diff --git a/backend/app/api/sources.py b/backend/app/api/sources.py
index 6500aa6..a9d3d1e 100644
--- a/backend/app/api/sources.py
+++ b/backend/app/api/sources.py
@@ -1,10 +1,13 @@
 """FC-3a: CRUD over Source rows. FC-3c adds POST /<id>/check."""
 
+from pathlib import Path
+
 from quart import Blueprint, jsonify, request
 from sqlalchemy import func, select
 
 from ..extensions import get_session
 from ..models import DownloadEvent, MembershipSync, PlatformMembership, Source
+from ..services import discord_poster_cleanup as poster_cleanup
 from ..services.artist_membership_service import ArtistMembershipService
 from ..services.artist_membership_service import rescan as membership_rescan
 from ..services.artist_service import ArtistService
@@ -463,3 +466,49 @@ async def adopt_membership():
             return jsonify({"already_tracked": exc.existing_id})
         artist_id = artist.id
     return jsonify({"source_id": record.id, "artist_id": artist_id}), 201
+
+
+# -- Discord: remove posts by people outside the poster list (#4486) --------------
+
+_IMAGES_ROOT = Path("/images")
+
+
+async def _poster_cleanup_preview(source_id: int):
+    async with get_session() as session:
+        return await session.run_sync(
+            lambda s: poster_cleanup.preview(s, source_id=source_id)
+        )
+
+
+@sources_bp.route("/<int:source_id>/discord/other-posters", methods=["GET"])
+async def other_posters_preview(source_id: int):
+    """What removing other posters' posts would delete. Nothing is touched."""
+    try:
+        projection = await _poster_cleanup_preview(source_id)
+    except LookupError:
+        return _bad("not_found", status=404)
+    except poster_cleanup.PosterCleanupError as exc:
+        return _bad("not_applicable", detail=str(exc), status=409)
+    projection["confirm_token"] = poster_cleanup.confirm_token(projection)
+    return jsonify(projection)
+
+
+@sources_bp.route("/<int:source_id>/discord/other-posters/remove", methods=["POST"])
+async def other_posters_remove(source_id: int):
+    """Delete them. `confirm` must be the token of the preview the operator saw:
+    a poster list edited since then changes the set, and the token with it."""
+    body = await request.get_json(silent=True) or {}
+    try:
+        projection = await _poster_cleanup_preview(source_id)
+    except LookupError:
+        return _bad("not_found", status=404)
+    except poster_cleanup.PosterCleanupError as exc:
+        return _bad("not_applicable", detail=str(exc), status=409)
+    expected = poster_cleanup.confirm_token(projection)
+    if body.get("confirm") != expected:
+        return _bad("confirm_mismatch", expected=expected)
+    async with get_session() as session:
+        result = await session.run_sync(
+            lambda s: poster_cleanup.apply(s, source_id=source_id, images_root=_IMAGES_ROOT)
+        )
+    return jsonify(result)
diff --git a/backend/app/services/discord_downloader.py b/backend/app/services/discord_downloader.py
index d83e354..c9f542a 100644
--- a/backend/app/services/discord_downloader.py
+++ b/backend/app/services/discord_downloader.py
@@ -195,6 +195,7 @@ class DiscordDownloader(BaseNativeDownloader):
             "parent": meta.get("parent"),
             "is_thread": meta.get("is_thread"),
             "author": author.get("username"),
+            "author_name": author.get("global_name"),
             "author_id": author.get("id"),
             "message": body,
             "date": post.get("timestamp"),
diff --git a/backend/app/services/discord_poster_cleanup.py b/backend/app/services/discord_poster_cleanup.py
new file mode 100644
index 0000000..507f00c
--- /dev/null
+++ b/backend/app/services/discord_poster_cleanup.py
@@ -0,0 +1,243 @@
+"""Remove a Discord source's posts by people outside its poster list (#4486).
+
+A creator's server is full of other members posting their own pictures. The
+poster list (`discord_authors`, #4481) stops a walk taking them; this removes
+the ones taken before the list existed. The operator sets the list first, then
+previews what would go, then applies.
