ai-app/PLAN.md

ai-app — plan

A phone interface to AI coding sessions — Claude Code and llama.cpp — built to replace the Claude app for day-to-day use. Two motivations: local models need a front end at all, and owning the client means fixing what the official app gets wrong (it won't deliver a typed message until the turn fully finishes, where the TUI injects it at the next tool boundary).

Same shape as ../dev-updater: a Rust (Axum) backend on the desktop, a Kotlin/Compose Android app, pinned self-signed TLS between them.

This file records decisions with their date, their rationale, and what was rejected. Update it in place when one changes; AGENTS.md is the working notes layer and must not become a second version of it.

The one idea everything hangs off

A session is a child process, translated into one common event model. The backend spawns it, translates its dialect into a common event stream, and keeps an append-only transcript. A new session type is a new driver — never a session-type branch in shared code (routes, transcript, app screens). SSH falls out of the same shape: a remote session is the identical command wrapped in ssh host …, and the driver never learns which it got.

Android app (Compose)
   │  HTTPS (pinned CA) — REST for actions, SSE for live events
   ▼
backend (Rust/Axum, desktop)
   ├─ SessionManager ── Session ── Driver (trait)
   │                      ├─ ClaudeDriver  (claude stream-json over stdio)
   │                      ├─ LlamaDriver   (llama-server over HTTP)
   │                      └─ EchoDriver    (the test rig)
   │        each driver's process is spawned through a Transport,
   │        locally or as `ssh host …`, decided by the setup it names
   ├─ usage.rs            (Anthropic OAuth usage endpoint, per machine)
   ├─ models.rs           (HuggingFace browsing and GGUF downloads)
   ├─ files.rs            (the file explorer's half of the backend)
   └─ config.ron + per-session transcript files

Architecture

Setups and providers (2026-08-28)

A setup is a machine, and it carries the providers that machine has. Optional ssh details, plus the list of what can be run there. Spawning is two choices in order: pick a setup, then pick one of its providers.

This replaced an independent providers × hosts cross-product, because the two axes are not independent: a provider is only real on a machine where that CLI is installed, so the cross-product offered combinations that cannot work — claude-cli on a machine with no claude, and every provider paired with a host the driver ignores (EchoDriver takes no host, so "Run on" was a control that silently did nothing).

• Echo is seeded, not implicit. It lives in the setup with no ssh, because it runs in-process and has no transport to cross. It is written into config.ron on first run rather than conjured at read time — a provider nobody can see in the file is one nobody can edit from the phone.
• Providers are discovered by asking the machine, never typed, so an enrolled token cannot introduce a command. The escape hatch for a binary somewhere unusual is editing config.ron, deliberately the one authority the phone does not have.
• Migration code is deleted once the update carrying it is received. The providers/hosts migration ran on the one host there is and is gone. A file in the old shape now fails to parse, which is correct because no such file exists.

Backend layout (server/)

axum 0.8, axum-server + rustls, tokio, serde, clap, tracing. Rust edition 2024, warning-clean, clippy clean.

• main.rs — bootstrap, TLS listener, auth layer, enrollment, wg0 binding.
• routes.rs — the whole HTTP table in its module doc comment. That comment is the surface's source of truth; this file does not repeat it.
• auth.rs — the bearer-token middleware.
• config.rs — the persisted schema.
• setups.rs — machines and provider discovery.
• files.rs — the file explorer (EXPLORER.md).
• usage.rs — Anthropic usage polling, per machine.
• models.rs — HuggingFace browsing and GGUF downloads.
• media.rs — the image media-type/extension table, shared by the four places that must agree: storing an upload, serving it back, handing one to a driver, and saving one a tool produced.
• session/mod.rs — SessionManager, the live registry; every mutation funnels through it so in-memory and on-disk state cannot come apart.
• session/driver.rs — the Driver trait and the common event model.
• session/claude.rs, session/llama.rs, session/echo.rs — the drivers.
• session/transcript.rs — the append-only JSONL event log per session, with monotonically increasing sequence numbers (the phone's resume cursor).
• session/transport.rs, ssh.rs — running a driver's command locally or over ssh.
• session/process.rs — the pid + start-time record that lets a process outlive the backend.
• session/import.rs — continuing a Claude Code session the machine has.
• session/pending.rs — operations in flight on importable sessions.

The certificates, enrollment, wg0 binding, owner-only file modes and RON house rules live in the wg-app-link submodule, shared with dev-updater.

The common event model

Driver output, whatever the dialect, is normalized into one enum before it touches the transcript or the phone. Every event is appended to the session's transcript with a sequence number, then fanned out to SSE subscribers. The phone renders purely from this stream: reconnecting is "give me events after seq N", so there is no separate history path to drift from the live one.

• UserMessage { text } — echoed into the transcript by the manager, not by drivers, so every device renders the conversation from one stream.
• AssistantText { delta } — streaming text, rendered as markdown.
• ToolStart / ToolUpdate / ToolEnd { tool, input, output }.
• Image { ref } — saved under the session dir, fetched by URL.
• Question { id, prompt, options } — anything needing a human. Claude's AskUserQuestion and permission requests (canUseTool) are the same shape; a permission is a question with two bare options, not a different kind.
• Answered { id, answer } — so a question card resolves on every connected device, not just the one that answered.
• Status { state } — idle / running / awaiting-input / compacting / exited.
• UsageDelta { tokens, context } — what a turn cost and how much the model was holding when it ended. context is prompt plus both cache figures, taken from the last assistant message rather than the turn's result: measured 2026-08-30 against CLI 2.1.237, the result adds a turn's messages up, so its cache read of 40,211 was the same conversation counted twice. It is carried rather than summed, because it goes down — a compaction replaces it and a clear leaves it unmeasured. driver::context_after is that rule and the phone folds with the same one. A session the server has no measurement of asks the CLI's own file instead of waiting for a turn (import::context_of).
• MessageQueued / MessageDropped — see "Taking a queued message back".
• PeerMessage — see "A message from another agent".
• Error { message }.

