# dev-updater

Serves locally-built debug APKs to a phone, and an Android app that
installs them. See `README.md` first for what this is and how to run it;
this file is the working notes on top of that.

The central design point, worth not undoing by accident: **an app is a
project path, not a file path.** Everything downstream — which APK, which
package it replaces, its label, whether it's worth stripping — is derived
from what's actually built under that path, at add time or per request.
Nothing about any particular project is compiled in, and the app list is
mutable at runtime from the phone.

## Layout

- `vendor/wg-app-link/` — a **submodule**, and the shared half of this and
  ai-app: the WireGuard binding, the CA the app pins, QR enrollment,
  owner-only file creation, and the RON house rules. A submodule rather
  than a published crate because it pins an exact commit, so the two
  servers cannot end up on versions of it that disagree. Clone with
  `--recurse-submodules`; `git::pull` runs `submodule update` after the
  merge, because a merge moves the recorded pointer without touching the
  submodule's working tree and the build would otherwise keep compiling
  the old contents.
  What stays here is what differs: this server's routes, registry, build
  walk and service contract, plus `auth.rs`, whose middleware is generic
  over each project's own state -- only the token functions underneath it
  are shared.
- `server/` — Rust + Axum. `main.rs` is the bootstrap and the two
  listeners; `routes.rs` has the whole HTTP table in its module doc
  comment. `auth.rs` is the bearer token every TLS request carries,
  applied once around the whole router so a new route cannot forget it. `registry.rs` owns the live app list and every mutation of it
  (config writes funnel through `AppState::update`, so in-memory and
  on-disk state can't come apart; the one other write is
  `AppState::new`'s startup reconciliation, before anything can read the
  list). `discover.rs` is the scanner,
  `config.rs` the persisted schema and the RON both config files are in,
  `apkinfo.rs` the `aapt2` reads,
  `strip.rs` the slim-APK pipeline, `sdk.rs` the SDK/NDK tool lookups.
- `app/` — Kotlin + Compose, a single `:androidApp` module. `UpdaterScreen.kt`
  is the list, `AddAppScreen.kt` the add/settings screen, `AppsApi.kt` the
  management calls, `UpdateManifest.kt` the read side, `ApkInstaller.kt` /
  `InstalledBuilds.kt` the download-and-install path, `DownloadServer.kt`
  the transport and `Link.kt` the two values it hands the shared library. `Theme.kt` is Catppuccin Mocha
  mapped onto Material's roles, plus the four `ActionTone`s buttons come in
  -- red takes something away, the scheme's mauve replaces it with the same
  thing, green brings it up, blue puts a new build on the phone. What a
  button does is said in colour rather than by which component it sits on,
  so the same consequence looks the same everywhere. The mapping that
  matters is the surface ladder: Mocha names its darks in order (Crust,
  Mantle, Base, Surface 0) and Material asks for the same thing under other
  names, so the page is Base, a component's outlined card stays Base beside
  it, and a project's card is Surface 0 -- one visible step, which is all
  the nesting has to say.
  `NerdIcons.kt` names the icon glyphs,
  which are drawn as *text* in a small Nerd Fonts subset rather than
  as vector assets -- an icon beside a line of text wants that line's size,
  colour and baseline, and a `Text` gets all three for free. The font is
  generated: add a codepoint in `NerdIcons.kt` **and** in
  `app/build-icon-font.sh`, then re-run the script, or the glyph silently
  isn't there.

## Checking your work

- Server, from `server/`: `cargo fmt`, `cargo clippy --all-targets`, and
  `../run-tests.sh`. All three every time, not just when a change looks
  big enough to warrant them. The build is warning-clean and
  `cargo fmt --check` passes; keep both true. Formatting is plain rustfmt
  defaults with no `rustfmt.toml` — layout is not something to decide per
  line, so take what it gives rather than hand-formatting against it.
- App: from `app/`, `. ./android-env.sh && ./gradlew :androidApp:compileDebugKotlin`
  (or `:androidApp:assembleDebug`), plus `./gradlew ktfmtFormat
  ktfmtFormatScripts :androidApp:ktfmtFormat :androidApp:ktfmtFormatScripts`
  and `./gradlew :androidApp:lintDebug`. Both are clean; keep them that
  way. ktfmt is `kotlinLangStyle()` with nothing else configured, so
  formatting is never a thing to decide per line.
- Neither replaces running it. `app/run-android.sh` builds, installs and
  launches on an emulator; screenshot with `adb shell screencap -p
  /sdcard/x.png && adb pull /sdcard/x.png <local>`. Package
  `com.example.devupdater`, activity `.MainActivity`.
- **`test-projects/` is what to point it at**, rather than a real project.
  Four fake ones -- a plain APK, one building two variants, one whose build
  fails on demand, and a `Server` + `Apk` pair with a service and a
  `resources:` declaration. They exist because a real project only does what
  it happens to do, where these can be asked to fail, to be slow, or to
  declare nothing. That directory's own README says how they are reached
  (they are deliberately not scanned) and why each one builds into an
  `app/` subdirectory; the short version of the second is that two levels is
  what `find_apks` matches, so a test APK any shallower is offered as a
  build of *this* project.
- The server is easy to exercise directly, which is usually faster than
  going through the UI — but it takes three things, and leaving any of
  them out looks like the server being broken:

  ```sh
  # The CA it actually presents is the one in its config dir, not the
  # stale certs/ left in the repo. The address is wg0's -- it binds that
  # and nothing else, so 127.0.0.1 refuses the connection unless the
  # server was started with --bind. And every route on this port needs
  # the enrolled bearer token.
  curl --cacert "${XDG_CONFIG_HOME:-$HOME/.config}/dev-updater/certs/ca.pem" \
      -H "Authorization: Bearer $TOKEN" \
      "https://$(ip -4 -o addr show wg0 | awk '{print $4}' | cut -d/ -f1):8090/manifest"
  ```

  Only the token's SHA-256 is stored, so there is no reading it back out
  of `config.ron`: either use one printed by `--rotate-token`, or run a
  throwaway server with `--config`/`--certs` pointed somewhere temporary
  and `--bind 127.0.0.1`, which prints a fresh token at startup.

