ai-app/PLAN.md

# ai-app — plan

A phone interface to AI coding sessions — Claude Code and llama.cpp for now —
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 the things
the official app gets wrong (e.g. it won't deliver a typed message until the
session fully finishes its turn, 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.

## The one idea everything hangs off

Both session types are **a child process speaking JSONL over stdio**:

- Claude Code: `claude -p --input-format stream-json --output-format stream-json`
  — bidirectional streaming JSON. User messages sent while a turn is running
  are injected at the next opportunity (the TUI behavior we want), a control
  protocol carries interrupts and permission requests, `--resume <id>` picks a
  session back up after a backend restart.
- llama.cpp: **pi in RPC mode** (`pi --mode rpc`), pointed at a llama-server
  endpoint. Same deal: JSONL on stdio, `prompt` (with images), `steer` for
  mid-run injection, `abort`, `set_model`, `compact` / `set_auto_compaction`,
  session files that survive restarts, structured events for streaming text
  and tool executions.

So the backend has one abstraction — spawn a process, translate its dialect to
a common event stream, keep an append-only transcript — and two translators.
SSH support falls out of the same shape: a remote session is the identical
command run as `ssh <host> <cmd>`; stdio doesn't care.

Decisions already made (2026-08-24):

- llama.cpp harness: **pi RPC now**, with the session abstraction kept clean
  enough that a custom Rust agent loop can be added as a third driver later.
- The backend **manages llama-server itself** (start with a chosen GGUF, stop,
  swap models), locally and over SSH.
- Claude permission prompts are **interactive in the app**, with a per-session
  permission mode chosen at spawn.
- **One backend** on the main machine; the phone talks only to it, and it
  reaches other hosts via SSH. Remote hosts need the CLIs installed but no
  backend.

## Architecture

### Setups and providers (decided 2026-08-28, superseding the below)

**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
then two choices in order: pick a setup, then pick one of its providers.

This replaces the independent providers × hosts model recorded below,
which is what the code does today. What went wrong with it: the two axes
are not actually independent. A provider is only real on a machine where
that CLI is installed, so a free cross-product offers combinations that
cannot work — `claude-cli` on a machine with no `claude`, and every
provider paired with a host the driver ignores entirely (`EchoDriver`
takes no host, so "Run on" is a control that silently does nothing for
it). Grouping providers under the machine they exist on makes the picker
show only what is true.

Open, and worth settling before this is built:

- **Where the built-in echo provider lives.** It needs no configuration
  and is the connectivity check that costs no tokens, so probably a
  provider of an implicit local setup rather than something configured.
- **Migration.** Sessions store the provider and host names they were
  spawned with; they would store a setup and a provider instead.
- **Setups are edited from the phone**, not by hand in `config.ron` — the
  standing preference for this app. Key material is the exception that
  cannot travel, so a setup names an identity file that must already exist
  on the backend machine.

The superseded model, for the reasoning it recorded:

Two independent axes, configured separately and chosen per session:

- A **provider** is *what* runs: a driver kind, the command to invoke, and
  the models worth offering. `claude-cli` is the first — named for the CLI
  specifically, since bare "claude" would suggest the credit-billed API,
  which this is not. llama.cpp becomes a second provider later.
- A **host** is *where* it runs: an ssh target. Absent means the backend
  machine itself.

Sessions name both. Keeping them independent is what the motivating setup
requires: the backend runs on the machine the phone can reach (where
WireGuard terminates), which is not necessarily where a CLI is installed —
here the Claude CLI lives only in a VM on that machine, while llama.cpp
will be on the host itself. Pinning a host into a provider would make "the
Claude CLI" and "the Claude CLI over there" two things to configure and
choose between, and would stop the same provider from being sent somewhere
else for one session.

```
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)
   │                      └─ PiDriver       (pi --mode rpc)
   │        each driver's process is spawned locally or as `ssh host …`,
   │        decided per session by the host it names
   ├─ LlamaServerManager  (llama-server lifecycle, local + SSH)
   ├─ UsageMonitor        (Anthropic OAuth usage endpoint)
   └─ config.ron + per-session transcript files
```

### Backend layout (`server/`)

Mirroring dev-updater's stack: axum 0.8, axum-server + rustls, tokio, serde,
clap, tracing. Rust edition 2024, warning-clean, clippy in CI habit.

