist, Post.artist_id == Artist.id)
+            .outerjoin(Source, Post.source_id == Source.id)
             .where(Post.id == post_id)
         )).one_or_none()
         if row is None:
@@ -260,7 +266,7 @@ class PostFeedService:
         return out
 
     def _to_dict(
-        self, post: Post, artist: Artist, source: Source,
+        self, post: Post, artist: Artist, source: Source | None,
         thumbs_map: dict, atts_map: dict,
     ) -> dict:
         plain_full = html_to_plain(post.description) if post.description else None
@@ -269,6 +275,9 @@ class PostFeedService:
         else:
             description_plain, truncated = truncate_at_word(plain_full, DESCRIPTION_LIMIT)
         thumbs_entry = thumbs_map.get(post.id, {"thumbs": [], "more": 0})
+        # `source` is null for filesystem-imported posts with no live
+        # subscription (alembic 0030). Frontend renders that as a
+        # "filesystem import" affordance instead of a platform chip.
         return {
             "id": post.id,
             "external_post_id": post.external_post_id,
@@ -279,7 +288,10 @@ class PostFeedService:
             "description_plain": description_plain,
             "description_truncated": truncated,
             "artist": {"id": artist.id, "name": artist.name, "slug": artist.slug},
-            "source": {"id": source.id, "platform": source.platform},
+            "source": (
+                {"id": source.id, "platform": source.platform}
+                if source is not None else None
+            ),
             "thumbnails": thumbs_entry["thumbs"],
             "thumbnails_more": thumbs_entry["more"],
             "attachments": atts_map.get(post.id, []),
diff --git a/backend/app/services/provenance_service.py b/backend/app/services/provenance_service.py
index 091feef..9c2739b 100644
--- a/backend/app/services/provenance_service.py
+++ b/backend/app/services/provenance_service.py
@@ -70,11 +70,15 @@ class ProvenanceService:
         rec = await self.session.get(ImageRecord, image_id)
         if rec is None:
             return None
+        # Artist via Post.artist_id (alembic 0030); Source via LEFT JOIN
+        # since both Post.source_id and ImageProvenance.source_id can be
+        # NULL for filesystem-imported content. Frontend renders source=
+        # null as "filesystem import."
         stmt = (
             select(ImageProvenance, Post, Source, Artist)
             .join(Post, Post.id == ImageProvenance.post_id)
-            .join(Source, Source.id == ImageProvenance.source_id)
-            .join(Artist, Artist.id == Source.artist_id)
+            .join(Artist, Artist.id == Post.artist_id)
+            .outerjoin(Source, Source.id == ImageProvenance.source_id)
             .where(ImageProvenance.image_record_id == image_id)
             .order_by(ImageProvenance.captured_at.asc(),
                       ImageProvenance.id.asc())
@@ -90,7 +94,7 @@ class ProvenanceService:
                     "captured_at": ip.captured_at.isoformat()
                     if ip.captured_at else None,
                     "post": _post_dict(post),
-                    "source": _source_dict(src),
+                    "source": _source_dict(src) if src is not None else None,
                     "artist": _artist_dict(art),
                 }
                 for ip, post, src, art in rows
@@ -99,10 +103,12 @@ class ProvenanceService:
         }
 
     async def for_post(self, post_id: int) -> dict | None:
+        # Same LEFT JOIN to Source — get_post must succeed for a
+        # NULL-source post.
         stmt = (
             select(Post, Source, Artist)
-            .join(Source, Source.id == Post.source_id)
-            .join(Artist, Artist.id == Source.artist_id)
+            .join(Artist, Artist.id == Post.artist_id)
+            .outerjoin(Source, Source.id == Post.source_id)
             .where(Post.id == post_id)
         )
         row = (await self.session.execute(stmt)).first()
@@ -111,7 +117,7 @@ class ProvenanceService:
         post, src, art = row
         return {
             "post": _post_dict(post),
-            "source": _source_dict(src),
+            "source": _source_dict(src) if src is not None else None,
             "artist": _artist_dict(art),
             "attachments": await self._attachments_for_posts([post.id]),
         }
diff --git a/backend/app/services/refetch_service.py b/backend/app/services/refetch_service.py
index 41832bc..f2e941e 100644
--- a/backend/app/services/refetch_service.py
+++ b/backend/app/services/refetch_service.py
@@ -86,7 +86,7 @@ def attempt_refetch(
     if src is None:
         return {"status": "no_source"}
 
-    # Remove the bad copy so gallery-dl (skip_existing) re-fetches it on
+    # Remove the bad copy so gallery-dl's archive-skip re-fetches it on
     # the source re-check instead of skipping the still-present corrupt
     # file.
     try:
diff --git a/backend/app/services/source_service.py b/backend/app/services/source_service.py
index 57a9571..144a994 100644
--- a/backend/app/services/source_service.py
+++ b/backend/app/services/source_service.py
@@ -62,6 +62,7 @@ class SourceRecord:
     check_interval_override: int | None
     consecutive_failures: int
     next_check_at: str | None
+    backfill_runs_remaining: int
 
     def to_dict(self) -> dict:
         return {
@@ -78,6 +79,7 @@ class SourceRecord:
             "check_interval_override": self.check_interval_override,
             "consecutive_failures": self.consecutive_failures,
             "next_check_at": self.next_check_at,
+            "backfill_runs_remaining": self.backfill_runs_remaining,
         }
 
 
@@ -85,6 +87,11 @@ class SourceRecord:
 
 _EDITABLE = {"enabled", "url", "config_overrides", "check_interval_override", "platform"}
 
+# Plan #544 follow-up: newly created enabled sources pre-arm backfill so
+# their first N polls walk gallery-dl's full post history with the longer
+# timeout (matches the manual "Deep scan" button's default).
+_NEW_SOURCE_BACKFILL_RUNS = 3
+
 
 class SourceService:
     def __init__(self, session: AsyncSession):
@@ -140,6 +147,7 @@ class SourceService:
             check_interval_override=source.check_interval_override,
             consecutive_failures=source.consecutive_failures or 0,
             next_check_at=nxt.isoformat() if nxt else None,
+            backfill_runs_remaining=source.backfill_runs_remaining or 0,
         )
 
     async def _row_to_record(self, source: Source) -> SourceRecord:
@@ -157,7 +165,7 @@ class SourceService:
         if artist_id is not None:
             stmt = stmt.where(Source.artist_id == artist_id)
         if not include_synthetic:
-            # Filesystem-import sidecar anchors (importer._source_for_sidecar)
+            # Pre-alembic-0030 sidecar synthetic anchors
             # have url='sidecar:<platform>:<slug>' and exist only to give
             # imported Posts a NOT-NULL Source FK. They aren't pollable
             # feeds; the Subscriptions UI used to render them as phantom
@@ -201,10 +209,21 @@ class SourceService:
             select(func.count(Source.id)).where(Source.artist_id == artist_id)
         )).scalar_one()
 
