DodoSSH/docs/android-port.md

# An Android client: what it would take

**Status: the decided scope is built. Steps 3–8 are done.** `src/DodoSSH.Client.Android` is a phone-first
head that builds and packages: the keychain and a terminal, which is exactly the scope
[decided](#scope-the-keychain-and-a-terminal), plus the sign-in and enrollment states needed to reach them
from a phone that has never been used before. The four decisions that shape the work are recorded in
[Decisions](#decisions-taken); everything below them is the audit they were taken against, and it has held
up — with three corrections and one addition, all marked **✅ settled** or **⚠️ corrected** where they
belong.

**What the spike came back with**, since everything downstream was gated on it:

- **The cryptography works.** `libsodium.so` and `libe_sqlite3.so` are both in the arm64 APK. NSec
  resolving its native half despite shipping no Android-specific build was the one dependency this
  document said was worth proving with a build, and it proves out.
- **`Avalonia.Controls.WebView` forces `targetSdk` 36**, which settles the open question about Android
  versions — see [Still open](#still-open). This head is minSdk 28 / targetSdk 36.
- **Cleartext to loopback has to be allowed explicitly.** Not in the original audit and easy to lose a day
  to: Android has blocked plaintext HTTP by default since API 28, so the terminal renderer needs a network
  security config scoped to `127.0.0.1` or the WebView loads nothing and the failure looks like a renderer
  that never attached. See `Resources/xml/network_security_config.xml`.

**Still unverified, and it is the honest limit of all this:** nothing has run on a device or an emulator.
No system image is installed here, so every statement below about *runtime* behaviour — Argon2id actually
completing at the 256 MiB profile on a phone, the WebView actually loading the renderer, the biometric
prompt actually releasing the key — remains reasoning from the code and the platform's rules. What is
verified is that it compiles, links, packages, and carries the right natives.

**The shape agreed:** a **phone-first** client that is the keychain plus a **terminal**, with sessions and
transfers protected by a **foreground service**. File transfer is not in the first scope; when it arrives it
is **one remote pane** with Android's document picker for moving files in and out. *It has since arrived,
both ways:* the pane, the queue, `ACTION_OPEN_DOCUMENT` going in and `ACTION_CREATE_DOCUMENT` coming out,
with the foreground service now counting transfers as well as shells.

**What was actually checked**, so the rest can be read with the right amount of trust:

- Every project's target framework, read from `Directory.Build.props` and the `.csproj` files.
- The target frameworks each pinned package ships, read out of the local NuGet cache — so these are the
  assemblies this solution would actually resolve, not what a package's README claims.
- Every site in `src/` that names a Windows API, a Windows path convention, or a desktop lifetime.

**What was not**: nothing was compiled for Android, nothing was run on a device or emulator, and no Android
SDK is installed here. Every statement below about *runtime* behaviour is reasoning from the code and the
platform's documented rules, and is marked where it matters.

---

## The headline

The port is smaller than it looks in one dimension and much larger in another.

**The core is already portable.** Every project targets plain `net10.0`, with no `net10.0-windows` anywhere
and no conditional compilation. All the Windows-specific code now sits in one project — `DodoSSH.Client.App`,
the desktop head. The cryptography, the sync engine, the local cache, the SSH layer, the item kinds and every
view model are platform-neutral today, and that is not luck: it is what the project structure has been
enforcing all along.

(One file was out of place when this was written — `WindowsDeviceKeyStore`, in `DodoSSH.Client.Session`. It
has since been moved, which is the only code change this audit produced; see §4.)

**The product is not.** DodoSSH is a two-pane file browser, a tab strip, a nav rail and a terminal, laid out
at a minimum of 880×560, driven by hover, right-click, middle-click and drag-and-drop. A phone is about
360dp wide and has none of those inputs. Roughly none of the *interface* ports; the question an Android
client really asks is not "will this compile" but "what is the Android product".

Two platform rules make that sharper, and they are the things most likely to be underestimated:

- **Scoped storage.** Android has no arbitrary local filesystem for an app to browse. The left-hand pane of
  the Files screen — this machine's drives and directories — has no Android equivalent at all.
- **Background execution.** Android stops a backgrounded process. A terminal client whose whole premise is
  that a shell survives locking the vault, and a transfer queue that runs for minutes, both assume a process
  that keeps running. On Android that needs a foreground service with a persistent notification, or the
  feature changes shape.

Neither is a porting problem; both were product decisions, and both have now been taken — a foreground
service, and a single remote pane. See [Decisions](#decisions-taken).

