ai-app/AGENTS.md

ai-app

A phone interface to AI coding sessions (Claude Code and llama.cpp via pi), replacing the Claude app for daily use. Rust/Axum backend on the desktop, Kotlin/Compose Android app, WireGuard + pinned self-signed TLS + bearer token between them.

PLAN.md is the design source of truth. Read it before building or changing anything structural. It records every decision with its date, its rationale, and the alternatives that were rejected and why — keep that habit when a decision changes: update the plan in place, don't let this file and the plan drift into two versions of the truth. This file is the working notes layer: conventions, commands, and things that have bitten.

The central design point, worth not undoing by accident: a session is a child process speaking JSONL over stdio, translated into one common event model. Claude Code (stream-json) and pi (RPC mode) are two translators behind one Driver trait; the transcript, the SSE stream, the phone UI, and SSH spawning (the same command wrapped in ssh host …) all work purely in the common model. A new session type is a new driver — never a session-type branch in shared code (routes, transcript, app screens).

Layout

Mirrors ../dev-updater deliberately — same stack (axum 0.8 + axum-server/rustls, tokio, clap; Kotlin 2.4.x + Compose Multiplatform, single :androidApp module), same cert scheme, same registry pattern (every session mutation funnels through the manager so in-memory and on-disk state can't come apart). Read dev-updater's README.md and AGENTS.md for the conventions before diverging from them; module-by-module intent for this repo is in PLAN.md's "Backend layout" section.

• server/src/models.rs — downloaded GGUF models and the HuggingFace browsing behind them. Downloads are keyed by the model rather than by who asked, so any device can watch one; they resume through HTTP Range, refuse to resume onto a partial from a different revision, and are checked against HuggingFace's published sha256 before the file gets its real name.
• server/ — Rust backend (ai-server). main.rs bootstraps (TLS, the auth layer, token/QR enrollment, wg0 binding), routes.rs has the HTTP table in its module doc comment, auth.rs the bearer-token middleware, config.rs the persisted schema and the RON its file is written in, session/ the manager (registry pattern), Driver trait + event model, EchoDriver, and transcripts.
• app/ — Compose Android app, single :androidApp module, package com.example.aiapp, label "AI Sessions". AppRoot.kt is the navigation when; Api.kt/EventStream.kt the REST + SSE clients; Events.kt the event model mirror; ServerConfig.kt settings + Keystore-sealed token; screens in SessionListScreen/SessionScreen/SpawnScreen/SettingsScreen.
• .dev-updater.ron — what Dev Updater is asked to do with this checkout: the backend (built in server/, installed and controlled through server/service) and then the APK (built in app/), in that order. The project it serves is the repository, not either half of it, which is why this sits at the root rather than in app/.
• server/src/certs.rs — the TLS certificates, generated in process on first start into $XDG_CONFIG_HOME/ai-app/certs: idempotent CA, leaf reissued every start covering every local IPv4 plus 127.0.0.1 and 10.0.2.2 (emulator → host). Regenerating the CA strands the installed app — the one-way door.

Status

Phases 1–3 done 2026-08-24 (see PLAN.md's phase list for what each verified): the skeleton pipe, the full Claude driver (streaming, tools, permission + AskUserQuestion cards, steering, interrupt, --resume crash recovery, images both ways), and the usage screen.

Phase 5 (SSH) is written and now exercised (2026-08-28). A session names a host, session::transport turns that into an ssh host … invocation, and the driver never learns which it got.

Phase 4 (llama.cpp) works on the server side (2026-08-28). Models are browsed and downloaded from HuggingFace (models.rs, resumable and verified), and session::llama runs one through llama-server, talking to its OpenAI-compatible streaming endpoint. Two things about it are deliberate and easy to undo by accident: the conversation is rebuilt from the transcript rather than kept in the driver, because driver memory is invisible to a second device; and a llama session is refused on an ssh host, because the model is reached over HTTP and forwarding that port is not built. No app screen yet — models are driven through the routes.

What is left is the models UI, and real-phone/WireGuard bring-up, which is operational rather than code.

Testing llama.cpp here: the prebuilt CPU build lives outside the repo at ~/.local/opt/llama.cpp (the 15 MB ubuntu-x64 release asset — no compiling, and it runs fine on Arch). It needs its own directory on LD_LIBRARY_PATH, so start the server as LD_LIBRARY_PATH=~/.local/opt/llama.cpp ai-server … and point a provider's command at ~/.local/opt/llama.cpp/llama-server. A 0.6B Q8_0 answers at usable speed on this VM's 8 cores. Do not test with a 2-bit quant: the IQ2_XXS of that model produces fluent nonsense, which reads exactly like a broken driver — llama-cli produces the same from the file directly, which is how to tell the two apart in a hurry.

How to test SSH here, since there is no second machine: ssh this VM to itself. Generate a throwaway key, append the public half to ~/.ssh/authorized_keys, and configure a host of bob@127.0.0.1 with identityFile pointing at it plus options: ["StrictHostKeyChecking=no", "UserKnownHostsFile=…"] so it touches nothing real. Point a provider's command at something harmless like /bin/echo rather than at claude: the transport is what is under test, the process exiting immediately is the signal, and it costs no tokens. A session spawned on that host logs running /bin/echo on loopback (bob@127.0.0.1) and lands status: exited in its transcript, which is the whole path — connection, remote exec, process death reported. Take the key back out afterwards; this VM's authorized_keys is not scratch space.

Note the remote login shell here is fish, not a POSIX shell. The remote script (cd '…' && exec '…') happens to be valid in both, and the POSIX single-quote escaping ssh.rs does happens to mean the same thing in fish — but that is luck rather than design, and a shell that isn't either would be the thing to suspect first if a remote spawn ever mangles an argument.

