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.

**`TRANSCRIPT_RENDERING.md` is the record of the transcript work** --
measurements, techniques, the harness, and the ordered list of what is
next. Read it before touching anything under `Markdown*.kt`,
`Transcript*.kt` or `SessionScreen.kt`'s list.

**`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/session/import.rs` — continuing a Claude Code session the
  machine already has. Claude Code keeps each one as JSONL under
  `~/.claude/projects/`, and the CLI resumes one with `--resume <id>` —
  which `claude.rs` already does for crash recovery, so an import is that
  same path with the token written up front rather than a second way to
  start a session. The phone picks an **id**, never a path: the server
  resolves which file that is, so an enrolled token cannot become "read me
  an arbitrary file" — the same rule that keeps a command out of
  `POST /setups`. Only the tail is replayed (`REPLAY_LINES`) because these
  files reach tens of megabytes and the CLI reads the real one itself; what
  crosses the tunnel is what a person reads, not what the model is given.
  Images in the replayed tail are written into the session's `files/` by
  the same function the live translator uses, so a screenshot looks the
  same whether it was watched happening or replayed afterwards, and the
  phone fetches the bytes only when it draws one.
  An imported session then **keeps itself level with that file**, so work
  done at a terminal appears without anyone pressing anything. Which new
  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`.
- `server/src/files.rs` — the file explorer's half of the backend:
  listing a directory, reading a file, writing one, creating a file or a
  directory, on whichever machine a setup names. Each is one small POSIX
  script run through `Transport`, so the local and the ssh case are the
  same code and a machine the backend cannot reach fails with ssh's own
  message. The path is a **positional argument**, never text spliced into
  the script; `PATH_PRELUDE` is the one line that gives a leading `~` its
  meaning, since a shell expands a tilde in text and not in an argument.
  A read has four answers — `text`, `binary`, `tooBig`, or the machine's
  own error — because a binary file drawn as text and a big one cut off
  silently are both wrong in ways the reader cannot see. A write carries
  the sha256 the read reported and is refused (409) when the file has
  moved on, which is the ordinary case when an agent is editing the same
  file. `EXPLORER.md` is the design.
- `server/src/usage.rs` — rate-limit windows, asked **of each machine that
  can run Claude**, not of the backend. Credentials are read through the
  session `Transport`, so a remote setup is an ssh round trip and the local
  one is unchanged; the HTTP call stays here. A machine with no Claude
  provider is never asked. The four states (`ok`, `notLoggedIn`,
  `unreachable`, `failed`) exist because a machine nobody logged in on is a
  choice rather than a fault, and one `error` string made it look like one.
- `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.
- **Attachments** are one list on a user message (`attachments`, the
  ref the files route serves), in two shapes. An image is `<hex>.<ext>`
  and goes to the model as an image block. Anything else is
  `<hex>-<name>` -- the name it was shared or picked under, cleaned by
  `safe_file_name` -- and the Claude driver appends `Attached file:
  /abs/path` to the message text, since the CLI reads files by path and
  a model cannot be shown a trace. `media::media_type_for` on the server
  and `isImageRef` on the phone tell the two apart; keep those lists
  level. The phone attaches from the photo picker, the file chooser and
  Android's share sheet (`Share.kt`; the manifest's SEND filter), all
  through one `attach` path in `SessionScreen`, streamed both from the
  phone and onto disk. A file for a session on another machine is also
  copied there during the upload (setup's `attachmentsDir`, else the
  session's cwd, else home) and the driver names that path, read from
  the `<name>.remote` marker beside the file -- PLAN.md's "Transport" has
  the reasoning.
- `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 (written in the shared RON house rules),
  `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`; `MainScreen.kt` the root's four tabs (sessions, import, models,
  setups) with settings and refresh on the title row; `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`.
  `Notifications.kt` is the foreground service holding the notification
  stream and the one place that decides where a notification is said --
  nothing for the session on screen, a `SessionAlerts` banner while the app
  is up, Android's drawer otherwise, never two of them. See PLAN.md's
  "Notifications: two places, never both".
  **Icons are Nerd Fonts glyphs from a committed subset**, not vector assets
  and not ordinary Unicode — `NerdIcons.kt` declares each codepoint and