+
+## What goes
+
+A post of this source whose record names its poster (`author_id` / `author`,
+written by `DiscordDownloader.write_post_record`) and names someone NOT on the
+list. Two kinds of post are never touched:
+
+* a post whose record names no poster — a message recorded before the native
+  ingester, whose poster FC cannot tell. Counted as `unknown`, never guessed;
+* a synthetic drop post (`synthesized_by`) — FC authored it, and it is handled
+  below as a consequence, not matched as a poster's post.
+
+An image goes when every REAL post it belongs to is going. A link to a
+synthetic drop does not keep an image: the drop only references its members'
+images. An image also on a kept post — the creator re-posting a piece someone
+else shared — stays.
+
+A drop that absorbed a removed message is deleted outright. Deleting a drop is
+its undo (discord_grouping's honesty rule): its remaining members return to
+the feed and the grouping sweep regroups them on its next run, so no half-
+rebuilt drop keeps text or thumbnails from someone it no longer contains.
+
+Preview and apply spread the same predicates (rule 93, snippet #3087).
+"""
+
+from __future__ import annotations
+
+import logging
+from pathlib import Path
+
+from sqlalchemy import and_, delete, exists, func, or_, select
+from sqlalchemy.orm import Session, aliased
+
+from ..models import ImageProvenance, ImageRecord, Post, PostAttachment, Source
+from .cleanup_service import delete_images
+from .discord_ingester import AUTHORS_KEY
+
+log = logging.getLogger(__name__)
+
+PLATFORM = "discord"
+# The record keys that name a message's poster. `author_name` (the display
+# name) is only on records written after 2026-09-28.
+_POSTER_KEYS = ("author_id", "author", "author_name")
+
+
+class PosterCleanupError(ValueError):
+    """The source can't be cleaned this way (not Discord, or no list)."""
+
+
+def source_authors(source: Source) -> list[str]:
+    """The source's poster list, lowercased; empty means everyone's wanted."""
+    authors = (source.config_overrides or {}).get(AUTHORS_KEY) or []
+    if not isinstance(authors, list):
+        return []
+    return sorted({str(a).strip().lower() for a in authors if str(a).strip()})
+
+
+def _poster(key: str):
+    return func.lower(Post.raw_metadata[key].as_string())
+
+
+def _has_poster():
+    return or_(*(Post.raw_metadata[k].as_string().isnot(None) for k in ("author_id", "author")))
+
+
+def _real_post_conditions(source_id: int) -> list:
+    return [Post.source_id == source_id, Post.synthesized_by.is_(None)]
+
+
+def _named_poster_conditions(source_id: int) -> list:
+    """A real post of this source whose record says who posted it."""
+    return [*_real_post_conditions(source_id), _has_poster()]
+
+
+def _other_poster_post_conditions(source_id: int, authors: list[str]) -> list:
+    """The posts that go: a named poster none of whose names is on the list."""
+    return [
+        *_named_poster_conditions(source_id),
+        *(func.coalesce(_poster(k), "").notin_(authors) for k in _POSTER_KEYS),
+    ]
+
+
+def _doomed_post_ids(source_id: int, authors: list[str]):
+    # correlate(None): used inside queries that are themselves over `post` (the
+    # drops, the delete), where auto-correlation would bind this to the outer
+    # row instead of scanning the table.
+    return (
+        select(Post.id)
+        .where(*_other_poster_post_conditions(source_id, authors))
+        .correlate(None)
+    )
+
+
+def _image_conditions(source_id: int, authors: list[str]) -> list:
+    """Images that belong to a removed post and to no kept real post."""
