refactor(capture): the HTTP layer reads through queries and writes through the service

Capture's routes (downloads, files, public watch links) and the token list no longer build SQL, call
the session or set a model's fields: reads are downloads/queries, writes the unit's service (service,
folders, links, quota), and each write flushes for the handler to commit. Whose a row is goes
through userscope (owned_by, owned_row), which owned_or_404 now uses too.

The fence holds Capture below its routes as well: it reads only Catalog's and Plex's tables, writes
no other unit's, filters owners through userscope and commits only in its jobs and the upload
ingest. A test per service use case, among them that the tray lists only the caller's files.

backend/app/downloads/credentials.py

@@ -35,6 +35,7 @@ from app.downloads import formats
 from app.downloads.adapters import _host_is
 from app.downloads.models import DownloadCredential, MediaAsset
 from app.security import decrypt_optional, encrypt
+from app.userscope import owned_by
 
 log = logs.get_logger(__name__)
 
@@ -157,7 +158,7 @@ def salt_for_enqueue(db: Session, user_id: int, url: str | None) -> str | None:
 def get_credential(db: Session, user_id: int, host_key: str) -> DownloadCredential | None:
     return db.execute(
         select(DownloadCredential).where(
-            DownloadCredential.user_id == user_id, DownloadCredential.host_key == host_key
+            owned_by(DownloadCredential.user_id, user_id), DownloadCredential.host_key == host_key
         )
     ).scalar_one_or_none()
 
@@ -214,7 +215,7 @@ def status_list(db: Session, user_id: int) -> list[dict]:
     have = {
         c.host_key: c
         for c in db.execute(
-            select(DownloadCredential).where(DownloadCredential.user_id == user_id)
+            select(DownloadCredential).where(owned_by(DownloadCredential.user_id, user_id))
         ).scalars()
     }
     out = []

backend/app/downloads/folders.py

@@ -33,6 +33,7 @@ from sqlalchemy.orm import Session
 from app import sysconfig
 from app.downloads.status import JobStatus
 from app.downloads.models import DownloadJob, FileFolder, MediaAsset
+from app.userscope import owned_by
 
 
 class FolderKind(StrEnum):
@@ -106,7 +107,9 @@ def source_key_for(db: Session, job: DownloadJob) -> str:
 def source_folder(db: Session, user_id: int, key: str) -> FileFolder:
     """The user's source folder for `key`, made on first use. A race on the unique (user, key) is
     settled by re-selecting, inside a SAVEPOINT so the caller's own pending writes survive."""
-    stmt = select(FileFolder).where(FileFolder.user_id == user_id, FileFolder.source_key == key)
+    stmt = select(FileFolder).where(
+        owned_by(FileFolder.user_id, user_id), FileFolder.source_key == key
+    )
     folder = db.execute(stmt).scalar_one_or_none()
     if folder is not None:
         return folder
@@ -131,7 +134,7 @@ def hub_folder(db: Session, user_id: int) -> FileFolder:
     """The user's Hub folder, made on first use; a race on its one-per-user index is settled like
     `source_folder`'s."""
     stmt = select(FileFolder).where(
-        FileFolder.user_id == user_id, FileFolder.kind == FolderKind.HUB
+        owned_by(FileFolder.user_id, user_id), FileFolder.kind == FolderKind.HUB
     )
     folder = db.execute(stmt).scalar_one_or_none()
     if folder is not None:
@@ -310,3 +313,28 @@ def delete_own(db: Session, folder: FileFolder) -> int:
     db.flush()  # the files leave before the folder goes: its foreign key RESTRICTs the delete
     db.delete(folder)
     return len(jobs)
+
+
+def create_own(db: Session, user_id: int, name: str) -> FileFolder:
+    """A new folder of the user's own; FolderError("file_folder_name_taken") when they already have
+    one by that name (the unique (user, lower(name)))."""
+    folder = FileFolder(user_id=user_id, kind=FolderKind.OWN, name=name)
+    try:
+        with db.begin_nested():
+            db.add(folder)
+            db.flush()
+    except IntegrityError as e:
+        raise FolderError("file_folder_name_taken") from e
+    return folder
+
+
+def rename(db: Session, folder: FileFolder, name: str) -> None:
+    """Rename one of the user's own folders (a source folder's name is its origin's)."""
+    if folder.kind != FolderKind.OWN:
+        raise FolderError("file_folder_not_own")
+    folder.name = name
+    try:
+        with db.begin_nested():
+            db.flush()
+    except IntegrityError as e:
+        raise FolderError("file_folder_name_taken") from e

backend/app/downloads/links.py

@@ -15,20 +15,24 @@ grant appended to the file URL, so the raw password never rides in the media URL
 import hashlib
 import hmac
 import secrets
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 
 from sqlalchemy import select
+from sqlalchemy import update as sql_update
 from sqlalchemy.orm import Session
 
-from app import security
+from app import audit, security
 from app.config import settings
 from app.downloads import storage
 from app.downloads.status import JobStatus
 from app.downloads.models import DownloadJob, DownloadLink, FileFolder, MediaAsset
+from app.models import User
+from app.utils import iso
+from app.userscope import owned_by
 