- `main.rs` — bootstrap, TLS listener.
- `routes.rs` — the whole HTTP table in one module doc comment (as in
  dev-updater).
- `session/mod.rs` — `SessionManager`: the live session registry, every
  mutation funnels through it (the `registry.rs` pattern: in-memory and
  on-disk state can't come apart).
- `session/driver.rs` — the `Driver` trait and the common event model.
- `session/claude.rs`, `session/pi.rs` — the two translators.
- `session/transcript.rs` — append-only JSONL event log per session, with
  monotonically increasing sequence numbers (the phone's resume cursor).
- `llama.rs` — `LlamaServerManager`.
- `ssh.rs` — the ssh command builder (host configs ended up in `config.rs`
  with the rest of the schema, so this module is only the wrapping; named
  for what it does rather than `hosts.rs` as first sketched).
- `usage.rs` — Anthropic usage polling.
- `config.rs` — persisted schema.
- `certs.rs` — the TLS certificates, generated in process on first start
  (added 2026-08-25, replacing a `gen-dev-cert.sh` that shelled out to
  openssl).
- `private.rs` — creating files and directories owner-only. One module
  owns the modes so "nothing this server writes is readable by anyone
  else" is checkable in one place instead of re-argued at each `create`
  (added 2026-08-25; config, certs, and session dirs had three copies).
- `media.rs` — the image media-type/extension table, shared by the four
  places that have to agree on it: storing an upload, serving it back,
  handing one to a driver's dialect, and saving one a tool produced.

`session/pi.rs` and `llama.rs` are phase 4 and not built yet; everything
else above exists.

### The common event model

Driver output, whatever the dialect, is normalized into one event enum before
it touches the transcript or the phone:

- `UserMessage { text }` — what the user sent, echoed into the transcript
  by the manager (not by drivers) so every device renders the conversation
  from the one stream. (Added 2026-08-24 during phase 1: without it,
  reconnects and second devices would lose the user's side.)
- `AssistantText { delta }` — streaming text (rendered as markdown).
- `ToolStart / ToolUpdate / ToolEnd { tool, input, output }` — the "view tools
  it's running" screen is just these.
- `Image { ref }` — images in output (screenshots from tools, etc.) are saved
  under the session dir and referenced by id; the phone fetches them by URL.
- `Question { id, prompt, options }` — anything the session needs a human for:
  Claude's AskUserQuestion, and **permission requests** (canUseTool) are the
  same shape with approve/deny options. Answered via one endpoint.
- `Answered { id, answer }` — the manager's record of a question being
  answered, so a rendered question card resolves on every connected device,
  not just the one that answered (added 2026-08-24, same reasoning as
  `UserMessage`).
- `Status { state }` — idle / running / awaiting-input / compacting / exited.
- `UsageDelta { tokens }` — per-turn token counts where the dialect reports
  them (both do).
- `Error { message }`.

Every event is appended to the session's transcript file with a sequence
number, then fanned out to any connected SSE subscribers. The phone renders
purely from this stream: reconnecting means "give me events after seq N" —
no separate "load history" path to drift from the live one.

Inbound, the driver trait is small:

```rust
trait Driver {
    fn send_user_message(&self, text: String, images: Vec<ImageRef>);
    fn answer_question(&self, id: QuestionId, answer: Answer);
    fn interrupt(&self);                       // stop mid-run, session survives
    fn set_model(&self, model: &str);
    fn compact(&self);                         // pi: native; claude: /compact
    fn shutdown(&self);                        // graceful process exit
}
```

`send_user_message` during a run is the point of the whole app: both dialects
queue it for injection at the next tool boundary rather than the end of the
turn. Claude's dialect: a `user` message on stdin mid-stream; pi's: `steer`.