+    doomed = _doomed_post_ids(source_id, authors)
+    keeper = aliased(Post)
+    on_doomed = or_(
+        ImageRecord.primary_post_id.in_(doomed),
+        exists().where(
+            ImageProvenance.image_record_id == ImageRecord.id,
+            ImageProvenance.post_id.in_(doomed),
+        ),
+    )
+    on_kept = or_(
+        and_(
+            ImageRecord.primary_post_id.isnot(None),
+            ImageRecord.primary_post_id.notin_(doomed),
+        ),
+        exists().where(
+            ImageProvenance.image_record_id == ImageRecord.id,
+            ImageProvenance.post_id == keeper.id,
+            keeper.synthesized_by.is_(None),
+            keeper.id.notin_(doomed),
+        ),
+    )
+    return [on_doomed, ~on_kept]
+
+
+def _drop_conditions(source_id: int, authors: list[str]) -> list:
+    """The synthetic drops that absorbed a removed message."""
+    member = aliased(Post)
+    return [
+        Post.source_id == source_id,
+        Post.synthesized_by.isnot(None),
+        exists().where(
+            member.absorbed_by_post_id == Post.id,
+            member.id.in_(_doomed_post_ids(source_id, authors)),
+        ),
+    ]
+
+
+def _attachment_conditions(source_id: int, authors: list[str]) -> list:
+    return [PostAttachment.post_id.in_(_doomed_post_ids(source_id, authors))]
+
+
+def _load(session: Session, source_id: int) -> tuple[Source, list[str]]:
+    source = session.get(Source, source_id)
+    if source is None:
+        raise LookupError(source_id)
+    if source.platform != PLATFORM:
+        raise PosterCleanupError("Only a Discord source has posters to filter by.")
+    authors = source_authors(source)
+    if not authors:
+        raise PosterCleanupError(
+            "Set this source's 'Only posts by' list first — with no list, "
+            "every poster is wanted and nothing would be removed."
+        )
+    return source, authors
+
+
+def _count(session: Session, stmt) -> int:
+    return session.execute(stmt).scalar_one()
+
+
+def preview(session: Session, *, source_id: int) -> dict:
+    """What `apply` would remove, per poster, without touching anything."""
+    _, authors = _load(session, source_id)
+    who = func.coalesce(
+        Post.raw_metadata["author_name"].as_string(),
+        Post.raw_metadata["author"].as_string(),
+        Post.raw_metadata["author_id"].as_string(),
+    )
+    rows = session.execute(
+        select(who, func.count(Post.id))
+        .where(*_other_poster_post_conditions(source_id, authors))
+        .group_by(who)
+        .order_by(func.count(Post.id).desc())
+    ).all()
+    posters = [{"poster": name, "posts": n} for name, n in rows]
+    unknown = _count(session, select(func.count(Post.id)).where(
+        *_real_post_conditions(source_id), ~_has_poster(),
+    ))
+    return {
+        "authors": authors,
+        "posters": posters,
+        "posts": sum(p["posts"] for p in posters),
+        "images": _count(session, select(func.count(ImageRecord.id)).where(
+            *_image_conditions(source_id, authors))),
+        "attachments": _count(session, select(func.count(PostAttachment.id)).where(
+            *_attachment_conditions(source_id, authors))),
+        "drops": _count(session, select(func.count(Post.id)).where(
+            *_drop_conditions(source_id, authors))),
+        "unknown_posts": unknown,
+    }
+
+
+def confirm_token(projection: dict) -> str:
+    """What the operator's apply must echo: the preview it was shown, so a
+    list edited between preview and apply can't delete an unseen set."""
+    return f"remove-{projection['posts']}-posts-{projection['images']}-images"
+
+
+def apply(session: Session, *, source_id: int, images_root: Path) -> dict:
+    """Remove them. Counts are taken before the deletes they describe — once
+    the rows are gone there is nothing left to count (snippet #3087 note 2)."""
+    projection = preview(session, source_id=source_id)
+    _, authors = _load(session, source_id)
+
+    image_ids = session.execute(
+        select(ImageRecord.id).where(*_image_conditions(source_id, authors))
+    ).scalars().all()
+    # Drops first-class: found BEFORE their members go, since the link that
+    # finds them is the member's absorbed_by_post_id.
+    drop_ids = session.execute(
+        select(Post.id).where(*_drop_conditions(source_id, authors))
+    ).scalars().all()
+
+    deleted = delete_images(session, image_ids=list(image_ids), images_root=images_root)
+    # Attachments before posts: post_attachment.post_id is SET NULL, and a
+    # NULL-post attachment collides on its partial unique index (see
+    # cleanup_service.delete_artist_cascade).