 _GRANT_TTL = 6 * 3600  # a watch session's grant is good for 6h, then the viewer re-unlocks
-# The most files a folder link lists: as many as the owner's own Files list shows (`routes.files.
-# MAX_LIST`; a test holds the two equal — this layer may not import that one).
+# The most files a folder link lists: as many as the owner's own Files list shows
+# (`queries.MAX_LIST`; a test holds the two equal — `queries` imports this module).
 FOLDER_MAX = 500
 
 
@@ -59,7 +63,7 @@ def in_folder(folder: FileFolder) -> tuple:
     moved out stops opening through the link at its next request; one moved in starts."""
     return (
         DownloadJob.folder_id == folder.id,
-        DownloadJob.user_id == folder.user_id,
+        owned_by(DownloadJob.user_id, folder.user_id),
         DownloadJob.status == JobStatus.DONE,
     )
 
@@ -170,3 +174,117 @@ def public_meta(
         "file_url": file_url,
         "poster_url": poster_url,
     }
+
+
+# --- the owner's writes --------------------------------------------------------------------
+# Each flushes and records its audit row; the handler commits.
+
+
+def expiry(days: int | None) -> datetime | None:
+    """None/0/negative → no expiry; otherwise N days out, capped at ~10 years."""
+    if not days or days <= 0:
+        return None
+    return datetime.now(timezone.utc) + timedelta(days=min(days, 3650))
+
+
+def audit_view(link: DownloadLink) -> dict:
+    """A link's settings as the audit records them: whether it has a password, never which."""
+    return {
+        "allow_download": link.allow_download,
+        "has_password": link.password_hash is not None,
+        "expires_at": iso(link.expires_at),
+    }
+
+
+def create(
+    db: Session,
+    user: User,
+    *,
+    password: str,
+    allow_download: bool,
+    expires_days: int | None,
+    **target: int,
+) -> tuple[DownloadLink, str]:
+    """A link to `target` (`job_id=` or `folder_id=`, already checked to be the user's), and the
+    token it is opened by — which is in hand only now."""
+    token = new_token()
+    link = DownloadLink(
+        **target,
+        created_by=user.id,
+        allow_download=allow_download,
+        password_hash=security.hash_password(password) if password else None,
+        expires_at=expiry(expires_days),
+    )
+    seal(link, token)
+    db.add(link)
+    db.flush()
+    audit.record(
+        db,
+        user.id,
+        audit.AuditAction.DOWNLOAD_LINK_CREATE,
+        target_type="download_link",
+        target_id=link.id,
+        after={**target, **audit_view(link)},
+    )
+    return link, token
+
+
+def update(
+    db: Session,
+    user: User,
+    link: DownloadLink,
+    *,
+    allow_download: bool | None = None,
+    expires_days: int | None = None,
+    password: str | None = None,
+    sent: frozenset[str] = frozenset(),
+) -> None:
+    """Change what the caller sent (`sent` names the fields, so `expires_days=None` can mean "never
+    expires"). Setting, clearing or changing the password bumps its version, so any grant issued
+    under the previous one stops working now rather than living out its TTL."""
+    before = audit_view(link)
+    if "allow_download" in sent:
+        link.allow_download = bool(allow_download)
+    if "expires_days" in sent:
+        link.expires_at = expiry(expires_days)
+    if "password" in sent:
+        pw = (password or "").strip()
+        link.password_hash = security.hash_password(pw) if pw else None
+        link.password_version += 1
+    after = audit_view(link)
+    if after != before or "password" in sent:
+        audit.record(
+            db,
+            user.id,
+            audit.AuditAction.DOWNLOAD_LINK_UPDATE,
+            target_type="download_link",
+            target_id=link.id,
+            before=before,
+            after=after,
+        )
+    db.flush()
+
+
+def revoke(db: Session, user: User, link: DownloadLink) -> None:
+    link_id = link.id
+    db.delete(link)
+    audit.record(
+        db,
+        user.id,
+        audit.AuditAction.DOWNLOAD_LINK_REVOKE,
+        target_type="download_link",
+        target_id=link_id,
+        after={"job_id": link.job_id} if link.job_id is not None else {"folder_id": link.folder_id},
+    )
+    db.flush()
+
+
+def count_view(db: Session, link: DownloadLink) -> None:
+    """One more opening of the link. In SQL, not `+= 1` on the loaded row: two opens at once would
+    both write the same count."""
+    db.execute(
+        sql_update(DownloadLink)
+        .where(DownloadLink.id == link.id)
+        .values(view_count=DownloadLink.view_count + 1)
+        .execution_options(synchronize_session=False)
+    )