### 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` at spawn. Permission mode (default/plan/acceptEdits/
  bypassPermissions) is chosen on the spawn screen.
- Interactive permissions: run with the stream-json control protocol's
  permission request flow (the same mechanism the Agent SDK's `canUseTool`
  uses) so tool approvals arrive as control requests, become `Question`
  events, and our answer goes back as the control response. **Verify the
  exact control-request wire format against the current CLI early in
  implementation** — it's the least-documented part of this plan.
- Interrupt: control-protocol interrupt request.
- Model change mid-session: try the control protocol's set-model; if the
  installed CLI doesn't support it, fall back to `shutdown` + respawn with
  `--resume <session_id> --model <new>` — cheap, since Claude persists
  sessions in `~/.claude/projects` anyway. That same resume path is the crash
  recovery story: a dead backend or a killed process loses nothing.
- Images in: base64 image content blocks in the stream-json user message.
- Working directory, host, and model are spawn-screen fields.

### pi driver specifics

- Spawn: `pi --mode rpc --provider openai-generic --model <name>` (endpoint =
  the llama-server the LlamaServerManager provides), `--session-dir` under
  our session storage so transcripts and pi's own session files live together.
- Auto-compaction on by default (`set_auto_compaction`), threshold
  configurable per session; manual `compact` exposed as a button.
- `steer` for mid-run messages, `abort` for stop, `set_model` when the target
  endpoint changes.
- pi's session JSONL gives resume-after-restart, same as Claude's.

### llama-server management

`config.ron` lists **models** (name → GGUF path or llama-server args, per
host) and **hosts**. The manager runs at most one llama-server per
`(host, model)`, spawned on demand when a session needs it:

- Spawn (local or `ssh host llama-server …`) on an allocated port, wait on
  `/health`, hand the endpoint to the pi driver.
- Refcounted by sessions. The path out, written in the same change as the
  spawn: the last session using an instance releasing it starts an idle
  timer (configurable, e.g. 10 min), after which it's killed. Delete of the
  last session kills it immediately.
- "Change model" on a llama session = acquire the new model's server,
  `set_model` on pi, release the old one. Context carries over (it's
  prompt-replayed by pi against the new endpoint).
- Remote llama-server output is only reachable from the backend host, and
  binds localhost on the remote side with an SSH local port forward
  (`ssh -L`) held by the manager — no LAN-exposed inference ports.

### SSH

- Host entries in `config.ron`: name, `user@host`, optional ssh options,
  which capabilities it has (claude / pi / llama-server, with paths if not on
  PATH). Key-based auth only, using the system `ssh` client via
  `tokio::process` — no Rust SSH library; this inherits `~/.ssh/config`,
  agents, and jump hosts for free. (Rule 23: openssh is already here and
  battle-tested; a library buys nothing but a second config surface.)
- A remote session is exactly a local one with the command wrapped in
  `ssh -T host …`. Process death ≙ connection death; the session shows as
  `exited` and both dialects resume (`--resume` / pi session file) on respawn,
  so a dropped SSH connection is an annoyance, not data loss.
- **The transport wraps the driver, not the other way round** (decided
  2026-08-28). A driver says what to run — program, arguments, working
  directory — and something above it turns that into a process, locally or
  through ssh. Today `ClaudeDriver::spawn` calls `ssh::command` itself,
  which puts transport knowledge inside a translator whose job is a wire
  format, and means every future driver has to remember to do the same.
  Inverting it also removes the "Run on" lie for free: a driver that emits
  no command, like the echo one, has nothing for a transport to wrap, and
  the picker can say so.
- The interface that inversion needs is **not just "run a command"**, and
  llama.cpp is the case that shows it: a managed `llama-server` is started
  as a process but then spoken to over HTTP, so a remote one needs a
  forwarded port (`ssh -L`) as well as a spawned process. A transport is
  therefore "run this" plus "reach this port", and the second operation is
  a no-op locally.
- Attachments need no file transfer, contrary to what this section said
  before: `attachment_block` base64s an uploaded image into the
  stream-json message itself, and produced images come back the same way
  for the translator to write out locally. Nothing has to exist on the
  remote filesystem, so there is no `scp` step to get wrong.

### Usage limits (Claude)

Poll `https://api.anthropic.com/api/oauth/usage` — the same endpoint behind
Claude Code's `/usage` — with the OAuth access token from Claude Code's local
credential store (`~/.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 any Claude session exists or the usage screen is
open, cache the last answer. Surface: 5-hour and weekly window utilization %
and reset times. It's undocumented, so `usage.rs` treats every field as
optional and degrades to "unavailable" rather than erroring. Structure it as
one `UsageProvider` per paid service so a second service later is a new impl,
not a parallel screen (rule 9).