Inbound, the Driver trait is small: send a message, answer a question, interrupt, set the model, compact, unqueue, and two ways out — detach (the server is going away and means to come back) and stop (the session is being deleted, so the process must not survive). Every driver owes exactly one of the two.

send_user_message during a run is the point of the whole app: the dialect queues it for injection at the next tool boundary rather than the end of the turn.

Claude driver specifics

Spawn: claude -p --verbose --input-format stream-json --output-format stream-json --permission-mode <mode> in the chosen working directory, plus --model and, where one has been chosen, --effort. Wire-format notes are pinned against CLI 2.1.237 in session/claude.rs's module doc: permissions need the hidden --permission-prompt-tool stdio flag, AskUserQuestion answers ride updatedInput.answers keyed by question text, and set_model/interrupt are control requests.

The thinking level is settled at launch (added 2026-09-04, because it is the largest saving available on a long session: output is about an eighth of what a session costs and thinking is the bulk of output, against the ~1.5% that is prose). The CLI's only two setting control requests are set_model and set_permission_mode -- checked against the 2.1.258 binary -- so there is no way to ask a running process to think differently. set_session_effort is therefore shaped like set_session_cwd rather than like set_session_model: it records the level and stops the process, and the next message or Start launches one that has it. It lives in the session settings dialog beside the working directory for that reason, not on the session bar beside the model and the mode, which do take effect mid-turn. None is a level in its own right -- the CLI's own default -- so the picker can return to it; a level this app named as the default instead would be this app choosing one.

What a new session starts at is Config::default_effort, applied in spawn_session rather than filled in by the spawn screen, so it holds for an import and a bare API call as well. It is set by the spawn screen's own picker, whose label says so: one control, where new sessions are made, rather than a settings page for a single value. It is not on a provider, because providers are discovered and the next rediscovery would erase it, and not on the phone, because a second device would then spawn at a level nobody there chose. GET/POST /defaults carry it, as a struct rather than a bare value so the permission mode -- still hardcoded to auto on the spawn screen -- can move there without a second route.

--resume only ever runs when nothing else has that session open. That is the rule behind the import refusal, the single ClaudeDriver::launch entry point, and the Exited correction below; two CLIs on one session file duplicate the conversation into it and bill the second for re-reading it all.

The llama driver

One llama-server per session, started through the same Transport as any other process and then reached over HTTP on a loopback port. Two things are deliberate and easy to undo by accident:

• The conversation is rebuilt from the transcript, not kept in the driver. A copy in driver memory is invisible to a second device and gone when the process restarts. That leaves the Claude driver as the odd one out rather than this one — the CLI's memory is a cache in front of the same transcript. Resolve any inconsistency in this direction.
• A llama session runs on whatever machine its setup names (2026-09-04, the last of phase 5). A transport is "run this" plus "reach this port", and the second half is Transport::reserve_port — the port the server binds there and the port that reaches it here, the same number locally — carried by Launch::reaching onto the connection that already runs the command. llama-server binds loopback on the far machine, so nothing is served to its network. The far port is a guess from a range below the ephemeral one, because no portable way to ask a machine for a free port avoids racing the bind anyway; a collision is not silent, since the server fails to bind and the readiness poll reports what its log said.
• The model file lives on the machine that serves it (2026-09-04). Each setup names its own models directory (SshConfig::models_dir, default ~/.local/share/ai-app/models expanded there), and a spawn resolves the key on that machine — one round trip answering "at /abs/path" or "missing", so a model that is not there is refused at the spawn rather than becoming a server that never becomes ready. The spawn screen offers GET /setups/{id}/models, that machine's list, rather than GET /models, which is this backend's downloads. Downloading to another machine is deliberately not built: a multi-gigabyte transfer with no progress anywhere, and the file gets there however anything else on that machine did.
• The readiness poll watches the process, not only the port. A model that will not load, a port already taken, a flag an older build does not know: all exit within a second and none will ever answer /health, so waiting out the 300s timeout turned the server's own account of the problem into "gave up". The failure carries the tail of llama-server.log, which on a remote session is the only copy anybody reading the phone can see.

Models (2026-08-28)

• A download belongs to the model, not to the request. Keyed by owner/repo/file.gguf and owned by the server, so a second device can watch one it did not start and an hour-long fetch survives a locked screen. Every run has an id and its outcome outlives it, because "not downloading" otherwise means finished, never started, or someone else's run ended while you were away.
• Progress is measured, never estimated: total is Content-Length, or Content-Range's last field on a resume, and absent when the server says nothing.
• Resume is guarded by identity, not by hope. A partial carries the ETag it was written against and a mismatch discards it. If-Range would be the tidy mechanism but HuggingFace's CDN ignores it (probed 2026-08-28). The published sha256 is checked before the file is renamed.
• Sampling parameters reach a driver as an untyped params map, so the shared schema does not grow llama.cpp's vocabulary.