+    attachments = session.execute(
+        delete(PostAttachment).where(*_attachment_conditions(source_id, authors))
+    ).rowcount or 0
+    posts = session.execute(
+        Post.__table__.delete().where(Post.id.in_(_doomed_post_ids(source_id, authors)))
+    ).rowcount or 0
+    drops = 0
+    if drop_ids:
+        drops = session.execute(
+            Post.__table__.delete().where(Post.id.in_(drop_ids))
+        ).rowcount or 0
+    session.commit()
+    log.info(
+        "discord poster cleanup (source %s, keeping %s): %d post(s), %d image(s), "
+        "%d attachment(s), %d drop(s) removed",
+        source_id, authors, posts, deleted["images_deleted"], attachments, drops,
+    )
+    return {
+        **projection,
+        "posts_deleted": posts,
+        "images_deleted": deleted["images_deleted"],
+        "files_deleted": deleted["files_deleted"],
+        "attachments_deleted": attachments,
+        "drops_deleted": drops,
+    }
diff --git a/frontend/src/components/subscriptions/PosterCleanupDialog.vue b/frontend/src/components/subscriptions/PosterCleanupDialog.vue
new file mode 100644
index 0000000..cc2873b
--- /dev/null
+++ b/frontend/src/components/subscriptions/PosterCleanupDialog.vue
@@ -0,0 +1,135 @@
+<template>
+  <!-- #4486. A Discord source's posts by people outside its "Only posts by"
+       list, taken before the list existed. Preview first, always: nothing is
+       deleted until the operator has seen the per-poster breakdown and typed
+       the token that preview returned. -->
+  <v-dialog :model-value="modelValue" max-width="560"
+            @update:model-value="$emit('update:modelValue', $event)">
+    <v-card>
+      <v-card-title>Remove posts from other posters</v-card-title>
+      <v-card-text>
+        <div class="text-caption mb-2">{{ source.display_name || source.url }}</div>
+        <v-progress-linear v-if="loading" indeterminate color="accent" class="mb-3" />
+        <v-alert v-else-if="error" type="warning" variant="tonal" density="compact">
+          {{ error }}
+        </v-alert>
+        <template v-else-if="result">
+          <v-alert type="success" variant="tonal" density="compact">
+            Removed {{ result.posts_deleted }} post(s), {{ result.images_deleted }} image(s),
+            {{ result.attachments_deleted }} attachment(s) and {{ result.drops_deleted }}
+            grouped post(s). Grouping rebuilds what remains on its next sweep.
+          </v-alert>
+        </template>
+        <template v-else-if="preview">
+          <p class="mb-2">
+            Keeping posts by <strong>{{ preview.authors.join(', ') }}</strong>.
+          </p>
+          <p v-if="!preview.posts" class="fc-dim">
+            Nothing to remove: every post with a known poster is by someone on the list.
+          </p>
+          <template v-else>
+            <v-table density="compact" class="mb-3">
+              <thead><tr><th>Poster</th><th class="text-right">Posts</th></tr></thead>
+              <tbody>
+                <tr v-for="p in preview.posters" :key="p.poster">
+                  <td>{{ p.poster }}</td>
+                  <td class="text-right">{{ p.posts }}</td>
+                </tr>
+              </tbody>
+            </v-table>
+            <p class="mb-1">
+              {{ preview.posts }} post(s), {{ preview.images }} image(s) found only on them,
+              {{ preview.attachments }} attachment(s).
+            </p>
+            <p v-if="preview.drops" class="mb-1">
+              {{ preview.drops }} grouped post(s) that include them are ungrouped; the
+              rest regroup on the next sweep.
+            </p>
+            <p class="fc-dim">
+              Images that also belong to a kept post stay. If a name you want to keep
+              appears above, add it to the source's "Only posts by" list first.
+            </p>
+          </template>
+          <p v-if="preview.unknown_posts" class="fc-dim mt-2">
+            {{ preview.unknown_posts }} older post(s) don't record who posted them and
+            are left alone.
