ds-chat/backend

DS Chat backend (Phase 1 + 2 + 4 + 5 + 6 + 7 + 8, image uploads, file attachments, admin-configurable upload size limits, emoji & reactions, user profiles, site invites & email, password reset, direct messages, active sessions)

FastAPI + SQLAlchemy 2.0 (async) + PostgreSQL + Redis. Implements auth (server-side, revocable sessions — see Active sessions below), room CRUD (open and private), room roles (owner/admin/member) and direct membership management, direct messages, a WebSocket chat endpoint that fans out across multiple app-server instances via Redis pub/sub, Web Push and email notifications for offline room members (plus a native desktop-notification bridge for DS Chat Desktop), a site-admin portal (user/room/bot management + an audit log), a bot/extension layer (scoped API tokens, live bot WebSocket access, incoming and outgoing webhooks, message editing), image uploads, inline-playable video attachments, and generic file attachments in chat messages, message deletion, emoji reactions (built-in Unicode plus site-wide custom/uploaded emoji, both usable in reactions and inline in message text), self-service user profiles (display name, avatar), self-service password change and a token-based forgot-password flow, and admin-issued email invites for new accounts plus email notifications when a user is added to a room. See ../ARCHITECTURE.md for the full system design and the phased build plan.

This is an invite-only site: there is no public registration endpoint. Accounts are created by an operator on the app server — see step 4 below.

Local dev setup

1. Postgres

Any local Postgres 14+ works. The quickest option is a container:

docker run -d --name ds-chat-postgres \
  -e POSTGRES_USER=ds_chat -e POSTGRES_PASSWORD=ds_chat -e POSTGRES_DB=ds_chat \
  -p 5432:5432 postgres:16-alpine

Then create the test database (used by the test suite, kept separate from dev data):

docker exec ds-chat-postgres psql -U ds_chat -d ds_chat -c "CREATE DATABASE ds_chat_test;"

(Docker here is purely a local-dev convenience for standing up Postgres quickly — the actual deployment target has no containers at all, see ARCHITECTURE.md §9.)

2. Redis

Used for cross-instance WebSocket fan-out and presence (see the section below). Required — there's no in-memory fallback.

docker run -d --name ds-chat-redis -p 6379:6379 redis:7-alpine

3. Python environment

cd backend
python3 -m venv .venv
.venv/bin/pip install -e ".[dev]"
cp .env.example .env
# edit .env: set SESSION_SECRET to a long random string, e.g.
#   python3 -c "import secrets; print(secrets.token_urlsafe(32))"

4. Migrations

.venv/bin/alembic upgrade head

5. Create a user

There's no public sign-up. Create accounts directly with the CLI (add --admin to grant is_site_admin, which unlocks the admin portal at /admin on the frontend and the /api/admin/* routes below):

.venv/bin/python -m app.cli create-user alice alice@example.com "some-password"

6. (Optional) Set up push notifications

Push works without any setup — VAPID_PUBLIC_KEY/VAPID_PRIVATE_KEY are unset by default and push delivery is silently skipped. To enable it:

.venv/bin/python -m app.cli generate-vapid-keys
# paste the three printed lines into backend/.env

7. Run the dev server

.venv/bin/uvicorn app.main:app --reload

API docs: http://localhost:8000/docs. WebSocket chat endpoint: ws://localhost:8000/ws/chat.

To try horizontal scaling locally, run a second instance on another port against the same Postgres + Redis (.venv/bin/uvicorn app.main:app --port 8001) — a message sent through one instance's WebSocket is delivered to clients connected to the other, purely via Redis.

8. Run tests

Tests run against a real Postgres database (ds_chat_test by default — native ENUM/UUID types aren't faithfully reproduced by SQLite) and a real Redis (db 15 by default, kept separate from dev use of db 0), with each test wrapped in a transaction that's rolled back afterward:

DATABASE_URL=postgresql+asyncpg://ds_chat:ds_chat@localhost:5432/ds_chat_test .venv/bin/pytest

Layout

app/
  main.py            create_app(), session middleware, router/WS mounting,
                        serves frontend/dist if it exists (see below)
  config.py           environment-driven settings (pydantic-settings)
  database.py          async engine/session, get_db() dependency
  dependencies.py       get_current_user (session cookie or Bearer token),
                           require_room_member, require_room_role,
                           require_site_admin, require_scope
  security.py            argon2 password hashing + token generate/hash (sha256)
  crypto.py               Fernet encrypt/decrypt keyed from SESSION_SECRET --
                             the only reversible secret this app stores in
                             the database (SMTP password), see Site invites
                             & email below
  storage.py              uploaded-image validation (Pillow), downscaling
                             (optionally square-cropped, for avatars), and
                             on-disk save/read -- see Image uploads below
  cli.py                  `python -m app.cli create-user` / `generate-vapid-keys`
  models/                 SQLAlchemy models (users, rooms, room_memberships,
                             messages, message_images, message_files,
                             message_reactions, message_mentions,
                             message_room_references, link_previews,
                             custom_emoji, custom_themes, sessions,
                             site_invites, password_resets, smtp_settings,
                             upload_settings, push_subscriptions,
                             admin_audit_log, api_tokens, webhooks_incoming,
                             event_subscriptions)
  schemas/                 Pydantic request/response models
  routers/                  auth, rooms, users, signup, push, admin,
                               bots, webhooks, health
  services/                  business logic called by routers
  ws/                        connection_manager (local sockets), presence +
                               broadcaster (Redis), /ws/chat handler
alembic/                      migrations
tests/                         pytest + httpx/TestClient tests