+        # Plan #544 follow-up: a freshly added subscription has no archive
+        # yet, so the first few polls would walk the full post history in
+        # tick mode and trip exit:20 after ~20 contiguous archive hits —
+        # except there are none yet, so tick mode would walk forever and
+        # blow the wall-clock cap. Pre-arm backfill so the initial syncs
+        # use the longer timeout + skip:True walk. Tick mode resumes once
+        # the budget is spent or the queue drains.
+        # Disabled sources (incl. sidecar synthetics, url='sidecar:...')
+        # are never polled, so leave their counter at 0.
+        backfill_runs = _NEW_SOURCE_BACKFILL_RUNS if enabled else 0
         source = Source(
             artist_id=artist_id, platform=platform, url=url,
             enabled=enabled, config_overrides=config_overrides,
             check_interval_override=check_interval_override,
+            backfill_runs_remaining=backfill_runs,
         )
         self.session.add(source)
         try:
@@ -264,6 +283,25 @@ class SourceService:
         await self.session.commit()
         return await self._row_to_record(source)
 
+    async def set_backfill_runs(
+        self, source_id: int, runs: int,
+    ) -> SourceRecord:
+        """Plan #544: arm a source for backfill mode. The next `runs`
+        download runs will use gallery-dl's full-walk config (skip: True
+        + 30-min timeout) instead of the catch-up default. Runs must be
+        1..10 — bigger is rejected to keep the operator from accidentally
+        setting a runaway budget."""
+        if not isinstance(runs, int) or runs < 1 or runs > 10:
+            raise ValueError("runs must be an integer in [1, 10]")
+        source = (await self.session.execute(
+            select(Source).where(Source.id == source_id)
+        )).scalar_one_or_none()
+        if source is None:
+            raise LookupError(f"source id={source_id} not found")
+        source.backfill_runs_remaining = runs
+        await self.session.commit()
+        return await self._row_to_record(source)
+
     async def delete(self, source_id: int) -> None:
         source = (await self.session.execute(
             select(Source).where(Source.id == source_id)
diff --git a/frontend/src/components/modal/ProvenancePanel.vue b/frontend/src/components/modal/ProvenancePanel.vue
index 5c36fd4..51d16f2 100644
--- a/frontend/src/components/modal/ProvenancePanel.vue
+++ b/frontend/src/components/modal/ProvenancePanel.vue
@@ -19,7 +19,12 @@
         v-for="e in state.entries" :key="e.provenance_id" class="fc-prov__card"
       >
         <div class="fc-prov__head">
-          <span class="fc-prov__platform">{{ e.source.platform }}</span>
+          <!-- Posts with no live subscription have source=null (alembic
+               0030); render an explicit "filesystem import" affordance
+               instead of a platform chip. -->
+          <span class="fc-prov__platform">
+            {{ e.source?.platform ?? 'filesystem import' }}
+          </span>
           <span v-if="postDate(e)" class="fc-prov__date">{{ postDate(e) }}</span>
         </div>
         <button
diff --git a/frontend/src/components/posts/PostCard.vue b/frontend/src/components/posts/PostCard.vue
index de62df4..a45f0a5 100644
--- a/frontend/src/components/posts/PostCard.vue
+++ b/frontend/src/components/posts/PostCard.vue
@@ -7,7 +7,12 @@
     @keydown.enter="onCardClick"
   >
     <div class="fc-post-card__head">
-      <v-chip size="x-small" variant="tonal">{{ post.source.platform }}</v-chip>
+      <!-- Posts with no live subscription have source=null (alembic
+           0030); show a "filesystem import" affordance instead of a
+           platform chip. -->
+      <v-chip size="x-small" variant="tonal">
+        {{ post.source?.platform ?? 'filesystem import' }}
+      </v-chip>
       <RouterLink
         :to="{ name: 'artist', params: { slug: post.artist.slug } }"
         class="fc-post-card__artist"
@@ -25,7 +30,7 @@
         v-if="post.post_url"
         :href="post.post_url" target="_blank" rel="noopener"
         icon="mdi-open-in-new" size="x-small" variant="text"
-        :aria-label="`open original post on ${post.source.platform}`"
+        :aria-label="`open original post on ${post.source?.platform ?? 'web'}`"
         @click.stop
       />
       <v-btn
diff --git a/frontend/src/components/subscriptions/FailingSourcesCard.vue b/frontend/src/components/subscriptions/FailingSourcesCard.vue
index 0ceb99e..5f16154 100644
--- a/frontend/src/components/subscriptions/FailingSourcesCard.vue
+++ b/frontend/src/components/subscriptions/FailingSourcesCard.vue
@@ -90,13 +90,24 @@ async function onViewLogs(s) {
 .fc-fail__title { font-weight: 600; }
 .fc-fail__body {
   padding: 0 14px 10px;
-  display: flex; flex-direction: column; gap: 2px;
+  display: flex; flex-direction: column; gap: 3px;
 }
 .fc-fail__row {
   display: flex; align-items: center; gap: 10px;
   padding: 6px 8px;
   border-radius: 4px;
   background: rgb(var(--v-theme-surface) / 0.4);
+  /* Zebra striping + hover highlight: gives the eye a horizontal track
+   * from the artist name on the left to the Logs/Retry buttons on the
+   * right. Operator-flagged 2026-06-01 — without these, all rows blur
+   * together and it's hard to pick which row a button belongs to. */
+  transition: background 80ms ease;
+}
+.fc-fail__row:nth-child(even) {
+  background: rgb(var(--v-theme-surface) / 0.55);
+}
+.fc-fail__row:hover {
+  background: rgb(var(--v-theme-error) / 0.18);
 }
 .fc-fail__artist { font-weight: 600; white-space: nowrap; }
 .fc-fail__count { flex: 0 0 auto; }
diff --git a/frontend/src/components/subscriptions/SourceRow.vue b/frontend/src/components/subscriptions/SourceRow.vue
index c30a45c..011645f 100644
--- a/frontend/src/components/subscriptions/SourceRow.vue
+++ b/frontend/src/components/subscriptions/SourceRow.vue
@@ -31,6 +31,12 @@
         v-if="(source.consecutive_failures || 0) > 0"
         size="x-small" color="error" variant="tonal" label
       >{{ source.consecutive_failures }}</v-chip>
+      <v-chip
+        v-else-if="(source.backfill_runs_remaining || 0) > 0"
+        size="x-small" color="info" variant="tonal" label
+      >
+        backfill ({{ source.backfill_runs_remaining }}×)
+      </v-chip>
       <span v-else class="fc-source-row__zero">0</span>
     </td>
     <td class="fc-source-row__actions">
@@ -42,6 +48,16 @@
         <v-icon>mdi-play</v-icon>
         <v-tooltip activator="parent" location="top">Check now</v-tooltip>
       </v-btn>
+      <v-btn
+        icon="mdi-magnify-scan" size="x-small" variant="text"
+        :disabled="(source.backfill_runs_remaining || 0) > 0"
+        @click.stop="$emit('backfill', source)"
+      >
+        <v-icon>mdi-magnify-scan</v-icon>
+        <v-tooltip activator="parent" location="top">
+          Deep scan — walk full history for next few runs
+        </v-tooltip>
+      </v-btn>
       <v-btn
         icon="mdi-pencil" size="x-small" variant="text"
         @click.stop="$emit('edit', source)"
@@ -69,7 +85,7 @@ const props = defineProps({
   checking: { type: Boolean, default: false },
   warningThreshold: { type: Number, default: 5 },
 })
-const emit = defineEmits(['edit', 'remove', 'toggle', 'check'])
+const emit = defineEmits(['edit', 'remove', 'toggle', 'check', 'backfill'])
 