+          </p>
+        </template>
+      </v-card-text>
+      <v-card-actions>
+        <v-spacer />
+        <v-btn variant="text" @click="$emit('update:modelValue', false)">
+          {{ result ? 'Close' : 'Cancel' }}
+        </v-btn>
+        <v-btn
+          v-if="preview && preview.posts && !result"
+          color="error" variant="flat" :loading="busy"
+          @click="confirmOpen = true"
+        >Remove {{ preview.posts }} post(s)</v-btn>
+      </v-card-actions>
+    </v-card>
+    <DestructiveConfirmModal
+      v-if="preview"
+      v-model="confirmOpen"
+      action="delete" kind="other posters' posts" tier="C"
+      :expected-token-override="preview.confirm_token"
+      :projected-counts="{ posts: preview.posts, images: preview.images,
+                           attachments: preview.attachments, grouped: preview.drops }"
+      @confirm="onConfirm"
+    />
+  </v-dialog>
+</template>
+
+<script setup>
+import { ref, watch } from 'vue'
+import { useSourcesStore } from '../../stores/sources.js'
+import DestructiveConfirmModal from '../modal/DestructiveConfirmModal.vue'
+
+const props = defineProps({
+  modelValue: { type: Boolean, default: false },
+  source: { type: Object, required: true },
+})
+defineEmits(['update:modelValue'])
+const store = useSourcesStore()
+
+const loading = ref(false)
+const busy = ref(false)
+const error = ref('')
+const preview = ref(null)
+const result = ref(null)
+const confirmOpen = ref(false)
+
+function message(e) {
+  return e?.body?.detail || e?.body?.error || e?.message || String(e)
+}
+
+watch(() => props.modelValue, async (open) => {
+  if (!open) return
+  preview.value = null
+  result.value = null
+  error.value = ''
+  loading.value = true
+  try {
+    preview.value = await store.previewOtherPosters(props.source.id)
+  } catch (e) {
+    error.value = message(e)
+  } finally {
+    loading.value = false
+  }
+})
+
+async function onConfirm(token) {
+  busy.value = true
+  try {
+    result.value = await store.removeOtherPosters(props.source.id, token)
+  } catch (e) {
+    error.value = message(e)
+  } finally {
+    busy.value = false
+  }
+}
+</script>
+
+<style scoped>
+.fc-dim { color: rgb(var(--v-theme-on-surface-variant)); }
+</style>
diff --git a/frontend/src/components/subscriptions/SourceActions.vue b/frontend/src/components/subscriptions/SourceActions.vue
index 3512b70..03e4ddc 100644
--- a/frontend/src/components/subscriptions/SourceActions.vue
+++ b/frontend/src/components/subscriptions/SourceActions.vue
@@ -50,6 +50,17 @@
           library — without re-downloading media
         </v-list-item-subtitle>
       </v-list-item>
+      <v-list-item
+        v-if="hasPosterList && !running"
+        prepend-icon="mdi-account-remove-outline"
+        @click="cleanupOpen = true"
+      >
+        <v-list-item-title>Remove posts from other posters</v-list-item-title>
+        <v-list-item-subtitle>
+          Preview, then delete the posts taken from people outside this
+          source's "Only posts by" list
+        </v-list-item-subtitle>
+      </v-list-item>
       <v-divider v-if="isNative && !running" />
       <v-list-item
         base-color="error"
@@ -59,12 +70,14 @@
         <v-list-item-title>Remove source</v-list-item-title>
       </v-list-item>
     </KebabMenu>
+    <PosterCleanupDialog v-if="hasPosterList" v-model="cleanupOpen" :source="source" />
   </div>
 </template>
 
 <script setup>
-import { computed } from 'vue'
+import { computed, ref } from 'vue'
 import KebabMenu from '../common/KebabMenu.vue'
+import PosterCleanupDialog from './PosterCleanupDialog.vue'
 
 const props = defineProps({
   source: { type: Object, required: true },
@@ -80,6 +93,10 @@ const recapturing = computed(() => !!props.source.backfill_recapture)
 // which those are (`native_ingester`); a copied list here went stale when
 // Discord moved over.
 const isNative = computed(() => !!props.source.native_ingester)
+// #4486: only a Discord source with an "Only posts by" list has other posters.