Production deployment (Phase 8)

See ../DEPLOYMENT.md for the full runbook. The one piece that lives in this backend's own code: app/main.py serves the built frontend directly (mounts frontend/dist/assets with far-future Cache-Control on Vite's content-hashed filenames, and a catch-all route that serves any other real file under frontend/dist or falls back to index.html for client-side routes like /rooms/<id> — index.html/ sw.js/manifest.webmanifest always get Cache-Control: no-cache instead, since caching any of those is exactly how a client ends up stuck on a stale app version after a deploy) — but only if frontend/dist exists at startup. It never does in local dev (the Vite dev server handles the frontend there instead), so this is fully inert until someone actually runs npm run build. The point: one Gunicorn port ends up serving the frontend and /api and /ws, which is what lets a reverse proxy (Nginx Proxy Manager, in the deployment this was built for) forward a whole domain to a single upstream with no custom per-path routing.

Admin portal (Phase 6)

Every /api/admin/* route (app/routers/admin.py) requires current_user.is_site_admin (checked via require_site_admin, app/dependencies.py) and is backed by app/services/admin_service.py:

• Users: list, deactivate/reactivate (User.is_active), reset password, promote/demote is_site_admin. An admin can't deactivate or demote their own account (CannotActOnSelfError → 400) — the one guard against an admin locking themselves out. Deactivation takes effect immediately, even for an already-open session: get_current_user re-checks is_active on every request since it already loads the user row.
• Rooms: list every room including private ones (unlike the member-facing GET /api/rooms, which is open-rooms-only), archive/ unarchive (Room.is_archived — archived rooms drop out of the open-room browse list but stay readable for existing members, matching how Mattermost archive works), and force a transfer of ownership to any existing member without needing to already be the owner (the "admin override" of the member-initiated transfer in room_service.py, which otherwise requires exactly that).
• Audit log: every mutating admin action writes one AdminAuditLog row (actor, action, target type/id, JSON metadata) in the same transaction as the change, listed newest-first via GET /api/admin/audit-log.

Bot/integration management (deferred from this phase originally) is now in place — see Phase 7 below. One item is still deliberately not here:

• System settings — no settings storage or concrete setting exists yet. The frontend has an empty "Settings" tab as a placeholder for when one does.

Bot/extension system (Phase 7)

Bots are User rows with is_bot=True (app/services/bot_service.py, admin-only, /api/admin/bots/*) — a generated-and-discarded password since bots never log in with one, and a {username}@bots.example.com placeholder email (.local/.invalid are rejected by EmailStr's special-use-TLD check; a subdomain of the real, if reserved-for-docs, .com isn't). A bot authenticates instead with a scoped API token (read:messages, write:messages, manage:rooms) — shown once at issuance, stored as a SHA-256 hash (security.hash_token, deliberately not argon2: a bearer token has to be looked up by itself with no username to key off first, which argon2's per-call random salt makes impossible; a fast hash of a 256-bit random token is the standard approach, same as GitHub/Stripe keys).

Auth: get_current_user (app/dependencies.py) checks for an Authorization: Bearer header before falling back to the session cookie; a resolved token is stashed on request.state.api_token so require_scope can gate specific actions. A token-authenticated bot is subject to the exact same room-membership/role checks as a session-authenticated human on every existing endpoint — the token only narrows things further, it doesn't grant anything a plain room membership wouldn't. Only read:messages/write:messages are actually scope-gated (on GET /api/rooms/{id}/messages and the WS message/edit handlers) — manage:rooms is a recognized, issuable scope with no separate enforcement yet, so a bot's room-management ability is bounded by its ordinary room role, same as any user; wiring real manage:rooms gating into the dozen room-management endpoints was cut from this phase's scope (confirmed with the repo owner) as disproportionate to the win. The WS handshake (app/ws/chat.py) accepts the same header directly (bots set it on the handshake; browsers use the cookie) — same /ws/chat endpoint a human client uses, per ARCHITECTURE.md's "same connection type" design.

Message editing: {"type": "edit", "room_id", "message_id", "content"} over the existing WS connection (message_service.edit_message — 403 if you're not the author), broadcasts {"type": "message_update", ...} via the same RoomBroadcaster.publish() new messages use, so it fans out cross-instance for free. Message.edited_at (present in the schema since Phase 1, unused until now) is exposed on MessageRead. The frontend also gets a minimal "edit your own message" UI affordance (hover a bubble you own) — not asked for by the issue, but the only practical way to exercise the pipeline by hand instead of only via a scripted bot client, and it's a small addition once the WS envelope exists anyway.