backend/app/downloads/queries.py

@@ -0,0 +1,406 @@
+"""Capture's reads: what the library, the download tray, the share dialogs and the public watch pages
+show. Each returns rows or plain values and writes nothing; whose a row is goes through
+`userscope.owned_by` / `owned_row`, so a row of someone else's reads as a missing one.
+
+The HTTP layer (`routes.downloads`, `routes.files`, `routes.public`) asks here and serializes; the
+writes are the service's (`service`, `folders`, `links`, `quota`)."""
+
+from collections.abc import Sequence
+from datetime import datetime, timezone
+
+from sqlalchemy import func, or_, select
+from sqlalchemy.orm import Session
+
+from app.apitokens import FilesCaller, Right
+from app.collation import collated
+from app.downloads import folders, links, quota
+from app.downloads.models import (
+    DownloadJob,
+    DownloadLink,
+    DownloadProfile,
+    DownloadQuota,
+    DownloadShare,
+    FileFolder,
+    LibraryState,
+    MediaAsset,
+)
+from app.downloads.status import FINISHED, JobStatus
+from app.models import User
+from app.userscope import owned_by, owned_row
+from app.utils import like_escape
+
+# Cap a listing so a heavy library can't return an unbounded result set (the old Download Center's
+# own cap; far beyond any real library).
+MAX_LIST = 500
+
+
+# --- jobs and their files ------------------------------------------------------------------
+
+
+def own_job(db: Session, user: User, job_id: int) -> DownloadJob | None:
+    return owned_row(db, DownloadJob, job_id, user)
+
+
+def job(db: Session, job_id: int) -> DownloadJob | None:
+    """A job by id, whoever's — for a public link, which already names its job."""
+    return db.get(DownloadJob, job_id)
+
+
+def accessible_job(db: Session, user: User, job_id: int) -> DownloadJob | None:
+    """A file the caller may read: their own, or one shared with them."""
+    row = db.get(DownloadJob, job_id)
+    if row is None:
+        return None
+    if row.user_id == user.id or shared_with(db, job_id, user) is not None:
+        return row
+    return None
+
+
+def readable_job(db: Session, caller: FilesCaller, job_id: int) -> DownloadJob | None:
+    """A file `caller` may read: as `accessible_job` for the user; for a token, one of the user's
+    own in a folder it may read."""
+    if caller.grants is None:
+        return accessible_job(db, caller.user, job_id)
+    row = own_job(db, caller.user, job_id)
+    if row is None or not caller.may(row.folder_id, Right.READ):
+        return None
+    return row
+
+
+def asset_of(db: Session, job: DownloadJob | None) -> MediaAsset | None:
+    """The file under a job, if it has one yet."""
+    return db.get(MediaAsset, job.asset_id) if job is not None and job.asset_id else None
+
+
+def assets_for(db: Session, jobs: Sequence[DownloadJob]) -> dict[int, MediaAsset]:
+    ids = {j.asset_id for j in jobs if j.asset_id}
+    if not ids:
+        return {}
+    rows = db.execute(select(MediaAsset).where(MediaAsset.id.in_(ids))).scalars()
+    return {a.id: a for a in rows}
+
+
+def positions_for(db: Session, user: User, jobs: Sequence[DownloadJob]) -> dict[int, int]:
+    """`user`'s resume point in each of `jobs` that has one (the library player's `library_states`)."""
+    ids = [j.id for j in jobs]
+    if not ids:
+        return {}
+    rows = db.execute(
+        select(LibraryState.job_id, LibraryState.position_seconds).where(
+            owned_by(LibraryState.user_id, user), LibraryState.job_id.in_(ids)
+        )
+    ).all()
+    return {job_id: pos for job_id, pos in rows}
+
+
+def source_keys(db: Session, jobs: Sequence[DownloadJob]) -> dict[int, str]:
+    """Where each file came from (its source folder's key), for the list's Source column, the
+    "back to its source folder" move and the download tray's site: a file in a source folder has its
+    folder's key; one moved into an own folder (or someone else's, shared) is traced back by
+    `folders.source_key_for`."""
+    ids = {j.folder_id for j in jobs if j.folder_id is not None}
+    by_id = (
+        {f.id: f for f in db.execute(select(FileFolder).where(FileFolder.id.in_(ids))).scalars()}
+        if ids
+        else {}
+    )
+    out: dict[int, str] = {}
+    for j in jobs:
+        folder = by_id.get(j.folder_id) if j.folder_id is not None else None
+        if folder is not None and folder.kind == folders.FolderKind.SOURCE and folder.source_key:
+            out[j.id] = folder.source_key
+        else:
+            out[j.id] = folders.source_key_for(db, j)
+    return out
+
+
+def queue(db: Session, user: User, recent: datetime) -> list[DownloadJob]:
+    """The download tray: what is waiting, running, paused or failed, and what finished (done or
+    canceled) since `recent`. A done job is timed from when it became done, never from its last
+    write: a rename, a move or the GC's expiry warning touches an old file's row, and the tray would
+    announce it as just finished."""
+    return list(
+        db.execute(
+            select(DownloadJob)
+            .where(
+                owned_by(DownloadJob.user_id, user),
+                DownloadJob.status.not_in(FINISHED)
+                | ((DownloadJob.status == JobStatus.DONE) & (DownloadJob.ready_at >= recent))
+                | ((DownloadJob.status == JobStatus.CANCELED) & (DownloadJob.updated_at >= recent)),