 function onToggleEnabled(value) {
   emit('toggle', { source: props.source, enabled: value })
diff --git a/frontend/src/components/subscriptions/SubscriptionsTab.vue b/frontend/src/components/subscriptions/SubscriptionsTab.vue
index bbd89a8..eb80cc1 100644
--- a/frontend/src/components/subscriptions/SubscriptionsTab.vue
+++ b/frontend/src/components/subscriptions/SubscriptionsTab.vue
@@ -174,6 +174,7 @@
                     @remove="removeSource"
                     @toggle="toggleSourceEnabled"
                     @check="onCheck"
+                    @backfill="onBackfill"
                   />
                   <tr v-if="item.sources.length === 0">
                     <td colspan="8" class="fc-subs__sources-empty">
@@ -431,6 +432,36 @@ async function onCheck(source) {
   }
 }
 
+// Plan #544: arm a source for backfill mode (gallery-dl walks the full
+// post history) for the next N download runs. Default 3 — enough budget
+// to finish a deep creator without re-prompting the operator across
+// timeout boundaries. The chip on the row reflects the remaining count.
+async function onBackfill(source) {
+  const raw = globalThis.window?.prompt(
+    `Deep scan "${source.artist_name} (${source.platform})" — walk full history for the next how many download runs? (1–10, default 3)`,
+    '3',
+  )
+  if (raw == null) return
+  const runs = parseInt(raw, 10)
+  if (!Number.isFinite(runs) || runs < 1 || runs > 10) {
+    toast({ text: 'Deep scan: runs must be 1–10', type: 'error' })
+    return
+  }
+  try {
+    await store.setBackfill(source.id, runs, source.artist_id)
+    toast({
+      text: `Deep scan armed for ${runs} run${runs === 1 ? '' : 's'}`,
+      type: 'success',
+    })
+    await store.loadAll()
+  } catch (e) {
+    toast({
+      text: `Deep scan failed: ${e?.detail || e?.message || e}`,
+      type: 'error',
+    })
+  }
+}
+
 async function checkAll(group) {
   let ok = 0
   let conflict = 0
diff --git a/frontend/src/stores/sources.js b/frontend/src/stores/sources.js
index a04c5a0..2e9406e 100644
--- a/frontend/src/stores/sources.js
+++ b/frontend/src/stores/sources.js
@@ -85,6 +85,15 @@ export const useSourcesStore = defineStore('sources', () => {
     }
   }
 
