Package a systemd user service

[onechat] / README.rst

#########
 OneChat
#########

OneChat is one AI agent in a single chat that never ends. A daemon owns
the agent and its files, and a terminal client and a Telegram bot talk
to it. It is in early development. Linux is supported.

****************
 Data directory
****************

OneChat keeps its data and its token file in one directory. It uses the
first of these:

#. ``ONECHAT_DIR``, when it is set.
#. ``$XDG_DATA_HOME/onechat``, when ``XDG_DATA_HOME`` is an absolute
   path. A relative value is ignored.
#. ``~/.local/share/onechat``. With no home directory, OneChat exits
   with an error.

OneChat creates the directory with mode 0700.

***************
 Configuration
***************

``config.json`` in the data directory holds the settings. OneChat does
not create it. A missing file or field takes the default, and an unknown
field is an error.

.. code:: json

   {
     "endpoint": "chatgpt",
     "compactor": {"model": "gpt-6.1-sol", "effort": "high"}
   }

``endpoint``
   ``chatgpt`` (the default) sends model calls to the ChatGPT backend
   with the subscription login. ``api`` sends them to the OpenAI API
   with the key in ``OPENAI_API_KEY``, which must then be set. With
   ``chatgpt``, OneChat ignores ``OPENAI_API_KEY``.

``compactor``
   The model and the reasoning effort of the summaries. The defaults are
   ``gpt-6.1-sol`` and ``high``.

*******
 Login
*******

The ``chatgpt`` endpoint needs a login with a ChatGPT account:

.. code:: console

   onechat login

The command shows a link and a code. Open the link on any device, enter
the code, and approve the login. Device code login must be allowed in
the ChatGPT security settings. OneChat writes the tokens to
``auth.json`` in the data directory, with mode 0600, and refreshes them
before they expire. The file belongs to OneChat only. Do not share it
with the Codex CLI, because each program rotates the refresh token and
logs the other out.

*******
 Agent
*******

Start the daemon, and then the client in another terminal:

.. code:: console

   onechat daemon
   onechat chat

The daemon owns the root agent in ``agent/`` in the data directory and
listens on the Unix socket ``onechat.sock`` there. In the client, each
line is a message to the agent, the line ``/stop`` interrupts the
running turn, the line ``/stop NAME`` stops the subagent NAME, and
Ctrl-D ends the client. The client shows the replies, the tool calls,
and the first lines of each tool result as they happen. It also shows
each message that the user sends from another client, with the client as
a mark, such as ``[telegram] text``. When a subagent starts, the client
shows ``[NAME] started``, and it shows the whole report of the subagent,
which starts with ``[NAME]``, but not the tool calls of the subagent.
The daemon is the only process that uses the token file while it runs,
so ``onechat login`` and ``onechat probe`` refuse to start until it
stops.

The agent runs commands with bash as the user in its working directory,
with no sandbox. It has the rights of the user, also on the token file.

When the user asks for it, the agent starts subagents for long tasks.
Each subagent has a name, such as ``GreenOtter``, and runs in the
background while the agent answers other messages. It gets the view of
the agent and its task, and it runs its tools as the agent does, in
``agent/subagents/NAME/work``. A task in a repository gives the path of
the repository. The steps of a subagent go to its own log in
``agent/subagents/NAME``, not to the chat, and its final reply comes
back to the agent as one message that starts with ``[NAME]``. The agent
can send a subagent more messages: a running subagent reads them between
its tool calls, and a finished one goes on from its log, and its reply
comes back in the same way. When the user stops a subagent, the chat
gets a note, and the report of the subagent is logged, but it starts no
turn. Each model call of a subagent has the name in the ``agent`` field
of ``agent/usage.jsonl``. ``agent/work.json`` holds the names of the
running subagents. A subagent that runs when the daemon stops goes on at
the next start: the chat gets the note that the daemon restarted, and
the subagent gets the same note and goes on from its log.

``agent/config.json`` holds the settings of the agent. The first start
writes it with the defaults and a random ID. Do not change the ID: the
prompt cache key comes from it.