Incoming webhooks (POST /api/rooms/{id}/webhooks/incoming, room-admin managed, mirrors how invites are nested under rooms): a room-scoped URL with no auth beyond the token in it being correct (webhooks_incoming.token is stored in the clear, unlike API tokens — the room admin needs to view/copy the full URL anytime). POST /api/webhooks/incoming/{token} (public, no auth dependency) creates a message attributed to the webhook's creator and runs the identical post-message pipeline a WS-originated message does (app/services/message_events.py's broadcast_new_message, shared by both call sites rather than duplicated).

Outgoing webhooks / event subscriptions (POST /api/rooms/{id}/event-subscriptions, room-admin managed; room-scoped or global via room_id=null): fires an HMAC-SHA256-signed POST (X-DS-Chat-Signature: sha256=...) on message.created/ message.updated, delivered via a backgrounded asyncio.create_task (app/services/webhook_delivery.py) — safe to background here, unlike the Phase 4 push lesson, since there's no DB session involved, just the already-serialized payload and secret. Fire-once, no retry/backoff — a failed delivery is logged and dropped, documented limitation, not a guarantee.

SSRF protection (app/services/ssrf.py): target URLs are validated at subscription-creation time — non-http(s) schemes rejected, hostname resolved and rejected if any address is private/loopback/link-local/ reserved/multicast. Not re-validated per delivery, so DNS rebinding between creation and a later send isn't defended against — a real gap, deliberately left open (confirmed with the repo owner) rather than building the meaningfully more involved per-request IP-pinning that would close it.

Rate limiting: ARCHITECTURE.md calls for rate-limiting bot API calls the same as human ones. Not implemented — there's no rate limiting anywhere in the app today (human or bot) to extend, and building one well is its own scope. Documented gap, not an oversight.

Cross-instance broadcast (Phase 5)

The WebSocket layer is split into three pieces so that running one app instance and running many behave identically:

• app/ws/connection_manager.py — purely local: which sockets on this process are in which room, used only to actually send_json to them.
• app/ws/broadcaster.py (RoomBroadcaster) — on a chat message, publish()s it to a Redis channel scoped to the room (room:{id}). Every app instance, including the publisher, runs a single background listen() task (started in app/main.py's lifespan) pattern-subscribed to room:*; each message it receives is handed to its own local ConnectionManager.broadcast(). One instance just talks to itself through Redis, so there's no separate single-instance code path.
• app/ws/presence.py (Presence) — a Redis hash per room (presence:{room_id}, field = user ID, value = connection refcount) is the cross-instance answer to "is this member connected anywhere right now," which is what the Phase 4 offline-push check uses instead of the local ConnectionManager. Refcounted so a user connected from two tabs (or two instances) isn't marked offline until every connection closes.

Known limitation: Presence has no heartbeat/TTL, so a hard process crash (not a clean disconnect) leaks that connection's increment forever — same category of simplification as the "no server-side session revocation" note below.

Push notifications (Phase 4)

POST /api/push/subscribe (upserts by endpoint) / DELETE /api/push/subscribe manage a user's push_subscriptions rows; GET /api/push/vapid-public-key gives the frontend the key it needs for PushManager.subscribe(). On every chat message, app/services/message_events.py computes room members - Presence.connected_user_ids(room_id) - {sender} (who's actually connected to that room right now, across every app instance — see Phase 5 below; the sender is subtracted explicitly rather than relied on to be "connected," since that's only true for WS-originated messages, not the Phase 7 incoming-webhook path) and sends each offline member a push via pywebpush, awaited inline against the same request-scoped session rather than fired as a background task — the broadcast to online members already happened by that point, so nothing online-facing is delayed, and it sidesteps asyncio.create_task()s outliving the session/event loop they were created on. An expired/invalid subscription (pywebpush 404/410) is deleted automatically.

Desktop notifications

DS Chat Desktop (a separate Electron wrapper, not this repo) has no push delivery service configured, so it can't receive Web Push. Instead, app/services/message_events.py's existing offline-member computation (room members - Presence.connected_user_ids(room_id) - {sender} — the same audience Web Push uses, described above) also broadcasts a desktop_notification WS envelope ({type, id, room_id, title, body}, id being the message's own id so the client can dedupe across reconnects) to every eligible offline member over their already-open authenticated socket, unconditionally — the server has no notion of which clients are running inside Electron. It's sent alongside the Web Push send, not instead of it, so a member with only a browser tab open is unaffected.