+            )
+            .order_by(DownloadJob.created_at.desc(), DownloadJob.id.desc())
+            .limit(MAX_LIST)
+        ).scalars()
+    )
+
+
+def statuses_by_source(db: Session, user: User, statuses: Sequence[str]) -> list[tuple[str, str]]:
+    """(source_ref, status) of each of `user`'s jobs in one of `statuses`."""
+    return list(
+        db.execute(
+            select(DownloadJob.source_ref, DownloadJob.status).where(
+                owned_by(DownloadJob.user_id, user), DownloadJob.status.in_(tuple(statuses))
+            )
+        ).tuples()
+    )
+
+
+def library(
+    db: Session,
+    user: User,
+    *,
+    folder_id: int | None,
+    listable: set[int] | None,
+    shared: bool,
+    term: str,
+    sort: str,
+    order: str,
+    lang: str,
+) -> list[DownloadJob]:
+    """The caller's done files (optionally one folder's, or only in the folders a token may list),
+    or the ones shared with them; searched by name and channel, sorted by when they were added, by
+    name (in the reader's alphabet) or by size. A file is added to its owner's list when it is done,
+    not when it was asked for (a download that failed for days and then went through is new); one
+    shared with the caller, when it was shared."""
+    stmt = (
+        select(DownloadJob)
+        .join(MediaAsset, MediaAsset.id == DownloadJob.asset_id)
+        .where(DownloadJob.status == JobStatus.DONE)
+    )
+    if shared:
+        stmt = stmt.join(DownloadShare, DownloadShare.job_id == DownloadJob.id).where(
+            owned_by(DownloadShare.to_user_id, user)
+        )
+    else:
+        stmt = stmt.where(owned_by(DownloadJob.user_id, user))
+        if folder_id is not None:
+            stmt = stmt.where(DownloadJob.folder_id == folder_id)
+        elif listable is not None:
+            stmt = stmt.where(DownloadJob.folder_id.in_(listable))
+    name = func.coalesce(DownloadJob.display_name, MediaAsset.title, "")
+    if term:
+        like = f"%{like_escape(term)}%"
+        stmt = stmt.where(
+            or_(
+                name.ilike(like),
+                func.coalesce(DownloadJob.display_uploader, MediaAsset.uploader, "").ilike(like),
+            )
+        )
+    key = {
+        "added": DownloadShare.created_at if shared else DownloadJob.ready_at,
+        "name": collated(name, lang),
+        "size": MediaAsset.size_bytes,
+    }[sort]
+    first = key.asc() if order == "asc" else key.desc()
+    tie = DownloadJob.id.asc() if order == "asc" else DownloadJob.id.desc()
+    return list(db.execute(stmt.order_by(first.nulls_last(), tie).limit(MAX_LIST)).scalars())
+
+
+def recent_jobs(db: Session) -> list[DownloadJob]:
+    """Everyone's newest jobs, for the admin's list."""
+    return list(
+        db.execute(
+            select(DownloadJob)
+            .order_by(DownloadJob.created_at.desc(), DownloadJob.id.desc())
+            .limit(MAX_LIST)
+        ).scalars()
+    )
+
+
+# --- shares --------------------------------------------------------------------------------
+
+
+def shared_with(db: Session, job_id: int, user: User | int) -> DownloadShare | None:
+    """The grant that hands this job to `user`, if there is one."""
+    return db.execute(
+        select(DownloadShare).where(
+            DownloadShare.job_id == job_id, owned_by(DownloadShare.to_user_id, user)
+        )
+    ).scalar_one_or_none()
+
+
+def shared_at(db: Session, user: User, jobs: Sequence[DownloadJob]) -> dict[int, datetime]:
+    rows = db.execute(
+        select(DownloadShare.job_id, DownloadShare.created_at).where(
+            owned_by(DownloadShare.to_user_id, user),
+            DownloadShare.job_id.in_([j.id for j in jobs]),
+        )
+    ).all()
+    return {job_id: at for job_id, at in rows}
+
+
+# --- folders -------------------------------------------------------------------------------
+
+
+def own_folder(db: Session, user: User, folder_id: int) -> FileFolder | None:
+    return owned_row(db, FileFolder, folder_id, user)
+
+
+def folders_by_id(db: Session, ids: set[int]) -> dict[int, FileFolder]:
+    """These folders, by id — for a reader that already knows which ones (a token's grants)."""
+    if not ids:
+        return {}
+    return {f.id: f for f in db.execute(select(FileFolder).where(FileFolder.id.in_(ids))).scalars()}
+
+
+def folders_with_totals(
+    db: Session, user: User, listable: set[int] | None
+) -> list[tuple[FileFolder, int, int]]:
+    """The user's folders (only `listable` ones, when given) with how many done files each holds and
+    their size. A source folder its files have all left stays (count 0)."""
+    done = (DownloadJob.folder_id == FileFolder.id) & (DownloadJob.status == JobStatus.DONE)
+    stmt = select(
+        FileFolder,
+        func.count(DownloadJob.id),
+        func.coalesce(func.sum(MediaAsset.size_bytes), 0),
+    ).where(owned_by(FileFolder.user_id, user))
+    if listable is not None:
+        stmt = stmt.where(FileFolder.id.in_(listable))
+    rows = db.execute(
+        stmt.outerjoin(DownloadJob, done)
+        .outerjoin(MediaAsset, MediaAsset.id == DownloadJob.asset_id)
+        .group_by(FileFolder.id)
+        .order_by(FileFolder.kind.desc(), FileFolder.source_key, FileFolder.name, FileFolder.id)
+    ).tuples()
+    return [(f, count, int(size or 0)) for f, count, size in rows]
+
+