+  // Plan #544: arm a source for backfill mode. The next `runs` download
+  // runs (default 3) walk gallery-dl's full post history instead of
+  // exiting early at the first contiguous archived block.
+  async function setBackfill(id, runs = 3, artistIdHint = null) {
+    const body = await api.post(`/api/sources/${id}/backfill`, { body: { runs } })
+    _invalidate(artistIdHint ?? body.artist_id)
+    return body
+  }
+
   function sourcesByArtistGrouped() {
     // returns [{artist: {id,name,slug}, sources: [...]}, ...]
     const arr = byArtist.value.get(null) ?? []
@@ -111,6 +120,7 @@ export const useSourcesStore = defineStore('sources', () => {
     loadAll, loadForArtist,
     create, update, remove,
     checkNow,
+    setBackfill,
     findOrCreateArtist, autocompleteArtist,
     loadScheduleStatus,
     sourcesByArtistGrouped,
diff --git a/tests/test_api_artist.py b/tests/test_api_artist.py
index f2b6587..9031df5 100644
--- a/tests/test_api_artist.py
+++ b/tests/test_api_artist.py
@@ -37,8 +37,8 @@ async def test_artist_overview_post_count(client, db):
     )
     db.add(s)
     await db.flush()
-    db.add(Post(source_id=s.id, external_post_id="p1"))
-    db.add(Post(source_id=s.id, external_post_id="p2"))
+    db.add(Post(source_id=s.id, artist_id=a.id, external_post_id="p1"))
+    db.add(Post(source_id=s.id, artist_id=a.id, external_post_id="p2"))
     await db.flush()
     await db.commit()
     resp = await client.get("/api/artist/lyra")
diff --git a/tests/test_api_posts.py b/tests/test_api_posts.py
index ab0cad6..2791e9f 100644
--- a/tests/test_api_posts.py
+++ b/tests/test_api_posts.py
@@ -25,7 +25,7 @@ async def seeded_post(db):
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id="API1",
+        source_id=source.id, artist_id=artist.id, external_post_id="API1",
         post_title="Hello", post_url="https://p/alice-api/1",
         post_date=datetime.now(UTC),
         description="<p>hi</p>",
@@ -123,7 +123,8 @@ async def post_timeline(db):
     posts = []
     for i in range(5):
         p = Post(
-            source_id=source.id, external_post_id=f"TL{i}",
+            source_id=source.id, artist_id=artist.id,
+            external_post_id=f"TL{i}",
             post_title=f"post {i}", post_date=base + timedelta(days=i),
         )
         db.add(p)
@@ -189,7 +190,7 @@ async def test_detail_returns_uncapped_thumbnails(client, db):
     db.add(s)
     await db.flush()
     p = Post(
-        source_id=s.id, external_post_id="DETAIL10",
+        source_id=s.id, artist_id=a.id, external_post_id="DETAIL10",
         post_title="big post", description="<p>body</p>",
     )
     db.add(p)
diff --git a/tests/test_api_provenance.py b/tests/test_api_provenance.py
index df0a2b7..47c49bf 100644
--- a/tests/test_api_provenance.py
+++ b/tests/test_api_provenance.py
@@ -26,7 +26,8 @@ async def _seed_full(db):
                     url="https://patreon.test/alice")
     db.add(source)
     await db.flush()
-    post = Post(source_id=source.id, external_post_id="555",
+    post = Post(source_id=source.id, artist_id=artist.id,
+                external_post_id="555",
                 post_url="https://patreon.test/p/555", post_title="Set 1",
                 post_date=datetime(2023, 8, 1, tzinfo=UTC),
                 description="<p>hi</p>", attachment_count=2)
diff --git a/tests/test_api_sources.py b/tests/test_api_sources.py
index 28d1a11..c72c8b9 100644
--- a/tests/test_api_sources.py
+++ b/tests/test_api_sources.py
@@ -193,3 +193,61 @@ async def test_list_derives_next_check_at_when_last_checked_set(
     )
     assert target["next_check_at"] is not None
     assert "T" in target["next_check_at"]  # ISO 8601
+
+
+# --- Plan #544: POST /api/sources/{id}/backfill ----------------------------
+
+
+@pytest.mark.asyncio
+async def test_backfill_endpoint_arms_source(client, artist, db):
+    src = Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice-backfill", enabled=True,
+    )
+    db.add(src)
+    await db.commit()
+    sid = src.id
+
+    resp = await client.post(f"/api/sources/{sid}/backfill", json={"runs": 5})
+    assert resp.status_code == 200
+    body = await resp.get_json()
+    assert body["backfill_runs_remaining"] == 5
+
+    # GET reflects the new state.
+    one = await client.get(f"/api/sources/{sid}")
+    assert (await one.get_json())["backfill_runs_remaining"] == 5
+
+
+@pytest.mark.asyncio
+async def test_backfill_endpoint_defaults_to_three(client, artist, db):
+    src = Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice-backfill-default", enabled=True,
+    )
+    db.add(src)
+    await db.commit()
+    resp = await client.post(f"/api/sources/{src.id}/backfill", json={})
+    body = await resp.get_json()
+    assert body["backfill_runs_remaining"] == 3
+
+
+@pytest.mark.asyncio
+async def test_backfill_endpoint_rejects_out_of_range(client, artist, db):
+    src = Source(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice-backfill-bad", enabled=True,
+    )
+    db.add(src)
+    await db.commit()
+    bad = await client.post(f"/api/sources/{src.id}/backfill", json={"runs": 0})
+    assert bad.status_code == 400
+    too_big = await client.post(
+        f"/api/sources/{src.id}/backfill", json={"runs": 99}
+    )
+    assert too_big.status_code == 400
+
+
+@pytest.mark.asyncio
+async def test_backfill_endpoint_404_when_source_missing(client):
+    resp = await client.post("/api/sources/999999/backfill", json={"runs": 3})
+    assert resp.status_code == 404
diff --git a/tests/test_artist_service.py b/tests/test_artist_service.py
index 9858af9..2d29fff 100644
--- a/tests/test_artist_service.py
+++ b/tests/test_artist_service.py
@@ -25,7 +25,7 @@ async def _fixture(db):
     db.add(src)
     await db.flush()
     post = Post(
-        source_id=src.id, external_post_id="p1",
+        source_id=src.id, artist_id=artist.id, external_post_id="p1",
         post_date=datetime(2026, 3, 1, tzinfo=UTC),
     )
     db.add(post)
diff --git a/tests/test_download_service.py b/tests/test_download_service.py
index 15ad337..ebced00 100644
--- a/tests/test_download_service.py
+++ b/tests/test_download_service.py
@@ -370,3 +370,179 @@ async def test_finalize_skipped_preserves_failures_clears_error(db):
     assert row.consecutive_failures == 4
     assert row.last_error is None
     assert row.last_checked_at is not None
+
+
+# --- Plan #544: backfill lifecycle + PARTIAL → status=ok -------------------
+
+
+@pytest.mark.asyncio
+async def test_backfill_decrements_after_run(
+    db, db_sync, tmp_path, seed_artist_and_source,
+):
+    """When backfill_runs_remaining > 0 going in, a non-clean / non-empty
+    run decrements by 1 — operator gets N runs to complete the deep scan
+    before tick mode resumes."""
+    from backend.app.services.download_service import DownloadService
+    from backend.app.services.importer import Importer
+
+    _artist, source = seed_artist_and_source
+    source.backfill_runs_remaining = 3
+    await db.commit()
+
+    images_root = tmp_path / "images"
+    f1 = images_root / "alice" / "patreon" / "post" / "a.jpg"
+    _make_jpg(f1, split="h")
+
+    fake_gdl = _fake_gdl_with_result(_make_fake_dl_result(
+        success=True, written_paths=[str(f1)], files_downloaded=1,
+        stdout=f"{f1}\n",
+    ))
+
+    sync_settings = db_sync.execute(
+        select(ImportSettings).where(ImportSettings.id == 1)
+    ).scalar_one()
+    importer = Importer(
+        session=db_sync, images_root=images_root, import_root=images_root,
+        thumbnailer=Thumbnailer(images_root=images_root), settings=sync_settings,
+    )
+    cred_service = CredentialService(db, CredentialCrypto(tmp_path / "key.b64"))
+    svc = DownloadService(
+        async_session=db, sync_session=db_sync,
+        gdl=fake_gdl, importer=importer, cred_service=cred_service,
+    )
+    await svc.download_source(source.id)
+
+    remaining = (await db.execute(
+        select(Source.backfill_runs_remaining).where(Source.id == source.id)
+    )).scalar_one()
+    assert remaining == 2
+
+
+@pytest.mark.asyncio
+async def test_backfill_auto_resets_on_clean_zero_files(
+    db, db_sync, tmp_path, seed_artist_and_source,
+):
+    """A clean run (rc=0) that downloaded zero files means the backfill
+    queue drained — reset to 0 immediately instead of wasting the rest of
+    the N-run budget on no-op walks."""
+    from backend.app.services.download_service import DownloadService
+    from backend.app.services.importer import Importer
+
+    _artist, source = seed_artist_and_source
+    source.backfill_runs_remaining = 3
+    await db.commit()
+
+    fake_result = _make_fake_dl_result(
+        success=True, written_paths=[], files_downloaded=0,
+    )
+    fake_gdl = _fake_gdl_with_result(fake_result)
+
+    sync_settings = db_sync.execute(
+        select(ImportSettings).where(ImportSettings.id == 1)
+    ).scalar_one()
+    importer = Importer(
+        session=db_sync, images_root=tmp_path / "images",
+        import_root=tmp_path / "images",
+        thumbnailer=Thumbnailer(images_root=tmp_path / "images"),
+        settings=sync_settings,
+    )
+    cred_service = CredentialService(db, CredentialCrypto(tmp_path / "key.b64"))
+    svc = DownloadService(
+        async_session=db, sync_session=db_sync,
