diff --git a/src/inkwell/app.py b/src/inkwell/app.py
index 667b5b2..c3ff79f 100644
--- a/src/inkwell/app.py
+++ b/src/inkwell/app.py
@@ -25,7 +25,7 @@ from .notes import bp as notes_bp
 from .proxy import is_https
 from .responses import json_error, not_found
 from .retention import run_sweeper
-from .settings import MAX_BODY_MB, get_public_config, get_setting, load_or_create_secret_key, refresh_live
+from .settings import MAX_BODY_MB, apply_session_ttl, get_public_config, get_setting, load_or_create_secret_key, refresh_live
 from .settings_api import bp as settings_bp
 from .shares_api import bp as shares_bp
 from .sync import bp as sync_bp, protocol_advertisement
@@ -114,8 +114,7 @@ def create_app() -> Quart:
         async with session_scope() as db:
             app.secret_key = await load_or_create_secret_key(db)
             try:
-                days = int(await get_setting(db, "session_ttl_days"))
-                app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=days)
+                apply_session_ttl(app, await get_setting(db, "session_ttl_days"))
             except (ValueError, TypeError, KeyError):
                 pass
             # The security settings the throttle and the proxy trust read on hot
diff --git a/src/inkwell/audit.py b/src/inkwell/audit.py
index fabd816..aa3f594 100644
--- a/src/inkwell/audit.py
+++ b/src/inkwell/audit.py
@@ -18,11 +18,11 @@ from __future__ import annotations
 
 import logging
 import uuid
-from datetime import datetime, timedelta, timezone
+from datetime import datetime, timezone
 
 from sqlalchemy import delete, select
 
-from .common import iso
+from .common import expired_before, iso
 from .db import session_scope
 from .models.audit_event import AuditEvent
 from .proxy import client_address
@@ -99,9 +99,9 @@ async def sweep_once(*, now: datetime | None = None) -> int:
     """Delete events older than `audit_retention_days`; 0 keeps them forever."""
     async with session_scope() as db:
         days = int(await get_setting(db, "audit_retention_days"))
-        if days <= 0:
+        cutoff = expired_before(now or datetime.now(timezone.utc), days)
+        if cutoff is None:
             return 0
-        cutoff = (now or datetime.now(timezone.utc)) - timedelta(days=days)
         deleted = (await db.execute(delete(AuditEvent).where(AuditEvent.at < cutoff))).rowcount
         await db.commit()
         return deleted
diff --git a/src/inkwell/auth.py b/src/inkwell/auth.py
index 85d2215..16220de 100644
--- a/src/inkwell/auth.py
+++ b/src/inkwell/auth.py
@@ -18,7 +18,7 @@ from .password_resets import INVALID as INVALID_RESET, claim as claim_reset, mai
 from .models.device_token import DeviceToken
 from .models.user import User
 from .proxy import client_address
-from .responses import json_error, not_found, parse_uuid
+from .responses import json_error, not_found, parse_uuid, too_many
 from .ratelimit import (
     register_by_address,
     reset_mail_by_account,
@@ -196,7 +196,7 @@ def _throttled(retry_after: int):
     genuinely needs.
     """
     logger.warning("throttled credential attempt from=%s retry_after=%ss", client_address(), retry_after)
-    return (*json_error("too many attempts — try again shortly", 429), {"Retry-After": str(retry_after)})
+    return too_many("too many attempts — try again shortly", retry_after)
 
 
 def _sign_in_block(email: str) -> int | None:
diff --git a/src/inkwell/client_dist.py b/src/inkwell/client_dist.py
index 185d13b..1587b80 100644
--- a/src/inkwell/client_dist.py
+++ b/src/inkwell/client_dist.py
@@ -82,7 +82,7 @@ from .auth import login_required
 from .config import Config
 from .proxy import is_https
 from .ratelimit import downloads_by_account
-from .responses import json_error
+from .responses import json_error, too_many
 
 
 @dataclass(frozen=True)
@@ -394,10 +394,7 @@ async def client_download(platform_id: str):
     account = str(g.user_id)
     wait = downloads_by_account.retry_after(account)
     if wait is not None:
-        response = jsonify({"error": "too many downloads from this account; try again later"})
-        response.status_code = 429
-        response.headers["Retry-After"] = str(wait)
-        return response
+        return too_many("too many downloads from this account; try again later", wait)
     downloads_by_account.record(account)
 