  `app/build-icon-font.sh` subsets the font. The two lists have to agree: a
  codepoint in the Kotlin that the script did not subset is a glyph that
  silently isn't there. Rerun the script and commit its output when adding
  one; it needs network access. `md-cog` and `md-refresh` are deliberately
  the same codepoints dev-updater uses and must not drift from it. The
  subset is the **Mono** face, where every glyph is one em square — that is
  what makes two icon buttons the same width without either being given
  one, and it is why `GLYPH_SIZE` is smaller than it looks like it should
  be.
- **The file explorer** — `FilesScreen.kt` (the navigation stack, the
  per-directory cache, the create dialog), `FileViewer.kt` (a `LazyColumn`
  of lines, each with its own colours from `FileLines.kt`, sharing one
  horizontal scroll so nothing wraps), `FileEditor.kt` (a
  `BasicTextField` with a `VisualTransformation` carrying the scanner's
  spans, which is the one Compose API that colours a field's own text).
  It draws **over** the session in `AppRoot`'s `Screen.Session`, so the
  session under it stays composed and coming back from a file costs
  nothing; back steps editor → viewer → directory → parent and only closes
  from where it opened. `EXPLORER.md` is the design and `server/src/files.rs`
  is the other half.
  To exercise it, `./ui-sandbox.sh` builds a fixture tree at the sandbox
  home's `~/files` holding the states that are otherwise only reachable by
  finding a real machine in one: an empty directory, a name with a tab in
  it and one with an apostrophe, a binary file, one over `FILE_LIMIT`, one
  `chmod 000`, a symlink to a directory and a broken one, and a source file
  per language. Point a session at it with
  `./ui-sandbox.sh api /sessions/<id>/cwd -X POST -H 'content-type: application/json' -d '{"cwd":"~/files"}'`.
  The 409 is produced by editing the file on the machine (`printf … > file`)
  between pressing the pencil and pressing save.
  **Reading is cheap and editing is not**, and the sizes are measured
  rather than guessed -- see EXPLORER.md's "What the measurements said".
  The viewer handles a 1 MiB, 28,000-line file because it draws one row per
  line; the editor is one `BasicTextField`, which costs two seconds a frame
  at 128 kB and stops the app at 1 MiB, so `EDIT_LIMIT` caps it at 32 kB
  with the reason said on screen. If you make the editor faster, that
  number is what to move.
- `.dev-updater.ron` — what Dev Updater is asked to do with this checkout:
  the server (built in `server/`, run as `service: Managed(...)`) and the
  APK (built in `app/`), built in parallel. The project it serves is the
  repository, not either half of it, which is why this sits at the root
  rather than in `app/`.
  It points at `resources.ron` beside it, which says this project keeps its
  state as `ai-app` — so the Uninstall dialog offers `~/.local/share/ai-app`
  and `~/.config/ai-app` instead of saying it cannot tell. That file is
  *ours*, not Dev Updater's: it ignores keys it doesn't know, so anything
  else worth keeping in one place belongs there too. Note what deleting the
  config directory takes with it — the CA under `certs`, which is the
  one-way door described below.
  `Managed` means Dev Updater supervises `ai-server` with its own built-in
  service implementation rather than a script kept here. ai-app had such a
  script until 2026-08-28 and it was the generic case exactly — no
  arguments, no environment — so the two projects were maintaining one
  behaviour twice, including the OpenRC branch neither can test from a
  systemd machine.
  Worth knowing before pressing it: **Stop** on the server card stops the
  server that a phone reaches through the tunnel, so on that phone it stays
  down until someone starts it again from Dev Updater. Dev Updater reaches
  it over its own port and is unaffected, which is what makes the button
  safe to press and easy to regret.
- `wg-app-link/` — a **git submodule**, and the half of this backend that
  dev-updater also needed: the pinned CA and leaf (`certs`), QR enrollment
  and the bearer token (`enroll`), wg0 binding and the certificate's SANs
  (`netif`), owner-only files (`private`), and the RON house rules
  (`format`). Both projects had written all five and they had drifted; see
  that repo's `README.md` for the diff that decided each one. Clone with
  `git clone --recurse-submodules`, or `git submodule update --init` in an
  existing checkout — `server/` will not build without it, since it is a
  path dependency rather than a registry one, which is what keeps the two
  projects version-locked to the commit this repo pins.
  The certificates are the one-way door: the CA is generated once on first
  start into `$XDG_CONFIG_HOME/ai-app/certs` and regenerating it strands
  the installed app.
  What deliberately did **not** move is the API surface and the config
  *schema* — routes, drivers, sessions and setups are what makes this
  project itself.
## Status