## Things that have bitten

- **Don't add a general recursive search to `discover.rs`.** It was
  measured and rejected; the numbers are in that module's doc comment and
  in the README. Extend `APK_PATTERNS` instead.
- **`aapt2` and the strip pipeline never run on the manifest path.** A
  process spawn or a zip walk there turns a 43 ms refresh into something a
  phone notices, and the manifest is fetched on every open, resume and
  Refresh. `aapt2` is add-time work cached in `config.ron`; stripping
  belongs to the download alone, which is why the manifest reports the
  size of whatever is on disk (`strip::serveable_now`) rather than
  producing the slim copy to measure it.
- **Both config files are RON with two house rules**, and
  `wg_app_link::format` is the only place that knows them -- ai-app's files
  are in the same shape, which is why they are shared rather than described
  twice. `config.rs`'s own `format` module is now only the migration hook
  in front of it, and goes when that does. A file is the *body*
  of the struct -- no outer parentheses, so nothing is indented for a
  wrapper -- because RON has no implicit top-level struct; `parse` adds the
  paren and `render` strips it. And `IMPLICIT_SOME` is set on the
  deserializer rather than by a header each file would have to carry, which
  is why every optional field also needs `skip_serializing_if` so nothing
  is written back that nobody typed. The two halves only round-trip
  together: change one and every file on disk still loads while only
  looking wrong, which is why the config test asserts the written shape.
- **A `Server` component is driven through one script, run as
  `<script> <subcommand>`.** `service.rs` knows the subcommands and the
  four words `status` may print (`running`, `stopped`, `failed`,
  `not-installed`); it knows nothing about systemd or OpenRC, and
  shouldn't. Scripts run with stdin closed, because one that prompts would
  hang rather than fail.
  **On OpenRC, `status` reads the exit code and never the text**
  (`0` started, `3` stopped, `32` crashed, anything else "could not find
  out"). `rc-service status` prints its status line to *stderr*, so the
  obvious check -- discard stderr, grep stdout for `crashed` -- throws away
  the word it is looking for and reports a crashed service as `stopped`,
  which is the exact lie the `failed` state exists to prevent. The codes
  also distinguish "could not find out", which the text cannot: an
  uninitialised user softlevel makes every call fail, and that is not a
  state the service is in. Assign the code through `|| code=$?`, or `set
  -e` kills the script before it can read one -- every answer but "running"
  is a non-zero exit. Measured on OpenRC 0.63.3, not read.
  **There is a guest to measure in**, at `~/vm/gentoo` on this machine --
  `./start.sh`, then `./shell.sh 'cmd'`, ssh on 127.0.0.1:2223 as `tester`
  with `guest_key`. Its own README is the reference. Everything in this
  section, and the restart behaviour below, was run there rather than
  reasoned about; do the same rather than trusting either the
  documentation or a systemd result. Detecting OpenRC is itself a trap:
  `rc-service --user --help` fails when `XDG_RUNTIME_DIR` is unset, so
  probing with it first reports "no service manager here" on a machine
  that has one.
- **Which script is what `service:` says**, and it is a sum:
  `Script("path")` for a project that carries its own, `Managed("the
  binary")` for one that wants dev-updater's built-in. Two variants rather
  than two optional fields, because a component picks one and "both" and
  "neither" would be states the file could express that mean nothing. The
  built-in is `server/src/service-default.sh`, compiled in, written to
  `$XDG_DATA_HOME/dev-updater/service-default` at every startup so an
  updated dev-updater cannot be driving last version's copy, and handed
  its identity as arguments (`--name <key>-<component> --exec "..."`) so
  the subcommand the caller appends still lands last. `service::driver` is
  the single place the two variants become one command -- everything
  downstream takes a command and cannot tell which it was, which is what
  lets a project switch between them without anything else changing.
  It is deliberately a *script* rather than an in-process implementation:
  a built-in that ran through Rust would put systemd and OpenRC knowledge
  back in the one place it has been kept out of, and the contract would
  become a special case of itself. **dev-updater declares `Managed` like
  anything else**, and has no service script of its own: nothing about
  restarting this server lives in a script, it lives in `restart.rs`, so
  there was nothing left for one to say. Its component carries `cwd: ".."`
  because the unit's working directory has to be the checkout root -- that
  is where this server looks for its own app project, and started anywhere
  else its card silently loses the branch line, its commit count and the
  Pull button. `start.sh` knows none of this: it runs
  `dev-updater --service <subcommand>` on the binary it has just built,
  which derives the name and the script from the same declaration the
  running server reads. One place decides how this service is named and
  invoked, which is the only reason a bootstrap script cannot drift away
  from `service::driver`.
  A managed service is named `<key>-<component>`, because a service
  manager's names are one flat namespace across every project on the
  machine. Switching a project from its own script to `Managed` therefore
  changes the unit's name: **uninstall the old one first**, or its unit is
  orphaned with nothing left pointing at it.
- **Service state is checked off the request path**, in `ServiceChecks`
  beside `git::RemoteChecks` and for the same reason: a process spawn per
  server component on `/manifest` is exactly what that path must not do.
  Which means it is subject to the same rule as a remote check: it lands
  *after* the response that started it, so `checksPending` counts both, and
  the phone waits on both (`ManifestEntry.checksOutstanding` for one card).
  And the answering starts at startup rather than on the first request
  (`main.rs`), so the window in which a component has no state is this
  server's own start rather than something a phone has to sit through --
  restarting is how this server is updated, which makes it the moment
  somebody is most likely to be looking at the list.
  Counting only remotes was a real bug and an invisible one: the state is
  unknown only until the first answer of a server's life, remote checks
  ordinarily outlast service ones, and the symptom is a component row with
  no buttons -- so it showed up as "the buttons vanish after a restart if I
  come back to the app too quickly", and only on whichever cards lost the
  race. Nothing looked again until somebody hit Refresh.
- **dev-updater declares itself as an ordinary `Server` + `Apk` pair**, but
  its server component *is this process*, and that changes one thing only:
  *when* it restarts. Running the script's `restart` inside the walk would
  kill it before the APK is built and before anyone is told how it went, so
  the restart is deferred past `finish`; the Restart route defers for the
  same reason, since a script that killed this process before it could
  answer would make a restart that worked read as a failed request. Once
  deferred, both go through the one function (`restart::deferred`), which
  asks the manager when the service is up and only otherwise execs the new
  binary itself. Going through the manager is what makes a refreshed unit
  apply -- an exec inherits the unit this process was started with, so a
  pull that changed the service script would otherwise land only at the
  next restart by hand. The button used to exec unconditionally, on the grounds
  that exec keeps the PID; that made it the one restart a rewritten unit