+        gdl=fake_gdl, importer=importer, cred_service=cred_service,
+    )
+    await svc.download_source(source.id)
+
+    remaining = (await db.execute(
+        select(Source.backfill_runs_remaining).where(Source.id == source.id)
+    )).scalar_one()
+    assert remaining == 0
+
+
+@pytest.mark.asyncio
+async def test_tick_mode_does_not_touch_backfill_counter(
+    db, db_sync, tmp_path, seed_artist_and_source,
+):
+    """When backfill_runs_remaining is already 0, downloads don't go
+    negative or otherwise mutate the counter."""
+    from backend.app.services.download_service import DownloadService
+    from backend.app.services.importer import Importer
+
+    _artist, source = seed_artist_and_source
+    assert source.backfill_runs_remaining == 0
+
+    fake_gdl = _fake_gdl_with_result(_make_fake_dl_result(
+        success=True, written_paths=[], files_downloaded=0,
+    ))
+
+    sync_settings = db_sync.execute(
+        select(ImportSettings).where(ImportSettings.id == 1)
+    ).scalar_one()
+    importer = Importer(
+        session=db_sync, images_root=tmp_path / "images",
+        import_root=tmp_path / "images",
+        thumbnailer=Thumbnailer(images_root=tmp_path / "images"),
+        settings=sync_settings,
+    )
+    cred_service = CredentialService(db, CredentialCrypto(tmp_path / "key.b64"))
+    svc = DownloadService(
+        async_session=db, sync_session=db_sync,
+        gdl=fake_gdl, importer=importer, cred_service=cred_service,
+    )
+    await svc.download_source(source.id)
+
+    remaining = (await db.execute(
+        select(Source.backfill_runs_remaining).where(Source.id == source.id)
+    )).scalar_one()
+    assert remaining == 0
+
+
+@pytest.mark.asyncio
+async def test_partial_error_type_maps_to_ok_status(
+    db, db_sync, tmp_path, seed_artist_and_source,
+):
+    """A non-zero gallery-dl exit accompanied by PARTIAL error_type
+    (real files were downloaded before the run was cut short) is treated
+    as status=ok by the orchestrator — next tick continues."""
+    from backend.app.services.download_service import DownloadService
+    from backend.app.services.gallery_dl import ErrorType
+    from backend.app.services.importer import Importer
+
+    _artist, source = seed_artist_and_source
+
+    images_root = tmp_path / "images"
+    f1 = images_root / "alice" / "patreon" / "post" / "a.jpg"
+    _make_jpg(f1, split="h")
+
+    fake_result = _make_fake_dl_result(
+        success=False, written_paths=[str(f1)], files_downloaded=1,
+        error_type=ErrorType.PARTIAL,
+        error_message="Downloaded 1 file; run did not complete in budget",
+        stdout=f"{f1}\n",
+    )
+    fake_gdl = _fake_gdl_with_result(fake_result)
+
+    sync_settings = db_sync.execute(
+        select(ImportSettings).where(ImportSettings.id == 1)
+    ).scalar_one()
+    importer = Importer(
+        session=db_sync, images_root=images_root, import_root=images_root,
+        thumbnailer=Thumbnailer(images_root=images_root), settings=sync_settings,
+    )
+    cred_service = CredentialService(db, CredentialCrypto(tmp_path / "key.b64"))
+    svc = DownloadService(
+        async_session=db, sync_session=db_sync,
+        gdl=fake_gdl, importer=importer, cred_service=cred_service,
+    )
+    event_id = await svc.download_source(source.id)
+
+    ev = (await db.execute(
+        select(DownloadEvent).where(DownloadEvent.id == event_id)
+    )).scalar_one()
+    assert ev.status == "ok"
+    assert ev.error is None
+    # And the source's failure counter isn't bumped — PARTIAL isn't a failure.
+    src_after = (await db.execute(
+        select(Source.consecutive_failures).where(Source.id == source.id)
+    )).scalar_one()
+    assert src_after == 0
diff --git a/tests/test_gallery_dl_service.py b/tests/test_gallery_dl_service.py
index af490d1..d3607a5 100644
--- a/tests/test_gallery_dl_service.py
+++ b/tests/test_gallery_dl_service.py
@@ -249,3 +249,80 @@ def test_truncate_log_caps_large_text(gdl):
 def test_truncate_log_passes_short_text(gdl):
     text = "small\n"
     assert gdl._truncate_log(text) == text
+
+
+# --- Plan #544: tick/backfill skip emission + PARTIAL classifier ------------
+
+
+def test_build_config_emits_tick_skip_value(gdl):
+    """Tick mode emits gallery-dl's exit:20 to short-circuit catch-up
+    scans once 20 contiguous archived items are seen."""
+    from backend.app.services.gallery_dl import TICK_SKIP_VALUE
+    cfg = gdl._build_config_for_source(
+        platform="patreon",
+        source_config=SourceConfig(),
+        artist_slug="alice",
+        skip_value=TICK_SKIP_VALUE,
+    )
+    assert cfg["extractor"]["skip"] == "exit:20"
+
+
+def test_build_config_emits_backfill_skip_value(gdl):
+    """Backfill mode keeps gallery-dl's default skip=True so it walks the
+    full post history."""
+    from backend.app.services.gallery_dl import BACKFILL_SKIP_VALUE
+    cfg = gdl._build_config_for_source(
+        platform="patreon",
+        source_config=SourceConfig(),
+        artist_slug="alice",
+        skip_value=BACKFILL_SKIP_VALUE,
+    )
+    assert cfg["extractor"]["skip"] is True
+
+
+def test_categorize_partial_when_files_downloaded_then_nonzero_exit(gdl):
+    """Non-zero exit + ≥1 file downloaded + no source-level error →
+    PARTIAL. Downstream maps to status=ok because the next tick continues."""
+    # stdout has a single downloaded file (line starting with `/`); no
+    # error-class indicators in stderr; non-zero return code.
+    etype, msg = gdl._categorize_error(
+        return_code=1,
+        stdout="/images/alice/patreon/post1/img.jpg\n",
+        stderr="",
+    )
+    assert etype == ErrorType.PARTIAL
+    assert "Downloaded 1 file" in msg
+
+
+def test_categorize_unknown_when_no_files_and_no_pattern(gdl):
+    """PARTIAL only kicks in when files were actually written. A non-zero
+    exit with no downloads and no recognized pattern still falls through
+    to UNKNOWN_ERROR — distinct from the partial-success case."""
+    etype, _ = gdl._categorize_error(
+        return_code=2,
+        stdout="",
+        stderr="some unrecognized noise\n",
+    )
+    assert etype == ErrorType.UNKNOWN_ERROR
+
+
+def test_categorize_tier_limited_wins_over_partial(gdl):
+    """A run that hit tier-limited warnings AND downloaded some files
+    classifies as TIER_LIMITED (the more specific category), not PARTIAL."""
+    stdout = "/images/alice/patreon/post1/img.jpg\n"
+    stderr = "[patreon][warning] Not allowed to view post 123\n"
+    etype, _ = gdl._categorize_error(
+        return_code=1, stdout=stdout, stderr=stderr,
+    )
+    assert etype == ErrorType.TIER_LIMITED
+
+
+def test_default_config_forwards_patreon_referer_to_ytdl(gdl):
+    """Operator-flagged 2026-06-01: Mux video playback restrictions reject
+    yt-dlp's manifest fetch when Referer/Origin don't match Patreon. The
+    fix is a static `downloader.ytdl.raw-options.http_headers` block, so
+    it's enough to assert the keys land in the default config."""
+    cfg = gdl._get_default_config()
+    headers = cfg["downloader"]["ytdl"]["raw-options"]["http_headers"]
+    assert headers["Referer"] == "https://www.patreon.com/"
+    assert headers["Origin"] == "https://www.patreon.com"
diff --git a/tests/test_gallery_provenance_filter.py b/tests/test_gallery_provenance_filter.py
index e2fc95b..10b2ffa 100644
--- a/tests/test_gallery_provenance_filter.py
+++ b/tests/test_gallery_provenance_filter.py
@@ -35,7 +35,7 @@ async def _post(db, artist_name, slug, ext):
                url=f"https://patreon.test/{slug}")
     db.add(s)
     await db.flush()
-    p = Post(source_id=s.id, external_post_id=ext)
+    p = Post(source_id=s.id, artist_id=a.id, external_post_id=ext)
     db.add(p)
     await db.flush()
     return a, s, p
diff --git a/tests/test_gallery_service.py b/tests/test_gallery_service.py
index 705747c..89d0c53 100644
--- a/tests/test_gallery_service.py
+++ b/tests/test_gallery_service.py
@@ -152,7 +152,8 @@ async def _seed_image_with_post(
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id=external_post_id,
+        source_id=source.id, artist_id=artist.id,
+        external_post_id=external_post_id,
         post_title="A Post", post_date=post_date,
     )
     db.add(post)
diff --git a/tests/test_importer_provenance_race.py b/tests/test_importer_provenance_race.py
index 68ba96c..970a76e 100644
--- a/tests/test_importer_provenance_race.py
+++ b/tests/test_importer_provenance_race.py
@@ -29,7 +29,6 @@ from backend.app.models import (
     ImageProvenance,
     ImageRecord,
     ImportSettings,
-    Source,
 )
 from backend.app.services.importer import Importer
 from backend.app.services.thumbnailer import Thumbnailer
@@ -139,9 +138,11 @@ def test_apply_sidecar_recovers_from_integrity_error(
     r = importer.import_one(m)
     assert r.status == "imported"
     rec = importer.session.get(ImageRecord, r.image_id)
-    src = importer.session.execute(select(Source)).scalar_one()
+    # alembic 0030 stopped creating synthetic Source rows for filesystem
+    # sidecars; the Post sits null-source and the provenance row points at
+    # it directly. The race-recovery path tested below operates on
+    # ImageProvenance regardless of Source presence.
     assert rec is not None
-    assert src is not None
 