+def folder_totals(db: Session, folder_id: int) -> tuple[int, int]:
+    count, size = db.execute(
+        select(func.count(DownloadJob.id), func.coalesce(func.sum(MediaAsset.size_bytes), 0))
+        .select_from(DownloadJob)
+        .outerjoin(MediaAsset, MediaAsset.id == DownloadJob.asset_id)
+        .where(DownloadJob.folder_id == folder_id, DownloadJob.status == JobStatus.DONE)
+    ).one()
+    return count, int(size)
+
+
+def linked_folders(db: Session, folder_ids: list[int]) -> set[int]:
+    """Which of these folders a live public link opens (one not past its expiry)."""
+    now = datetime.now(timezone.utc)
+    rows = db.execute(
+        select(DownloadLink.folder_id).where(
+            DownloadLink.folder_id.in_(folder_ids),
+            or_(DownloadLink.expires_at.is_(None), DownloadLink.expires_at > now),
+        )
+    ).scalars()
+    return {folder_id for folder_id in rows if folder_id is not None}
+
+
+# --- links ---------------------------------------------------------------------------------
+
+
+def own_link(db: Session, user: User, link_id: int) -> DownloadLink | None:
+    """A link to one of the user's files or folders."""
+    link = db.get(DownloadLink, link_id)
+    if link is None:
+        return None
+    target = (
+        db.get(DownloadJob, link.job_id)
+        if link.job_id is not None
+        else db.get(FileFolder, link.folder_id)
+    )
+    if target is None or target.user_id != user.id:
+        return None
+    return link
+
+
+def links_to(
+    db: Session, *, job_id: int | None = None, folder_id: int | None = None
+) -> list[DownloadLink]:
+    """The links to one file or one folder, newest first."""
+    target = (
+        DownloadLink.job_id == job_id if job_id is not None else DownloadLink.folder_id == folder_id
+    )
+    return list(
+        db.execute(select(DownloadLink).where(target).order_by(DownloadLink.id.desc())).scalars()
+    )
+
+
+def link_folder(db: Session, link: DownloadLink) -> FileFolder | None:
+    return db.get(FileFolder, link.folder_id) if link.folder_id is not None else None
+
+
+def folder_job(db: Session, folder: FileFolder, job_id: int) -> DownloadJob | None:
+    """One of the files a link to `folder` reaches (`links.in_folder`), while it is in it."""
+    return db.execute(
+        select(DownloadJob).where(DownloadJob.id == job_id, *links.in_folder(folder))
+    ).scalar_one_or_none()
+
+
+def owner_suspended(db: Session, job: DownloadJob) -> bool:
+    """The job's owner is suspended (or gone): the worker leaves their queued jobs where they are."""
+    owner = db.get(User, job.user_id)
+    return owner is None or owner.is_suspended
+
+
+# --- profiles ------------------------------------------------------------------------------
+
+
+def profiles_for(db: Session, user: User) -> list[DownloadProfile]:
+    """The built-in format profiles, then the user's own."""
+    return list(
+        db.execute(
+            select(DownloadProfile)
+            .where(DownloadProfile.is_builtin.is_(True) | owned_by(DownloadProfile.user_id, user))
+            .order_by(
+                DownloadProfile.is_builtin.desc(), DownloadProfile.sort_order, DownloadProfile.id
+            )
+        ).scalars()
+    )
+
+
+def own_profile(db: Session, user: User, profile_id: int) -> DownloadProfile | None:
+    """One of the user's own profiles (a built-in is no one's to change)."""
+    p = owned_row(db, DownloadProfile, profile_id, user)
+    return None if p is None or p.is_builtin else p
+
+
+def usable_profile(db: Session, user: User, profile_id: int) -> DownloadProfile | None:
+    """A profile the user may enqueue with: a built-in, or their own."""
+    p = db.get(DownloadProfile, profile_id)
+    if p is None or (not p.is_builtin and p.user_id != user.id):
+        return None
+    return p
+
+
+def default_profile(db: Session) -> DownloadProfile | None:
+    """The first built-in, for an enqueue that named no format."""
+    return db.execute(
+        select(DownloadProfile)
+        .where(DownloadProfile.is_builtin.is_(True))
+        .order_by(DownloadProfile.sort_order)
+        .limit(1)
+    ).scalar_one_or_none()
+
+
+# --- storage and quota (admin) -------------------------------------------------------------
+
+
+def storage_totals(db: Session) -> tuple[int, int, int]:
+    """(files on disk, their bytes, every asset row). On disk is `quota.ON_DISK`: ready files, and
+    uploads waiting for or failed in their conversion — the same disk the footprint and the GC cap
+    count."""
+    on_disk = db.execute(
+        select(func.count(), func.coalesce(func.sum(MediaAsset.size_bytes), 0)).where(quota.ON_DISK)
+    ).one()
+    total_assets = db.execute(select(func.count()).select_from(MediaAsset)).scalar_one()
+    return on_disk[0], int(on_disk[1]), total_assets
+
+
+def done_files_per_user(db: Session) -> dict[int, int]:
+    """How many finished files each user's Files lists."""
+    return dict(
+        db.execute(
+            select(DownloadJob.user_id, func.count())
+            .where(DownloadJob.status == JobStatus.DONE)
+            .group_by(DownloadJob.user_id)
+        )
+        .tuples()
+        .all()
+    )
+
+
+def custom_quota(db: Session, user_id: int) -> DownloadQuota | None:
+    """The admin's own limits for this user, if any were set."""
+    return db.get(DownloadQuota, user_id)