### HTTP surface (phone ⇄ backend)

REST for actions, one SSE stream per open session screen for events, all over
the pinned TLS listener. SSE over WebSocket because resume-by-cursor
(`Last-Event-ID` = transcript seq) is native to it and the inbound direction
is plain POSTs anyway.

```
GET  /providers                       what can be spawned (name, kind, models)
GET  /hosts                           machines a session can be run on
GET  /sessions                        list (id, provider, host, title, model, status, last activity)
POST /sessions                        spawn {provider, host, model, cwd, permission_mode, title}
GET  /sessions/:id/events?after=N     SSE: transcript replay from N, then live
POST /sessions/:id/message            {text, attachment_ids}
POST /sessions/:id/answer             {question_id, answer}   (questions and permissions)
POST /sessions/:id/interrupt
POST /sessions/:id/model              {model}
POST /sessions/:id/compact            (llama sessions)
POST /sessions/:id/attachments        multipart upload → id (referenced by /message)
GET  /sessions/:id/files/:ref         images the session produced or was sent
DELETE /sessions/:id                  kill process, release llama-server, delete transcript+files
GET  /usage                           cached usage windows
GET/PUT /hosts, /models               config editing from the phone
```

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

### Security

- TLS with a self-signed CA, pinned in the app — same
  idempotent-CA/reissued-leaf scheme as dev-updater, same one-way-door
  caveat about regenerating the CA, but generated **in process on first
  start** (`certs.rs`) rather than by a shell script calling openssl
  (2026-08-25). One place then 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 — and there is
  no setup step to forget.
  - Unlike dev-updater, the pinned CA is **not a constant in the source**:
    the build reads `$XDG_CONFIG_HOME/ai-app/certs/ca.pem` from the machine
    doing the build and generates the constant (`generatePinnedCert` in
    `app/androidApp/build.gradle.kts`; `AI_APP_CA` overrides). Decided
    2026-08-25, and it does three things at once — the trust anchor follows
    the build machine, so an APK built on the backend host pins that host
    and one built in the dev VM pins the VM's throwaway CA and is only good
    for its emulator; there is no second anchor to add for development and
    forget to remove; and regenerating a CA needs a rebuild rather than a
    paste, so a stale constant can't quietly disagree with the server.
- **The dev VM is untrusted** (decided 2026-08-25): a machine that isn't
  malicious but could become so. It matters because the repo is a
  read-write virtiofs mount shared between the VM and the backend host, so
  under this model everything in it — source, `server/target/` binaries,
  and the shell scripts the host runs, some with sudo — is
  attacker-writable. Two consequences:
  - **Nothing secret lives in the repo.** Certificates are generated on
    the machine that serves them and written to
    `$XDG_CONFIG_HOME/ai-app/certs` (0700, keys 0600); `config.ron` and
    session transcripts go to the XDG config and data directories, per
    machine. 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 — pinning against a CA the attacker holds is no pinning at
    all. Transcripts move for a plainer reason: they are whole
    conversations. As a bonus this ends the host and VM sharing one
    config, which had already produced a test token live on the backend,
    and takes state out of reach of `git clean -xdf`.
  - **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.
  - Development in the VM generates its own throwaway CA. Whatever is
    installed on the real phone must pin only the host's.
  - The CA key is not needed by the server at all (only `leaf.pem` and
    `leaf-key.pem` are read), so it can move offline once the setup is
    stable; reissuing a leaf is the only time it is wanted.
  - Not addressed, and 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 is strictly more dangerous than the updater: its 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. Threat model: the token
  gates LAN-reachable RCE; it does not (and cannot) defend a compromised
  backend host or phone — those are inside the trust boundary, and a
  compromised phone is handled by rotation.
  - **Generation**: 256 bits from the OS CSPRNG on first run, base64url. A
    machine credential, never typed twice, so unguessable costs nothing; at
    this entropy no key stretching is needed.
  - **Enrollment**: printed once as a terminal QR code (`qrcode` crate,
    ANSI), encoding `aiapp://enroll?host=…&port=…&token=…`. The CA stays
    embedded in the APK (`PinnedCert.kt` pattern), so the QR carries no
    trust material — photographing the terminal leaks only the token
    (rotatable), never a way to weaken pinning. The app registers an intent
    filter for the `aiapp://enroll` scheme as a fallback, for a camera app
    that redirects a scanned URI straight to `MainActivity` (2026-08-24).