     # From the SAME directory the metadata came from, or a drop-in appearing between
diff --git a/src/inkwell/common.py b/src/inkwell/common.py
index 1c958e0..b6d72ad 100644
--- a/src/inkwell/common.py
+++ b/src/inkwell/common.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
-from datetime import datetime
+import asyncio
+from datetime import datetime, timedelta
 
 # Small, dependency-free value coercions shared across the blueprints. Kept in one
 # place so the "parse an ISO date" / "is this flag truthy" logic has a single
@@ -47,3 +48,28 @@ def normalize_email(raw: str | None) -> str:
     one from a request goes through here, so "Ana@Example.com " and "ana@example.com"
     are one account at sign-up, sign-in, reset and invite alike."""
     return (raw or "").strip().lower()
+
+
+def detach(running: set[asyncio.Task], coro) -> asyncio.Task:
+    """Start `coro` without waiting for it, held in `running` until it finishes.
+
+    The event loop keeps only a weak reference to a task, so one nobody holds can be
+    collected mid-flight. Each caller keeps its own set, which is what its `drain()`
+    awaits in tests. Raises RuntimeError when there is no running loop."""
+    task = asyncio.create_task(coro)
+    running.add(task)
+    task.add_done_callback(running.discard)
+    return task
+
+
+def expired_before(now: datetime, retention_days: int) -> datetime | None:
+    """The cutoff: anything older than this has expired. `None` = retention is off.
+
+    Kept separate from the query so the window arithmetic — including the two ways
+    to say "never" (0 and negative, the latter reachable by typing a stray minus in
+    Settings) — is testable without a database. Trash and the audit log both expire
+    through it.
+    """
+    if retention_days <= 0:
+        return None
+    return now - timedelta(days=retention_days)
diff --git a/src/inkwell/groups_api.py b/src/inkwell/groups_api.py
index ec7d880..6260919 100644
--- a/src/inkwell/groups_api.py
+++ b/src/inkwell/groups_api.py
@@ -18,7 +18,8 @@ from .db import session_scope
 from .models.group import Group, GroupMember
 from .models.user import User
 from .responses import json_error, not_found, parse_uuid
-from .share_sync import bump_note, group_notes, joined_group, left_group, recipients, revoke
+from .serialize import serialize_person
+from .share_sync import bump_note, group_notes, joined_group, left_group, recipients, revoke_lost
 
 bp = Blueprint("groups", __name__, url_prefix="/api/groups")
 
@@ -49,11 +50,17 @@ async def _serialize_groups(db, groups: list[Group]) -> list[dict]:
     members: dict = {}
     for group_id, user in rows:
         members.setdefault(group_id, []).append(
-            {"id": str(user.id), "display_name": user.display_name, "email": user.email}
+            serialize_person(user)
         )
     return [{"id": str(gr.id), "name": gr.name, "members": members.get(gr.id, [])} for gr in groups]
 
 
+async def _get_group(db, group_id: str) -> Group | None:
+    """The group a route's path names, or None for a malformed or unknown id."""
+    gid = parse_uuid(group_id)
+    return await db.get(Group, gid) if gid else None
+
+
 async def _answer(db, group: Group, status: int = 200):
     return jsonify((await _serialize_groups(db, [group]))[0]), status
 