  never applied to, which is the kind of surprise a special case buys.
  Deciding it in one place is what stops the two drifting again. `BuildState::is_self` is the flag, and it is passed in
  rather than declared -- a file that could claim it is a file that can
  make this server exec an arbitrary binary. A build that changed nothing
  skips the restart altogether (`restart::binary_unchanged`): exec-ing into
  an identical binary drops the phone's connection to deliver the build it
  already had. It is a `stat` of the binary against what it was at startup
  rather than a hash -- cargo installs a new binary by renaming over the
  old one, so the inode alone answers it, and reading tens of megabytes to
  learn the same thing would cost more than the restart it avoids. It says
  "changed" whenever it cannot tell, because a needless restart costs a
  second while a skipped one leaves the old build serving and reads as the
  update having silently failed. The Restart *button* is unconditional --
  somebody asked. Stop and Uninstall do go
  through the script, and do strand the phone; the app confirms them
  rather than hiding them.
- **A component's freshness covers its own directory plus whatever it
  declared with `alsoWatch`** (`Component::watched_paths`, handed to
  `git::subtree_head` and `subtree_dirty` as pathspecs -- git takes
  several, so it stays one call). Scoping to `cwd` is right about where a
  component's files are and wrong about what its build reads: tdep-survey's
  two clients each source one shared `scripts/android-sdk-env.sh`, so a fix
  committed there changed what every build does, moved no component's
  subtree head, rebuilt nothing, and left every card correctly reporting
  "current" -- the narrower-question shape, where nothing is wrong and
  nothing says so. Declared rather than inferred because which files a
  build reads is not knowable from here, and both wrong guesses are
  expensive: too wide rebuilds everything on every commit, too narrow is
  that silence. It is part of the acceptance gate like every other
  declared field -- `same_declaration` destructures exhaustively, which is
  what forced the decision when the field was added.
- **A declaration that cannot be read says so on the card.** RON's
  `deny_unknown_fields` discards the *whole* declaration rather than the
  key it did not recognise, so a machine that takes a project's commit
  before it takes a dev-updater new enough to understand it loses that
  project's components, `strip`, `staleWhen` and resources at once -- and
  the card does not look broken, it looks like a project that declares
  nothing, which is the ordinary case. That was the only difference
  between the two states: a line in this server's log, on a machine the
  person holding the phone cannot read. `config::project_config` now
  answers a `ProjectFile` carrying the parse error beside the
  declaration, `AppEntry::declaration_state` returns both halves from one
  read (the manifest wants both, and the file is on that path), and the
  card draws its own sentence about what it means followed by the
  parser's own words -- selectable, since the fix happens on the other
  machine. Nothing is *blocked* by it: what was already accepted is what
  runs, so an unrelated typo cannot stop a project that was working.
  Worst on the self entry, where `reconcile_self` derives the row from
  that file at every startup: unreadable, and this server's own card
  silently loses its server component and its build commands rather than
  merely stopping noticing changes.
- **The debug keystore is not `~/.android/debug.keystore`** -- that is the
  last of five places, and `sdk::android_prefs_dirs` resolves it the way
  AGP does, because the only thing that makes it the right key is being
  the file Gradle signed with. Measured against AGP 32.3.2 by running real
  builds: `$ANDROID_USER_HOME` is the preferences directory itself with no
  `.android` under it, `$ANDROID_PREFS_ROOT` and `$ANDROID_SDK_HOME` get
  `.android` appended, then `$XDG_CONFIG_HOME/.android` **but only when
  that directory already exists** (the bytecode tests it and falls
  through), then `$HOME/.android`. That fourth step is the whole bug: an
  ordinary desktop Linux machine with `XDG_CONFIG_HOME` set signs its APKs
  with a keystore this server never looked at, so it reported "no debug
  keystore" about a machine that had one and was using it -- and this VM
  sets no `XDG_CONFIG_HOME`, which is why the case could not appear here.
  The failure names a keystore found further down the list, because an
  inert one and an absent one look identical from a phone: mistaking one
  for the other is what turned "this machine has none" into a signature
  mismatch nobody could explain.
- **A stripped copy is only serveable if it is signed by the key the
  build was.** `strip.rs` re-signs with `~/.android/debug.keystore`, and
  nothing about a debug keystore says which builds it made -- it is per
  machine, and one recreated after an APK was built signs as an entirely
  unrelated certificate (measured: a fresh AGP-parameter keystore against
  the existing one, no relation, as a new RSA keypair should be). Where
  they differ Android refuses the package and the phone says "App not
  installed" with no cause, which reads as the download rather than the
  signing and is among the most expensive sentences here to be handed. So
  the two are compared -- `apksigner verify --print-certs` on the source
  and on what was just signed, as sets of digests so a v2 source and a v3
  output still match -- and a mismatch is refused with both certificates
  and the keystore path named. Measured on the files rather than inferred
  from the keystore, so it stays true if the signing step changes. The
  slim copy is deleted on refusal: with no stamp beside it nothing would
  serve it, but `serveable_now` reports the size of whatever slim file is
  on disk, so leaving it would have the card describing a download
  nothing can install. Empty digests mean "not compared" rather than "no
  signer", and say so in the log rather than refusing -- an APK apksigner
  cannot read is one this comparison has no opinion about.
- **A 500 answers with its message.** `ApiError::Internal` used to be a
  bare status with an empty body, on the grounds that an internal cause
  is not safe to hand back -- but every route here is behind the bearer
  token of a device somebody enrolled themselves, so there is no third
  party to withhold it from, and what these actually say is which tool on
  the build machine could not be found or would not run. Withheld, a
  missing NDK reached the phone as "Server returned HTTP 500", with the
  explanation in a log on a machine the person holding it cannot see; the
  app has always shown a failure body when there is one, so the whole fix
  was on this side. The log keeps the same `{err:#}` chain.
- **A remote git failure is shortened and explained in one place**
  (`git::remote_failure`). Git's stderr runs to a paragraph of generic
  advice, so the card gets the first line and the log gets all of it; and
  when the failure was authentication, what this process can see of the
  ssh agent is appended, because "works in my terminal, fails from the
  service" is almost always `SSH_AUTH_SOCK` not being inherited by a
  daemon, and that is invisible from a phone. Asked rather than assumed --
  the note can say the agent is fine, which is what stops it being blamed.
- **A branch with no upstream is not a broken one.** `can_pull` requires an
  upstream as well as a checkout, which is what stops the card reporting
  the same fact twice -- once as its own note and once as the check's
  complaint about it -- and stops it offering a Pull that `git::pull`
  would refuse. It is also not worth *saying*: plenty of checkouts have no
  remote deliberately, and a card that mentions it every time is nagging
  about a choice somebody made.