     # Monkeypatch session.execute so the FIRST select inside _apply_sidecar's
     # existence-check returns a "no row" wrapper. Subsequent selects (e.g.
diff --git a/tests/test_importer_upsert_helpers.py b/tests/test_importer_upsert_helpers.py
index 7f8882e..04e2fc6 100644
--- a/tests/test_importer_upsert_helpers.py
+++ b/tests/test_importer_upsert_helpers.py
@@ -88,11 +88,36 @@ def test_find_or_create_post_idempotent(importer, artist_row, db_sync):
     )
     p1 = importer._find_or_create_post(
         source_id=src.id, external_post_id="ext-001",
+        artist_id=artist_row.id,
     )
     p2 = importer._find_or_create_post(
         source_id=src.id, external_post_id="ext-001",
+        artist_id=artist_row.id,
     )
     assert p1.id == p2.id
+    assert p1.artist_id == artist_row.id
+
+
+def test_find_or_create_post_idempotent_with_null_source(
+    importer, artist_row, db_sync,
+):
+    """Post.source_id is nullable since alembic 0030 — filesystem-imported
+    posts with no live subscription have NULL source_id. The partial
+    unique index `uq_post_artist_external_id_null_source` on
+    (artist_id, external_post_id) WHERE source_id IS NULL guards the
+    dedup; the helper matches on the same (artist_id, external_post_id)
+    keys when source_id is None."""
+    p1 = importer._find_or_create_post(
+        source_id=None, external_post_id="fs-001",
+        artist_id=artist_row.id,
+    )
+    p2 = importer._find_or_create_post(
+        source_id=None, external_post_id="fs-001",
+        artist_id=artist_row.id,
+    )
+    assert p1.id == p2.id
+    assert p1.source_id is None
+    assert p1.artist_id == artist_row.id
 