The client decides whether to act on it: frontend/src/lib/desktopBridge.ts feature-detects window.dsDesktop (the bridge Electron's preload script exposes, per-method rather than via user-agent sniffing — an older wrapper build may be missing individual methods) and only calls showNotification when the bridge is present and the user's localStorage-backed preference (ds-chat-desktop-notifications-enabled, default on) allows it. This preference is deliberately a plain client-side flag rather than reusing PushSubscription — desktop notifications need no server round trip to enable/disable, unlike a push subscription which has a row to create/delete. frontend/src/components/DesktopNotificationBridge.tsx is mounted once, as a sibling of the routed pages inside the user.id-keyed ChatSocketProvider, so it subscribes exactly once per authenticated session; it also wires window.dsDesktop.onNotificationClick to navigate to the notification's room.

No User/PushSubscription schema change was needed for this feature — the only backend change is the new desktop_notification envelope type, covered by backend/tests/test_desktop_notifications.py.

Email notifications for missed messages

Two related, separately-scoped email triggers layered on top of Web Push/ desktop notifications, both in app/services/message_events.py:

DMs (_maybe_email_dm_notification) — always on, no opt-in toggle. Emails a DM's other participant when they're genuinely offline (GlobalPresence.is_online, not just "not connected to this room's own channel" the way the Web Push/desktop-notification audience is computed — someone actively using the app in a different room shouldn't get emailed for a DM) or have appear_offline set. Debounced to the first unread message in the conversation, not one email per message in a burst, by checking whether any other unread message already exists in the room since the recipient's last_read_at.

Regular rooms (_maybe_email_room_notifications) — opt-in per member, per room (RoomMembership.email_notifications, toggled via PATCH /api/rooms/{id}/notifications; rejected for a DM — CannotModifyDmError → 400 — since DMs already get the always-on behavior above). Two triggers, not one: the room's first unread message debounces the same way DMs do, but a message that @mentions the subscriber always emails regardless of that debounce — a mention is a stronger, individually-addressed signal that shouldn't get silently absorbed by an earlier plain message in the same burst already having used up the "first unread" email.

Both paths go through the same email_service.send_email used by invites/room-membership notifications above, so they're silently skipped if SMTP isn't configured and never block message delivery on an SMTP outage.

Room roles and membership (Phase 2)

Rooms can be open (anyone can join via POST /api/rooms/{id}/join) or private (is_private: true at creation — joinable only by being added). Room roles are owner > admin > member:

• member: post messages, leave the room
• admin: edit room settings, add/remove plain members
• owner: everything admin can, plus delete the room, remove admins, change member roles, and transfer ownership

Adding to a private room: an admin+ calls POST /api/rooms/{id}/members with an existing user's user_id — this adds them straight to room_memberships (no accept/decline step) and fires a "you've been added" notification email (see Site invites & email below; silently skipped if SMTP isn't configured). There used to be a separate accept/decline RoomInvite flow here; it was removed in favor of direct add + notify, since nothing meaningful was gained by making the target confirm first. GET /api/rooms/mine lists every room (open + private) the current user belongs to, alongside their role.

Direct messages

A DM is a Room with is_dm=True and a deterministic, never-shown internal name (dm_room_name(user_a, user_b) — the two user ids sorted and joined, so it's the same string regardless of who initiates), not a separate model — POST /api/rooms/dm (find_or_create_dm) looks up an existing DM by that name and creates one (is_private=True, both participants as plain member) only if none exists yet, so starting a DM with the same person twice always resolves to the one conversation. The frontend never renders Room.name for a DM; MyRoomItem.dm_partner (DmPartnerInfo: the other participant's id/username/display name/avatar/status) is precomputed server-side instead, batched per request rather than N+1.

Hiding a DM: RoomMembership.hidden_at lets one participant remove a DM from their own sidebar without touching the other participant's copy or deleting anything — a DM has no sensible "leave" (it would violate find_or_create_dm's exactly-two-members assumption). POST /api/rooms/{id}/hide sets it; it's cleared automatically (un-hiding the DM) whenever a new message arrives in it or find_or_create_dm resolves back to an already-hidden one — both count as the conversation being active again, matching how a re-opened DM in Slack/Discord reappears on its own rather than needing an explicit "unhide."

Message deletion

DELETE-shaped over WS ({"type": "delete", "room_id", "message_id"}, message_service.delete_message) — author-only (NotMessageAuthorError → error frame otherwise, no admin/moderator override yet). A real delete of content, not a UI-only hide: content, image_id, file_id, and preview_url are all cleared and any attached MessageImage/MessageFile row (plus its on-disk file) is actually removed, only deleted_at (and id/room_id/user_id/created_at, so the tombstone still occupies its place in history) survives. The attachment's storage filename is read and the DB row/file only unlinked after a successful commit — same ordering delete_room already uses, so a rolled-back transaction never leaves an already-destroyed file with no way back. Broadcasts {"type": "message_deleted", "id", "room_id"}; the frontend renders a "message deleted" placeholder rather than removing the row, so the conversation doesn't visibly shift when someone deletes something above.