Transport (ssh)

• A remote session is a local one with the command wrapped in ssh -T host …, every argument shell-quoted, run with exec so dropping the connection takes the CLI down rather than orphaning it. Key-based auth only, through the system ssh client, which inherits ~/.ssh/config, agents and jump hosts for free.
• The transport wraps the driver, not the other way round (2026-08-28). A driver says what to run; something above it turns that into a process. Otherwise transport knowledge sits inside a translator whose job is a wire format, and every future driver has to remember to do the same.
• A forwarded launch gets a pty and every other one does not (measured 2026-09-04). Killing the ssh client ends a CLI because it closes the stdin that CLI is reading; llama-server never reads its stdin, so the same kill left it running on the far machine with the model loaded — one orphan per stopped session. With -tt the far side takes SIGHUP when the connection goes. Its log then arrives through a line discipline, which nothing parses. -T stays everywhere else, where a pty would rewrite the JSONL.
• command -v follows ssh's non-login PATH, which is narrower than an interactive shell's, so a binary somewhere unusual is invisible to discovery. Point command at an absolute path.
• Images need no file transfer. attachment_block base64s an upload into the stream-json message, and produced images come back the same way.
• Any other file is told to the session by path (2026-09-03): a trace, a log, a zip — things a model cannot be shown and the CLI can read. The upload is streamed to disk under the session's attachments on this machine, and the message ends with Attached file: /abs/path. For a session on another machine the upload also copies the file there in the same request, over one ssh invocation, landing in the setup's attachmentsDir if set, else the session's cwd, else the login home. The resolved remote path is recorded beside the file (<name>.remote) and is what the driver names. A copy that fails fails the upload, so no message ever names a file that is not there.

Moving a session to another directory (2026-08-31)

POST /sessions/{id}/cwd, from the session settings dialog. A working directory is settled when the process is spawned, so this records the new one and ends the process in the old one. It does not start a replacement: a session with no process starts on the next thing said to it or on Start, which is this app's rule everywhere else.

The path is checked against the session's own machine and refused if it is not there, rather than corrected. The spawn path corrects instead, because it is resuming a directory the machine recorded, which can be gone through nobody's fault; a path somebody has just typed is different, and a mistyped one accepted here surfaces much later as a session that will not start.

Nothing of Claude Code's own is moved. Measured against CLI 2.1.237: claude --resume <id> finds a session from any working directory. Relocating the file would mean reproducing a rule this app cannot see the whole of — the project directory is the path with every non-alphanumeric character replaced by -, truncated at 200 characters with a hash appended, and overridable.

A message from another agent (measured 2026-08-31)

Measured by sending a real cross-session message to a real stream-json session on CLI 2.1.237: the CLI emits no user record for it, and nothing in the partial-message stream mentions it. The whole of it arrives as an origin object on the turn's result, in the same shape the session file records — so import::peer_message reads both and there is one function for one wire format. Only peer-caused turns carry it.

The cost is the position, and it is paid on the wire rather than on screen. The event cannot be recorded in place: at no earlier point does the CLI say why the turn started, and the transcript is append-only, so by the time anyone knows, everything the message caused is already written above it. Tailing the CLI's own session file instead was rejected and stays rejected — two sources of truth for one conversation and a poll per live session.

So PeerMessage carries a turnStart: the seq of the Status that opened the turn, stamped by the pump, which is the only thing that knows a seq and sees every driver's turns. The phone draws the note at that seq. A status draws no row, so there is nothing to collide with and the list stays sorted, which is what the scroll anchor and paging depend on. turnStart is absent where there is nothing to correct — a message replayed by import is already in the right place. The echo driver models both shapes: /peer and /peer-turn.

Taking a queued message back (2026-08-31)

POST /sessions/{id}/unqueue, answered by Driver::unqueue and recorded as Event::MessageDropped so every device loses the bubble and a reconnect does not replay it.

The answer has three states rather than a yes/no, and that is the whole design: Dropped, AlreadySent, and Unknown. The Claude driver can only ever give the middle one — it writes a steer into stdin the instant it arrives, which is what makes a steer reach the model at the next tool boundary instead of the end of the turn. What waits in awaiting is the announcement, not the message. Holding the write until a boundary would make the drop real everywhere but costs a steer one model call, which is the latency the immediate write removed. So the refusal is the honest answer, and it is reported on the bubble the reader pressed rather than in the screen's error row a screen away.

Unknown is not "we could not find out": a driver that is gone reported everything it was holding when it closed.

Session processes outlive the backend (2026-08-29)

A session's process is left running when the backend stops and adopted again when it starts. A rebuild, a service restart or a crash must not end a turn somebody is waiting on, and a turn can be minutes long. What this replaced leaked processes either way: shutdown_all asked every driver to stop and then exited immediately, with the SIGKILL escape hatch on a timer inside the dying runtime, and whatever survived was orphaned with nothing written down to find it by.

Inside the session directory, beside the transcript:

• process.json — the pid, the kernel's start time for that pid, and how much of the output log has been read. The start time is what makes the pid an identity: pids are reused, and adopting a stranger's would mean never resuming the real conversation and signalling something unrelated.
• stdin.fifo — opened read-write and inherited by the process, so it is its own last writer and never reads EOF when the server goes away. Closing stdin therefore stops being the graceful-exit signal; ending a process is a signal, and only Driver::stop sends one.
• stdout.log / stderr.log — plain appended files, read from a byte offset. A fifo would fill its 64 KB buffer and block the process while nothing drained it, stalling the very turn this exists to protect.

Remote sessions are adopted too, and the recorded pid is the ssh client's — the process the backend owns, which lives exactly as long as the remote command does. The far claude always has an sshd pipe on stdin whichever version started it, since the fifo is on the backend's side, so a remote session's stdin says nothing about which server started it.

A zombie is dead. /proc/<pid>/stat keeps the entry, with the same pid and start time, until the exit status is collected — so a finished process answered "still there" for as long as nothing reaped it, and Alive is the word that makes Exited unsayable. process::stat_of reads the state field alongside the start time.