 
 def test_find_or_create_source_recovers_from_integrity_error(
@@ -147,13 +172,13 @@ def test_find_or_create_source_recovers_from_integrity_error(
     assert recovered.id == pre_existing.id
 
 
-def test_source_for_sidecar_reuses_existing_subscription(
+def test_lookup_source_for_sidecar_returns_existing_subscription(
     importer, artist_row, db_sync,
 ):
-    """The filesystem-import sidecar resolver should attach to whatever
-    Source already exists for (artist, platform) — the canonical subscription
-    Source — regardless of its URL. Without this, every imported post
-    spawned its own Source row.
+    """The sidecar-import Source lookup returns the existing Source for
+    (artist, platform) when one exists — letting filesystem-imported
+    content attach to the artist's real subscription instead of being
+    orphaned.
     """
     canonical = Source(
         artist_id=artist_row.id, platform="patreon",
@@ -162,84 +187,30 @@ def test_source_for_sidecar_reuses_existing_subscription(
     db_sync.add(canonical)
     db_sync.flush()
 
-    resolved = importer._source_for_sidecar(
+    resolved = importer._lookup_source_for_sidecar(
         artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
     )
+    assert resolved is not None
     assert resolved.id == canonical.id
 
 
-def test_source_for_sidecar_creates_synthetic_anchor_when_none_exists(
+def test_lookup_source_for_sidecar_returns_none_when_no_subscription(
     importer, artist_row, db_sync,
 ):
-    """No subscription Source for this (artist, platform) yet. The helper
-    creates one synthetic anchor (enabled=False, url='sidecar:<plat>:<slug>')
-    so subsequent imports reuse it instead of spawning per-post Sources.
+    """Alembic 0030 made Post.source_id nullable; the importer no
+    longer creates synthetic `sidecar:<platform>:<slug>` anchor rows
+    when no real subscription exists. The lookup returns None and the
+    caller carries that through as a NULL source_id on the new Post.
     """
-    resolved = importer._source_for_sidecar(
+    resolved = importer._lookup_source_for_sidecar(
         artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
     )
-    assert resolved.url == f"sidecar:pixiv:{artist_row.slug}"
-    assert resolved.enabled is False
-    assert resolved.artist_id == artist_row.id
-    assert resolved.platform == "pixiv"
+    assert resolved is None
 
-    # Second call returns the same row (no new Source spawned).
-    again = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
-    )
-    assert again.id == resolved.id
-
-
-def test_source_for_sidecar_distinct_platforms_distinct_anchors(
-    importer, artist_row, db_sync,
-):
-    """One synthetic anchor per (artist, platform). Different platforms get
-    different anchors even when no campaign Source exists for either.
-    """
-    p = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
-    )
-    x = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="pixiv",
-        artist_slug=artist_row.slug,
-    )
-    assert p.id != x.id
-    assert p.platform == "patreon"
-    assert x.platform == "pixiv"
-
-
-def test_source_for_sidecar_prefers_real_over_synthetic_when_both_exist(
-    importer, artist_row, db_sync,
-):
-    """When BOTH a synthetic anchor AND a real Source exist for the same
-    (artist, platform), the resolver must return the REAL one. This is the
-    fix for the 2026-05-31 phantom-subscription bug: alembic 0022 had
-    rewritten an older per-post Source row into a sidecar synthetic, and
-    the operator later added the real subscription. The old `ORDER BY
-    id ASC LIMIT 1` lookup picked the older synthetic (lower id),
-    silently attaching every gallery-dl download to the wrong Source.
-    """
-    synthetic = Source(
-        artist_id=artist_row.id, platform="patreon",
-        url=f"sidecar:patreon:{artist_row.slug}", enabled=False,
-    )
-    db_sync.add(synthetic)
-    db_sync.flush()
-    real = Source(
-        artist_id=artist_row.id, platform="patreon",
-        url="https://www.patreon.com/testartist", enabled=True,
-    )
-    db_sync.add(real)
-    db_sync.flush()
-    assert synthetic.id < real.id  # ordering precondition
-
-    resolved = importer._source_for_sidecar(
-        artist_id=artist_row.id, platform="patreon",
-        artist_slug=artist_row.slug,
-    )
-    assert resolved.id == real.id
-    assert resolved.url == "https://www.patreon.com/testartist"
+    # Verify no Source row was created as a side effect.
+    count = db_sync.execute(
+        select(Source).where(
+            Source.artist_id == artist_row.id, Source.platform == "pixiv",
+        )
+    ).all()
+    assert count == []
diff --git a/tests/test_migration_0007.py b/tests/test_migration_0007.py
index d452f2e..6f716f4 100644
--- a/tests/test_migration_0007.py
+++ b/tests/test_migration_0007.py
@@ -17,7 +17,7 @@ async def _post(db, **post_kwargs):
     db.add(src)
     await db.flush()
     post = Post(
-        source_id=src.id, external_post_id="p1",
+        source_id=src.id, artist_id=artist.id, external_post_id="p1",
         post_date=datetime(2026, 3, 1, tzinfo=UTC),
         **post_kwargs,
     )
diff --git a/tests/test_migration_0008.py b/tests/test_migration_0008.py
index d3261b5..0d7552a 100644
--- a/tests/test_migration_0008.py
+++ b/tests/test_migration_0008.py
@@ -62,7 +62,7 @@ async def _run_backfill(db):
 async def test_backfill_primary_post(db):
     rec = await _img(db, 1)
     a, s = await _artist_source(db, "Alice", "alice")
-    post = Post(source_id=s.id, external_post_id="1")
+    post = Post(source_id=s.id, artist_id=a.id, external_post_id="1")
     db.add(post)
     await db.flush()
     rec.primary_post_id = post.id
@@ -78,7 +78,7 @@ async def test_backfill_primary_post(db):
 async def test_backfill_provenance_fallback(db):
     rec = await _img(db, 1)
     a, s = await _artist_source(db, "Bob", "bob")
-    post = Post(source_id=s.id, external_post_id="2")
+    post = Post(source_id=s.id, artist_id=a.id, external_post_id="2")
     db.add(post)
     await db.flush()
     db.add(ImageProvenance(image_record_id=rec.id, post_id=post.id,
diff --git a/tests/test_phash_dedup.py b/tests/test_phash_dedup.py
index 83b5725..da57ac2 100644
--- a/tests/test_phash_dedup.py
+++ b/tests/test_phash_dedup.py
@@ -15,7 +15,6 @@ from backend.app.models import (
     ImageRecord,
     ImportSettings,
     Post,
-    Source,
     Tag,
     TagKind,
 )
@@ -197,10 +196,11 @@ def test_supersede_applies_new_file_sidecar(importer, import_layout):
     assert post.post_title == "Set 1"
     assert "big version" in (post.description or "")
 
-    source = importer.session.execute(
-        select(Source).where(Source.id == post.source_id)
-    ).scalar_one()
-    assert source.platform == "patreon"
+    # Filesystem sidecars no longer create a synthetic Source (alembic 0030).
+    # The Post sits null-source; the platform context is captured in the
+    # sidecar JSON / raw_metadata, not in a phantom Source row.
+    assert post.source_id is None
+    assert post.artist_id is not None
 
     prov_count = importer.session.execute(
         select(func.count(ImageProvenance.id))
diff --git a/tests/test_post_feed_service.py b/tests/test_post_feed_service.py
index 651cbca..4924ab2 100644
--- a/tests/test_post_feed_service.py
+++ b/tests/test_post_feed_service.py
@@ -7,6 +7,7 @@ boundary, and the thumbnails/attachments composition.
 from datetime import UTC, datetime, timedelta
 