Image uploads

A message can carry an image (Message.image_id, nullable), a caption (Message.content, nullable), or both — a CheckConstraint requires at least one. Images live on the app server's local disk (<repo root>/uploads, resolved the same way app/main.py locates frontend/dist — see app/storage.py), not S3, matching this project's plain-two-servers deployment; see ../DEPLOYMENT.md for the production directory and its (currently missing) backup coverage.

• POST /api/rooms/{room_id}/images (room-member gated, multipart) — app/storage.read_capped rejects (413) as soon as the streamed byte count passes 8 MB, before buffering the whole body. app/storage.process_image then opens the result with Pillow to confirm it's a genuinely decodable image (not just a spoofed Content-Type header — 400 if not) and downscales it so its longer side is ≤2000px, except GIF, left untouched so animation isn't collapsed to a single frame. Returns the new message_images row's id; the frontend attaches it to a message afterward, it isn't a message by itself.
• GET /api/rooms/{room_id}/images/{image_id} (room-member gated) — 404s if the image doesn't belong to that room, otherwise streams it with Cache-Control: private, max-age=31536000, immutable (content-addressed by a generated UUID filename, so once served it never changes).
• The WS "message" handler (app/ws/chat.py) accepts an optional image_id, validated against the room before attaching. Push notification bodies (app/services/message_events.py) say "{username} sent an image" for an image-only message instead of a body that's just "username: ".

Known gap: an uploaded-but-never-sent image (a user attaches a file, then navigates away before hitting Send) leaks an orphaned file on disk — no cleanup job for this yet. Not a security issue, since serving still goes through the same room-membership gate as everything else; just an eventual disk-space housekeeping item.

File attachments

A message can also carry a generic file attachment (Message.file_id, nullable, alongside the pre-existing content and image_id) — a parallel MessageFile model/table, not a generalization of MessageImage, so the working image feature stayed untouched. app/storage.py's save_image/delete_image were content-agnostic already (no Pillow usage) and were renamed to save_file/delete_file now that both features share them; ImageTooLargeError was likewise renamed to UploadTooLargeError.

• POST /api/rooms/{room_id}/files (room-member gated, multipart) — same 8 MB cap as images (MAX_FILE_BYTES, currently an alias of MAX_IMAGE_BYTES; a real, independently-configurable size-limit redesign is a separate later task — see the open file/image size-limit issue), but no content-type allowlist — arbitrary file types are the point of this endpoint, unlike /images.
• GET /api/rooms/{room_id}/files/{file_id} (room-member gated) — 404s if the file doesn't belong to that room, otherwise streams it via FileResponse(..., filename=...). Passing filename= makes Starlette set Content-Disposition: attachment, which forces a download in the browser regardless of content-type — the deliberate mitigation against a user-uploaded .html/.svg executing script same-origin (session-cookie theft) if opened directly. This is why there's no content-type blocklist on top of it: forcing a download already neutralizes that whole class of risk.
• The WS "message" handler and message_events.py push-body/broadcast logic mirror the image path exactly (an optional file_id, validated against the room; push body says "{username} sent a file" for a file-only message).

Same orphaned-upload disk-space caveat as images applies here too.

Inline video playback: a browser-natively-playable video attachment (INLINE_SAFE_VIDEO_CONTENT_TYPES in app/storage.py — a strict allowlist, video/mp4/video/webm/video/ogg, deliberately not "every video/* type") is served without the filename= param above, so it plays inline in a <video> tag instead of forcing a download — the same reasoning MessageImage's own always-inline endpoint already relies on: these are content types a browser only ever interprets as media, never as something that could execute script, so the Content-Disposition: attachment mitigation doesn't need to apply to them. Anything outside that allowlist (e.g. .mov/video/quicktime) still forces a download like any other file.

Upload size limits

The 8 MB image/file/avatar cap is no longer hardcoded — it's an admin-configurable site setting (UploadSettings, single-row table, same "fetch-or-create" convention as SmtpSettings), editable from the Admin portal's Settings tab. Unlike SmtpSettings (where "no row yet" means "unconfigured, skip"), a missing row here still needs a usable value, so upload_settings_service.get_upload_settings creates it with the 8 MB default (storage.DEFAULT_MAX_UPLOAD_BYTES) on first read instead of returning None.

• GET/PUT /api/admin/settings/uploads (site-admin only) — read/update the cap. Bounds-checked to 1–500 MB (UploadSettingsUpdate) to guard against a fat-fingered 0 or an unbounded figure that could exhaust disk.
• GET /api/uploads/limit — unlike the admin endpoints, this one is open to any authenticated user (same Depends(get_current_user)-only pattern as /api/push/vapid-public-key), since every room member needs to know the cap, not just admins. The frontend composer fetches it once per mount and rejects an oversized file client-side before ever hitting the network; the server still enforces the same value independently via read_capped(file, cap=...), so the client-side check is a UX nicety, not the actual security boundary.
• All three upload endpoints (room image, room file, avatar) now call get_upload_settings(db) and pass the live value into read_capped instead of relying on a module-level constant; their 413 error messages interpolate the actual configured limit (upload_settings_service. format_mb) rather than a hardcoded "8 MB" string.