.. code:: json

   {
     "name": "OneChat",
     "id": "0123456789abcdef0123456789abcdef",
     "model": "gpt-6.1-sol",
     "effort": "medium",
     "workdir": "/home/user"
   }

``workdir`` is an absolute path, and its default is the home directory.
``agent/instructions.md`` holds the user's instructions: who they are,
how their files are organized, and how they want work done. The prompt
ends with them, and a change applies at the next call.

**************
 User service
**************

The Nix package includes ``share/systemd/user/onechat.service``. It runs
``onechat daemon`` from that package, starts at login when enabled, and
restarts 5 seconds after a failure. A stop sends SIGTERM to the daemon
and allows up to 120 seconds for cleanup. Its output goes to the user
journal. The service has the rights of the user, as the terminal daemon
does.

Build a package with a separate result link. Keep this link so that Nix
does not collect the package while the service uses it:

.. code:: console

   nix build --out-link result-service
   systemctl --user link --force "$(realpath result-service/share/systemd/user/onechat.service)"
   systemctl --user edit onechat.service

In the editor, set the data directory with this drop-in. Replace
``DATA_DIR`` with an absolute path to the data directory. Set the same
``ONECHAT_DIR`` for each terminal client. Without a drop-in, the data
directory rules above apply to the environment of the user manager, not
to the development shell.

.. code:: ini

   [Service]
   Environment="ONECHAT_DIR=DATA_DIR"

The service does not read the environment of an open terminal. If the
agent needs tools from a shell, set ``Environment="PATH=TOOLS_PATH"`` in
the same drop-in, with ``TOOLS_PATH`` replaced by the complete search
path, including bash. For the API endpoint, use
``EnvironmentFile=ENV_FILE``, with ``ENV_FILE`` replaced by an absolute
path to a mode 0600 file that sets ``OPENAI_API_KEY``. Keep secrets out
of the unit and Nix sources.

Use the existing data directory, or copy the development data before the
first service start. For a copy, first stop the terminal daemon with
Ctrl-C and wait for it to exit. Replace ``DATA_DIR`` below with a new,
empty destination. If the development shell uses a custom
``ONECHAT_DIR``, replace ``.devenv/onechat`` with that source. Copy the
whole directory so that ``auth.json``, ``telegram.json``,
``config.json``, ``agent/``, and ``whatsapp/`` stay together, including
the WhatsApp session and its database files. The copy preserves the file
modes and the source as a backup. Do not copy or use the same data from
two running daemons.

.. code:: console

   install -d -m 0700 DATA_DIR
   cp -a .devenv/onechat/. DATA_DIR/

After the terminal daemon exits and the data is ready, enable and start
the service:

.. code:: console

   systemctl --user daemon-reload
   systemctl --user enable --now onechat.service
   systemctl --user status onechat.service
   ONECHAT_DIR=DATA_DIR ./result-service/bin/onechat chat
   journalctl --user -u onechat.service -f

The service starts with the user manager at login, not at boot without a
login. To stop it, or also remove its start at login:

.. code:: console

   systemctl --user stop onechat.service
   systemctl --user disable onechat.service

**********
 Telegram
**********

The daemon also connects the agent to a Telegram bot when
``telegram.json`` exists in the data directory. It polls the Bot API for
new messages, so it needs no open port.

#. Make a bot with BotFather and keep its token.

#. Find your numeric Telegram user ID.

#. Write the token and the ID to ``telegram.json``, and give the file
   mode 0600, because the token is a secret. The daemon refuses the file
   with any other mode.

#. Start the daemon, open a private chat with the bot, and write.

.. code:: json

   {"token": "123456:ABC-token-from-BotFather", "owner": 123456789}

The bot reads only the private chat of the owner and ignores all other
updates. Each text message goes to the agent as a user message, the line
``/stop`` interrupts the running turn, and the line ``/stop NAME`` stops
the subagent NAME. The bot sends the replies in parts of at most 4096
characters, with their Markdown as Telegram formats: bold, italic,
strikethrough, code, code blocks, links, and headings as bold text. When
Telegram refuses the formats of a part, the bot sends the part again as
plain text. Each error goes as a short message in plain text. It shows
the typing action while a turn runs. It does not send the tool calls.
For a subagent it sends only ``[NAME] started`` and ``[NAME] finished``,
``[NAME] stopped``, or ``[NAME] failed``, because the reply of the agent
carries the content of the report. It sends each message that the user
types in the terminal client, with the mark ``[terminal]``.