 import pytest
+from sqlalchemy import select
 
 from backend.app.models import (
     Artist,
@@ -59,8 +60,13 @@ async def _seed_post(
     db, source_id: int, *, external_id: str,
     post_date=None, downloaded_at=None, title=None, description=None,
 ):
+    # Post.artist_id is NOT NULL since alembic 0030; look it up from
+    # the source so callsites don't have to thread the artist through.
+    artist_id = (await db.execute(
+        select(Source.artist_id).where(Source.id == source_id)
+    )).scalar_one()
     p = Post(
-        source_id=source_id, external_post_id=external_id,
+        source_id=source_id, artist_id=artist_id, external_post_id=external_id,
         post_title=title, post_date=post_date,
         description=description,
     )
diff --git a/tests/test_provenance_service.py b/tests/test_provenance_service.py
index 7cc2aed..bd61081 100644
--- a/tests/test_provenance_service.py
+++ b/tests/test_provenance_service.py
@@ -37,7 +37,7 @@ async def _seed_post(db, *, artist_name, slug, platform, ext_id,
     db.add(source)
     await db.flush()
     post = Post(
-        source_id=source.id, external_post_id=ext_id,
+        source_id=source.id, artist_id=artist.id, external_post_id=ext_id,
         post_url=f"https://{platform}.test/p/{ext_id}",
         post_title=title, post_date=datetime(2023, 8, 1, tzinfo=UTC),
         description=desc, attachment_count=count,
diff --git a/tests/test_sidecar_import.py b/tests/test_sidecar_import.py
index f9ebabc..1984d99 100644
--- a/tests/test_sidecar_import.py
+++ b/tests/test_sidecar_import.py
@@ -75,9 +75,15 @@ def test_sidecar_creates_provenance(importer, import_layout):
     r = importer.import_one(m)
     assert r.status == "imported"
     rec = importer.session.get(ImageRecord, r.image_id)
-    src = importer.session.execute(select(Source)).scalar_one()
     post = importer.session.execute(select(Post)).scalar_one()
-    assert src.platform == "patreon"
+    # Filesystem-imported sidecar posts no longer create a synthetic Source
+    # (alembic 0030 / nullable post.source_id refactor). The Post is linked
+    # to the artist via Post.artist_id; Post.source_id stays NULL until a
+    # real subscription for the (artist, platform) gets added.
+    assert post.source_id is None
+    assert importer.session.execute(
+        select(func.count()).select_from(Source)
+    ).scalar_one() == 0
     assert post.external_post_id == "555"
     assert post.post_url == "https://patreon.com/posts/555"
     assert post.post_title == "Set 1"
@@ -106,9 +112,11 @@ def test_reimport_same_post_idempotent(importer, import_layout):
     _sidecar(m2, payload)
     r2 = importer.import_one(m2)
     assert r2.status == "imported"
+    # No synthetic Source after alembic 0030; both imports still resolve to
+    # a single null-source Post (deduped by uq_post_artist_external_id_null_source).
     assert importer.session.execute(
         select(func.count()).select_from(Source)
-    ).scalar_one() == 1
+    ).scalar_one() == 0
     assert importer.session.execute(
         select(func.count()).select_from(Post)
     ).scalar_one() == 1
@@ -164,5 +172,11 @@ def test_sidecar_artist_used_when_no_folder_artist(importer, import_layout):
     a = importer.session.execute(
         select(Artist).where(Artist.slug == "yuki")
     ).scalar_one()
-    src = importer.session.execute(select(Source)).scalar_one()
-    assert src.artist_id == a.id
+    # No synthetic Source after alembic 0030; the artist linkage lives on
+    # Post.artist_id (NOT NULL FK).
+    post = importer.session.execute(select(Post)).scalar_one()
+    assert post.artist_id == a.id
+    assert post.source_id is None
+    assert importer.session.execute(
+        select(func.count()).select_from(Source)
+    ).scalar_one() == 0
diff --git a/tests/test_source_service.py b/tests/test_source_service.py
index f6df9f3..2806421 100644
--- a/tests/test_source_service.py
+++ b/tests/test_source_service.py
@@ -138,7 +138,7 @@ async def test_update_changes_fields(db):
 @pytest.mark.asyncio
 async def test_list_hides_sidecar_synthetic_anchors(db):
     """Filesystem-import synthetic Sources (url='sidecar:<platform>:<slug>',
-    enabled=False — see importer._source_for_sidecar) used to leak into the
+    enabled=False — historical pre-alembic-0030 artifact) used to leak into the
     Subscriptions UI as phantom subscriptions because list() didn't filter
     them. They aren't pollable feeds; hide by default."""
     artist = await _artist(db, "Alice")
@@ -169,3 +169,75 @@ async def test_list_hides_sidecar_synthetic_anchors(db):
     assert {s.url for s in everything} >= {
         "https://patreon.com/alice", "sidecar:patreon:alice",
     }
+
+
+# --- Plan #544: backfill counter -------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_set_backfill_runs_arms_source(db):
+    """The service method overrides backfill_runs_remaining (regardless of
+    the auto-arm-on-create starting value) and returns the updated record
+    so the API can echo it back."""
+    artist = await _artist(db, "Alice")
+    svc = SourceService(db)
+    rec = await svc.create(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice",
+    )
+    updated = await svc.set_backfill_runs(rec.id, 5)
+    assert updated.backfill_runs_remaining == 5
+
+    db_value = (await db.execute(
+        select(Source.backfill_runs_remaining).where(Source.id == rec.id)
+    )).scalar_one()
+    assert db_value == 5
+
+
+@pytest.mark.asyncio
+async def test_set_backfill_runs_rejects_out_of_range(db):
+    artist = await _artist(db, "Alice")
+    svc = SourceService(db)
+    rec = await svc.create(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice",
+    )
+    with pytest.raises(ValueError):
+        await svc.set_backfill_runs(rec.id, 0)
+    with pytest.raises(ValueError):
+        await svc.set_backfill_runs(rec.id, 11)
+
+
+@pytest.mark.asyncio
+async def test_set_backfill_runs_raises_when_source_missing(db):
+    svc = SourceService(db)
+    with pytest.raises(LookupError):
+        await svc.set_backfill_runs(99999, 3)
+
+
+@pytest.mark.asyncio
+async def test_new_enabled_source_starts_in_backfill_mode(db):
+    """Plan #544 follow-up: freshly added enabled sources have no archive
+    yet, so the first few polls would blow the wall-clock cap in tick
+    mode. Pre-arm backfill so the initial walks use the longer timeout."""
+    artist = await _artist(db, "Alice")
+    svc = SourceService(db)
+    rec = await svc.create(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice-new",
+    )
+    assert rec.backfill_runs_remaining == 3
+
+
+@pytest.mark.asyncio
+async def test_new_disabled_source_skips_backfill(db):
+    """Disabled sources (incl. sidecar synthetics that arrive disabled) are
+    never polled, so don't burn a backfill budget on them."""
+    artist = await _artist(db, "Alice")
+    svc = SourceService(db)
+    rec = await svc.create(
+        artist_id=artist.id, platform="patreon",
+        url="https://patreon.com/alice-disabled",
+        enabled=False,
+    )
+    assert rec.backfill_runs_remaining == 0