+const hasPosterList = computed(() => props.source.platform === 'discord'
+  && (props.source.config_overrides?.discord_authors || []).length > 0)
+const cleanupOpen = ref(false)
 </script>
 
 <style scoped>
diff --git a/frontend/src/stores/sources.js b/frontend/src/stores/sources.js
index d823db8..ec67600 100644
--- a/frontend/src/stores/sources.js
+++ b/frontend/src/stores/sources.js
@@ -149,6 +149,15 @@ export const useSourcesStore = defineStore('sources', () => {
     return body
   }
 
+  // #4486: a Discord source's posts by people outside its poster list.
+  // The preview touches nothing and hands back the token the remove must echo.
+  async function previewOtherPosters(id) {
+    return api.get(`/api/sources/${id}/discord/other-posters`)
+  }
+  async function removeOtherPosters(id, confirm) {
+    return api.post(`/api/sources/${id}/discord/other-posters/remove`, { body: { confirm } })
+  }
+
   function sourcesByArtistGrouped() {
     // returns [{artist: {id,name,slug}, sources: [...]}, ...]
     const arr = byArtist.value.get(null) ?? []
@@ -179,6 +188,7 @@ export const useSourcesStore = defineStore('sources', () => {
     stopBackfill,
     recoverSource,
     recaptureSource,
+    previewOtherPosters, removeOtherPosters,
     findOrCreateArtist, autocompleteArtist, reassign,
     loadScheduleStatus,
     sourcesByArtistGrouped,
diff --git a/tests/test_discord_poster_cleanup.py b/tests/test_discord_poster_cleanup.py
new file mode 100644
index 0000000..839fb8c
--- /dev/null
+++ b/tests/test_discord_poster_cleanup.py
@@ -0,0 +1,131 @@
+"""Removing a Discord source's posts by people outside its poster list (#4486).
+
+Real Postgres (db_sync): the predicates read `raw_metadata->>'author'`, which
+only the database can evaluate. The test that matters runs preview and apply
+on one fixture and asserts they agree AND that the rows went (snippet #3087).
+"""
+
+import pytest
+from sqlalchemy import func, select
+
+from backend.app.models import (
+    Artist,
+    ImageProvenance,
+    ImageRecord,
+    Post,
+    PostAttachment,
+    Source,
+)
+from backend.app.services import discord_poster_cleanup as cleanup
+
+pytestmark = pytest.mark.integration
+
+
+def _image(db, artist, tmp_path, name, post):
+    f = tmp_path / f"{name}.png"
+    f.write_bytes(b"x")
+    img = ImageRecord(
+        artist_id=artist.id, path=str(f), sha256=name.ljust(64, "0"),
+        size_bytes=1, mime="image/png", origin="downloaded", primary_post_id=post.id,
+    )
+    db.add(img)
+    db.flush()
+    return img
+
+
+def _post(db, source, mid, raw, **extra):
+    p = Post(
+        source_id=source.id, artist_id=source.artist_id, external_post_id=mid,
+        raw_metadata=raw, **extra,
+    )
+    db.add(p)
+    db.flush()
+    return p
+
+
+def _fixture(db, tmp_path, authors=("Todding",)):
+    """Todding's post, two of Jake's (one sharing an image with Todding's), an
+    old post with no poster, and a drop that absorbed Todding's and Jake's."""