Stopping and starting a session's process (2026-08-30)

POST /sessions/{id}/stop and /start: end the process without ending the session, and start it again on the same conversation. Three decisions worth not undoing:

• Stop signals the recorded process and says nothing else. It does not go through the driver and does not announce Exited. The record is the session's rather than any dialect's, so this works for a session whose driver is in no state to be asked, and the driver's own reader already reports the death correctly. Announcing it here would be a guess arriving ahead of the measurement, and wrong for the grace period.
• Start replaces the driver and nothing else. The transcript, the event pump and every open SSE stream stay where they were, so starting again is not a reconnect for anybody watching, and there is still exactly one writer of the transcript. LiveSession and Commands share one Mutex<Arc<dyn Driver>> rather than each holding a copy.
• Start is refused unless the session is known to have exited. Unknown means nobody could find out, and starting on that is exactly the two-CLIs-on-one-conversation fault session::process exists to prevent.

Exited is a claim about a process, and the record is what settles it. It is the one status that draws the phone's Start button and lets start_session build a driver, so it is checked against session::process before it is believed (corrected, called in launch and start_session). A record not known to be dead makes it false and the session reports Unknown instead. Every other status is left alone — those are the pump's, written from what the process itself said. Without this, a session adopted at a backend start kept the transcript's Exited while its CLI ran, Start was accepted every press, and each press attached another reader to one process: one reply drawn interleaved several times over (GotGotGot it — it — it —). A driver that start_session replaces gets Driver::detach, because swapping the Arc does not end the tasks the old one is running.

Who says so matters as much as what is said. A status written into the manager's view alone is two screens disagreeing — the list reads the manager's status and the session screen replays the transcript, which showed up as a stop button turning into a play button a moment after the screen opened. So a driver announces the state it starts in, through the event sink. It says Idle only when it started a process; adopting says nothing, because a process already running may be mid-turn and the transcript's last word is the better answer until its output says otherwise.

A message or a command starts the process if there isn't one. Refusing was work handed back: read the status word, find the other button, press it, type the thing again. --resume puts the new process on the same conversation, so nothing about what was typed changes. A rename is included for a sharper reason: Claude Code keeps its own copy of the name, that copy is what its session picker and other agents' session lists show, and a session is only ever given a name at birth since every later start is a --resume — so a rename reaching no process would leave the two lists disagreeing permanently. Its save happens before the telling, so a failure there says the telling failed rather than the rename.

start_if_exited is one function under one write lock, which is what stops two requests arriving together from starting two CLIs. Its callers want opposite answers: "there is already a process" is a refusal worth showing to somebody who pressed Start, and nothing at all to a message. Only Exited starts anything — Unknown has a process that may well be reading its fifo. run_command judges against what start_if_exited returned rather than re-reading a status the pump may not have caught up with.

On the phone this is one button in the composer, left of Send, whose mark and colour say what pressing it would do now: an orange pause while a turn runs (interrupt — the process stays), a red stop when it is not (end the process), a green play when it has exited. One button rather than three that come and go, so its presence is never the signal. It is disabled while its own request is in flight, as a courtesy; the server refuses the second request either way.

A backend start adopts, and starts nothing (2026-08-30)

SessionManager::new takes charge of the processes still running and leaves every other session exactly as it found it — listed, with its transcript, its pump and its SSE stream, and no driver until somebody asks for one. It used to launch a driver for every session in the config, and ClaudeDriver::launch starts a process when there is none to adopt, so a session somebody had deliberately stopped came back at the next rebuild, and the Idle the new driver announced stamped it as active at the moment of the restart. On the phone that read as every session idle and "just now", with the list sorted by that time in an order that meant nothing.

• Launching is the parameter that says which it is, and an import's seed rides on the asked-for variant, because a restart re-seeding a transcript would write the imported conversation into it twice.
• A session with no process has no driver. DriverCell is an option rather than a driver whose requests go nowhere, so "nothing is running this" is a state the code can be asked about instead of one it discovers by sending into a dead fifo. LiveSession::ask answers it with an Event::Error naming what could not happen — a request nobody can carry out is reported, never swallowed.
• A launch never moves a session's clock. A status a launch has to correct is written at the time of the last thing the session actually did, not at now(). Taking charge of nothing, every word but Exited is disproved at once — a backend killed mid-turn leaves a transcript saying Running, which draws a stop button for a turn that ended hours ago — but stamping the correction with now is the same lie in the same field that Transcript::last_activity exists to prevent.
• A session that has never done anything reports when it was created. Its transcript is empty, since a driver announcing the state it starts in is not news, so it is the one session with no line to read a time off. Not the file's mtime, which is a worse answer for a checkout that can be copied; SessionConfig::created is recorded rather than inferred.

Sessions spawned while testing clean themselves up (2026-08-30)

--throwaway-sessions, on by default in a debug build. Every session such a server spawns is marked throwaway in the config, and a marked session's process is stopped when the server exits or is signalled.

Leaving processes running is right for the sessions somebody is using and exactly wrong for the ones a test made: those leave a claude behind that every later server adopts, they cost tokens if anything speaks to them, and nothing says they are there — twelve accumulated on this machine in a day.

• The flag marks; the mark decides. What a server was told at startup governs only the sessions it spawns, and the mark is written into the session, so it outlives that server. A session spawned deliberately keeps running whichever server is up when one exits, and a throwaway one is cleaned away even by a server started without the flag. The alternative — the exiting server stopping whatever it has marked in memory — makes cleanup depend on which process is up.
• Stopping is not asking. process::stop leaves its SIGKILL on a tokio timer, which a shutting-down runtime never runs; that is precisely how the original shutdown_all leaked. The exit path waits with process::wait_gone — one deadline for all of them, since they were signalled together — and kills whatever is left.