@@ -87,9 +94,8 @@ async def rename_group(group_id: str):
     name = _name(await request.get_json(silent=True) or {})
     if name is None:
         return json_error("give the group a name", 400)
-    gid = parse_uuid(group_id)
     async with session_scope() as db:
-        group = await db.get(Group, gid) if gid else None
+        group = await _get_group(db, group_id)
         if group is None:
             return not_found()
         if await _name_taken(db, name, but=group.id):
@@ -104,9 +110,8 @@ async def rename_group(group_id: str):
 async def delete_group(group_id: str):
     """Delete the group and every share made to it. Whoever could see a note only
     through it loses the note, and their devices are told."""
-    gid = parse_uuid(group_id)
     async with session_scope() as db:
-        group = await db.get(Group, gid) if gid else None
+        group = await _get_group(db, group_id)
         if group is None:
             return not_found()
         note_ids = await group_notes(db, group.id)
@@ -114,7 +119,7 @@ async def delete_group(group_id: str):
         await db.delete(group)  # members and shares go with it (ON DELETE CASCADE)
         await db.flush()
         for nid in note_ids:
-            await revoke(db, nid, before[nid] - await recipients(db, nid))
+            await revoke_lost(db, nid, before[nid])
             # The owner's devices learn whether the note is still shared at all.
             await bump_note(db, nid)
         await db.commit()
@@ -125,10 +130,9 @@ async def delete_group(group_id: str):
 @require_admin
 async def add_member(group_id: str):
     data = await request.get_json(silent=True) or {}
-    gid = parse_uuid(group_id)
     uid = parse_uuid(str(data.get("user_id") or ""))
     async with session_scope() as db:
-        group = await db.get(Group, gid) if gid else None
+        group = await _get_group(db, group_id)
         if group is None:
             return not_found()
         if uid is None or await db.get(User, uid) is None:
@@ -147,10 +151,9 @@ async def add_member(group_id: str):
 @bp.delete("/<group_id>/members/<user_id>")
 @require_admin
 async def remove_member(group_id: str, user_id: str):
-    gid = parse_uuid(group_id)
     uid = parse_uuid(user_id)
     async with session_scope() as db:
-        group = await db.get(Group, gid) if gid else None
+        group = await _get_group(db, group_id)
         if group is None or uid is None:
             return not_found()
         membership = await db.scalar(
diff --git a/src/inkwell/mailer.py b/src/inkwell/mailer.py
index 448a2a1..57fd665 100644
--- a/src/inkwell/mailer.py
+++ b/src/inkwell/mailer.py
@@ -17,6 +17,7 @@ import ssl
 from dataclasses import dataclass
 from email.message import EmailMessage
 
+from .common import detach
 from .settings import get_setting, mail_configured
 
 logger = logging.getLogger(__name__)
@@ -91,9 +92,7 @@ def send_later(job) -> None:
     For the forgot-password route, where waiting would also be an oracle: an address
     with an account would answer as slowly as a mail server, and one without, at once.
     `job` handles and logs its own failures."""
-    task = asyncio.create_task(job)
-    _running.add(task)
-    task.add_done_callback(_running.discard)
+    detach(_running, job)
 
 
 async def drain() -> None:
diff --git a/src/inkwell/responses.py b/src/inkwell/responses.py
index f464377..fed6301 100644
--- a/src/inkwell/responses.py
+++ b/src/inkwell/responses.py
@@ -19,6 +19,12 @@ def not_found():
     return json_error("not found", 404)
 
 
+def too_many(message: str, retry_after: int):
+    """429 with `Retry-After`, the one thing a client that was slowed down needs to
+    know: how long to wait. Never which limit it hit."""
+    return jsonify({"error": message}), 429, {"Retry-After": str(retry_after)}
+
+
 def parse_uuid(raw: object) -> uuid.UUID | None:
     """Parse a path/body UUID, returning None on anything malformed. Pair with
     not_found() for the ubiquitous 'bad id in the URL → 404' guard."""
diff --git a/src/inkwell/retention.py b/src/inkwell/retention.py
index dada529..8dfe0a8 100644
--- a/src/inkwell/retention.py
+++ b/src/inkwell/retention.py
@@ -22,12 +22,13 @@ from __future__ import annotations
 
 import asyncio
 import logging
-from datetime import datetime, timedelta, timezone
+from datetime import datetime, timezone
 
 from sqlalchemy import delete as sa_delete
 from sqlalchemy import select
 
 from . import audit
+from .common import expired_before
 from .config import Config
 from .db import session_scope
 from .models.label import NoteLabel
@@ -56,18 +57,6 @@ SWEEP_STARTUP_DELAY_SECONDS = 60
 SWEEP_BATCH = 200
 