- **Unrelated histories are the one pull failure the phone may override.**
  A checkout sharing no commit with its upstream has no fast-forward and
  never will, so with nothing offered the card is one that can never be
  pulled again -- and the way out is on the build machine, which is
  exactly where the person holding the phone isn't. So `?force=true` on
  the pull route resets onto the upstream instead of merging, behind a
  dialog that names the branch it is about to overwrite (the only place
  that is seen before it goes). Whether this *is* that failure is decided
  structurally -- `git merge-base` finding no common ancestor -- and never
  by matching what git printed: those messages are translated, and a
  button that appeared only on an English build machine is worse than no
  button. It travels as `PullError::unrelated_histories` rather than
  inside the message for the same reason. The dirty-tree refusal stays in
  front of it, so a forced pull can only ever discard something that was
  committed, and a merely *diverged* history is not offered it -- there is
  something better than throwing that away.

- **The branch line is how a failed remote check is visible at all.** With
  it gone, `newCommits` stays false and the card reads as an app with no
  updates -- the same silent failure the self-entry note below describes.
  It was deleted once by accident in a refactor and nothing failed; only
  the display went quiet.

- **Forcing git onto IPv4 is done in `GIT_SSH_COMMAND`, not on the git
  subcommand.** `git fetch` takes `-4`; `git ls-remote` does not, and
  answers "unknown switch `4'". `ls-remote` is what the new-commits check
  runs, so splicing the flag onto every remote command turned the setting
  into a switch that broke every card's commit count -- which is how it
  was first written, and what `git::ssh_command` and
  `forcing_ipv4_does_not_break_the_check` now hold in place. `fetch` keeps
  the flag as well, since that is what carries the preference to an https
  remote; ssh is covered either way.

- **This server's own project is a row in `config.projects` like every
  other, and everything in that row except `gitIpv4` is re-derived at
  startup** by `registry::reconcile_self`. The row is what gives a
  per-project setting one home -- it used to have to be keyed in a
  separate `config.settings` list, because the one card that is always in
  the list was the one card the setting could not be a field on. What is
  derived stays derived: the path is the working directory (see below),
  and the label and components come from the checkout's own
  `.dev-updater.ron`, so a re-clone or a moved repo fixes itself at the
  next start instead of leaving the row naming a directory nobody pulls.
  Only what somebody chose is carried across. The declaration is accepted
  by construction there, which is why `AppEntry::pending_declaration`
  answers nothing for it: between a pull that rewrites the declaration and
  the restart that follows, the row and the file can differ without that
  meaning anything is waiting to be accepted. A config still carrying the
  old keyed `settings` list loses it silently -- `Config` ignores fields it
  does not know -- so a machine that skips straight past the version that
  migrated one has its `gitIpv4` to set again.

- **A component has two kinds of log, and the kind is an axis of its
  own.** The build log is what this server captured while building it; the
  runtime log is what the component wrote while running, reported by its
  service script. They are asked for one kind at a time (`?kind=`), and the
  modal gives each a tab -- opening on runtime, since what a service is
  doing now is the usual question, and on build for the component a build
  stopped at (`build_failed`). They were one list indexed by generation
  once, and because build logs came first the runtime one sat at an index
  nothing ever asked for: unreachable, and silent about it. ANSI escapes
  are rendered rather than stripped (`AnsiLog.kt`) -- the colour is how a
  process marked its own errors -- and sequences with no meaning on a
  phone are consumed rather than printed, so a cursor movement cannot
  arrive looking like a corrupted log.
- **There are three sizes of refresh, and using the wrong one is what
  makes the list feel like it has a mind of its own.** `refresh()` drops
  the list to a spinner and asks every remote -- it belongs to arriving,
  resuming, and the Refresh button, which are the moments somebody asked
  to be shown the current state. Pull-to-refresh is the same ask without
  the spinner, since the gesture brings its own indicator and taking the
  list away underneath it would say the same thing twice. `applyOne` reads `GET /apps/{key}`
  and puts that one entry back, so an action on one card cannot move or
  change any other; every card action uses it, including adding one --
  the Add screen hands back the key and the list fetches just that app.
  `awaitCheck` is the middle one: ask a single checkout's remote and wait
  on *that* answer, which the card's own refresh control and a freshly
  added app both use. Waiting on the whole list to settle would make one
  card's refresh sit behind another card's.
  Arriving and resuming are **one** event, not two: `LifecycleResumeEffect`
  runs when the screen first reaches RESUMED, so there is no
  `LaunchedEffect(Unit)` beside it and one thing decides when the list is
  read. It refreshes from *any* state including a failed one -- guarded on
  "loaded", as it used to be, a card that had gone red stayed red until
  somebody found the Refresh button, which is the opposite of what
  returning to an app should do. `loadingList` is what stops the first
  composition and the first resume stacking two reads, and it is claimed
  *before* the coroutine launches, because both run in the same frame and
  a flag set inside the coroutine is set too late to be a guard.

- **A failure that lands while nobody is looking is not shown.** Work
  started before the app went away keeps running -- deliberately, since a
  download that finishes in the background is a download that worked -- and
  when the device sleeps or the link drops it fails. Reported, that meant
  coming back an hour later to a five-second read timeout that said nothing
  about the server and that there was nothing left to do about. So every
  catch in `UpdaterScreen.kt` goes through `failure(e)`, which answers null
  while the screen is not resumed, and **null means clear, never leave** at
  every site -- a dropped failure that left the card alone would leave a
  spinner up for an operation that has already stopped. `setProject` and
  `setComponent` both take a nullable state so the answer can be handed
  straight over. Iris asked for this on 2026-09-01: "I got a socket timeout
  by leaving the app for too long. Make sure not to show that if the app
  just gets unloaded."
  The other half of the same complaint is the read on the way back *in*:
  the link may have been asleep as long as the app was, and the first
  request across one still coming back times out at the five seconds every
  request gets. So the resume's read alone retries once (`afterAGap`),
  which costs nothing when the server really is down -- a refused
  connection comes back at once rather than waiting out a timeout. That is
  a retry, not a guess: nothing is displayed that was not measured.
  Dropping a failure is only safe *because* the resume re-reads from any
  state; the two changes hold each other up, and undoing either alone
  leaves the list stuck on a spinner or stuck on a stale error.

- **The Add screen is drawn over the list, not in place of it.** Swapped
  out, the list is composed again from nothing on the way back -- and
  rebuilding it means fetching it, which is the whole-list refresh that
  adding an app has no business causing. `describe` in `routes.rs` is the
  one place a card is built, so `/manifest` and `GET /apps/{key}` cannot
  come to describe the same app differently.