    That was meant to be the only path — "the app side needs no QR library
    at all" — but reversed the same day: not every phone's stock camera
    redirects a scanned URI to an app reliably, so the Settings screen also
    scans in-app via `zxing-android-embedded`'s `ScanContract` (a ready-made
    scanner Activity reached through the AndroidX Activity Result API,
    fully offline, no Play Services/ML Kit model download) and feeds the
    decoded URI to the same `parseEnrollmentUri` (2026-08-25).
  - **Storage**: server keeps only the SHA-256 in `config.ron` (plain hash
    is enough for high-entropy random input; buys that a leaked config
    doesn't leak the credential). No "show token again" — lost means rotate.
    Phone side: sealed with an Android Keystore AES-GCM key (a small
    hand-rolled helper in `ServerConfig.kt` — Jetpack's
    EncryptedSharedPreferences is deprecated with no drop-in successor, and
    Google's guidance is now "use Keystore directly"; 2026-08-24).
  - **Transport**: `Authorization: Bearer` header on every request including
    the SSE GET. Never a query parameter (URLs leak into logs). The tracing
    layer must not log the header — covered by a test so a logging change
    can't silently start leaking it.
  - **Verification**: one middleware wrapping the entire router in `main.rs`,
    never per-route, so a new route can't 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 (infeasible at 256 bits) but so scanners show up
    in the log.
  - **Rotation (the path out)**: `--rotate-token` regenerates, invalidates
    the old hash immediately, reprints the QR. That's the whole lost-phone
    story. Config stores a *list* of `{name, hash}` (of one, today) so
    per-device tokens with individual revocation are a config entry later,
    not a schema migration.
  - **Why not mTLS**: stronger in theory (key never leaves the Keystore, no
    bearer secret to exfiltrate), 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 ceremony and a
    worse new-phone story than a QR scan. Revisit if this outgrows
    single-user-on-LAN.
- **Off-network access: plain WireGuard** (decided 2026-08-24; no third
  party). The backend binds to the WireGuard interface (`wg0`) only; the
  phone runs the official WireGuard app (always-on VPN, per-app tunneling),
  enrolled by scanning its config as a terminal QR
  (`qrencode -t ansiutf8 < phone.conf` — same gesture as token enrollment).
  The only internet-visible thing is one forwarded UDP port that is silent
  to unauthenticated packets — scanners see it as closed — so the app's
  pre-auth surface (rustls handshake, hyper parsing, auth middleware) is
  reachable only from enrolled peers, and the token becomes defense in depth
  rather than the sole gate. Addressing stays single-path: the phone reaches
  the backend at its WireGuard address (e.g. `10.66.0.1`) from everywhere —
  one address in the app, one SAN in the leaf cert (`SERVER_IP=`/SAN
  override in the cert script), no home/away distinction. Another machine
  later is one keypair + one `[Peer]` block.
  - Operational needs, accepted: a public endpoint hostname. The home IP is
    mostly static but not guaranteed, so the phone's endpoint is a DDNS name
    (free, e.g. DuckDNS, or the router's built-in client; a curl cron on the
    backend host works too) that tracks changes automatically. One WireGuard
    nuance: the phone app resolves the endpoint hostname when the tunnel
    comes up and does not re-resolve on its own, so on the rare IP change
    the fix is toggling the tunnel off/on once DDNS has caught up (minutes).
    The symptom is obvious (app can't reach the backend) and lossless — the
    SSE cursor design means reconnects replay whatever was missed. Also:
    at-home traffic rides NAT hairpinning on the router (verify early; most
    support it, and the fallback is toggling the tunnel off at home).
  - Rejected: **Tailscale** — same WireGuard underneath with easier setup
    (no port forward, LAN peer discovery), but it adds a third-party
    coordination service and account this setup doesn't need at two or
    three devices; **Headscale** — self-hosting that coordination server is
    strictly more moving parts than one wg config per peer at this scale;
    **forwarding the HTTPS port directly** — puts every internet scanner
    one pre-auth bug away from RCE on a machine holding SSH keys.
  - The server still refuses to start without TLS — no plaintext listener
    exists even inside the tunnel, so the token can't travel unencrypted by
    misconfiguration, and interface binding failing closed (refuse to start
    if `wg0` is absent, rather than falling back to 0.0.0.0) is part of the
    same guarantee. Development gets `--bind <ip>` as an *explicit, logged*
    override (loopback for curl, a LAN address for a pre-WireGuard phone) —
    a deliberate flag, never a fallback, so the fail-closed default is
    untouched (2026-08-24).
- The bootstrap-over-HTTP trick from the updater is unnecessary here — the
  app installs via Dev Updater.