Importing refuses a session that is already open (2026-08-29)

Claude Code keeps a descriptor per live session at ~/.claude/sessions/<pid>.json carrying the sessionId and a procStart — the same pid-plus-start-time identity used above. So "is this session open right now" is a measurement, and the import list reports it as no / yes / unknown. Three answers because a machine that keeps no such record cannot answer, and "could not check" is not "nobody is using it".

yes is refused. On 2026-08-29 an agent imported the session it was itself running in: two claude --resume processes on one file, the whole 65 MB conversation with 154 embedded screenshots duplicated into it under a new prompt id, and the adopted copy billed for re-reading all of it. It ended at the account's session limit.

Importing and deleting run on the server, and a batch is handed over in one call. POST /setups/{id}/importable/{delete,import} each take a list of ids, answer 202, and do the work in spawned tasks — the phone that asked is free to leave, and used to cancel its own batch by doing so. A list rather than a route per session because one request per row made a handover only as atomic as the network, and a row nobody asked for looks exactly like a row nobody picked. Only the registering is atomic; the work settles per row, since six deletes that all roll back together is not something a filesystem offers.

What replaces the reply is session::pending: every row carries pending and error, and /importable/events streams the changes. Both, not either — the stream is a broadcast with no memory, so an operation that starts and finishes while it is still connecting is one nothing will ever be said about, which left a row marked "waiting" for ever. A single tap still waits, because "continue this and take me to it" needs the session it made and 202 does not carry one; the batch and the tap share spawn so the two cannot drift about what importing means.

An imported session keeps itself level with the CLI's file, so work done at a terminal appears without anyone pressing anything. Which lines came from here is answered by counting the events this session has recorded, not by looking at its status — a turn that starts and finishes between two polls reads as idle at both, and its own output gets replayed on top of itself. That bug was visible on screen as donedone.

Usage limits (Claude)

Poll https://api.anthropic.com/api/oauth/usage — the endpoint behind Claude Code's /usage — with the OAuth token from ~/.claude/.credentials.json, headers anthropic-beta: oauth-2025-04-20 and User-Agent: claude-code/<version> (without the User-Agent it lands in an aggressively rate-limited bucket). Poll at ≥180 s, only while a Claude session exists or the usage screen is open, and cache the last answer. It is undocumented, so usage.rs treats every field as optional and degrades rather than erroring.

Per provider, not per machine (2026-09-04). A machine is not what is metered; the provider a session runs is. One machine offers echo, the Claude CLI and a local model side by side, and only the second spends anything — so pairing a session with a snapshot by machine alone drew the CLI's five-hour window under every echo session on it, a quota that session cannot spend. A session now names its meter (usageProvider, from DriverKind::usage_provider, which usage::providers_for reads too, so the two lists cannot disagree) and GET /usage is matched on machine and provider. None is a session that meters nothing, and the phone draws nothing at all for it — not a zero, and not "unknown".

DriverKind::Echo names a meter of its own that exists only when a test has asked for one: /usage in an echo session sets an invented answer (usage::Fixture), and with none set there is no snapshot and no bar. That is what makes those screens' states reachable — a number near the top, a window between blocks with no reset time, a machine nobody logged into, one that could not be reached — without spending real quota to arrange them, which is why none of them had ever been looked at.

Per machine, not per backend (2026-08-29). The credential store that matters is the one on the machine the session runs on, because that is the account being billed — and in the layout this aims at, ai-server is on the host, the host has no claude, and the CLI machine is a remote. So credentials are read through the session Transport ($HOME expanded by the far shell, because a path built locally is the wrong home), one snapshot per setup that offers Claude. The HTTP call stays on the backend, so the far end needs nothing but a shell.

The snapshot says which of four things happened rather than carrying a flag and a message: ok, notLoggedIn, unreachable, failed. notLoggedIn is the one that matters — a machine nobody put an account on is working as configured, and collapsing it into an error string made a healthy setup read as broken. A machine with no Claude provider is not asked at all.

The five-hour window has no reset time between blocks, and that is not a missing value. Measured 2026-08-31: the API anchors the window to the block it started in, and when no block is running there is nothing to reset, so resets_at is null. The weekly windows always have one because a week is always running. So absent means not running, and only a timestamp that arrives and cannot be parsed is unknown. WindowEnd in ResetCountdown.kt is the one rule both readers go through.

Auto-resume (2026-09-05)

A session may pick itself back up when the account's usage limit lifts. Off unless somebody switched that session to it, because it spends quota the moment quota exists and does so with nobody looking — that is not a thing a default may decide. It sends one message, continue unless another was typed, and then it is done; there is no retry loop around the conversation itself.

Running out of quota is a state, not an error. Event::LimitReached carries the dialect's reset time where it gave one, and recognising it belongs to the driver — the Claude CLI ends the turn with is_error and Claude AI usage limit reached|1788546972, and nothing above the driver matches on a string. Two detectors, since 2026-09-06: that sentence, and the CLI's own rate_limit_event lines, whose rate_limit_info.status says where the account stands and whose resetsAt is the same hint. One detector was a single point of failure for a feature whose whole job runs unattended — if the wording or the shape of a failed turn ever changes, nothing is scheduled and the session simply never comes back, with nothing on screen saying why. Only the change into being refused is reported, and only a status that is not an allowed… word counts as refused: an unfamiliar word is read as out of quota and logged, because the cost of being wrong that way is one extra question to the meter, and the cost the other way is the feature silently not existing. The transcript draws it as a divider, like a clear or a compaction: what a reader scrolling back wants from it is why the conversation stops at that line.

The schedule is a plan to ask, never a plan to send. Every reset time available here is untrustworthy in the direction that matters: the dialect's is written when the turn fails, and the endpoint's moves when the window does. So the wait ends in a question to usage.rs, and only ok with no window at 100% sends anything. A window still spent reschedules to its own reset time — which is what makes a limit that lifts later than promised wait longer, and one that lifts sooner resume sooner. A meter that cannot be asked at all is a longer wait too, never a send: "we could not find out" must not be able to produce the same action as "there is room".