- **A progress bar is drawn from counts the build reports, never from an
  estimate**, and the knowledge of how to get those counts belongs to this
  server rather than to each project. Two ways in, both ending as
  `@@progress done/total` on the build's output:
  cargo reports its own once `CARGO_TERM_PROGRESS_WHEN=always` is set,
  which `spawn` sets for every build command, so a cargo build needs
  nothing and must not be wrapped. Gradle cannot -- an init script is
  refused by the configuration cache, and its rich console reports a
  percentage only as a full-screen redraw that would make the output
  unreadable -- so `server/src/build-progress.sh` does the `--dry-run`
  count and the `> Task` tally, shipped by this server (`crate::shipped`)
  and offered to build scripts as `$DEV_UPDATER_PROGRESS`. A script tests
  for the variable rather than depending on it, so building by hand still
  works. This is what stops each project carrying its own copy of the
  same twenty-five lines.
  Reading the output means splitting on carriage returns as well as
  newlines: a tool redrawing a counter in place puts several updates and
  then real output inside one `\n`-delimited line.
- **Discovery must stay side-effect free.** It runs on every manifest
  request and every suggestion scan.
- **An app in the list is a *project*, and what it produces is its
  components.** Ordinarily one `Apk`; a project that also runs a server on
  the build machine declares a `Server` beside it. They are a sum, not one
  struct with both halves' fields, and the common fields are repeated per
  variant so the file reads `Apk(name: ...)` with nothing nested inside a
  `kind`. `Component::same_declaration` destructures exhaustively, so
  adding a field anywhere fails to compile until someone has said whether a
  project declares it or this server measures it.
- **A build reinstalls every server component's unit, not just changed
  ones.** The unit is generated from a script in the repository, so a pull
  can change how a service is *defined* rather than what it runs -- and
  that has to land even when the build produced a byte-identical binary,
  which is the ordinary case for a pull that only touched the script.
  Installing is safe on a running service (it writes the unit and reloads;
  it stops nothing), which is why `start.sh` has always done it every run.
  It is deliberately not gated on `restart::binary_unchanged`: that answers
  whether a *restart* is worth the interruption, and unit staleness is a
  different question. Wiring the two together left the unit stale exactly
  when the build had nothing to do.
- **A build runs every component at once, and each reports for itself.**
  They are independent -- a Rust build and a Gradle build share nothing but
  the machine -- and measured here, together takes about three quarters of
  the time one after the other does. The saving only appears when more than
  one has work, which is what a pull produces.
  The status is per component (`ComponentStatus`), so a card draws each
  component's bar and last line inside that component's own row;
  the project's own area at the bottom keeps only what belongs to the whole
  project, which is fetching and pulling. A bar under the card could only
  ever say that *something* was happening, and with everything building at
  once that is exactly what the reader is trying to find out.
  A failure no longer stops the others -- they are already running -- and
  it is reported against the component whose command it was, never as the
  project's. The phone draws every component in
  a card of its own, including a project with only one: the flat layout it
  used to get meant two shapes to keep in step, and put that APK's size up
  beside the card's corner controls where it read as belonging to them.
- **There is a build slot per component, not per project, and the two
  halves have to agree on that.** A component being built neither blocks
  another's build nor disables its controls: `Inner` has no `building`
  flag, only a `ComponentRun` per component whose open `step` *is* the
  answer, and `claim` writes that entry synchronously under the same lock
  the route answers from -- so nothing can read a component the request
  just claimed as idle, which the phone would take for "the build is
  over". `BuildStatus::building` stays, but it means "anything at all is
  happening here" and is only for the controls that act on the whole
  checkout; anything about one component reads that component's `step`.
  The app mirrors the split exactly: `ProjectState` for the pull and the
  project-wide Rebuild, `ComponentState` keyed by component name for
  everything a single component is asked to do. One map keyed by project
  alone is what the bug was -- pressing Update on one client of a
  two-client project disabled the other's button and drew this one's
  download bar under it -- and two hierarchies rather than one keyed by a
  pair is what stops it coming back, since a download has no
  project-wide meaning to be stored with.
  The exception, and it is worth keeping visible so it does not read as
  more of the same: **a pull really is exclusive with everything.** There
  is one checkout, and it rewrites the files every component builds from,
  so `Inner::pulling` blocks any component from being claimed and waits
  for any still building. Ending the pull and claiming what it decided to
  build happen under one lock for the same reason `claim` is
  synchronous -- a phone polling in the gap would see a project that is
  neither pulling nor building and call the run finished.
- **Text a command produced is selectable; text this app wrote is not.**
  `Theme.kt`'s `OutputText` is the whole of it, and every failure message
  goes through it -- a component's build or download, a service action, a
  checkout's remote check, and the log dialog's own failure line -- plus a
  `SelectionContainer` around the log body, which cannot use `OutputText`
  because it is an `AnnotatedString` the ANSI renderer coloured inside its
  own scrolling panel. The reason is that this is the one text on screen a
  person has to take somewhere else, and the machine that produced it is
  not the machine in their hand. A status word or a button label stays
  unselectable on purpose: selection handles on those are noise, and a
  card that starts a selection on long-press fights the gestures it
  already has. Iris asked for exactly that line on 2026-09-01: "not the
  'failed' but the command output for build errors and stuff".
  `OutputText` also renders the ANSI escapes rather than printing them,
  through the same `ansiAnnotated` the log dialog uses -- a compiler marks
  its own errors in colour and the tail of a failed build is that output
  verbatim, so raw it arrived as `[1;31merror` with punctuation welded
  onto the one line somebody was trying to read. Selection copies
  `AnnotatedString.text`, which is the message with every escape already
  gone, so what lands on the clipboard is what was on screen rather than
  what was on the wire.
- **A finished component shows nothing, and its button goes back to
  normal.** Iris's call, 2026-09-01: "you shouldn't see the time it took
  once it finishes, it should just go back to its normal enabled button
  state." So `ComponentBuildProgress` draws only while the step is open,
  and the elapsed times are gone from both halves of the wire -- a bar, a
  count and a last line all describe something happening *now*, and every
  one of them sits there looking live beside a sibling that genuinely is.
  What says the build landed is the control becoming pressable again and
  the card's own freshness. The failure is the exception, because it is an
  outcome rather than residue; it is drawn by the component card next to
  the Retry that acts on it, in the one place that reports that
  component's failures whether they came from a build, a download or a
  service action.
- **A card being worked on has no freshness, rather than the one from
  before the press.** Nothing re-reads the manifest during a run -- the
  entry was fetched before the button was pressed and read again only
  once the run is over -- so "out of date" drawn beside the bar that is
  making it current is last minute's answer wearing this minute's
  clothes. `UpdaterScreen` therefore maps a busy component's `freshness`
  to `unknown` in the one place the component list is built for the
  cards, which is what makes both readers of it -- the row's own note and
  `MismatchedPairNote` -- go quiet without either having to know why. The
  condition is deliberately the same pair that disables the Update button
  (`projectState.busy || componentState.busy`): what cannot be acted on
  is exactly what cannot be measured just now. It comes back the instant
  the run ends, still saying "out of date" if the build failed, because
  by then the entry has been read again -- withheld is not the same as
  cleared.
- **A project's own `.dev-updater.ron` is a request, never an
  instruction.** It only runs once accepted from the phone, which copies
  it into `config.ron`; `AppEntry::pending_declaration` is the whole gate.
  Evaluate it *fresh* rather than caching it on the entry — the file
  changes on a pull, and a pull writes no config, so nothing rebuilds the
  entry list. Caching it meant a pull could swap the command out from
  under a previous acceptance and nothing noticed until an unrelated
  config write. Enforce it wherever a command would actually run, not
  only where the list is built.
  Two things follow that both went wrong the moment `resources:` joined
  the gate. **Whatever `Declaration::matches_accepted` compares,
  `AppState::approve_declaration` has to write** -- it compared the
  resources declaration and wrote only the components, so accepting stored
  half of what was being read back and the gate could never clear. The
  press succeeded, so there was no error either; the card simply kept
  asking. Adding a field to one without the other is the shape to watch
  for, and the tests are what let it through: they built an "accepted"
  config by hand instead of calling `approve_declaration`, so they
  asserted a copy of the rule rather than the rule.
  And **on the pull path the gate is asked after the fast-forward, never
  before it** (`build_state::pull_and_build` takes a closure for exactly
  this reason). The declaration lives in the checkout, so the pull is the
  one thing that changes the answer -- a bool computed at the call site is
  the answer for the commit being replaced, which made a pull that changed
  the declaration build anyway. Pulling stays allowed while a request is
  unaccepted, since taking commits runs git rather than the project's
  command, and it is how the new request arrives to be read.
- **Which build variant to serve is the phone's choice, not the server's.**
  It arrives as `?variant=` on the download, beside the `?component=` that
  says whose build it is, and is validated against *that component's*
  discovered builds -- an unvalidated path would let a phone name any file
  on disk to be served. Storing it server-side meant one enrolled device
  silently changing what another was offered. The stored choice is keyed
  by project *and* component on the device, so pinning one client to a
  release build says nothing about the other.