Phases 1–3 done 2026-08-24 (PLAN.md's phase list says 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 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 end to end, phone included (2026-08-28).
Models are browsed and downloaded from HuggingFace (`models.rs`, resumable
and verified), and `session::llama` runs one through `llama-server` over
its OpenAI-compatible streaming endpoint. Two things 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.

Setups — machines, each carrying what it can run — are added, renamed,
re-probed and removed from the app; providers are **discovered by asking
the machine**, never typed, so the enrolled token cannot introduce a
command. What is left is real-phone/WireGuard bring-up, which is
operational rather than code.

**`command -v` follows PATH under a non-interactive ssh session**, which is
not the PATH a login shell shows, so a binary somewhere unusual is
invisible to discovery — llama.cpp unpacked into `~/.local/opt` needs a
symlink into `~/.local/bin` before a setup finds it. The escape hatch for
anything odder is editing `config.ron` on the backend, deliberately the one
authority the phone does not have.

**Testing llama.cpp here:** the prebuilt CPU build lives outside the repo
at `~/.local/opt/llama.cpp` (the 15 MB `ubuntu-x64` release asset). 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.

**No script that drives this app's UI presses a coordinate.** Every control
is found by the name it already carries for assistive technology --
`ui-trace record --do "tap 'Session settings'"`, which resolves the label
against the screen at the moment of the gesture and fails the whole run
when it is not there. `app/bench-lib.sh` is what `transcript-bench.sh` and
`stream-bench.sh` share for it. A coordinate is a position measured once by
hand, and anything that moves the control makes the tap land on whatever
now sits there -- the bench then reports a number that was never measured,
which reads exactly like a result. Both scripts pressed the render report
at `tap 723 205` until that button moved into the session settings dialog
on 2026-09-03. The check that none has crept back:

    grep -n "tap [0-9]" app/*.sh

Swipes are still coordinates, deliberately: a gesture across a scrolling
area is a distance rather than a control.

**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. **Take the key back out afterwards.** Note the remote login shell
here is **fish**; the remote script (`cd '…' && exec '…'`) and `ssh.rs`'s
POSIX quoting happen to mean the same thing in both, but that is luck
rather than design, and a shell that isn't either is the thing to suspect
first if a remote spawn ever mangles an argument.