Bounded, because something has to be: a day after the limit was hit the wait stops and says so in the session's own transcript. A machine that can never be asked would otherwise be retried for ever with nothing on screen saying so.

The schedule is persisted on the session (resume: Some(ScheduledResume)), not held in memory: a five-hour window routinely outlasts a backend restart, and a wait forgotten across one is a session that silently never comes back. resume.rs is the top layer — it holds the manager and the monitor and neither holds it — which is what lets the decision be a pure function of a snapshot and a clock. The pump reports limits downward on a broadcast, for the reason Shared exists: the pump runs underneath the manager.

Exercised with echo, never with a real account. /limit [minutes] in an echo session reports the same event a real driver does, and /usage sets what the meter answers — deliberately two commands, because the two disagreeing is the state the whole design is about. The loop was driven end to end that way on 2026-09-05: the wait moved from the dialect's two minutes to the meter's seven when the meter changed its mind, and the message went out on the first check after the meter came back under the limit.

Subagents (2026-09-05)

A subagent is a second transcript owned by a session, in the same event model, with no process and no controls of its own. Full design and wire shape in SUBAGENTS.md, kept separate because the app half is being built against it in parallel and it is the shared contract between the two. The one-paragraph reason: a session's Task-tool helpers already speak the common event model on the parent's own stdout (each line carrying parent_tool_use_id), so giving each one its own small transcript — same file format, same paging routes, same SSE stream, reused by addressing rather than by copying — costs a routing step in the translator and a registry (session/subagent.rs) rather than a second session type with a driver, a process and a config entry it does not need.

HTTP surface

routes.rs's module doc comment is the table. REST for actions, one SSE stream per open session screen for events, all over the pinned TLS listener. SSE rather than WebSocket because resume-by-cursor (Last-Event-ID = transcript seq) is native to it and the inbound direction is plain POSTs.

Sessions live in config.ron ($XDG_CONFIG_HOME/ai-app/) plus a per-session directory under $XDG_DATA_HOME/ai-app/sessions/ (transcript, attachments, produced images, process record), owner-only. Deleting a session is the complete path out of everything spawning one created.

Every request body refuses fields it does not know (serde(deny_unknown_fields)). A caller that misspells permissionMode got a 200 and a session in the default mode, which is indistinguishable from success at the place they are looking. Query strings are deliberately permissive.

A phone that falls behind is answered with reset. Past CATCH_UP_LIMIT the stream sends a reset frame and the newest window, and the client rebuilds from it exactly as it does when the screen opens. Not optional: without it the window is spliced onto rows no longer adjacent to it, which reads as ordinary output. The stream used to replay everything after the client's cursor, unbounded, while opening a session was bounded to a page — so a long disconnect delivered thousands of events one frame at a time.

The file explorer (2026-09-03)

EXPLORER.md holds this design. The one-line version: a machine's filesystem, seen from the phone through the backend, keyed on the setup rather than on a session (a session only says where to start), with every operation one fixed shell script run through Transport so the local and the ssh case are one implementation.