- **A project can produce more than one APK, and each component's builds
  are found under its own `cwd`.** `APK_PATTERNS` is anchored at
  `project.join(cwd)` rather than at the project root, which is what
  `cwd` already meant everywhere else -- the directory the build command
  runs in, the subtree `subtree_head` scopes staleness to, a server's
  `WorkingDirectory`. A component that declares none sits at the root,
  which is what every single-APK project has always meant, so nothing
  about that case changed. tdep-survey is the project that needed it: one
  checkout, a backend and *two* independent Android clients, where the
  root-anchored patterns reached the first and stopped.
  The alternative -- naming the file on the component, `apk: "path"` --
  was rejected because it makes a component a file path, and **an app
  being a project path rather than a file path** is the invariant at the
  top of this document.
  Everything downstream is per component in consequence: `package`,
  `strip`, the variant list, the size, the mtime and the rename note.
  Those were all `apk_component()`'s *first* match before, which was
  correct only while a project had one. Two clients install over
  different packages and differ in whether their symbols are worth
  carrying to a phone, so first-wins would have checked the installed
  state of one app and reported it as the other's -- the expensive kind
  of wrong, because it looks exactly like an answer.
  **A download that names no component is refused, not guessed**
  (`ApiError::AmbiguousApk`), for that reason. Naming none still answers
  for a project with one, which is nearly all of them and is what lets
  the frozen `/self/apk` keep working -- it cannot carry a component, and
  the project it describes has a single APK.
  The measurement carried across an acceptance is keyed by name *and*
  `cwd` (`registry::component_id`): once the directory decides which
  builds a component has, a reused name is not the same APK, and handing
  it the old one's package would be wrong until that component happened
  to be downloaded.
- **`/prepare` and `/build` take `?component=` to build one component
  instead of every one with a command.** Without it, pressing Update on
  one client of a multi-client project ran every component's build to
  get the one that was actually asked for -- fine when a project had one
  APK, expensive the moment it had two and one of them was slow.
  `named_component` in `routes.rs` is the one place a name from the phone
  is checked against the project's own components, so `/prepare` and
  `/build` cannot disagree about what an unknown name means, and
  `BuildState::{trigger_if_needed,build_now,run_build,is_stale}` all take
  the same `Option<&str>` -- `None` still means the whole project, which
  is what `Pull & Build`, the project-row `Rebuild`, and every project
  with a single component keep doing. **Each component's row carries its
  own Rebuild**, which is `/build` scoped to it. That used to be
  deliberately absent, on the grounds that Update already builds a
  component that needs it -- but Update runs `/prepare`, which builds only
  when the staleness rules say the output is behind, and those rules are
  blind to everything a commit does not describe: a command reading files
  nobody declared, an output changed underneath this server, a signing key
  replaced since the APK was made. In all of them nothing reads as stale,
  so Update does nothing, and the only force was a project-wide Rebuild
  that rebuilds every sibling too. Iris asked for the per-component
  button on 2026-09-01. The two are the same action at two scales, so
  they share a word and a colour, and each sits at the right-hand end of
  its own row.
  A component with no command of its own draws no Rebuild -- `hasBuild`
  on the manifest component says so per component, which the project's
  own `needsBuild` (the OR of every component's) cannot. Absent rather
  than disabled, matching the project row, because having no build step
  is not a state a component is in.
  A server's Rebuild sits in its service row but outside the condition
  that draws the service buttons: those wait for the script's answer,
  while a server whose script cannot be reached is still one this machine
  can compile.
  **Where `component.dir()` belongs is now one definition**
  (`Component::dir` in `config.rs`), because a second one very nearly
  shipped a real bug: `component_is_stale`'s "never built at all" check
  still asked `find_apks` of the *project root* after per-component
  discovery had already moved everywhere else to `component.dir()`. A
  project with two `Apk` components has one's output sitting under the
  root-anchored patterns too -- `*/build/outputs/apk/*/*.apk` matches any
  one-level subdirectory, regardless of which component put it there --
  so the moment *either* component had ever been built, the whole
  project read as "something is built here," and the *other* component,
  never built, silently stopped being offered its own first build:
  `prepare` saw a component with a command and no output and declared it
  current. Caught by testing the actual behaviour of a two-APK project
  rather than trusting that scoping the build implied scoping the
  staleness check that decides whether to run it -- they are two
  different reads of "which directory is this component's," and only one
  of them had been moved.
  The same check is deliberately *not* asked of a `Server`: a service
  never has an APK to find under its own directory by definition, so
  asking would report every server "never built" forever. Guarded on
  `matches!(component, Component::Apk { .. })` for that reason.
- **The self entry's project is the working directory itself**, so this
  server has to be started from the root of its own checkout -- which is
  where everything else here is driven from, and what the service unit
  sets (`WorkingDirectory=$REPO_ROOT`, not `server/`). Its components then
  say where they live from there, exactly as any other project's do; there
  is nothing special about this one's layout, which is the point of it not
  being `app/` any more. It used to be
  `CARGO_MANIFEST_DIR`, fixed when the binary was *compiled*, so a
  re-clone or a move left the card watching a directory nobody pulls. The
  symptom is why this is worth remembering: the entry keeps working and
  keeps serving an APK, but silently loses its branch line, its Pull
  button and its commit count, so it reads as an app that simply never has
  an update. It took a "why can't my server see the new commits?" to find.
  Startup warns when there is no checkout at the resolved path, which is
  the only cheap moment to notice.
- **A configured project pointing at this server's own project is a second
  card for it.** `add_app` refuses it (the self entry is in the list it
  checks against, and `self_project` is canonicalized so a symlink can't
  make one directory look like two), so this only survives from a config
  written while the self entry resolved somewhere else. It is not merely
  redundant: it is not the self entry, so `is_self` is false and a build
  through it would restart this server partway through its own build. `build_entries` warns rather than dropping
  it -- dropping it would leave a config entry with no card and so no way
  to remove it from the phone. The built-in card has no Remove button, so
  the duplicate is the one that does.
- **A project says where its own state is; nothing infers it.** The
  `resources:` declaration points at a RON file, a script that prints the
  same RON, or an inline struct, and it holds what a project would
  otherwise write down in several places -- its `name`, and its `data` and
  `config` directories when those are not `$XDG_*_HOME/<name>`. **The file
  is the project's, not this server's**: its own code is meant to read the
  same one, which is why `ResourceFacts` ignores unknown keys where
  `Declaration` sets `deny_unknown_fields`, and why it goes through
  `wg_app_link::format` like every other RON here.
  A project that says nothing gets nothing -- the dialog reports not
  knowing rather than filling in a directory. Two guesses were tried and
  both rejected: the config key (`updater`, `app`, which resolve to
  `~/.config/updater` and `~/.local/share/app`, neither of which exists)
  and the checkout's directory name (right for both projects here, and
  still an inference presented as a fact). Iris's call, and the reason is
  the failure mode: a wrong path does not error, it reads as "this
  component keeps nothing here".
  Read **off the request path**, through `crate::checks` beside the git
  and service checks, because `Script` spawns a process and `/manifest` is
  fetched on every open, resume and Refresh. It is in `checksPending` with
  the other two -- counting only some of them is the bug that once left
  components with no buttons after a restart. And it is part of the
  acceptance gate, since a `Script` runs: comparing the whole declaration
  rather than the variant means changing which file is read is a change
  somebody is asked about.

