macltok

# macltok design decisions

the contract the working tree actually implements. if the code disagrees with

this, one of them is lying and it should be fixed

## two ways in, one way out

state changes are commands. `ClientHandle::send` queues one and hands back a

`Pending`, `execute` queues and waits, and there's an awaited convenience method

for every command. each command answers exactly once with

`Result<CommandOutput, Error>`. drop the `Pending` if you don't care, the

command still runs

pure reads skip the engine and ask the sdk directly through the handle. rooms,

members, power levels, account data, devices, push notification resolution,

and media bytes all live here

the event stream carries state and only state. timelines, history, typing,

rooms, connection, encryption, verification, upload progress, session. no

command results ride on it. drain it from its own task, it's bounded and the

engine waits for you

one error type for everything, `Error { kind, message, challenge }`. match on

`kind`. `Interrupted` means the engine stopped, the room closed, or the task

doing the work died before it could answer. `challenge` turns up with

`InteractiveAuthRequired`

## engine

the run loop routes and does nothing slow. every task it spawns is registered

with a context. a command task that panics costs its caller an `Interrupted`

and gets logged. a watcher or a room actor that panics takes the engine down,

emitting `Failed` then `Stopped`

sync restarts itself with backoff after an error or an unexpected stop, and

`ConnectionChanged` shows `Offline` meanwhile. a run that drops again inside

thirty seconds counts as a failure too, or a server that answers `/versions`

but refuses sync would bounce us between online and offline forever. every return to `Online` re-arms

the send queues, since the sdk parks a room's queue on any send failure and

never unparks it. a recoverable failure while online gets the room another go

after a few seconds

logout and a rejected token both stop the engine. `Shutdown` answers once

`Stopped` has gone out, every one of them if several were queued

`Engine::run` hands back a boxed future. the real one nests deep enough that

every crate spawning it would trip the compiler's query depth

## rooms

one actor per open room. the engine holds a slot per room, `Active` with a

sender or `Closing` with a fifo of opens and closes that arrived while it wound

down. those replay in order once the actor exits. a room you leave, or get

kicked or banned from, closes itself. it tells the engine first, and anything

already queued to it comes back to be answered or replayed, so an open racing a

leave still gets a fresh actor

opening sends `TimelineReset` on the stream before it answers. opening an

already open room sends a fresh reset, so a second frontend gets a snapshot

sends, edits and replies run on the actor in order, so they reach the send

queue in the order they were asked for. redactions, reactions and read

receipts are network calls, so they run beside the actor and a slow one

doesn't queue the room behind it. closing lets them finish rather than lie

threads belong to their room's actor. commands for a thread that's still

opening wait behind the open, up to the actor's queue capacity

pagination runs one request at a time per timeline and emits `HistoryChanged`

around each. the sdk remembers where history starts, we don't, because a gappy

sync can unload it again

the actor's watchers are supervised, and a panic in any of them panics the

actor. its command work isn't, a panicking redaction just answers `Interrupted`

and gets logged

## timelines

`TimelineDiff::try_apply` refuses a diff whose indices don't fit your snapshot

and leaves the snapshot alone. stop applying, `resync`, and carry on from the

next `TimelineReset`. resync kills the old watcher before the new reset goes

out, so no stale diff can land after it

`TimelineId` tells a room from a thread by its root event

every item is an event, a day divider, the read marker or the start. an event

carries its sender with avatar and name ambiguity, and a `TimelineContent`

saying what it actually is. messages keep their msgtype, membership and profile

changes and the common room state changes get their own variants, and anything

else is `OtherState` or `Other` with its type. nothing is flattened into english

in a body field

thread receipts for a thread that isn't open go straight to the room, so

marking a thread read works the same whether its room is on screen or not

replies carry the replied-to event once it's loaded. the watcher asks the sdk

for any it hasn't got, once per event, since the sdk won't on its own

edit, redact and react take an `EventRef`, so your own message can be edited or

reacted to before the server has echoed it back. redacting an unsent one just

cancels it

## mutations

membership, moderation, power levels, room creation and account data writes go

through one keyed fifo scheduler. same room, same alias, same dm partner or

same account data type run in order, everything else runs at once.

`create_direct` hands back the existing dm when there is one

notifications and encryption each get one serial worker. the encryption worker

owns the verification controller outright

power level changes build one state event from the local mapping, since the

sdk's own patcher is private

## media

media is a read. `ClientHandle::media` takes a `MediaId` a retained timeline

handed you, `mxc_media` takes any plain mxc uri. both share one bounded

download path with the byte cap the sdk's own download lacks, an hour's total

deadline instead of the sdk client's thirty seconds, and a minute's patience

for a stalled stream. concurrent asks for the same bytes share one flight.

a thumbnail the server won't make falls back to the file itself.

`MediaId` parses from a string, since a web client has to round trip it

the cache holds plaintext, keyed like the sdk keys it, so the sdk and macltok

can read each other's entries. that's how your own encrypted uploads come back.

the sdk keys plain and encrypted sources alike, so a plain event pointing at

someone's encrypted file can leave ciphertext in the cache. an encrypted read

checks the cached bytes against the file's hash and decrypts them if they match

media ids are registered as timelines render and forgotten when their timeline

closes, least recently seen first once the cap is hit

uploads are commands that answer once the send queue has them. progress only

goes out on a room's own send queue channel, so each room that uploads gets a

forwarder, subscribed before the upload is queued and restarted for uploads the

sdk resumes from last time. failures do reach the client-wide channel, so one

watcher there reports them

## sessions and secrets

`Session::login_password`, `begin_oauth` and `restore` share one client builder

with encrypted sqlite, refresh tokens and threads. secret-bearing inputs don't

derive `Clone`

the caller owns the saved record. save `Session::record()` after login and

replace it atomically with `ClientHandle::session_record()` on every

`SessionTokensChanged`. logout and a hard rejection kill the record and the

store. a soft logout keeps the store for a same-device login, or the e2ee keys

go with it. a bare `Stopped` kills nothing. one store directory per login

## room lists, spaces and profiles

`RoomSummary` has what a room list row needs without a second query. topic,

alias, member counts, heroes for nameless rooms, the inviter, where an upgraded

room went, a latest event preview, the joined spaces listing it, and for a

space the children it lists

parents come from one lazily built `SpaceService` shared by every handle.

children come straight from the space's local state, joined or not.

`space_hierarchy` pages through the server's view for browsing rooms you

haven't joined, and holds its place between pages

`own_profile` and `user_profile` read profiles. name and avatar changes are

commands, and uploading an avatar gets the same byte cap as any upload

## notifications and room data

the notification client is built lazily and shares the engine's sync service.

sdk ui types stay behind the boundary

`rooms` normalises on demand with bounded concurrency and sorts by latest event,

then name, then id. `RoomsChanged` is an invalidation, coalesced so one sync

touching fifty rooms is one event

## verification

`Accept`, `Confirm`, `Reject` and `Cancel`. a request another device sends

shows up as `Incoming` and waits for `Accept`, or `Cancel` to turn it down. one

is only taken up while nothing else is in flight. reject tells the other side

the emoji didn't match. the watchers subscribe before they look at the current

state, since the sdk only reports what changes after you ask. the watcher and

the action paths claim the terminal event, so a racing

cancel can't turn `Done` into `Cancelled`

## public model

owned ruma ids and typed data wherever there's a stable shape, `Raw` where

arbitrary content has to survive. anything expected to grow is

`#[non_exhaustive]`. `Engine::from_client` stays public for people who built

their own client