## Checking your work

- Server: `./run-tests.sh` from the repo root (or `cargo test` from
  `server/`) +
  `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
  :androidApp:testDebugUnitTest` — format, typecheck, lint and test, the
  app-side equivalent of the line above. The unit tests are JVM-only and
  cover the syntax highlighter's scanner, which is the app's one piece of
  pure logic with no Android in it. 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.
  **The phone gets the release build**, signed with a key the script
  generates once under `~/.config/ai-app/release.jks` (never in the repo);
  `./build-apk.sh debug` builds the other variant, and Dev Updater's build
  modes call the script with exactly that word.
  The emulator scripts stay on the debug build; a debuggable build runs
  Compose at a fraction of release speed, so never read a frame time from
  one as the app's -- the render report now says which build it came from.
  Dev Updater lists every variant under `build/outputs/apk`, so pick
  `release` there; a phone still holding the debug build has to uninstall
  it first, since the two are signed differently.
- **A row something is happening to is dimmed, drained of colour, inert,
  and says which operation in a word** -- `BusyItem`, used by both the
  session list and the import list so the appearance is learned once. The
  word rather than a bare spinner because "deleting" and "importing" differ
  in kind. It dims and desaturates but does **not** make the row inert: the
  caller disables its own click handler while it passes a label. An overlay
  consuming pointer events was tried and swallowed the drag along with the
  tap, so a list could not be scrolled while anything in it was busy.
- **Importing and deleting run on the server, not in the request, and a
  batch is handed over in one call.** `POST
  /setups/{id}/importable/delete` and `POST /setups/{id}/importable/import`
  each take a list of session ids, answer 202, and do the work in spawned
  tasks -- because 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: some
  rows started and the rest were never asked for, and a row nobody asked
  for looks exactly like a row nobody picked. Every id is registered as in
  flight before the 202 goes back. Only the *registering* is atomic; the
  work itself 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 of the listing carries `pending` and
  `error`, and `GET /setups/{id}/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 -- that left a row marked "waiting" for
  ever, and the listing is what repairs it. So the screen fetches again
  after a handover when anything still looks outstanding, and takes the row
  states from the answer rather than from what it remembers.
- **A single tap still waits.** "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` on the server so the two cannot drift about what importing means.
- **The import screen selects in batches: hold to enter, tap to add.** The
  options that act on a selection appear along the bottom, and are Delete
  and Import only. Submitting clears the selection immediately and marks
  every chosen row -- the one in flight as "importing" or "deleting", the
  rest as "waiting" -- 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. What that costs is that the rows below slide up
  under the reader's finger, so a row that has just moved ignores taps for
  half a second (`SETTLE_MS`).
- **An answered question keeps its options and marks the one that was
  taken**, in the same purple that says "picked" while it is still open --
  it does not collapse into a line repeating the answer. The options are
  what the question *was*, and "Deny" alone does not say that Allow was the
  alternative. One rule in two places (`AskedQuestion` and `PermissionAsk`),
  since a permission is a question with two bare options rather than a
  different kind of thing. An answer typed into **Other** matches no option,
  so that one is still written out -- the state the marking cannot say.
- **Anything that is a note *about* the conversation rather than a turn in
  it is closed by default**: a tool call, a peer message, and now a memory
  note (`<cc-memory>`). 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.
- **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 everything it remembered goes, the open dialog included. Somebody
  looking at a screenshot was thrown back to the transcript because the
  session made another tool call. `/tools n gap` puts an image on its first
  call so this is reproducible: open it, wait a gap, watch the row regroup.
- **All transcript text is selectable, from one `SelectionContainer` around
  the whole list** (`TranscriptList.kt`). Not per row: a transcript is one
  body of text to a reader, so a selection has to be able to run from a
  reply into the tool output under it -- and a container per row leaves
  whatever was drawn without one silently unselectable, which nothing on
  screen reports. Rows keep their tap handlers; selection is a long press.
  **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 -- see
  `appendCodeChip` in `MarkdownLinks.kt` and TRANSCRIPT_RENDERING.md.
- **A session can be moved to another directory** from the settings dialog
  (`POST /sessions/{id}/cwd`). It stops the process, because a working
  directory is settled at spawn; the next message starts it in the new one.
  **`claude --resume <id>` finds a session from any directory** -- measured
  on 2.1.237 -- so nothing of Claude Code's is relocated, and should you ever
  be tempted, its project directory is the path with every non-alphanumeric
  character replaced by `-`, cut at 200 characters with a hash appended, and
  overridable besides.
- **A message from another agent reaches a live session on the turn's
  `result`, not before.** Measured on CLI 2.1.237 by sending a real
  cross-session message to a real stream-json session: no `user` record, and