Checking your work

• Server: from server/, ./run-tests.sh (or cargo test) + cargo clippy --all-targets + cargo fmt. The build stays warning-clean and rustfmt-clean at the defaults — there is no rustfmt.toml and there should not be one.
• App: from app/, . ./android-env.sh && ./gradlew :androidApp:ktfmtFormat :androidApp:compileDebugKotlin :androidApp:lintDebug — format, typecheck and lint, the app-side equivalent of the line above. Then ./build-apk.sh to produce the APK to install on a phone (through Dev Updater), or ./run-android.sh to build, install, and launch on the emulator.
• Android Lint is not optional and is not run by a build. It found a crash that had been shipping: java.time on a minSdk-24 app with desugaring off. It is clean now apart from Compose 1.11.1 having a 1.12.0 available; keep it that way, and suppress with tools:ignore plus a written reason rather than by lowering the bar.
• The APK pins the CA of the machine that builds it, read at build time from $XDG_CONFIG_HOME/ai-app/certs/ca.pem (AI_APP_CA overrides) and generated into a constant. So the server must have started once on that machine first — the build stops with that instruction otherwise — and an APK built in this VM only works against a server in this VM.
• Run the server for development with --bind 127.0.0.1. Without it the server binds wg0, which exists here but is unreachable from the emulator (it dials 10.0.2.2). First run prints the enrollment QR/URI with the token — capture it from the log.
• Prefer exercising the server directly over going through the UI: curl --cacert ~/.config/ai-app/certs/ca.pem -H "Authorization: Bearer …" https://127.0.0.1:8443/sessions. The CA is wherever --certs put it — by default under $XDG_CONFIG_HOME (~/.config when that is unset), never in the checkout, so a relative certs/ca.pem finds nothing. The emulator app reaches it at https://10.0.2.2:8443; enroll it with adb shell "am start -a android.intent.action.VIEW -d 'aiapp://enroll?host=10.0.2.2&port=8443&token=…'" (quote so the device shell doesn't eat the &s).

Where things run (host vs this VM)

Established 2026-08-25, and it decides more than it looks like. The machine itself — the two boxes, the shared ~/repos mount, gitea, and why the VM is treated as untrusted — is described once in ~/.claude/MACHINE.md; what follows is only what that means for this project.

• ai-server belongs on the host in production. That is where the LAN address the phone can reach is, and where WireGuard terminates. wg-setup-host.sh sets that up (keys, wg0.conf, the phone's QR); run it there with sudo WG_ENDPOINT=<ddns name>.
• The tunnel and the real phone can never terminate in the VM, because nothing outside can open a connection into it. Phone bring-up is host work.
• wg0 (10.66.0.1) now exists in this VM too, so the production path — ai-server with no --bind — is exercisable during development. It has no reachable peer and doesn't need one; the interface existing is what the server requires. Consequence: with no --bind, the emulator can't reach the server (it dials 10.0.2.2), so keep using --bind 127.0.0.1 for app work.
• ./test-wg-tunnel.sh up|test|down builds a real tunnel between two network namespaces inside one machine and drives the server through it — a genuine handshake against 10.66.0.1 with pinned TLS, no router or phone involved. That's the way to verify the wg0-only posture.
• The claude CLI is only in the VM, so from the host it is a remote. The backend reaches it the way it would any other machine: a configured host, and a session that names it. For the host to ssh in, the VM needs an inbound port forward it does not have by default.
• Nothing secret goes in the repo, which is shared with the host and attacker-writable under this project's threat model (PLAN.md's security section). So state lives outside it: $XDG_CONFIG_HOME/ai-app/config.ron and certs/, $XDG_DATA_HOME/ai-app/sessions/, owner-only.
• Certificates are generated by the server, on first start, into $XDG_CONFIG_HOME/ai-app/certs (--certs overrides). The CA is created once and then left alone; the leaf is reissued every start, so covering a new address is a restart. Starting the server in the VM therefore makes a separate throwaway dev CA for emulator work — never install a build pinning that on the real phone.
• Point development at a scratch state directory rather than the real one: --config /tmp/…/config.ron --data-dir /tmp/…/sessions --port 8444, or XDG_CONFIG_HOME=… XDG_DATA_HOME=….

Things that have bitten

Project-specific only — a lesson that would bite any project on this machine belongs in ~/.claude/TOOLCHAIN.md (toolchain versions) or ~/.claude/MACHINE.md (the machine itself) instead.

• tracing caches callsite interest process-wide. A test that hits a tracing::warn! with no subscriber installed can poison the interest cache for a concurrent test that captures logs (flaky "nothing was logged" failures). Keep every exercise of a logging code path under the one capturing subscriber — that's why the auth middleware has a single combined gating+logging test.
• The keyboard pans the window unless the activity opts into resize. Without android:windowSoftInputMode="adjustResize", opening the IME slides the whole window up (top bar off screen) instead of resizing — imePadding() alone doesn't fix it and the transcript looks empty.
• A PEM constant must start at the opening quotes. A generated """\n-----BEGIN CERTIFICATE----- costs Android's CertificateFactory its preamble sniff, so it tries DER instead and fails at runtime with ASN.1 ... DECODE_ERROR — nowhere near the code that produced it.
• ZXing only looks for a dark code on a light ground. The enrollment QR is block characters in the terminal's foreground colour, so a dark-themed terminal renders it as a negative and the in-app scanner silently never matches — while the phone's own camera app, which tries both, does. The scanner asks for Intents.Scan.MIXED_SCAN, which alternates normal and inverted frames; keep it that way rather than making the server dictate the colours. EnrollmentScanActivity also turns off the library's 10% framing-rect inset (it decodes only what is inside it) and its laser/result-point decorations.