---

## What ports as it stands

Verified from the resolved package assemblies.

| Dependency | Ships for Android | Note |
| --- | --- | --- |
| `libsodium` 1.0.22 | ✅ `android-arm64`, `android-arm`, `android-x64`, `android-x86` | The native half of all the cryptography |
| `NSec.Cryptography` 26.4.0 | ⚠️ no Android-specific build | Ships `net9.0` plus iOS/tvOS/MacCatalyst. The plain `net9.0` assembly should load, since the platform-specific part is libsodium — but this is the one dependency worth proving with a build before anything else |
| `SSH.NET` 2025.1.0 | ✅ `netstandard2.0`, `net8.0` | Sockets only; needs the `INTERNET` permission |
| `SQLitePCLRaw.bundle_e_sqlite3` 2.1.12 | ✅ `net6.0-android31.0` | The local cache |
| `AWSSDK.S3` 4.0 | ✅ `netstandard2.0`, `net8.0` | |
| `CommunityToolkit.Mvvm` 8.4.2 | ✅ `netstandard2.0` | Every view model |
| `Avalonia.Controls.WebView` 12.0.1 | ✅ `net10.0-android36.0` | The surprise — see below |
| `Avalonia.Desktop` 12.1.1 | ❌ `net10.0` only | Replaced by `Avalonia.Android`, not ported |

So: **`DodoSSH.Client.Domain`, `.Storage`, `.Sync`, `.Api`, `.Auth`, `.Ssh`, `.Terminal`, `.Transfer`,
`.ObjectStore`, `.Import` and `.Crypto` should all target `net10.0-android` unchanged.** That is the great
majority of the code, including all of the cryptography and all of the sync protocol.

`DodoSSH.Client.Session` needed one file moved and no longer does — see §4. `DodoSSH.Client.App` is the
desktop head and does not port; an Android head would be a sibling project sharing its view models.

---

## What does not port, in order of how much it costs

### 1. The interface — the largest item by far, and it is not a port

880×560 minimum, a 54-pixel nav rail, a 268-pixel host sidebar, a two-pane file browser with six columns per
pane, a tab strip, and a layout suite (`DodoSSH.Client.App.Layout.Tests`, 64 tests) whose entire premise is
that everything fits at that minimum. (Those are the numbers this audit was taken against. The desktop's own
v2 has since widened the rail to 190 and the minimum to 1016×574, and the suite is 69 cases — which makes
the point below larger rather than smaller.)

None of it survives a phone. What an Android client would be is a different product with the same core:
probably a host list, a terminal, and a single-pane file browser, with the keychain, snippets, logs and pins
as screens rather than as a rail. The desktop screens are not a starting point for that — they are a
different answer to a different question.

**This is where the real effort is**, and it is design effort before it is engineering effort. Everything
else on this list is a week or two of work; this is the product.

**Decided: phone first.** See [Decisions](#phone-first) — which means a redesign rather than a reflow, and
rules out the cheaper tablet route deliberately.

### 2. The Files screen's left pane has no Android equivalent

Scoped storage means an app sees its own directory and whatever the user hands it through the system
picker. There is no browsable `C:\` or `/home`. So the two-pane layout — the thing the whole screen is built
around — does not exist on Android.

The honest shapes are: a one-pane remote browser with **download to** and **upload from** going through the
system document picker, or a remote-to-remote transfer tool with no local side at all. Both are fine; both
mean the transfer queue's local half (`LocalDirectory`, the drive list, the breadcrumb trail) is desktop-only
code.

Note what *does* carry: `FileTransferQueue` itself, and `IRemoteFileStore` — Phase 6 already proved that
seam holds two very different remotes, and a `Uri`-backed Android document would be a third. (**⚠️ That last
clause is wrong, and the build is what corrected it**: a document URI cannot resume, so what shipped stages a
copy and hands over a path. See the note under the decision below.)

**Decided: one remote pane and the document picker**, and out of the first scope. See
[Decisions](#file-transfer-when-it-comes-one-pane-and-the-document-picker).

### 3. Background execution

`TerminalWorkspace` keeps shells running across a vault lock, deliberately and documented. `FileTransferQueue`
runs one transfer at a time for as long as it takes. `VaultViewModel` runs an auto-sync pass every minute.
All three assume a process Android will stop.

The options are a foreground service with a notification for as long as a session or a transfer is live
(which is what every serious SSH client on Android does), or accepting that backgrounding the app drops the
connection. The first is not hard; it is a decision about what the app is allowed to do to the user's
battery and notification shade, and it wants taking deliberately.

**Decided: a foreground service** while a shell or a transfer is live. See
[Decisions](#sessions-survive-backgrounding-via-a-foreground-service).