  nothing in the partial-message stream -- the whole of it is an `origin`
  object on the `result`, the same shape the session file records, which is
  why `import::peer_message` reads both. So it is *recorded* after the reply
  it caused, and cannot be recorded anywhere else in an append-only log --
  which is why the event carries `turnStart`, the seq of the status that
  opened its turn, and the phone draws the note at that seq instead of where
  it arrived. Exercise it with the echo driver's `/peer-turn`; plain `/peer`
  is the in-place shape an import replays. See PLAN.md.
- **A queued message can be tapped to take it back**, which is
  `POST /sessions/{id}/unqueue` and a `messageDropped` event -- see PLAN.md's
  "Taking a queued message back". On a **Claude** session it always refuses,
  and that is correct rather than broken: the driver writes a steer into the
  CLI the moment it arrives, so what the bubble is waiting for is the CLI
  *reading* it, not this server sending it. The refusal is drawn on the
  bubble. The echo driver really does hold its queue, so that is the rig for
  the case where the drop succeeds.
- **Deleting a session offers to take the machine's own transcript with
  it.** `DELETE /sessions/{id}?deleteForeign=true`, behind a switch in the
  confirmation, and only where the driver keeps a record of its own
  (`keepsOwnTranscript`, which today means Claude Code). Off by default,
  because leaving that copy is what makes an ordinary delete recoverable --
  and the dialog's paragraph is rewritten when it is on rather than
  appended to, since the sentence promising the conversation "should still
  be there to import again" is exactly the one the switch makes false. The
  server deletes the machine's copy *first*, so a machine it cannot reach
  leaves the session where it was instead of half-deleted.
- **One Claude Code session id can name two files, and the listing offers
  it once.** Resuming a session from a different working directory makes
  the CLI write a second transcript with the same id under that
  directory's project folder -- an ordinary state of a machine, not
  corruption. Everything downstream addresses a session by id (`--resume`,
  the delete glob, the in-flight registry) and the phone keyed its list on
  it, so two rows sharing one *closed the app* on a Compose duplicate-key
  throw. `parse_listing` keeps the copy with the most lines, because the
  other is usually a few-hundred-byte stub and is often the *newer* of the
  two -- so recency is the wrong key. Deleting removes every copy rather
  than the first, or the row came back after a delete that reported
  success. The phone's half is `uniqueItems`, which every list keyed on a
  server-chosen id goes through: a repeat there must never be able to
  close the app, whatever produced it.
- **A reply is drawn as pieces of one parse, never as re-parsed
  substrings.** `MarkdownPieces.kt`: 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 `State.Success` that `ParsedReplies` cached and
  `warm` made. That is what bounds a lazy-list item (one paragraph, one
  bullet) without parsing a message more than once, and it is why a
  forty-item list of sources is forty units rather than one. The renderer
  is still the parser and the environment: `MarkdownRoot` provides its
  locals and `MarkdownElement` dispatches a whole block through our
  component table, so paragraphs, headings and table cells are span-linked
  `LinkedText` (links as spans with one tap detector per text, not a layout
  node per link -- the cost that made a list of sources bumpy) and lists
  are ours wherever the dispatch meets one. A heading's words are its
  `ATX_CONTENT`/`SETEXT_CONTENT` child; the inline builder draws nothing
  for a node type it does not know, so hand it the child.
- **A markdown table wraps its cells and never cuts one off.** The
  renderer's own 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, so nothing on screen says anything was cut.
  `Markdown.kt` supplies its own rows (`LinkedTableRow`): as many lines as
  a cell needs, cells aligned to the top of the row so a two-line cell
  does not re-centre its neighbours, and each cell a `LinkedText`. Width is
  the other half: a column narrows to 136dp and no further, and past that
  the whole table scrolls sideways rather than squeezing -- 136 because it
  is the widest floor that still fits three columns across a phone, which
  is the commonest table there is. Exercise it with the echo driver's
  `/table N` (default six columns), which writes long cells on purpose:
  a fixture of tidy one-word values renders fine whether or not the
  truncation is fixed.
- **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 — and later a permission check that silently dropped every
  notification on Android 12 and below. It is fully clean as of 2026-08-31;
  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. `ai-server --enroll-link` (same
  `--config`/`--bind`/`--port`) mints one more device's link while the
  server keeps running and prints only the URI; the server adopts that
  token on its first use. It is what Dev Updater's Enroll button runs.
- **`app/debug-transcript.sh` puts a real conversation on the emulator.**
  The echo driver stays the right rig for most things and is the wrong one
  for anything whose cost scales with what was actually written: a real
  reply is longer, is real markdown, and carries tool calls whose input and
  output are kilobytes rather than a word. Two faults were invisible until
  a real transcript was loaded — a page of history landing mid-fling threw
  the reader back to the newest end, and parsing one real reply took 51ms
  against 4.6ms for a synthetic one. `-b` takes the biggest conversation on
  the machine rather than the newest, which is what a scrolling test wants;
  `--stop` takes it all down again.
  It copies the transcript into `/tmp` and gives the server a `HOME` of its
  own, so the import can only see the copy — importing spawns `claude