- **Uninstall can take three things away, and the path on screen is the
  only guard.** The dialog offers logs, data and config as separate
  toggles -- only logs on by default, and ticking data forces logs on,
  since a service that writes its log inside its own data directory would
  lose it either way. `purge.rs` is the whole of it. Where the data and
  config are comes from the project's `resources:` declaration, above; a
  project that does not say gets two disabled toggles saying so, and the
  four reasons a toggle is disabled are distinguishable on screen because
  "couldn't read the resources" is a fault to fix while "doesn't say" is
  an ordinary project.
  A path is removed **wherever it points**, with no check that it
  sits under the XDG directories -- Iris's call, over the alternative of
  refusing anything outside them. What replaces that check is the dialog
  showing each resolved path before the button can be pressed, so the
  phone never asks for a path nobody saw. Anything that stops the path
  being displayed removes the only guard there is.
  Log paths are collected *before* the uninstall runs, because the script
  that reports where a service's log lives is the thing being removed.

- **The self entry can't be removable.** The app can only be updated
  through this server, so an updater that can drop itself from its own list
  strands the installed copy (recovery is a manual reinstall over the
  bootstrap port).
- **`/self` and `/self/apk` are a frozen contract, and the only rescue the
  app has.** Every other route is reachable only by an app new enough to
  understand it: change what `/manifest` says and an older app cannot read
  the list, which is where the button that would replace it lives. So the
  path that fetches a newer app depends on nothing likely to change --
  two numbers, no nesting, no variants, no query parameters -- and the app
  asks it on every launch and again after building its own project, which
  is the moment the newer copy exists and the server it must keep talking
  to has just changed. Add fields at your peril and never rename one;
  anything richer belongs on a route an old app never calls. It does not
  survive a changed CA, port or token, since those break the connection
  before any route is reached: those stay one-way doors and `--download`
  stays their answer.
- **There is deliberately no general migration mechanism.** Iris's call:
  each app decides its own, and the updater's job is only to be able to
  get both halves of *itself* to the next version. A project that renames
  or restructures its service is uninstalled and reinstalled from the card,
  which works because dev-updater is not the thing being stopped.
- **The bootstrap link (`--download`) serves the APK already on disk and
  builds nothing.** Shipping a stale one there is the expensive mistake,
  because a fresh install is not enrolled and everything that would replace
  it -- Update, and the QR scan that enrols a device at all -- lives in the
  copy being installed, so the only way out is another trip through
  `--download`. It cost a round of "the scanner fix never landed" when the
  fix was in the checkout the whole time. The startup line names the
  variant and the build's age for that reason; run `./app/build-apk.sh`
  first.
- **Changing the pinned CA is a one-way door for any installed copy.** Same
  reason. `wg_app_link::certs` deliberately won't regenerate an existing
  CA; only the leaf is reissued, on every start.
- **State is per machine, not in the repo**:
  `$XDG_CONFIG_HOME/dev-updater/{config.ron,certs}`, owner-only. This
  repo is shared with a VM at a different path, so a shared config hands
  each machine the other's project paths, and a CA key in it is one that VM
  could sign with. The APK pins the CA of whatever machine builds it
  (`app/build-apk.sh`, `DEV_UPDATER_CA` overrides).
- Freshness is the APK's **mtime** versus `PackageInfo.lastUpdateTime`, not
  a version code — these are ad hoc rebuilds with nothing bumping a
  version. It follows that a build and an install landing in the same
  second can briefly read as "update available"; that's inherent, not a
  bug to chase.