### 4. The device key store — the cheap one, because the seam exists

`WindowsDeviceKeyStore` is DPAPI over a TPM-held key. `IDeviceKeyStore` is already the interface everything
else uses, with three methods and an `IsAvailableAsync` that exists precisely so a platform without a
keystore can say no.

Android's equivalent is the Android Keystore, with StrongBox where the hardware has it, and it is a closer
match than the Windows one: it can require biometric or device-credential authentication to release the key,
which is what the unlock screen would want anyway. **This is a straightforward implementation of an existing
interface**, and it is the piece of Android integration most clearly worth doing well.

**Done, ahead of any decision:** `WindowsDeviceKeyStore` used to sit in `DodoSSH.Client.Session`, which was
the one thing keeping that project from being portable. It now lives in `DodoSSH.Client.App/Platform/`, and
its factory is `DesktopDeviceKeyStores` — named for the head it belongs to. `IDeviceKeyStore` and
`UnavailableDeviceKeyStore` stayed behind, because they are the seam rather than an implementation.

The move cost nothing but a namespace, which is the useful part of the finding: the session layer takes a
store and has never known which one, so an Android implementation drops into the same hole. Verified by the
build and the suite, with the two Windows-only tests moving to `DodoSSH.Client.App.Tests` alongside it.

### 5. Sign-in

`BrowserLauncher` uses `Process.Start(UseShellExecute: true)`; `LoopbackCallbackListener` implements RFC 8252
§7.3 loopback redirect with a raw `TcpListener`.

Neither is right on Android. `Process.Start` does not exist; the platform way is an `Intent`, and the
platform way to receive the redirect is a Custom Tab plus an app link or a custom scheme. Loopback redirect
*might* work, and should not be used: on a shared device any other app can bind a loopback port, which is
exactly the attack RFC 8252 §8.3 warns about and the reason app links exist.

So this is a second implementation of an existing shape rather than a port. The PKCE flow, the discovery, the
key binding and the token handling above it are all unchanged.

### 6. `ClientPaths`

Branches Windows / macOS / XDG, with an explicit comment about wanting a *local, non-roaming* directory
because two machines sharing one cache file corrupts the outbox. On Android the right answer is the app's own
`filesDir`, which is per-app, non-roaming and not user-visible — it satisfies the requirement more cleanly
than any desktop platform does. One more branch, or better, the value injected by the head. `ClientPaths`
already takes an explicit directory for exactly this reason.

### 7. `Environment.MachineName`

Used as the device name on connection and activity log entries, and when registering a device. On Android it
returns something like `localhost`, which would make every log entry from a phone indistinguishable. Needs a
real device name from the head.

**Done** — `PhoneEnvironment.DeviceName` reads what the user typed into Android's own Settings, falling back
to the marketing model, and `MainWindowViewModel` takes it as an optional constructor argument that the
desktop head does not pass. It reaches all three places the machine name was: enrollment, device
registration, and every connection log entry. The registration is the one that had to be fixed before the
device key could be offered on a phone at all — the account's device list is what a lost handset is revoked
from, and a list of identical `localhost` rows is a revocation nobody dares press.

### 8. The Windows-only bits of the desktop head

Listed for completeness; none of these is ported, they are simply absent from an Android head.

- `NativeKeyboardFocus` — `user32.dll SetFocus`, and the whole documented asymmetry about focus not
  returning from the WebView. Android's focus model is different and this problem may simply not exist there.
- `Program.Main` — `[STAThread]` (required by WebView2 specifically) and `StartWithClassicDesktopLifetime`.
  An Android head is an `AvaloniaMainActivity` instead.
- Middle-click tab close, right-click, hover states, drag-and-drop between panes.

### 9. The terminal — better news than expected, with one unknown

`Avalonia.Controls.WebView` ships a `net10.0-android36.0` target, which was the single fact most likely to
sink this. And the transport underneath is more portable than it looks: `TerminalDataPlane` serves the page
and the binary protocol over a **loopback WebSocket**, and an Android WebView can load `http://127.0.0.1:port`
just as WebView2 does. The xterm.js bundles are embedded resources and are platform-neutral.

**Unverified, and it is the thing to check first if this goes ahead:** whether Avalonia's Android WebView
composites the same way — a native view above everything Avalonia draws. If it does, the occlusion rule in
`docs/platform-flags.md` applies unchanged and `IsTerminalShowing` keeps doing its job. If it does not, the
rule is unnecessary rather than wrong, which is the harmless direction.

The parts that are definitely different are the on-screen keyboard, and the fact that a terminal on a phone
needs Ctrl, Esc, Tab and arrows that the software keyboard does not offer — every Android SSH client ships an
accessory key row for this. That is UI work, not porting.

---

## Decisions taken

Four, each recorded with the reasoning that was actually weighed rather than only the outcome.