Emoji & reactions

The built-in emoji picker in the frontend composer is purely client-side (a static curated unicode list, no backend involvement). Message reactions are full-stack: message_reactions (app/models/message_reaction.py) has message_id, user_id, emoji, and a UniqueConstraint on all three backing toggle semantics — the same user reacting with the same emoji on the same message twice removes it (Slack/Mattermost convention). message_service.toggle_reaction is a plain select-then-delete-or-insert, no upsert needed. emoji is String(32), sized to hold either a raw unicode glyph or a custom emoji's :shortcode: reference (see Custom emoji below) — the WS reaction envelope's own length check matches this exactly, not an arbitrary smaller cap.

WS "reaction" envelope (room_id, message_id, emoji) toggles a reaction; the server broadcasts the message's full recomputed reaction list ({"type": "reaction_update", "id", "room_id", "reactions": [...]}), not an add/remove delta — same approach message_update already uses for edits, keeping client-side state a simple replace rather than a merge. GET /{room_id}/messages embeds each message's reactions too (message_service.get_reactions_for_messages, batched, not N+1), so a page reload doesn't lose reaction state that only ever arrived over WS.

Scope cuts: no outgoing-webhook event type for reactions (VALID_EVENT_TYPES in webhook_service.py is unchanged — same restraint as image uploads), no reaction-count limit or rate limiting.

Custom emoji

Site-wide (not room-scoped), uploadable by any authenticated user — distinct from the built-in Unicode picker above. CustomEmoji (app/models/custom_emoji.py): shortcode (unique, 30 chars max — sized so a :shortcode: reference fits MessageReaction.emoji's column alongside its own colons with zero width change), storage_filename, content_type, uploaded_by.

• POST /api/custom-emoji (multipart: shortcode form field + file) — reuses app/storage.py's upload primitives (read_capped, process_image(..., square=True, max_dimension=128), save_file), same pattern as avatars. Shortcode format (^[a-z0-9_-]{2,30}$) and uniqueness are checked before processing/saving the image, so a rejected upload never orphans a file on disk.
• GET /api/custom-emoji — full list, any authenticated user.
• DELETE /api/custom-emoji/{id} — the uploader or a site admin only (NotEmojiOwnerError → 403 otherwise).
• GET /api/custom-emoji/{shortcode}/image — serves the file, Cache-Control: private, no-cache (not immutable, and deliberately not a long max-age either — a shortcode can be deleted and re-uploaded with different image data under the same URL, and a timed cache let a browser keep serving the old image for its full duration after that happened; no-cache forces revalidation on every use, still cheap since FileResponse's own ETag/Last-Modified make an unchanged file a 304, not a full re-transfer).

A :shortcode: reference is stored/sent as literal text everywhere (message content, reaction values) and resolved to an image only at render time on the frontend — the same convention the built-in Unicode shortcode autocomplete already used for glyphs, extended to a case with no unicode codepoint to substitute. No server-side collision check against the ~950 built-in shortcode names (that list only exists in the frontend); the upload UI warns about a colliding name but doesn't hard-block it.

User profiles

Display name and avatar live directly on User (display_name, avatar_filename, avatar_content_type, all nullable) — no separate profile table, since it's a strict 1:1 with no room-scoping concern the way message images have. Bio was considered and explicitly scoped out.

• PATCH /api/auth/me — updates display_name (app/routers/auth.py). Empty/whitespace clears it back to None, falling back to the username everywhere it's displayed.
• POST /api/auth/me/avatar / DELETE /api/auth/me/avatar — reuse app/storage.py's upload primitives (read_capped, process_image, save_file) from image uploads, but call process_image(..., square=True, max_dimension=512) — a new option that center-crops before downscaling, since avatars need a fixed square shape at a much smaller size than a message image. Unlike message images (which never delete), the previous avatar file is deleted on replace/remove (storage.delete_file) — safe to do here because it's strictly one file per user, no accumulation risk to accept the way an orphaned message-image upload has.
• GET /api/users/{user_id}/avatar (app/routers/users.py, new router) — serves the file. Two deliberate divergences from the message-image serving endpoint: not room-membership-gated (avatar visibility matches username visibility — any authenticated user can see anyone's), and Cache-Control: private, max-age=300 rather than immutable (an avatar URL is identity-addressed and its content changes on re-upload, unlike a message image's permanent content-addressed URL).

RoomMemberRead and AdminUserRead both carry display_name/ avatar_filename so the frontend can render an avatar and a preferred name anywhere a user appears (message list, room member list, admin Users tab, TopBar) — MessageRead deliberately does not carry them; the frontend resolves both live from the room's member list instead of freezing them per-message, which is the more correct behavior for a field the sender can change after the fact.