backend/app/downloads/quota.py

@@ -27,6 +27,7 @@ from sqlalchemy.orm import Session
 from app import sysconfig
 from app.downloads.status import JobKind, JobStatus
 from app.downloads.models import DownloadJob, DownloadQuota, MediaAsset
+from app.userscope import owned_by
 
 # Jobs a user is considered to be "holding" (occupy a job slot / footprint). Terminal failures
 # (error, canceled) don't count.
@@ -85,7 +86,7 @@ def footprint(db: Session, user_id: int) -> int:
     held_assets = (
         select(DownloadJob.asset_id)
         .where(
-            DownloadJob.user_id == user_id,
+            owned_by(DownloadJob.user_id, user_id),
             or_(
                 DownloadJob.status.in_(_HOLDING),
                 and_(DownloadJob.job_kind == JobKind.UPLOAD, DownloadJob.status == JobStatus.ERROR),
@@ -109,7 +110,7 @@ def _count(db: Session, user_id: int, states) -> int:
         db.execute(
             select(func.count())
             .select_from(DownloadJob)
-            .where(DownloadJob.user_id == user_id, DownloadJob.status.in_(states))
+            .where(owned_by(DownloadJob.user_id, user_id), DownloadJob.status.in_(states))
         ).scalar()
         or 0
     )
@@ -201,3 +202,46 @@ def usage(db: Session, user_id: int) -> dict:
         "max_jobs": lim.max_jobs,
         "unlimited": lim.unlimited,
     }
+
+
+def set_custom(
+    db: Session,
+    user_id: int,
+    *,
+    max_bytes: int | None = None,
+    max_concurrent: int | None = None,
+    max_jobs: int | None = None,
+    unlimited: bool | None = None,
+) -> None:
+    """The admin's own limits for a user: starts from what applies now, then each value given (a
+    size floored at 0, a count at 1). The handler commits."""
+    row = db.get(DownloadQuota, user_id)
+    if row is None:
+        cur = resolve(db, user_id)
+        row = DownloadQuota(
+            user_id=user_id,
+            max_bytes=cur.max_bytes,
+            max_concurrent=cur.max_concurrent,
+            max_jobs=cur.max_jobs,
+            unlimited=cur.unlimited,
+        )
+        db.add(row)
+    if max_bytes is not None:
+        row.max_bytes = max(0, max_bytes)
+    if max_concurrent is not None:
+        row.max_concurrent = max(1, max_concurrent)
+    if max_jobs is not None:
+        row.max_jobs = max(1, max_jobs)
+    if unlimited is not None:
+        row.unlimited = unlimited
+    db.flush()
+
+
+def reset_custom(db: Session, user_id: int) -> bool:
+    """Back to the defaults; False when the user had no limits of their own."""
+    row = db.get(DownloadQuota, user_id)
+    if row is None:
+        return False
+    db.delete(row)
+    db.flush()
+    return True

backend/app/downloads/service.py

@@ -1,16 +1,19 @@
-"""Enqueue + cache resolution for the download center (the per-user layer over MediaAsset).
+"""Capture's writes: enqueue + cache resolution, the job transitions, and what the library's
+dialogs change (profiles, resume points, shares, a file's display fields).
 
 `enqueue` is the single entry point used by the API: it resolves (or creates) the shared
 MediaAsset for the requested source+format, links a per-user DownloadJob to it, and — on a
 cache hit (asset already ready) — marks the job done instantly with no re-download. The worker
-handles everything else. State transitions used by the routes (pause/resume/cancel/delete) and
-the worker live in `worker.py` / the routes; this module owns enqueue + asset bookkeeping.
+handles everything else. Every function here flushes and leaves the commit to its caller (the
+handler); the folder, link and quota writes are `folders`, `links` and `quota`.
 """
 
 import uuid
 from datetime import datetime, timezone
 
+from sqlalchemy import delete as delete_rows
 from sqlalchemy import func, select, update
+from sqlalchemy.dialects.postgresql import insert as pg_insert
 from sqlalchemy.exc import IntegrityError
 from sqlalchemy.orm import Session
 