## App (`app/`)

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

1. **Session list** — cards: kind icon, title, host, model, status
   (running / awaiting answer / idle / exited), last activity. Spawn FAB;
   swipe/long-press to delete (confirm). Sessions awaiting an answer sort to
   the top — that's the "your turn" inbox.
2. **Spawn** — kind, host (from config), model (Claude list is static+editable;
   llama list from config), working directory, permission mode (Claude),
   title.
3. **Session screen** — the core:
   - Transcript rendered from the event stream: markdown text, inline images,
     collapsed-by-default tool cards (name + input summary, expandable to
     output; a spinner while `ToolStart` has no matching `ToolEnd`).
   - Question cards inline: option buttons for AskUserQuestion, allow/deny for
     permissions, free-text where allowed.
   - Input bar: text, attach (camera/gallery/file), send — **always enabled**;
     mid-run sends become steering messages.
   - Top bar: model chip (tap to change), stop button while running, token
     count, compact button (llama), overflow → delete.
4. **Usage** — window bars for the 5-hour and weekly limits with reset times.
5. **Settings** — server address + token, hosts editor, llama model list
   editor.

Networking mirrors dev-updater's app layer (`AppsApi.kt` style thin client +
pinned transport), plus an SSE client with `after=` resume driven by
connectivity/lifecycle. The app keeps no persistent transcript store — the
backend's transcript is the source of truth; the app caches only for the
screen it's showing.

### Deferred polish

Noticed and deliberately not fixed yet, so they are not re-found from
scratch. None is a defect; each is a decision waiting for the app to have
been used enough to say which way.

- **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 — the same 8dp reads as more. 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.

## Compaction: options explored

Context: raw llama-server has no conversation memory management; the context
window just fills.

1. **pi's auto-compaction** — *chosen*. When the prompt nears the model's
   context limit, pi summarizes older history with the model itself and
   replaces it with a structured summary; threshold configurable; manual
   `compact` also exposed. Battle-tested, zero work for us.
2. **Manual compaction in a custom Rust loop** — *the later third driver*.
   The design when we build it: every llama-server response reports prompt +
   completion token counts; track them against `n_ctx` (from `/props`); at a
   threshold (~75%), pause, run a summarization request over all but the last
   few turns ("state of the task, decisions made, open items, relevant
   file/tool state"), replace those turns with the summary as a system-adjacent
   message, continue. Keep the full pre-compaction transcript on disk — the
   phone view never loses history, only the model's view shrinks. Worth doing
   eventually for control over the summarization prompt and for tool-loop
   experiments pi doesn't allow.
3. **llama-server `--context-shift`** — *rejected* as the strategy. It
   truncates old KV cache entries: silent forgetting, no summary, and it
   corrupts the harness's view of what the model knows. Fine as a server-side
   safety net; not memory management.