Site invites & email

Two related gaps closed together: creating a new account was CLI-only, and neither a brand-new invitee nor an existing user added to a room got any notification. Site admins (only) invite a brand-new person by email from the Admin portal; being added directly to a room (see Room roles and membership above) sends a "you've been added" email too.

Email sending (app/services/email_service.py, using aiosmtplib): send_email(db, to, subject, paragraphs, *, cta_label=None, cta_url=None, theme_user=None) is the fire-and-forget path used by invite/notification flows — if SmtpSettings isn't configured yet it logs (at .warning, not .debug — this app has no logging config lowering the root level below Python's own WARNING default, so anything below that is silently invisible in production) and returns, and it never raises on delivery failure (an SMTP outage must not block an invite/membership/notification action that already succeeded in the database). send_test_email(db, to) is the one exception — used only by the admin "send test email" button, it raises so the UI can show why it failed instead of a silent no-op. paragraphs (a list[str], not a flat body: str) renders both an HTML email — styled with theme_user's own selected theme palette when given, falling back to the default palette — and a plain-text fallback part from the same source, rather than a single pre-formatted string that can't cleanly become HTML without re-parsing it.

SMTP configuration (app/models/smtp_settings.py, app/routers/admin.py's /settings/smtp endpoints) lives in the database, not the env file — the Admin Settings tab edits it at runtime with no redeploy. It's the first reversible secret this app stores in the database (password_hash is one-way, API tokens are looked up by hash and never decrypted), so it's encrypted at rest via app/crypto.py: a Fernet key derived from the already-required SESSION_SECRET rather than a new env var. A blank password on update means "keep the current one" — the frontend never has the plaintext to send back, only whether one is set (has_password).

Site invites (app/models/site_invite.py, app/services/site_invite_service.py) — distinct from adding an existing user to a room: this targets an email address for the site, no room involved. The raw token exists only in the email link, stored hashed (security.hash_token, the same convention API tokens use — it's a bearer secret looked up by itself). POST /api/signup (app/routers/signup.py) is the first genuinely public, unauthenticated endpoint in this app that creates a User row — it calls the existing auth_service.register_user directly for identical hashing/uniqueness handling, then session_service.start_session (see Active sessions below) so they land in the app already signed in. No new rate limiting on it — the unguessable, single-use, expiring token is the actual protection, inheriting the same "no rate limiting on human/bot traffic" gap already documented below, not a new one.

POST /api/admin/invites/{id}/resend (site-admin only, resend_site_invite) issues a fresh token and resets the 7-day expiry rather than re-sending the original link — the old link stops working the moment this runs, and it means resending something close to expiring buys the full week again, not just whatever was left. Only valid for a still- pending invite (SiteInviteNotPendingError otherwise).

Room-membership email: room_service.add_member sends one email to the target user after creating the RoomMembership, using the live request's base_url for the link — no new "public URL" config needed.

Scope cuts: no outgoing-webhook event type for these (matching image uploads/reactions).

Self-service password change and reset

Two related, previously-missing pieces: a logged-in user changing their own password, and a "forgot password" flow for someone locked out.

Change password (PATCH /api/auth/password, authenticated) — takes current_password + new_password; verifies the current one with security.verify_password before setting password_hash = hash_password(new_password). Same self-service shape as PATCH /api/auth/me (profile update): mutate current_user, commit, done. Doesn't proactively revoke any other logged-in session for that account — a session table now exists (see Active sessions below), but changing your password doesn't walk it and revoke everything else; if you suspect a specific device, use Active sessions to revoke it directly instead.

Forgot password (app/models/password_reset.py, app/services/password_service.py) — same hashed-token-with-expiry shape as site invites, but a shorter 15-minute lifetime (a reset link is meant to be used immediately, unlike a signup invite someone might not open for days) and a boolean used flag instead of an enum (there's no third state to track). POST /api/auth/forgot-password always returns 204, whether or not the email matched an account — the response must never reveal which emails are registered, so a miss is a silent no-op (no row created, no email sent) after a single SELECT. GET /api/auth/reset-password/validate lets the frontend show a "this link is invalid" state before rendering the password form. POST /api/auth/reset-password completes it and — like signup — logs the user in immediately (session_service.start_session, see Active sessions below), since they've just proven they control the account's email.

Scope cuts: no rate limiting on /forgot-password (inherits the same documented gap as every other endpoint below, not a new one — the unguessable expiring token is the actual protection once a request is made), no cleanup job for expired/used password_resets rows (same as site_invites, which has never had one either).

Active sessions

Replaces the previously-stateless signed cookie (a bare user_id) with a real server-side Session table (app/models/session.py) — the cookie now only ever carries an opaque session id, resolved against this table via session_service.resolve_session on every request (get_current_user in app/dependencies.py, and the WS handshake in app/ws/chat.py), which is the single choke point that makes revocation actually take effect on a session's very next request rather than only once its cookie happens to expire.