Security

• TLS with a self-signed CA, pinned in the app. Generated in process on first start into $XDG_CONFIG_HOME/ai-app/certs, so one place decides the extensions, the file modes and which addresses the leaf covers — every local IPv4 plus loopback and the emulator's host alias, so nobody maintains a hardcoded IP. The CA is created once and left alone; the leaf is reissued every start, so covering a new address is a restart. Regenerating the CA strands the installed app — the one-way door.
  • Unlike dev-updater, the pinned CA is not a constant in the source: the build reads $XDG_CONFIG_HOME/ai-app/certs/ca.pem from the machine doing the build and generates the constant (generatePinnedCert in app/androidApp/build.gradle.kts; AI_APP_CA overrides). That does three things at once — the trust anchor follows the build machine, so an APK built in the dev VM is only good for its emulator; there is no second anchor to add for development and forget to remove; and regenerating a CA needs a rebuild rather than a paste, so a stale constant cannot quietly disagree with the server.
• The dev VM is untrusted (2026-08-25): not malicious, but it could become so. The repo is a read-write mount shared between the VM and the backend host, so everything in it — source, binaries, and the shell scripts the host runs — is attacker-writable.
  • Nothing secret lives in the repo. A CA private key the VM could read would let it mint a leaf the pinned app accepts, which is precisely the attack pinning exists to stop. Transcripts move for a plainer reason: they are whole conversations.
  • The host should not execute what the VM can write — build and run the backend from a host-only checkout rather than the shared mount. Moving the keys closes the smaller door; this is the larger one.
  • Accepted: a compromised VM can return anything it likes from the sessions it runs, since running an agent there is the point. The blast radius is that session's content, not the backend.
• This server's API is remote code execution (spawn a bypass-permissions Claude on any ssh host). Pinning authenticates the server to the phone but not the phone to the server, so a bearer token adds the other direction. The token gates LAN-reachable RCE; it cannot defend a compromised backend host or phone — those are inside the trust boundary, and a compromised phone is handled by rotation.
  • No route accepts a command. Listing, reading and writing files are fixed scripts in files.rs; the phone chooses only the path and the bytes. Provider discovery asks the machine rather than taking a command.
  • The explorer's routes take a path, and that is deliberate (EXPLORER.md's decision 3). Elsewhere the phone picks an id and the server resolves which file it names, so an enrolled token cannot become "read me an arbitrary file" — the import listing is written that way. The explorer is different because the path is the whole feature, and it grants nothing new: the same token already spawns a bypass-permissions agent in any directory on any machine a setup names. The import rule stands where it is, because there a path was unnecessary.
  • Generation: 256 bits from the OS CSPRNG, base64url. A machine credential, never typed twice, so at this entropy no stretching is needed.
  • Enrollment: printed once as a terminal QR code encoding aiapp://enroll?host=…&port=…&token=…. The CA is embedded in the APK, so the QR carries no trust material — photographing the terminal leaks only the token, never a way to weaken pinning. The app registers an intent filter for the scheme, and the Settings screen also scans in-app via zxing-android-embedded, because not every phone's stock camera redirects a scanned URI to an app reliably.
  • Storage: the server keeps only the SHA-256 in config.ron; a plain hash is enough for high-entropy random input. No "show token again" — lost means rotate. The phone seals it with an Android Keystore AES-GCM key (ServerConfig.kt; Jetpack's EncryptedSharedPreferences is deprecated with no drop-in successor and Google's guidance is now "use Keystore directly").
  • Transport: Authorization: Bearer on every request including the SSE GET, never a query parameter, since URLs leak into logs. The tracing layer must not log the header — covered by a test, so a logging change cannot silently start leaking it.
  • Verification: one middleware wrapping the entire router, never per-route, so a new route cannot forget auth. Zero unauthenticated endpoints, /health included. Hash-then-constant-time-compare (subtle); failures logged with peer address plus a small fixed delay — not against brute force, but so scanners show up in the log.
  • Rotation (the path out): --rotate-token regenerates, invalidates the old hash, reprints the QR. Config stores a list of {name, hash}, so per-device revocation is a config entry later, not a migration.
  • Why not mTLS: stronger in theory, but given pinning the delta is only "someone reads the token off a device already inside the trust boundary", and it costs Android client-cert provisioning and a worse new-phone story. Revisit if this outgrows single-user-on-LAN.
• Off-network access: plain WireGuard (2026-08-24, no third party). The backend binds wg0 only; the phone runs the official WireGuard app, enrolled by scanning its config as a terminal QR. The only internet-visible thing is one forwarded UDP port silent to unauthenticated packets, so the pre-auth surface is reachable only from enrolled peers and the token becomes defence in depth rather than the sole gate. Addressing stays single-path: the phone reaches the backend at its WireGuard address from everywhere.
  • Accepted operationally: the endpoint is a DDNS name, since the home IP is not guaranteed static. The WireGuard app resolves it when the tunnel comes up and does not re-resolve, so a rare IP change is fixed by toggling the tunnel once DDNS catches up. The symptom is obvious and lossless — the SSE cursor design replays whatever was missed.
  • Rejected: Tailscale and Headscale, which add a coordination service this setup does not need at two or three devices; forwarding the HTTPS port directly, which puts every internet scanner one pre-auth bug away from RCE on a machine holding SSH keys.
  • The server refuses to start without TLS, so the token cannot travel unencrypted by misconfiguration, and binding fails closed — refusing to start if wg0 is absent rather than falling back to 0.0.0.0. --bind <ip> is an explicit, logged override for development, a deliberate flag and never a fallback.

App (app/)

Kotlin + Compose Multiplatform, single :androidApp module, same versions as dev-updater (Kotlin 2.4.x, CMP 1.11.x, JDK 21).

1. Session list — kind icon, title, setup, model, status, last activity. Sessions awaiting an answer sort to the top: the "your turn" inbox.
2. Import — Claude Code sessions the machine already has, selected in batches (hold to enter, tap to add), with Delete and Import along the bottom. Submitting clears the selection immediately and marks every chosen row, so the bar goes away and the affected set is what says the work is happening. Rows are taken out as each one lands rather than all at the end: a finished row still sitting there looks exactly like one that has not been imported, and tapping it starts a second CLI on the same transcript. That makes rows below slide up under the reader's finger, so a row that has just moved ignores taps for SETTLE_MS.
3. Models and Setups — browsing and downloading GGUFs; adding, renaming, re-probing and removing machines.
4. Session screen — the core:
   • The transcript rendered from the event stream: markdown, inline images, tool cards, question cards.
   • Anything that is a note about the conversation rather than a turn in it is closed by default — a tool call, a peer message, a memory note. Open-ness is the screen's, never the card's: a card that remembered for itself forgets the moment the lazy list stops composing it, so a note opened and scrolled past would shut behind the reader.
   • An answered question keeps its options and marks the one taken, in the same purple that says "picked" while it is open — it does not collapse into a line repeating the answer. The options are what the question was, and "Deny" alone does not say Allow was the alternative. One rule in two places (AskedQuestion and PermissionAsk). An answer typed into Other matches no option, so that one is still written out.
   • Expanding a row keeps still the end nearest the tap: touch a row's upper half and its top edge holds, so it opens downwards; touch its lower half and the bottom edge holds, as the list does by default. Which half, rather than which control, so everything that opens behaves alike whether or not it has a control at each end. The transcript is laid out from the bottom, so a bottom edge is anchored for free and the top one has to be arranged: Modifier.holdTopEdge asks the list to shift during the layout phase, before anything is drawn. From an effect instead, the wrong position is drawn once first, which reads as a flick.
   • The full-screen image lives on the screen, not in the row that drew the thumbnail (SessionImageViewer). A Read whose result is an image is a row of one call until the next call arrives and makes it a group — a different composable in a different part of the tree, so the old subtree and its open dialog go. Somebody looking at a screenshot was thrown back to the transcript because the session made another tool call.
   • All transcript text is selectable, from one SelectionContainer around the whole list. Not per row: a transcript is one body of text, so a selection has to run from a reply into the tool output under it — and a container per row leaves whatever was drawn without one silently unselectable. An inline code chip is drawn behind the text rather than as the renderer's span background, because a span background is part of the text's own drawing and hid the selection under it.
   • Input bar: text, attach, send — always enabled; mid-run sends become steering messages. A queued message can be tapped to take it back.
   • The composer's process button (interrupt / stop / start) as above.