@@ -21,10 +24,17 @@ from app.downloads import credentials
 from app.downloads import edit as editmod
 from app.downloads import folders, formats, mediakind, quota, storage
 from app.downloads.status import HOLDING, JobKind, JobStatus
-from app.models import DISPLAY_TEXT_MAX, Channel, PlexItem, PlexShow, Video
-from app.downloads.models import DownloadJob, MediaAsset
+from app.models import DISPLAY_TEXT_MAX, Channel, PlexItem, PlexShow, User, Video
+from app.downloads.models import (
+    DownloadJob,
+    DownloadProfile,
+    DownloadShare,
+    LibraryState,
+    MediaAsset,
+)
 from app.plex import lookups as plex_lookups
 from app.plex import paths as plex_paths
+from app.userscope import owned_by, owned_row
 
 
 class EditError(Exception):
@@ -223,8 +233,7 @@ def enqueue(
         folders.stamp_done(db, job)
         asset.last_access_at = datetime.now(timezone.utc)
 
-    db.commit()
-    db.refresh(job)
+    db.flush()
     return job
 
 
@@ -303,8 +312,7 @@ def enqueue_edit(
         folders.stamp_done(db, job)
         asset.last_access_at = datetime.now(timezone.utc)
 
-    db.commit()
-    db.refresh(job)
+    db.flush()
     return job
 
 
@@ -392,8 +400,7 @@ def enqueue_clip(
         folders.stamp_done(db, job)
         asset.last_access_at = datetime.now(timezone.utc)
 
-    db.commit()
-    db.refresh(job)
+    db.flush()
     return job
 
 
@@ -501,8 +508,8 @@ def release_asset(db: Session, job: DownloadJob) -> None:
 # --- Job state transitions ---------------------------------------------------------------------
 # The single home for the pause/resume/cancel/delete/redownload transitions + their asset
 # bookkeeping (release, failed-asset reset, fresh-asset rebuild), so the routes are thin callers and
-# the worker/GC could share the same definitions (B-sub-8). Each commits its own transition; the
-# route keeps only auth + HTTP mapping + serialization.
+# the worker/GC could share the same definitions (B-sub-8). Each flushes its transition and the caller
+# commits it; the route keeps only auth + HTTP mapping + serialization.
 
 
 def pause(db: Session, job: DownloadJob) -> None:
@@ -510,7 +517,7 @@ def pause(db: Session, job: DownloadJob) -> None:
     in any other state."""
     if job.status in (JobStatus.QUEUED, JobStatus.RUNNING):
         job.status = JobStatus.PAUSED
-        db.commit()
+        db.flush()
 
 
 def resume(db: Session, job: DownloadJob) -> None:
@@ -534,7 +541,7 @@ def resume(db: Session, job: DownloadJob) -> None:
                 asset.status = "pending"
                 asset.error = None
         job.status = JobStatus.QUEUED
-        db.commit()
+        db.flush()
 
 
 def _follow_the_cookie(db: Session, job: DownloadJob, asset: MediaAsset) -> MediaAsset:
@@ -569,14 +576,14 @@ def cancel(db: Session, job: DownloadJob) -> None:
     if job.status not in (JobStatus.DONE, JobStatus.CANCELED):
         release_asset(db, job)  # release while the job still counts as holding
         job.status = JobStatus.CANCELED
-        db.commit()
+        db.flush()
 
 
 def delete(db: Session, job: DownloadJob) -> None:
     """Delete a job, releasing its asset hold first (which frees the file iff this was the last holder)."""
     release_asset(db, job)
     db.delete(job)
-    db.commit()
+    db.flush()
 