 
-def expired_before(now: datetime, retention_days: int) -> datetime | None:
-    """The cutoff: trash older than this has expired. `None` = retention is off.
-
-    Kept separate from the query so the window arithmetic — including the two ways
-    to say "never" (0 and negative, the latter reachable by typing a stray minus in
-    Settings) — is testable without a database.
-    """
-    if retention_days <= 0:
-        return None
-    return now - timedelta(days=retention_days)
-
-
 async def purge_note(db, note: Note, edited_at: datetime | None = None) -> None:
     """Turn a note into a content-less tombstone: delete its children (and the
     attachment files on disk), clear its content, stamp `purged_at`.
diff --git a/src/inkwell/serialize.py b/src/inkwell/serialize.py
index e53b862..92857dd 100644
--- a/src/inkwell/serialize.py
+++ b/src/inkwell/serialize.py
@@ -7,6 +7,7 @@ from __future__ import annotations
 
 from .common import iso
 from .models.label import Label
+from .models.user import User
 
 
 def serialize_label(label: Label) -> dict:
@@ -24,3 +25,10 @@ def serialize_label_sync(label: Label) -> dict:
         "purged_at": iso(label.purged_at),
         "created_at": iso(label.created_at),
     }
+
+
+def serialize_person(user: User) -> dict:
+    """Someone as another member sees them: a name and an email, which is what
+    choosing them takes and all a fellow member needs to know. The share directory,
+    a share's recipient and a group's members all show people this way."""
+    return {"id": str(user.id), "display_name": user.display_name, "email": user.email}
diff --git a/src/inkwell/settings.py b/src/inkwell/settings.py
index 3d76510..37c26a1 100644
--- a/src/inkwell/settings.py
+++ b/src/inkwell/settings.py
@@ -3,7 +3,7 @@ from __future__ import annotations
 import json
 import secrets
 from dataclasses import dataclass
-from datetime import datetime, timezone
+from datetime import datetime, timedelta, timezone
 from typing import Any, Literal
 
 from .common import coerce_bool
@@ -394,6 +394,12 @@ def live(key: str) -> Any:
     return _live[key]
 
 
+def apply_session_ttl(app, days) -> None:
+    """Sessions signed from now on last `days` days. At boot and on every admin save,
+    so a changed lifetime applies without a restart (rule 25)."""
+    app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=int(days))
+
+
 async def refresh_live(db) -> None:
     """Re-read the hot settings into the cache. Called at boot and after every save."""
     for key in _LIVE_KEYS:
diff --git a/src/inkwell/settings_api.py b/src/inkwell/settings_api.py
index 2af9434..d0fc08b 100644
--- a/src/inkwell/settings_api.py
+++ b/src/inkwell/settings_api.py
@@ -1,7 +1,5 @@
 from __future__ import annotations
 
-from datetime import timedelta
-
 import logging
 
 from quart import Blueprint, current_app, g, jsonify, request
@@ -11,7 +9,7 @@ from .db import session_scope
 from .mailer import mail_settings, send
 from .responses import json_error
 from .models.user import User
-from .settings import get_admin_settings, get_setting, refresh_live, set_settings, validate_updates
+from .settings import apply_session_ttl, get_admin_settings, get_setting, refresh_live, set_settings, validate_updates
 
 logger = logging.getLogger(__name__)
 
@@ -50,7 +48,7 @@ async def update_settings():
 
     # Apply the live-tunable knob without a restart (rule 25).
     if "session_ttl_days" in clean:
-        current_app.config["PERMANENT_SESSION_LIFETIME"] = timedelta(days=int(clean["session_ttl_days"]))
+        apply_session_ttl(current_app, clean["session_ttl_days"])
 
     return jsonify({"settings": result})
 
diff --git a/src/inkwell/share_sync.py b/src/inkwell/share_sync.py
index 9d4451c..5652c83 100644
--- a/src/inkwell/share_sync.py
+++ b/src/inkwell/share_sync.py
@@ -80,6 +80,12 @@ async def granted(db, note_id: uuid.UUID, user_id: uuid.UUID) -> None:
 # cursor, and losing it leaves a revocation.
 