## Running the server for real

`./start.sh` is the shortest way back to a working state: it builds both
halves, rewrites the service unit (so a pull that changes the service script
takes effect) and starts or restarts it. Use it after a pull, or when the
running server and the checkout have drifted.

To run one by hand instead, launch it **from the repo root** -- that is
where it looks for its own app project (`app/`), and started anywhere else
its own card has no checkout -- and **fully detached from the calling
shell**, not via an agent's background-task tracking, which ties its
lifetime to the session:

```sh
setsid nohup /path/to/dev-updater </dev/null >server/dev-updater.log 2>&1 & disown -h
```

Verify with `ps -o pid,ppid,pgid,sid,tty,comm -p <pid>` — detached means
`PPID 1`, its own `SID`, `TT ?`. Check for a stale instance first
(`pgrep -af "[d]ev-updater" || true`): a second instance fails to bind and
silently leaves the old one answering. Stop with
`pkill -f "[d]ev-updater" || true`.

**Run `pgrep -f`/`pkill -f` as a command of its own, with nothing else on
the line, and bracket the first character of the pattern**
(`"[d]ev-updater"`). Both also exit nonzero when nothing matches, which is
the normal case; `|| true` that.

Why the pattern alone isn't enough, since this keeps catching people: each
command runs as `bash -c '<the whole command text>'`, so the wrapper's own
argv contains every word you wrote. An unbracketed pattern therefore
matches the shell running it — `pgrep` reports phantom matches and `pkill`
kills that shell outright (exit 144, truncated output, reads exactly like
the thing under test having crashed). Bracketing the pattern fixes only
*that* word: any **other** mention of the same string on the line re-arms
it. And you usually can't fix the other mention, because it is the real
command —

```sh
# Kills its own shell: the pattern is bracketed, but the path below
# still puts the plain string "target/debug/dev-updater" in the argv,
# and bracketing *that* would change which file gets executed.
pkill -f "[t]arget/debug/dev-updater" || true; setsid nohup ./target/debug/dev-updater …
```

so the only rule that always works is to keep them in separate commands:
one to stop, one to start.

One more way this bites, which bracketing does nothing about: `-f` matches
the **whole command line**, so it also catches processes that merely have
the string somewhere in a path. An agent's scratchpad directory is named
after the repository, so anything launched with a path through it -- the
Android emulator, say -- matches `[d]ev-updater` and gets killed along
with the server. Match the binary rather than the project when stopping
one: `pkill -f "[t]arget/debug/dev-updater"`.

## Environment notes

The machine itself — where the Android SDK is, that each command runs in a
fresh shell so exports have to be chained, and each repo having its own
emulator — is described once in `~/.claude/MACHINE.md`, which every
session reads. What follows is what that means here.

- `app/android-env.sh` applies the SDK override unconditionally, and
  `.claude/settings.json` puts `platform-tools` alone on `PATH` so `adb`
  works without sourcing anything. Everything else needs the env script.
- **This repo has its own AVD, named `dev-updater`**, which is what
  `app/run-android.sh` and `app/enroll-emulator.sh` default to; every
  Android project on this machine has one named after it, and none of them
  share. Two sessions in two repos on one emulator each silently replace
  the app the other just installed, which reads as a build that never
  landed rather than as interference.
- **To exercise installing, add a throwaway test app**, not another repo's
  real one. This server's whole job is putting *other* projects' builds on a
  device, so trying that out needs something to install -- and a scratch
  project you wrote is better for it than a real app, because you can make
  it do whatever the case under test needs: fail its build, produce two
  variants, change its label, bump nothing at all. A real app only does what
  it happens to do. It goes in the list like any other project, so nothing
  here needs to know it is a test.
- **To actually drive the app on the emulator, use
  `app/enroll-emulator.sh`** rather than working enrolment out again. There
  is no camera to scan the QR with, so it fires the `devupdater://enroll`
  intent the app already accepts, generating a token once and adding it to
  `config.ron` beside any real phone's. Two things it exists to stop you
  rediscovering: `adb shell am start -d` loses everything after the first
  unescaped `&`, because the URI reaches the *device's* shell; and the
  server must be started with `--bind 0.0.0.0` for the emulator to reach
  it at all, since it otherwise binds wg0 and the emulator has no route
  there. The script's header has the detail.
  **It names the device rather than assuming there is only one**, which
  matters more now that every repo has its own AVD: a second emulator
  running beside this one makes every bare `adb` call exit 1 with "more
  than one device/emulator", and the version that ran `adb get-state` read
  that as *no emulator running* -- the opposite of what had happened, which
  sends you off to start a third. It resolves the serial by AVD name the
  way `run-android.sh` always has, defaults to `dev-updater`, takes
  `--avd NAME` or `AVD_NAME=`, and when it cannot find that one it lists
  what *is* attached instead of guessing which of the three situations it
  is in.
- The server needs `aapt2` (SDK build-tools) to add an app, and, for an
  app that needs stripping, `llvm-strip` (NDK), `zipalign` and
  `apksigner` (build-tools) **and `~/.android/debug.keystore`** -- the
  last is the least guessable of the four, since it belongs to no SDK,
  is created as a side effect of any Gradle Android build, and is
  consumed by the pipeline's final step. A machine that builds APKs and
  has no keystore is odd rather than new: something removed it after the
  build, and the APK it produced is signed by a key that is now gone. **It has to find
  both without an environment**, because the way this server usually
  starts is from a service manager, and one hands its process a scrubbed
  environment: measured in the Gentoo guest, an OpenRC user service gets
  19 variables with neither `$ANDROID_HOME` nor `$ANDROID_NDK_HOME` among
  them, and a systemd user unit inherits an equally bare one unless
  somebody imported theirs. Neither branch of `service-default` passes any
  through, so this is not a Gentoo quirk and "export it in the unit" is
  not the fix. `HOME` does survive, which is what the home-relative
  candidates in `sdk.rs` are for. The trap it produces is a build that
  *succeeds* and a download that 500s -- a project's own build script
  sources its `android-env.sh` and repairs the environment inside its own
  process, while the strip runs in-process here and sources nothing.
  So `sdk_roots` lists candidates and every lookup takes the first that
  actually contains the tools it needs: an `$ANDROID_HOME` that exists is
  not one with the tools in it (this machine's system-wide
  `/opt/android-sdk` has a `build-tools/36.0.0` holding nothing but
  `package.xml`), and taking it blamed `zipalign` for a root that should
  never have been chosen. Filter *before* taking the newest, too --
  `newest_child_where` exists because filtering the single newest child
  can only reject that one directory, so `Sdk` sitting beside
  `android-ndk-r27c` in `~/Android` hid the NDK from a message that said
  "install one".