+    artist = Artist(name="Todding", slug="todding-cleanup")
+    db.add(artist)
+    db.flush()
+    src = Source(
+        artist_id=artist.id, platform="discord",
+        url="https://discord.com/channels/1/2",
+        config_overrides={"discord_authors": list(authors)} if authors else None,
+    )
+    db.add(src)
+    db.flush()
+    todd = _post(db, src, "10", {"author": "todding", "author_name": "Todding", "author_id": "1"})
+    jake1 = _post(db, src, "11", {"author": "jakeboii", "author_id": "8"})
+    jake2 = _post(db, src, "12", {"author": "jakeboii", "author_id": "8"})
+    old = _post(db, src, "13", {"category": "discord"})
+    drop = _post(db, src, "fc-drop:10", None, synthesized_by="discord_drop")
+    todd.absorbed_by_post_id = drop.id
+    jake1.absorbed_by_post_id = drop.id
+
+    art = _image(db, artist, tmp_path, "art", todd)
+    meme = _image(db, artist, tmp_path, "meme", jake1)
+    shared = _image(db, artist, tmp_path, "shared", jake2)
+    legacy = _image(db, artist, tmp_path, "legacy", old)
+    db.add_all([
+        ImageProvenance(image_record_id=shared.id, post_id=todd.id, source_id=src.id),
+        ImageProvenance(image_record_id=art.id, post_id=drop.id, source_id=src.id),
+        ImageProvenance(image_record_id=meme.id, post_id=drop.id, source_id=src.id),
+        PostAttachment(
+            post_id=jake2.id, artist_id=artist.id, sha256="z" * 64,
+            path="/store/z/f.zip", original_filename="f.zip", ext=".zip", size_bytes=1,
+        ),
+    ])
+    db.commit()
+    return src, {
+        "todd": todd.id, "jake1": jake1.id, "jake2": jake2.id, "old": old.id,
+        "drop": drop.id, "art": art.id, "meme": meme.id, "shared": shared.id,
+        "legacy": legacy.id,
+    }
+
+
+def test_preview_matches_apply_and_the_rows_go(db_sync, tmp_path):
+    src, ids = _fixture(db_sync, tmp_path)
+
+    projected = cleanup.preview(db_sync, source_id=src.id)
+    assert projected["authors"] == ["todding"]
+    assert projected["posters"] == [{"poster": "jakeboii", "posts": 2}]
+    assert projected["unknown_posts"] == 1
+
+    done = cleanup.apply(db_sync, source_id=src.id, images_root=tmp_path)
+    assert projected["posts"] == done["posts_deleted"] == 2
+    assert projected["images"] == done["images_deleted"] == 1  # the meme only
+    assert projected["attachments"] == done["attachments_deleted"] == 1
+    assert projected["drops"] == done["drops_deleted"] == 1
+
+    post_ids = set(db_sync.execute(select(Post.id).where(Post.source_id == src.id)).scalars())
+    assert post_ids == {ids["todd"], ids["old"]}
+    image_ids = set(db_sync.execute(
+        select(ImageRecord.id).where(ImageRecord.id.in_(
+            [ids["art"], ids["meme"], ids["shared"], ids["legacy"]]))
+    ).scalars())
+    # The meme was only Jake's. The shared piece is also on Todding's post, and
+    # the drop's link to the art was never what kept it.
+    assert image_ids == {ids["art"], ids["shared"], ids["legacy"]}
+    assert not (tmp_path / "meme.png").exists()
+    # Todding's message is back in the feed, for the sweep to regroup.
+    assert db_sync.get(Post, ids["todd"]).absorbed_by_post_id is None
+    assert db_sync.execute(select(func.count(PostAttachment.id)).where(
+        PostAttachment.sha256 == "z" * 64)).scalar_one() == 0
+
+
+def test_a_poster_matches_by_display_name_or_id_too(db_sync, tmp_path):
+    src, _ = _fixture(db_sync, tmp_path, authors=("8",))
+    projected = cleanup.preview(db_sync, source_id=src.id)
+    assert projected["posters"] == [{"poster": "Todding", "posts": 1}]
+
+
+def test_no_list_means_nothing_to_remove(db_sync, tmp_path):
+    src, _ = _fixture(db_sync, tmp_path, authors=())
+    with pytest.raises(cleanup.PosterCleanupError):
+        cleanup.preview(db_sync, source_id=src.id)
+
+
+def test_the_token_names_what_the_preview_showed():
+    assert cleanup.confirm_token({"posts": 2, "images": 1}) == "remove-2-posts-1-images"