 
 def redownload(db: Session, job: DownloadJob) -> None:
@@ -625,4 +632,181 @@ def redownload(db: Session, job: DownloadJob) -> None:
     job.queue_pos = next_queue_pos(db)  # tail of the queue, not its stale original slot
     job.expires_at = None  # stamped again when the rebuild is done
     job.expiry_warned = False
-    db.commit()
+    db.flush()
+
+
+# --- the library's writes ------------------------------------------------------------------
+# What the HTTP layer changes for a user: each flushes, the handler commits.
+
+
+def lock_own_job(db: Session, user: User, job_id: int) -> DownloadJob | None:
+    """One of the user's jobs, re-read under a row lock, for a transition that moves its asset's ref
+    count (resume, cancel, delete, redownload) or writes the status those decide on (pause). Two
+    overlapping requests for one job run one after the other and the second decides on the first's
+    committed result — never both releasing the same hold, and never a pause turning a job a cancel
+    just released back into a holder; either can free a file another job still holds. None: not
+    theirs, or gone.
+
+    The asset is locked BEFORE the job: the order a finishing worker child takes them in
+    (`finalize_if_running`), so the two can never deadlock."""
+    while True:
+        owned = owned_row(db, DownloadJob, job_id, user)
+        if owned is None:
+            return None
+        asset_id = owned.asset_id
+        if asset_id is not None:
+            db.execute(select(MediaAsset.id).where(MediaAsset.id == asset_id).with_for_update())
+        job = db.execute(
+            select(DownloadJob)
+            .where(DownloadJob.id == job_id)
+            .with_for_update()
+            .execution_options(populate_existing=True)
+        ).scalar_one_or_none()
+        if job is None:
+            return None
+        if job.asset_id == asset_id:
+            return job
+        db.rollback()  # another request moved the job to another asset meanwhile: lock that one
+
+
+def hold_for_share(db: Session, user: User, job_id: int) -> DownloadJob | None:
+    """One of the user's files, held (FOR SHARE) for the rest of the transaction: a delete of it at
+    the same moment (the user's, or the retention sweep's) waits and takes the new link with it,
+    rather than failing the link's foreign key — or, done first, leaves None."""
+    if owned_row(db, DownloadJob, job_id, user) is None:
+        return None
+    return db.execute(
+        select(DownloadJob)
+        .where(DownloadJob.id == job_id)
+        .with_for_update(read=True)
+        .execution_options(populate_existing=True)
+    ).scalar_one_or_none()
+
+
+def create_profile(db: Session, user: User, name: str, spec: dict) -> DownloadProfile:
+    """A format profile of the user's own, after their others."""
+    maxpos = db.execute(
+        select(func.coalesce(func.max(DownloadProfile.sort_order), 100)).where(
+            owned_by(DownloadProfile.user_id, user)
+        )
+    ).scalar_one()
+    p = DownloadProfile(
+        user_id=user.id, name=name[:80], spec=spec, is_builtin=False, sort_order=maxpos + 1
+    )
+    db.add(p)
+    db.flush()
+    return p
+
+
+def update_profile(profile: DownloadProfile, *, name: str | None, spec: dict | None) -> None:
+    """Rename a profile and/or replace its spec; None leaves that one as it is."""
+    if name is not None:
+        profile.name = name[:80]
+    if spec is not None:
+        profile.spec = spec
+
+
+def delete_profile(db: Session, profile: DownloadProfile) -> None:
+    db.delete(profile)
+    db.flush()
+
+
+def set_position(db: Session, user: User, job_id: int, position: int) -> None:
+    """The library player's resume point in a file the user can play; 0 clears it.
+
+    A clear is a statement, not a loaded row's delete: the periodic checkpoint and the pagehide beacon
+    of one stop may both clear it, and the second then deletes nothing rather than failing. A set is
+    an upsert, one row per (user, job) even when two checkpoints race, not a read-then-insert that
+    the second would fail on the unique key."""
+    if not position:
+        db.execute(
+            delete_rows(LibraryState).where(
+                owned_by(LibraryState.user_id, user), LibraryState.job_id == job_id
+            )
+        )
+        return
+    now = datetime.now(timezone.utc)
+    db.execute(
+        pg_insert(LibraryState)
+        .values(user_id=user.id, job_id=job_id, position_seconds=position, progress_updated_at=now)
+        .on_conflict_do_update(
+            constraint="uq_library_user_job",
+            set_={"position_seconds": position, "progress_updated_at": now},
+        )
+    )
+
+
+def share(db: Session, job: DownloadJob, sender: User, recipient: User) -> bool:
+    """Hand a file to another user, with a notice for them; False when it was already theirs."""
+    from app.notifications import create_notification
+
+    exists = db.execute(
+        select(DownloadShare.id).where(
+            DownloadShare.job_id == job.id, owned_by(DownloadShare.to_user_id, recipient)
+        )
+    ).first()
+    if exists is not None:
+        return False
+    db.add(DownloadShare(job_id=job.id, from_user_id=sender.id, to_user_id=recipient.id))
+    create_notification(
+        db,
+        user_id=recipient.id,
+        type="download_shared",
+        title=(job.display_name or "A download") + " was shared with you",
+        # The client names the notice in the reader's language from `data`; the title is the
+        # English fallback only.
+        data={
+            "kind": "download_shared",
+            "from": sender.email,
+            "job_id": job.id,
+            "title": job.display_name,
+        },
+        commit=False,
+    )
+    db.flush()
+    return True
+
+
+def unshare(db: Session, job_id: int, recipient: User) -> bool:
+    """Take a file back from one user (its owner's act, or the recipient's own dismissal); False
+    when it was not theirs."""
+    row = db.execute(
+        select(DownloadShare).where(
+            DownloadShare.job_id == job_id, owned_by(DownloadShare.to_user_id, recipient)
+        )
+    ).scalar_one_or_none()
+    if row is None:
+        return False
+    db.delete(row)
+    db.flush()
+    return True
+
+
+# The display fields a user may set on their file; the file on disk keeps its own name.
+DISPLAY_FIELDS = frozenset(
+    {"display_name", "display_uploader", "display_uploader_url", "extra_links"}
+)
+
+
+def set_display(job: DownloadJob, **fields: object) -> None:
+    """Set a file's display fields (each already cleaned by the caller); a field not given is left."""
+    unknown = set(fields) - DISPLAY_FIELDS
+    if unknown:
+        raise ValueError(f"not a display field: {sorted(unknown)}")
+    for name, value in fields.items():
+        setattr(job, name, value)
+
+
+def touch(asset: MediaAsset) -> None:
+    """The file was just served: the cache's idle clock starts again."""
+    asset.last_access_at = datetime.now(timezone.utc)
+
+
+def store_sha256(db: Session, asset_id: int, digest: str) -> None:
+    """Keep a file's hash once it is known — only where none is, so a concurrent hash of the same
+    file never overwrites the first."""
+    db.execute(
+        update(MediaAsset)
+        .where(MediaAsset.id == asset_id, MediaAsset.sha256.is_(None))
+        .values(sha256=digest)
+    )