  --resume`, and against the real file that is a second CLI writing to a
  conversation somebody may still be in. **A transcript never goes in this
  repository**: they hold whatever was said, read and written in that
  session, and `~/repos` is shared with the host besides.
- **`app/ui-sandbox.sh` is the rig for driving the UI against invented
  sessions.** It starts a second `ai-server` with its own `$HOME`, config
  and data directory, holding eight invented Claude Code transcripts and a
  `claude` that is two lines of shell. That isolation is the point: the
  import screen lists whatever is in `~/.claude/projects`, which in this VM
  is real agent transcripts, so exercising *delete* against the ordinary
  server deletes somebody's conversation and exercising *import* starts a
  real `--resume` on the owner's account. Neither is a price worth paying to
  look at a list. It shares the real TLS certificates, because the
  installed APK pins that CA.
  Its port and root are derived from the checkout's name, so two checkouts'
  sandboxes (and the emulators enrolled against them) cannot reach each
  other, and its token is generated once into
  `~/.config/ai-app/sandbox-token` and carried across restarts along with
  any tokens the server's own enrolment flow appended -- so the emulator app
  is enrolled **once** (the start banner prints the command) and stays
  enrolled. It also carries the driving verbs every UI investigation needs,
  so none of this is re-derived per session:
  `./ui-sandbox.sh spawn [title]` (an echo session, prints its id),
  `./ui-sandbox.sh send SID text|@file`, and
  `./ui-sandbox.sh api /path [curl args]` for everything else.
  `./ui-sandbox.sh keep` restarts the server without wiping the sessions and
  enrolment already there -- for when the fixture under test was expensive to
  build (a long delta-heavy transcript, say) and should survive a rebuild of
  the server binary; plain `start` wipes them, which is right for the
  list-screen fixtures and wrong for that.
  It passes `--delay` by default for the reason the next entry gives, and
  `AI_SANDBOX_BIG_MB` puts one large transcript among the small ones --
  `AI_SANDBOX_SPAWN_DELAY` makes the fake CLI slow to start. Both exist
  because operations that finish in milliseconds have states on the way that
  nothing can observe, and an unobservable state is one where broken and
  working look identical.
- **`app/transcript-bench.sh` is the standard scroll measurement.** It
  opens the first session (or `-k` keeps the current screen), scrolls a
  fixed gesture loop, and prints the app's render report -- the same one
  the in-app copy button produces, whose `on screen:` line names what the
  viewport was actually holding. Compare two runs of it with the same
  gestures; the emulator's absolute frame times transfer nothing, the
  report's accounting does.
- **`ai-server --delay MS` holds every response back.** Over the tunnel a
  phone's requests take tens to hundreds of milliseconds, and several
  faults live entirely in what the app does *while* one is outstanding. On
  a loopback server those windows close before anything can be observed,
  so the bug looks like it is not there.
- **A fake CLI exercises the process lifecycle without a token.** Point a
  `claude_cli` provider's `command` at a two-line script — `#!/bin/sh` and
  `cat > /dev/null` — and it behaves the way the lifecycle code cares
  about: it holds the fifo open, records a real pid, writes nothing, and
  dies on a signal. So adopt, stop, restart and start are all drivable
  without a real `--resume` and without spending a turn on somebody's
  account. Sibling to `debug-transcript.sh`, and the two cover different
  halves: reach for this when what is under test is *whether a process is
  running*, and for the script when it is *what the transcript draws*.
  (From the ai-app-2 session, 2026-08-30, which found a clock bug with it
  that the tests did not have.)
- 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
  `$XDG_CONFIG_HOME` (`~/.config` when that is unset), never in the
  checkout, so a relative `certs/ca.pem` finds nothing.
  The emulator app reaches it at `https://10.0.2.2:8443`; enroll it with
  `adb -s "$SERIAL" 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).
- **The emulator is `~/repos/emulator-tools`' business, not this repo's.**
  `emu up` creates and boots the AVD named after this checkout — whatever
  `emu name` prints, never a name typed out here, since this file is the same
  in every clone — refusing when the machine has no room for one; `emu list`
  says what is attached and what it costs; `emu down` stops it.
  `run-android.sh` is that plus a build and an install. Run that repo's
  `install.sh` once if `emu` is missing.
  The `adb` on `PATH` after sourcing `android-env.sh` is that repo's wrapper,
  which fills in `-s` from the same rule — so a bare `adb shell` reaches this
  checkout's emulator and refuses to reach another one's. That defaulting is
  what makes the old advice unnecessary rather than wrong: with two attached
  and no `-s`, a bare `adb shell pm list packages` comes back **empty**,
  which reads as the app having been uninstalled rather than as the question
  being ambiguous.
  **Gradle does not go through that wrapper**, so it had the same hole until
  2026-08-31: `installDebug`, `uninstallDebug` and `connectedAndroidTest` ask
  the adb server for every attached device and act on all of them, which is
  how one session's debug build landed on another's emulator. A Gradle init
  script from `emulator-tools` now runs `emu check` before those tasks and
  fails the build rather than fanning out. When it refuses, say which device
  you mean at the moment you use it — `ANDROID_SERIAL=$(emu serial)
  ./gradlew …` — rather than exporting a serial into the shell, which goes
  stale the next time an emulator restarts and another checkout's takes the
  port.