Markdown

A reply is drawn as pieces of one parse, never as re-parsed substrings. A Piece addresses a top-level block of the message's tree, or one item of a top-level list, and every piece is drawn from the same cached parse. That is what bounds a lazy-list item without parsing a message more than once, and it is why a forty-item list of sources is forty units rather than one. Links are spans with one tap detector per text, not a layout node per link — the cost that made a list of sources bumpy.

A table wraps its cells and never cuts one off. The renderer's defaults draw every cell at one line with an ellipsis, which on a phone loses most of a table — and an elided cell looks exactly like a short one. LinkedTableRow gives a cell as many lines as it needs, aligned to the top of the row so a two-line cell does not re-centre its neighbours. A column narrows to 136dp and no further, past which the whole table scrolls sideways; 136 because it is the widest floor that still fits three columns across a phone. Exercise it with the echo driver's /table N, which writes long cells on purpose — a fixture of tidy one-word values renders fine either way.

The transcript cache

The backend's transcript is the source of truth, and the app keeps a copy of what it has already been sent — see TRANSCRIPT_CACHE.md (2026-09-04), because reopening a session over the tunnel was re-downloading a conversation the phone had just read. It is the server's own event lines, per session, under cacheDir; it is checked against the server before a stream is resumed from it, thrown away rather than patched when that check fails, and never load-bearing — every path that reads it has a network path beside it giving the same answer. What the app does not keep is anything derived: the folded rows are rebuilt from events every time.

Notifications: two places, never both (2026-08-30)

GET /notifications is one SSE stream of attention-wanting moments, and the app decides where each one is said. Three outcomes, in one place (NotificationService.show):

• Nothing at all if the session is the one on screen. The transcript in front of the reader is already saying it.
• A banner over the app if the app is up — SessionAlerts, queued, one per session replacing that session's own, dismissable by a push in either direction and otherwise retiring itself when the bar across its foot runs out.
• A row in Android's drawer otherwise, which is what the foreground service exists for.

Never two of them for one moment. A drawer that fills up behind an app that showed you each one is a drawer nobody reads. Which of the three applies is answered without a flag anybody has to keep level: the session on screen is registered by the one composable that draws one, and "the app is up" is the banner queue being collected, since it collects only while it is on screen.

What counts as finished is decided in notification_for, and since 2026-08-31 it takes the number of messages the session has been given and not started reading. With one waiting, a turn ending is not the work ending: a message written into the tail of a turn is read the moment that turn's result lands, so the session goes idle and immediately runs again — and the phone that sent it was told its work had finished seconds before any of it was done. The count is kept in pump, the one place that sees every event in transcript order. It does not suppress awaiting input: a question is worth saying whatever is queued behind it.

Rejected: giving the app its own connection to /notifications while it is in front. That is a second stream per device saying the same thing, and it puts the "which of these two shows it" decision in two processes' worth of code instead of one function.

Deferred polish

Noticed and deliberately not fixed, so they are not re-found from scratch.

• The session screen's header is lopsided. The row is padding(horizontal = 8.dp), so the status on the right sits exactly 8dp from the edge while "Back" on the left is a TextButton whose touch target is wider than its text. It is the "align the mark, not the box" case: either align the button's content or size the button to what it draws, rather than nudging with a hardcoded offset.

Status

Phases 1–3 (the skeleton pipe, the full Claude driver, the usage screen) done 2026-08-24. Phase 4 (llama.cpp: model browsing, downloads, and llama-server through its OpenAI-compatible endpoint) and phase 5 (ssh) done 2026-08-28, except for the remote llama-server and its port forward, which landed 2026-09-04. The file explorer and the transcript cache followed in September. What is left is real-phone/WireGuard bring-up, which is operational rather than code.

Each phase ended runnable and verified against the real thing. The backend gets tests where logic is pure — event normalization, transcript cursors, config persistence, the syntax scanner; the app is UI over the API and is verified by running it, matching dev-updater's posture.

Open questions and risks

• The Claude stream-json control protocol is the least-documented dependency and is version-coupled to the installed CLI. What works is pinned in session/claude.rs's module doc against the version it was measured on.
• The usage endpoint is undocumented and has changed rate-limit behaviour before; treat as best-effort.
• Compaction for llama sessions is not built. LlamaDriver::compact refuses. The design when it is built: every response reports prompt and completion token counts, so track them against n_ctx (from /props), and at ~75% summarize all but the last few turns and replace them, keeping the full pre-compaction transcript on disk so the phone's view never loses history. llama-server's own --context-shift is rejected as the strategy: it truncates old KV cache entries, which is silent forgetting with no summary, and it corrupts the harness's view of what the model knows. Fine as a server-side safety net; not memory management.
• Remote llama-server needs its port forwarded (ssh -L) and is not built; such a session is refused rather than misdirected.
• Claude sessions over ssh need the remote machine logged in to Claude. Usage reporting reads each machine's own credentials, so this is visible rather than silent.

References

• llama-server API (/health, /props, OpenAI-compatible endpoints): https://github.com/ggml-org/llama.cpp/blob/master/tools/server/README.md
• Usage endpoint (GET https://api.anthropic.com/api/oauth/usage, bearer token from ~/.claude/.credentials.json, headers anthropic-beta: oauth-2025-04-20 + User-Agent: claude-code/<version>, ≥180 s polling; a wrong User-Agent lands in an aggressive 429 bucket): https://github.com/anthropics/claude-code/issues/31637
• The sibling project this repo's conventions mirror: ../dev-updater (README.md + AGENTS.md — server/registry/routes layout, cert scheme, testing posture).