## Phases

1. **Skeleton** — *done 2026-08-24.* Repo layout, cert script, TLS + token
   auth, wg0-bound listener (fail closed if the interface is missing),
   config.ron, session registry with a fake `EchoDriver`, session list +
   session screen in the app end-to-end over SSE. Proves the whole pipe
   before any AI is involved. Verified: 10 server tests + clippy clean;
   curl end-to-end over pinned TLS (auth rejection, spawn, SSE
   replay/resume by cursor, question round trip, restart continuing seq
   numbers, delete); the app on the `tdep` emulator against the real
   server (QR-style enrollment via deep link, spawn, streamed echo turn,
   question answer, tool card).
2. **Claude local** — *done 2026-08-24.* ClaudeDriver: spawn, stream
   text/tools, mid-run send, interrupt, permission questions,
   AskUserQuestion, images both ways, delete.
   *Milestone: daily-drivable Claude replacement on localhost.*
   Wire-format notes live in `session/claude.rs`'s module doc (pinned
   against CLI 2.1.237): permissions need the hidden
   `--permission-prompt-tool stdio` flag; AskUserQuestion answers ride
   `updatedInput.answers` keyed by question text; `set_model`/`interrupt`
   are control requests; 2.x permission modes are acceptEdits / auto /
   bypassPermissions / manual / dontAsk / plan (no more "default").
   Attachments/files were re-homed under `/sessions/:id/…` (table above)
   so their lifecycle is the session directory's — delete stays the
   complete path out.
3. **Usage screen** — *done 2026-08-24.* The undocumented endpoint's
   `limits[]` array parsed defensively into labeled window bars; cached
   behind the ≥180 s minimum with no background polling.
4. **llama.cpp** — LlamaServerManager (local), PiDriver, model change,
   compaction controls. *Deferred (2026-08-24): pi/llama-server aren't set
   up in this VM, so this phase isn't testable here — Claude first; the
   driver seam is ready when it is.*
5. **SSH** — host config, remote spawn for both kinds, remote llama-server
   with port forward, attachment shipping. *Host config and remote spawn
   done 2026-08-25* (any session of any provider can name a host; the
   command is the identical one wrapped in `ssh -T`, with every argument
   shell-quoted). Attachment shipping turned out to be unnecessary for the
   Claude driver — images ride the stdio JSONL as base64 in both
   directions, so nothing needs `scp`. Still outstanding: remote
   llama-server with its port forward, which comes with phase 4.
   Two things learned doing it: a remote session inherits ssh's non-login
   PATH, which is narrower than an interactive shell's (point `command` at
   an absolute path if a CLI isn't found), and the remote command is run
   with `exec` so dropping the connection takes the CLI down rather than
   orphaning it.
6. **Polish** — reconnect edges, notification when a session awaits an answer
   (the "your turn" push), transcript search, whatever daily use surfaces.

Each phase ends runnable and verified against the real thing (rule 22); the
backend gets tests where logic is pure (event normalization, transcript
cursors, config persistence, refcounting) — the app is UI over the API and is
verified by running it, matching dev-updater's posture.

## Open questions / risks

- **Claude stream-json control protocol details** (permission requests,
  set-model, interrupt wire format) are the least-documented dependency and
  version-coupled to the installed CLI. Phase 2 starts by probing the
  installed version and pinning what works; the `--resume` respawn fallback
  covers whatever the control channel can't do.
- The **usage endpoint is undocumented** and has changed rate-limit behavior
  before; treat as best-effort.
- **pi RPC schema drift** — pin a pi version; the translator is one file.
- Whether **notifications** need FCM or a foreground-service polling
  connection — decide in phase 6; the SSE cursor design already supports
  either.
- Claude sessions over SSH need the remote host **logged in to Claude**; usage
  reporting reads only the backend host's credentials. Acceptable for now
  (same account everywhere); revisit if not.

## References

Research behind the decisions above (verified 2026-08-24; re-check against
installed versions when each phase starts):

- pi RPC protocol: https://github.com/badlogic/pi-mono/blob/main/packages/coding-agent/docs/rpc.md
  — commands (`prompt`, `steer`, `follow_up`, `abort`, `set_model`,
  `compact`, `set_auto_compaction`, session ops) and the event stream.
- pi + llama-server in practice: https://medium.com/@tolgaeren/running-pi-with-local-llms-c596aa14b062
- llama-server API (`/health`, `/props`, OpenAI-compatible endpoints,
  `--context-shift`): https://github.com/ggml-org/llama.cpp/blob/master/tools/server/README.md
  and the offline-agentic-coding walkthrough:
  https://github.com/ggml-org/llama.cpp/discussions/14758
- 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; wrong User-Agent → aggressive 429 bucket):
  https://github.com/anthropics/claude-code/issues/31637 and
  https://github.com/Maciek-roboblog/Claude-Code-Usage-Monitor/issues/202
- Sibling project this repo's conventions mirror: `../dev-updater`
  (README.md + AGENTS.md — server/registry/routes layout, cert scheme,
  testing posture, Android env notes).