## Where things run (host vs this VM)

Established 2026-08-25. The machine itself — the two boxes, the shared
`~/repos` mount, and why the VM is untrusted — is described once in
`~/.claude/MACHINE.md`; what follows is only what that means here.

- **`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) 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. 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 how 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 as it would any other machine: a configured host,
  and a session that names it.
- **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). 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 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 — 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`.

## Sessions outlive the backend

Since 2026-08-29 a session's process is **deliberately left running when
`ai-server` stops**, and adopted again when it starts — so restarting the
backend does not end a turn. PLAN.md has the design; what matters day to
day:

- **Stopping the server no longer stops the sessions.** After `pkill
  ai-server` the `claude` processes are still there, on purpose, and the
  next start picks them up (`reattaching to the claude-cli it left
  running` in the log). To end one, either `POST /sessions/{id}/stop` —
  which keeps the session and its transcript, and `POST .../start` brings
  the process back on the same conversation — or delete the session, which
  ends the conversation too.
- **A message or a command sent to a stopped session starts it.** `POST
  .../message`, `.../command` and `.../compact` go through
  `SessionManager::send_message` and `::run_command`, which start a process
  first when the session is known to have exited and then hand the thing to
  the driver that has one behind it. Only on `exited`: `unknown` has a
  process that may well be reading its fifo. `/rename` starts one too, and
  for a sharper reason than the rest: the CLI 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 — every
  later start is a `--resume` — so a rename that reached no process would
  leave the two lists disagreeing for good. Its save happens before the
  telling, so a failure there says the telling failed rather than the
  rename. So the Start button is for when you want a process and nothing to
  say to it yet.
- **A backend start adopts and starts nothing** (2026-08-30). It picks up
  the processes still running and leaves every other session as it found
  it: listed, with its transcript and its stream, reporting `exited`, with
  no process and no driver until somebody asks for one. Restarting the
  server used to relaunch a driver for every session, which started a CLI
  for each one that had none — so a session stopped on purpose came back at
  the next rebuild, and the `Idle` the new driver announced stamped every
  row as active just now. If you are looking for a stopped session's
  process after a restart, there is deliberately none; press Start, or send
  it anything.
- **A launch never moves a session's clock.** A status it has to correct is
  written at the time of the last thing the session actually did, not at
  `now()`, and a session that has never done anything reports
  `SessionConfig::created` rather than the clock — its transcript is empty,
  since a driver announcing the state it starts in is not news, so there is
  no line to read a time off. Both are the same rule as
  `Transcript::last_activity`: a restart has been told nothing, so it must
  not claim anything happened.
- **A session spawned while testing cleans itself up: `--throwaway-sessions`**
  (2026-08-30), which a **debug build defaults to on**. Every session
  spawned by such a server is marked `throwaway: true` in `config.ron`, and
  its process is stopped — SIGTERM, then SIGKILL after
  `process::STOP_GRACE` — when the server exits or is sent SIGTERM/SIGINT.
  Sessions outliving the backend is right for the ones somebody is using
  and wrong for the ones a test made: those leave a `claude` behind that
  every later server adopts, and they pile up unnoticed (twelve on this
  machine in a day, each holding a conversation open).
  Two things worth knowing. The flag decides only what **new** sessions are
  marked as; what happens on the way out is decided by the **mark**, which
  is the session's own — so a session you 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. And the waiting
  is not optional: `process::stop` leaves its SIGKILL on a tokio timer,
  which a runtime that is shutting down never runs, so
  `process::wait_gone` does the waiting on the way out. Pass
  `--throwaway-sessions=false` to keep what a development server spawns.
- **A process that has exited but not been reaped reads as dead**, not
  alive. `/proc/<pid>/stat` keeps the entry — same pid, same start time —
  until the status is collected, so a zombie used to answer "still there",
  which made `exited` unsayable: the session showed `unknown`, its Start
  button never appeared, and stopping it said there was nothing to stop.
  `process::stat_of` reads the state field alongside the start time.
- **Each session directory now holds `process.json`, `stdin.fifo`,
  `stdout.log` and `stderr.log`.** `stdout.log` is the driver's input, read
  from the byte offset in `process.json`; removing either by hand while the
  session is live loses output or replays it.
- **`--resume` only ever runs when nothing is running.** That check is the
  fix for the incident below, and the reason there is one entry point
  (`ClaudeDriver::launch`) rather than a spawn and an attach. The status a
  launch reports obeys the same rule: a session recorded as `exited` whose
  launch has just started a process reports `idle`, because `exited` is the
  word that refuses every command and offers a phone the chance to start a
  second CLI on a live conversation.
- **`exited` is never taken on trust; it is checked against the process
  record** (`corrected` in `session/mod.rs`). It is the one status that draws
  the phone's Start button and lets `start_session` build a driver, so a
  record that is not known to be dead makes it false and the session reports
  `unknown` instead. Without that, a session adopted at a backend start kept
  the transcript's `exited` while its CLI was running, Start was accepted
  every press, and each press left another reader on the same process —
  which reads on screen as one reply written several times, interleaved
  (`GotGotGot it — it — it —`), not as anything to do with a button.
  A driver that `start_session` replaces gets `Driver::detach` for the same
  reason: swapping the `Arc` does not end the tasks the old one is running.
- Remote sessions are adopted too. The pid recorded for one is the **`ssh`
  client's**, on this machine — that is the process the backend owns, and it
  lives as long as the remote command does. (This said "local only" until
  2026-08-29; the code never had that branch.) Note the far `claude` always
  has an sshd pipe on stdin whichever version started it, since the fifo is
  on the backend's side — so you cannot tell a backend's version by looking
  at a remote session's stdin.