``agent/telegram-offset.json`` holds the ID of the next update. The bot
moves it past an update only after the message is durable in the log, so
a restart of the daemon does not lose a message. A crash just after the
write of a message can make the message repeat once. A network failure
or a rate limit makes the bot wait and try again, and does not stop the
daemon.

**********
 WhatsApp
**********

The daemon connects to the WhatsApp account of the user as a linked
device. The terminal client and Telegram take three commands:

``/whatsapp pair PHONE``
   Links the account of PHONE, the number with its country code, such as
   ``+15550001111``. The daemon answers with the steps and then with a
   pairing code in its own message: in WhatsApp on the phone, open
   Linked devices, tap Link a device, then tap Link with phone number
   instead, and enter the code. The code expires in about 2 minutes, and
   the same command gives a new code. When the link succeeds, the daemon
   answers with the linked number. Linked devices on the phone shows the
   device as OneChat. The name applies at the pairing, so an existing
   link keeps its old name until ``/whatsapp unlink`` and a new
   ``/whatsapp pair PHONE``.

``/whatsapp status``
   Shows the link: not linked, linked and connected, or linked and
   disconnected, with the times of the connection.

``/whatsapp unlink``
   Ends the link and deletes the session. When WhatsApp is disconnected,
   the phone does not get the logout, so remove the device in Linked
   devices on the phone.

The answers go only to the client that asked, and the commands do not go
to the agent, so the agent never gets the phone number or the code. The
chat gets only the notes that WhatsApp is linked or unlinked.

The session is ``whatsapp/session.db`` in the data directory, with mode
0600 in a directory with mode 0700. It gives full access to the WhatsApp
account, so the daemon refuses the file when its mode is not 0600. The
shell of the agent runs as the user, so it can read the session. If the
session leaks, remove the linked device in WhatsApp on the phone, and
the session stops working. Without the file, WhatsApp is not linked.

The daemon reads the text messages of the private chats and the groups,
from other people and from the user. It does not read media, reactions,
edits, deletions, view-once and disappearing messages, or the history
from before the link. The messages of one chat form one batch until the
chat is quiet for 20 seconds, for 2 minutes or 50 messages at the most.
Each batch goes to the chat of the agent as one work message that starts
with ``[WhatsApp]``, with the name and the ID of the chat, and the time,
the sender, and the text of each message. The messages of the user show
as ``You``. ``whatsapp/state.json``, with mode 0600, keeps the batches
that are not in the chat yet, so they survive a restart, and the records
of the sends. A crash just after a batch goes to the chat can make the
batch repeat once.

A batch of a private chat with a message of another person starts a
turn, and so does a batch of a group with a message that mentions the
user or replies to a message of the user. The other batches go to the
chat with no turn, and the agent sees them at its next turn. A batch
that starts a turn ends with a line that tells the agent to end its turn
with an empty reply when nothing in the batch needs the user. No client
shows an empty reply, so such a batch gives no message in Telegram. The
terminal client shows each batch, and Telegram shows none.

The phone number of the user never goes to the chat: a mention of the
user shows as ``@you``, the number shows as ``OWN``, and the chat of the
user with itself is not read. But the IDs of the other chats go to the
chat and to the model, because the agent needs them to send. The ID of a
private chat holds the phone number of the contact, such as
``15550002222@s.whatsapp.net``, and the ID of a group can hold the
number of the person who made it.

While the daemon is stopped or disconnected, the WhatsApp servers keep
the messages for the linked device and send them at the next connection.
They keep them only for a limited time, so a long stop can lose
messages. These messages form batches by their original times, as live
messages do. The daemon waits for the end of this catch-up, or one
minute at the most, and then gives all its batches to the agent in one
turn, not one turn for each chat. The batches of ``whatsapp/state.json``
at the start wait for the first catch-up in the same way.