Each row records ip_address (X-Forwarded-For's first entry, since production sits behind Nginx Proxy Manager — falls back to the direct peer address with nothing in front locally), user_agent, created_at, and a throttled last_seen_at (only bumped if stale by more than 5 minutes — get_current_user resolves a session on every authenticated request, so writing on every single one would turn a read into a write storm for no real benefit). session_service.start_session is the one place every "log this browser in" call site (login, signup completion, password-reset completion) creates the row and stashes its id in the cookie.

• GET /api/auth/sessions — every non-revoked session for the current user, newest-last-seen first, with a parsed "Browser on OS" label (app/services/user_agent_service.py — plain substring checks against the User-Agent header, no new dependency; special-cases an Electron/ token as "DS Chat Desktop" rather than the underlying Chromium version) and is_current (compares against request.state.session_id, set by get_current_user) so the frontend can label "this device" and treat revoking it as a self-logout.
• DELETE /api/auth/sessions/{id} — any of the current user's own sessions, including their own current one (a remote sign-out of the same device is a legitimate thing to do); 404 if it belongs to someone else or is already revoked.
• POST /api/auth/logout also revokes the session row, not just clears the cookie (revoke_session_unchecked — no ownership check needed, since a session can only ever log itself out, and never fails even if the row is already gone).

Scope cuts: changing your password doesn't proactively revoke other sessions (see Self-service password change and reset above) — this is a deliberate scope boundary, not an oversight, since it's a meaningfully different feature (auto-revoke-everywhere-on-password-change) from "let a user see and manually revoke what's logged in."

Link previews

Slack/Discord-style unfurling: the first http(s):// URL found in a message's content (link_preview_service.extract_first_url) gets a small preview card fetched from that page's Open Graph tags (og:title, og:description, og:image, og:site_name, falling back to <title>).

• Never blocks the send. create_message extracts and stores the URL on Message.preview_url synchronously (cheap, no I/O), but the actual fetch runs in a background asyncio.create_task from message_events.broadcast_new_message/broadcast_message_update, on its own DB session (async_session_factory(), never the caller's session — see push_service.send_push_to_user's docstring for why sharing a session across a fire-and-forget task is unsafe). Once it resolves, a separate "link_preview" WS envelope carries the result to the room; the initial "message"/"message_update" broadcast always has link_preview: null.
• SSRF protection is the real security boundary here, more so than for outgoing webhooks — a webhook's target_url is admin-configured, but a link-preview URL comes from any room member's message content. Reuses app/services/ssrf.py's validate_target_url (originally webhook-only, the exception renamed from UnsafeWebhookUrlError to UnsafeUrlError now that it's shared), but re-validates before every hop of a redirect chain instead of once up front — redirects are followed manually (httpx.AsyncClient(follow_redirects=False)) specifically so each intermediate URL is checked before it's ever connected to, not after. Same accepted DNS-rebinding gap as the webhook case (see that module's docstring); response body capped at 512 KB and only fetched if Content-Type is text/html.
• Cached by URL, not by message (link_previews table, unique on url) — a URL posted by five different people in five different rooms within the same short window fetches once. A row also gets written on a failed fetch (fetch_failed=True) so a URL that genuinely doesn't unfurl (SSRF rejection, timeout, no usable title) isn't re-attempted on every message that references it; both kinds expire after 5 minutes (_CACHE_TTL — #70: was 7 days, confirmed live as far too long, a re-posted URL whose title/content had genuinely changed kept showing the stale first-fetch preview for up to a week).
• Parsed with stdlib html.parser.HTMLParser, not a new dependency — only meta-tag scraping is needed, not general HTML parsing.
• Editing a message re-extracts the URL; if it changed or was removed, the frontend clears the now-stale preview immediately (preview_url on the message_update envelope) rather than leaving the old one showing while a new fetch (if any) is in flight.
• Scope cuts: one preview per message (the first URL only, matching the issue's "a small preview" framing), no way to dismiss/suppress a preview before sending, no re-fetch-on-demand if a cached preview goes stale mid-TTL.

Notes / scope decisions

• Invite-only site registration: no POST /api/auth/register. Accounts are provisioned with python -m app.cli create-user (see step 4 above), or via a site invite (see Site invites & email above). This is separate from adding an existing user to a private room — site accounts vs. room membership.
• Sessions are backed by a real server-side table (app/models/session.py, see Active sessions above) — the signed cookie (Starlette SessionMiddleware) now only ever carries an opaque session id, resolved against that table on every request, which is what makes revocation possible. Carrying auth through the WebSocket handshake automatically is still why it's cookie-based at all, per ARCHITECTURE.md's original rationale.
• No CSRF token yet — SameSite=Lax cookies plus a same-origin frontend dev proxy (see ../frontend/vite.config.ts) is the accepted phase-1 mitigation.
• Deleting a room explicitly deletes its messages/memberships first (room_service.delete_room) rather than relying on DB-level cascades.
• admin_audit_log has no admin UI for filtering/searching yet — it's a flat newest-first list with limit/offset pagination, no filter by actor/action/target. Fine at current scale; revisit if the log grows.