The import list reports each session's **size as well as its line count**,
because the two disagree in the way that matters: these transcripts embed
screenshots as base64, so one line can be a megabyte. On this machine a
69 MB session has 3,427 lines and a 44 MB one has 6,792 — nothing about a
line count tells you what continuing a session will cost. Shown, not warned
about; importing a large session is a choice somebody is entitled to make.

**Never import a Claude Code session that is open in a terminal.** The app
refuses it now — it reads `~/.claude/sessions/<pid>.json`, which Claude
Code keeps for every live session, and checks the pid's start time so a
descriptor left by a crashed CLI doesn't count. Refused rather than warned
about, because on 2026-08-29 an agent imported the session it was *itself*
running in. That put two `claude --resume` processes on one file: the whole
65 MB conversation, 154 embedded screenshots included, was re-appended to
the transcript under a new prompt id, both copies replayed each other's
writes as work done elsewhere, and the adopted one was billed for re-reading
all of it. It ended at the account's session limit, with three `claude`
processes running against one checkout.

## 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 composer can get stuck floating above the bottom of the screen after
  the keyboard closes, while a reply is streaming.** The composer's position
  and the transcript's bottom padding are both driven by the raw, animated
  `WindowInsets.ime` value read inside a `graphicsLayer` block, to avoid
  recomposing the whole screen every frame of the keyboard's animation (see
  the layout note above it). That animation is carried by a
  `WindowInsetsAnimationCallback`, and a callback interrupted mid-flight
  leaves whatever it was carrying frozen at its last value with nothing
  left to correct it, since no further keyboard movement will fire it
  again. A streaming reply invalidates the view every frame, which is
  exactly the condition known to starve that callback of its `onEnd`.
  `WindowInsets.isImeVisible` (`ExperimentalLayoutApi`) does not share the
  failure mode -- it is set once, from the platform's own start/end of the
  transition over a different path -- so it is read once per keyboard
  toggle and used to force both places back to zero the moment the
  platform says the keyboard is gone, whatever the animated value still
  claims.
  **The guard is a boolean; the inset itself must never be read in the
  composable body.** That correction first shipped as a `padding(bottom =
  ... imeInsets.getBottom(this) ...)` computed in `SessionScreen`, which
  subscribes the whole screen to a value that changes every frame of the
  animation: measured on the emulator at **16 full recompositions of
  `SessionScreen` per keyboard open, against 1**, and it put the
  transcript's position behind a recomposition while the composer's stayed
  a draw-phase read of the same frame, so the two were only together while
  that recomposition kept landing inside the frame. It is `.then(if (imeVisible) Modifier.imePadding() else
  Modifier)` instead -- `imePadding` reads the inset in the layout phase,
  which is what the comment above the transcript box means by "the whole of
  what the keyboard re-measures", and dropping the modifier is the same
  coercion to zero that the boolean was added for. The counter to check is
  `session screen recomposed` in the debug button's report, which should
  move by one across a keyboard open, not by the number of frames it took.
- **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.
- **A reconnecting phone used to be sent the entire backlog.** The SSE
  stream replayed 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. Past
  `CATCH_UP_LIMIT` the stream now sends a `reset` frame and the newest
  window instead, and the client rebuilds from it exactly as it does when
  the screen opens. The reset is not optional: without it the window is
  spliced onto rows that are no longer adjacent to it, which reads as
  ordinary output.
- **The five-hour window has no reset time between blocks, and that is not
  a missing value.** The usage API anchors it to the block it started in --
  measured 2026-08-31, the reset came back as exactly five hours after work
  resumed, and the weekly windows in the same response carried the identical
  microsecond, so both are computed from one `now()` at request time. When
  no block is running there is nothing to reset and `resets_at` is `null`;
  the same response shows other idle windows with the same shape. The weekly
  ones always have a reset because a week is always running, which is why
  "the others seem fine".
  So `resets_at` absent means **not running**, and only a timestamp that
  arrives and cannot be parsed is unknown. The app collapsed both into one
  null and the session bar said "reset time unknown" for a machine behaving
  perfectly -- while the usage dialog, reading the same field, quietly drew
  nothing. `WindowEnd` in `ResetCountdown.kt` is now the one rule both go
  through.
- **Resolving one importable session used to list every one of them.**
  `import::delete` and the import seed both called `list`, which reads every
  transcript Claude Code has ever written -- measured at 3.7 seconds against
  the 867 MB in this VM, paid once per session in a batch. `import::find`
  takes the same script with one glob narrower, and `delete` resolves the
  path itself: 78ms. Ids are checked (`is_session_id`) before they reach
  that glob, since a `/` or `..` in one walks it out of the projects
  directory and `delete` removes what it lands on.
- **A transcript page used to cost the whole transcript.** `read_window`
  read and parsed every line and then kept the last `limit` of them, so the
  work was the size of the conversation rather than the size of the answer:
  on a 21 MB, 24,000-event transcript one page took ~500ms of server time to
  return 620 KB, and took the same 500ms whichever page was asked for. A
  phone scrolling back paid it per page and every stream reconnect paid it
  again to find out nothing had happened. It is a bisection now
  (`Indexed` in `transcript.rs`) -- sequence numbers only increase, so the
  edge of a range is found by parsing one line per halving and only the
  window is built. Same page, ~110ms, of which ~20ms is the file scan. The
  file is still read whole; that is where the remaining cost is, and going
  further means a chunked backwards reader.
  `RUST_LOG=ai_server=debug` logs each page with what was asked and what
  came back, which is how to see a phone paging back in real time.
- **Paging back has two failures that look like "there is simply no more
  history", and neither says anything on screen.** Both fixed 2026-08-31,
  both invisible on a loopback server and reproducible at `--delay 150`.
  The pager fires on the *first layout*, before any event has arrived --
  `moreHistory` starts true, so the history spinner is in the list and
  `visibleItemsInfo` is not empty -- and `before = 0` asks for the events
  before the first one, which is none, which is exactly how this code is
  told it has reached the start. `loadOlderPage` refuses `oldestSeq == 0`
  now. And `joinPages` only ran `adoptRun` on the path where a *split* call
  had been found, so a boundary landing cleanly between two calls -- most of
  them -- left one run of tool calls drawn as two groups with the seam
  wherever the reader happened to have paged. Reproducing either takes a
  boundary placed on purpose: the opening page is 80 events, so arrange the
  transcript so that event counts back from the newest.
- **A page is 800 events and a screen is a handful of rows, and the two
  have no fixed ratio.** A run of thirty-five tool calls is one row; a reply
  is hundreds of text deltas folded into one. So anything that budgets in
  rows has to measure a screen rather than name a number: the history
  cushion was eight rows, which on a tool-heavy transcript is less than one
  screenful, and the reader hit the end of what was loaded on every swipe
  and stood there for a round trip. It is `HISTORY_SCREENS` viewports now,
  counted from what is actually on screen. Measured at the server, which is
  the one number here that does not depend on how the emulator renders:
  against a 24,000-event transcript, ten swipes asked for ten pages before
  and three after.
- **What the transcript screen costs to scroll, for whoever measures it
  next.** Taken 2026-08-30 on the GPU emulator (`emu up` provides one; a
  frame number from the software rasteriser means nothing -- see
  `~/.claude/MACHINE.md`), against a real imported transcript with the debug
  server at `--delay 120`. Settled and flinging fast, both into fresh
  history and back through rows already drawn: **5.2-5.9% janky frames, 99th
  percentile 29-32ms, 0-2 slow UI-thread frames.** The stock Settings app on
  the same device is 3.3% and 38ms, so this is at the platform floor and
  what is left is the emulator rather than the app. The number that is *not*
  at the floor is the first few seconds after opening a session, where every
  row on the way is being composed for the first time; that is inherent to a
  lazy list and it is why a measurement taken before the screen settles
  reads three times worse. **Settle first, then reset `gfxinfo`.**
- **Only `fetchTranscript` was off the main thread; the fold was not.**
  `foldEvent` returns a new list per event, so a page is that many copies of
  a growing list -- fine at 80 events and about 300,000 element copies at
  800, run in the middle of the scroll that asked for it. `warm` had the
  same shape: the `markdownIn` scan that decides *what* to parse ran before
  the hop to `Dispatchers.Default`, over every assistant message loaded, on
  every page. Both are off it now. The shape to watch for is a
  `withContext` that wraps the *fetch* and leaves the work done with the
  result outside 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.