The agent finds a chat with the tool ``whatsapp_find``: it gives the
contacts and the groups whose name holds a text, with no regard to case
and accents, with their IDs. The names of the contacts come from the
session, and the names of the groups from WhatsApp, kept in memory for
one hour. The names arrive from the phone some minutes after the link,
and until then the tool says that they are not ready. The agent sends a
text message with the tool ``whatsapp_send``, only when the user asks
for it. Each send has an ID that the agent gives: a repeated call with
the same ID gives the answer of the first call and sends nothing. The
state file keeps the last 1000 send records. When the daemon stops
during a send, the result is not known, and the tool tells the agent to
ask the user to look at the chat in WhatsApp. Without a link, both tools
tell the agent to ask the user to run ``/whatsapp pair PHONE``. Only the
agent has the WhatsApp tools, not its subagents.

Each batch of a group goes to the chat, also with no turn, and the
memory tree summarizes it with model calls, which use the quota.

When the session holds a linked device, the daemon connects at its
start, and after a network failure it connects again by itself. When a
disconnection lasts 10 minutes, all clients get one notice, and one more
when the connection comes back. When WhatsApp ends the connection for
good, for example because another program uses the same session, all
clients get a notice at once. When the user removes the device in the
phone, the daemon deletes the session and tells all clients one time.

***********
 Schedules
***********

The agent sets reminders and timed tasks when the user asks for them,
such as "remind me tomorrow at 9" or "every weekday at 8, tell me what
my WhatsApp groups talked about". A schedule has a text, the task for
the agent, and either one time or a cron expression. The agent also
lists the schedules with their next times, and removes one when the user
asks. Only the agent has the schedule tools, not its subagents.

A cron expression has five fields: minute, hour, day of month, month,
and day of week, where 0 and 7 are Sunday. A field is a comma list of
``*``, ``N``, and ``N-M``, and ``*`` and ``N-M`` can have a step ``/S``,
as in ``0 8 * * 1-5`` or ``*/15 9-17 * * *``. When both day fields start
with something other than ``*``, a day matches when either field
matches. Names such as ``MON``, macros such as ``@daily``, the
characters ``? L W #``, and ``N/S`` are refused. The runs must be at
least 5 minutes apart, because each run is a full turn that uses the
quota, so ``*/5 * * * *`` is the shortest schedule.

The times use the time zone of the machine. A time that the clock skips
at the start of daylight saving time runs later by the length of the
skip. A time that the clock repeats at its end runs once, at its first
occurrence.

At its time, a schedule goes to the chat as a work message that starts
with ``[Schedule ID]``, with its time and its text, and it starts a
turn. The message ends with a line that tells the agent to end its turn
with an empty reply when nothing needs the user. The terminal client
shows the message, and Telegram shows only the reply. After its run, a
one-time schedule goes, and a repeating schedule gets its next time.

``agent/schedules.json``, with mode 0600, holds the schedules. Each
change writes it before the tool answers, so the schedules survive a
restart. A schedule that came due while the daemon was stopped runs once
at the next start, with its original time and a line that says that the
run is late. A repeating schedule that missed several times runs once. A
crash just after a run goes to the chat can make the run repeat once.

*******
 Probe
*******

``onechat probe LOG COUNT [BUILDS]`` measures the compactor on a log. It
appends the first COUNT messages of LOG, one JSON object ``{"kind",
"text"}`` on each line, to a new chat in ``probe/`` in the data
directory, and builds its tree with real model calls. The calls use the
quota of the account. The run stops at the first failed call, after 660
calls, or when the used percent of a quota window grows by more than 15
points. At the end it reports the calls per message, the cached share of
the input tokens, the retries, the line sizes, and the quota at the
first and the last call. BUILDS, from 1 to 8, limits the model calls at
once in the run.

A test writes a generated log of readable made-up messages:

.. code:: console

   ONECHAT_PROBE_LOG=probe.jsonl go test -run TestProbeLogHasTheSyntheticMix

*************
 Development
*************

Nix supplies the Go toolchain and all tools. Enter the development shell
with direnv:

.. code:: console

   direnv allow

Or enter it directly:

.. code:: console

   nix develop

The shell sets ``ONECHAT_DIR`` to ``.devenv/onechat`` in the checkout,
unless it is already set. Development data goes there, and Git ignores
``.devenv``.

Build and run:

.. code:: console

   nix build
   ./result/bin/onechat

Format and check all files:

.. code:: console

   bin/format
   bin/check
   nix flake check

``bin/check`` and ``nix build`` run a short replay of the synthetic log.
``nix flake check`` also runs the full replay of 100,000 messages.