 
+async def revoke_lost(db, note_id: uuid.UUID, before: set[uuid.UUID]) -> None:
+    """After a share or a group goes: tell the devices of whoever could see the note
+    `before` and no longer can. Someone still reached another way keeps it."""
+    await revoke(db, note_id, before - await recipients(db, note_id))
+
+
 async def group_notes(db, group_id: uuid.UUID) -> list[uuid.UUID]:
     """The notes shared with this group."""
     rows = await db.scalars(
diff --git a/src/inkwell/shares_api.py b/src/inkwell/shares_api.py
index ce44a11..6a9798f 100644
--- a/src/inkwell/shares_api.py
+++ b/src/inkwell/shares_api.py
@@ -25,15 +25,12 @@ from .models.share import Share
 from .models.user import User
 from .notes.helpers import _get_owned
 from .responses import json_error, not_found, parse_uuid
-from .share_sync import bump_note, granted, recipients, revoke
+from .serialize import serialize_person
+from .share_sync import bump_note, granted, recipients, revoke_lost
 
 bp = Blueprint("shares", __name__, url_prefix="/api")
 
 
-def _member(user: User) -> dict:
-    return {"id": str(user.id), "display_name": user.display_name, "email": user.email}
-
-
 def _group(group: Group, counts: dict) -> dict:
     return {"id": str(group.id), "name": group.name, "member_count": counts.get(group.id, 0)}
 
@@ -64,7 +61,7 @@ async def directory():
         ).all()
         groups = (await db.scalars(select(Group).order_by(func.lower(Group.name)))).all()
         counts = await _member_counts(db, [gr.id for gr in groups])
-    return jsonify({"members": [_member(u) for u in users], "groups": [_group(gr, counts) for gr in groups]})
+    return jsonify({"members": [serialize_person(u) for u in users], "groups": [_group(gr, counts) for gr in groups]})
 
 
 async def _shares_of(db, note_id: uuid.UUID) -> list[dict]:
@@ -83,7 +80,7 @@ async def _shares_of(db, note_id: uuid.UUID) -> list[dict]:
     return [
         {
             "id": str(share.id),
-            "member": _member(user) if user is not None else None,
+            "member": serialize_person(user) if user is not None else None,
             "group": _group(group, counts) if group is not None else None,
             "permission": share.permission,
             "created_at": iso(share.created_at),
@@ -167,9 +164,7 @@ async def unshare_note(note_id: str, share_id: str):
         before = await recipients(db, note.id)
         await db.delete(share)
         await db.flush()
-        # Only the people who can no longer see it: someone still reached through a
-        # group keeps the note on their devices.
-        await revoke(db, note.id, before - await recipients(db, note.id))
+        await revoke_lost(db, note.id, before)
         # The owner's devices learn the note is no longer shared.
         await bump_note(db, note.id)
         await db.commit()
diff --git a/src/inkwell/unfurl_queue.py b/src/inkwell/unfurl_queue.py
index 37090d8..8de071f 100644
--- a/src/inkwell/unfurl_queue.py
+++ b/src/inkwell/unfurl_queue.py
@@ -30,6 +30,7 @@ import uuid
 
 from sqlalchemy import select
 
+from .common import detach
 from .db import session_scope
 from .models.note import Note
 from .models.note_link_preview import NoteLinkPreview
@@ -118,10 +119,8 @@ def schedule(note_id: uuid.UUID, body: str | None) -> None:
     if not body or not detect_urls(body):
         return
     try:
-        task = asyncio.create_task(_unfurl_new_urls(note_id, body))
+        detach(_running, _unfurl_new_urls(note_id, body))
     except RuntimeError:
         # No running loop — a script or a test calling the write path directly. The
         # note is saved either way; only the preview is skipped.
         return
-    _running.add(task)
-    task.add_done_callback(_running.discard)
diff --git a/tests/test_retention.py b/tests/test_retention.py
index 3b68a36..2f06371 100644
--- a/tests/test_retention.py
+++ b/tests/test_retention.py
@@ -2,11 +2,11 @@ from datetime import datetime, timedelta, timezone
 
 import pytest
 
+from inkwell.common import expired_before
 from inkwell.retention import (
     SWEEP_BATCH,
     SWEEP_INTERVAL_SECONDS,
     SWEEP_STARTUP_DELAY_SECONDS,
-    expired_before,
     sweep_expired_trash,
 )
 from inkwell.settings import REGISTRY, get_public_config, validate_updates