### Scope: the keychain and a terminal

Not a companion, and not the file browser. Everything that is already a list or a form — hosts, groups,
keys, passwords, snippets, pins, logs — plus opening a shell.

The terminal is the expensive half and it is the half that makes it an SSH client rather than a viewer. It
depends on the WebView spike coming back clean; if it does not, the companion subset is what is left and is
still worth shipping, so the work is ordered to find that out early.

### File transfer, when it comes: one pane and the document picker

Out of the first scope, decided now so the seams are not built the wrong way. A single remote pane, with
Android's document picker for moving files in and out.

This is the shape scoped storage allows, and the interesting part is how little it costs: `FileTransferQueue`
and `IRemoteFileStore` both carry over unchanged. Phase 6 already put a bucket behind that interface beside
an SFTP host, so a picker-granted document is a third implementation of a seam that has been exercised twice.
What is desktop-only is the *left* pane — `LocalDirectory`, the drive list, the breadcrumb trail.

> **⚠️ Corrected by the build. Both directions shipped, and neither as a third `IRemoteFileStore`.** A document
> URI cannot sit behind that interface honestly: the queue seeks, because an upload resumes from the byte the
> last attempt reached, and a `content://` stream promises no seek, no stable length, and no grant that
> survives the document being edited underneath it. So `DocumentStaging` copies the chosen document into the
> application's cache and hands the queue an ordinary path — which cost one class in the head and *nothing*
> in the shared layers, rather than a third implementation of a seam and every resume rule rewritten to cope
> with a stream that cannot rewind. The copy is deleted when the transfer completes, kept while it is stopped
> so RESUME can read it, and swept at the next launch.
>
> **Outbound is the mirror image, with one decision the inbound half did not have to take: when to ask.** The
> save picker is raised *before* the transfer, so `QueueDeliveredDownload` runs into the same staging
> directory and hands the finished bytes to a callback the head supplied. Asking afterwards would put the
> picker minutes away from the button that caused it and, on a phone, frequently in the background — where
> Android will not show one. The cost is that `ACTION_CREATE_DOCUMENT` creates its file when it is
> dismissed, so a download that then fails leaves an empty one; that is said on the screen and in the
> README rather than left to be found. A delivery that fails keeps the staged bytes for the sweep instead of
> deleting the one copy of something that was just fetched over somebody's network.

### Sessions survive backgrounding, via a foreground service

A persistent notification for as long as a shell or a transfer is live.

It costs the user a notification and some battery. It buys the behaviour the desktop client already promises
and documents — that a shell outlives a vault lock, and that a transfer finishes — and the alternative was
to make `TerminalWorkspace`'s guarantee desktop-only, which is a worse thing to have to write down than a
notification is to look at.

### Phone first

About 360dp wide. The tablet route was cheaper — a landscape tablet is close to the existing 880×560 minimum
and much of the current layout could have been reused — and the phone is the device people have with them,
which for an SSH client is most of the point.

So the interface is a redesign rather than a reflow, and that is the largest single item of work here. The
nav rail, the 268-pixel sidebar and the two-pane browser do not survive. What does survive is everything
behind them: every view model, every command, every piece of state.

---

## What the interface actually has to carry

Written for designing the phone client. It is an inventory of what exists today and what each part is
*for* — not a layout, and not a claim that any of it should look the same.

**Read it as a checklist of things that need somewhere to go.** The desktop has room to put a warning, a
confirmation and a form on screen at once; a phone does not, and the states most easily lost are the ones
that appear rarely and matter most. Those are marked **◆**.

### Getting in: six states before the app is usable

`ShellState`, and every one of them is a screen.

1. **Starting** — reading the local cache to find out whether this machine is enrolled.
2. **Needs a server** — nothing cached: name a server, sign in through the browser. The only state that
   requires a network.
3. **Needs enrollment** — signed in, but the account has no vault key yet. Choose a passphrase.
4. **◆ Showing the recovery code** — *the user must not be able to click past this.* It is the only moment
   the code exists; losing it along with the passphrase means the vault is unrecoverable, and there is no
   server-side reset by design. On desktop it is a whole screen with a confirmation. It needs to stay one.
5. **Locked** — the unlock screen. Passphrase box, optional device unlock (biometric on Android), a status
   line, and the line saying this works with no network. **◆** Also carries two disclosures: how many shells
   are still connected behind the lock screen, and the paragraph explaining that *locked* describes the
   keychain and not this machine's access to the hosts. Plus **reset this machine** for a forgotten
   passphrase.
6. **Unlocked** — everything below.

### Chrome that is present on every screen

- **Titlebar** — vault name, account name, a search affordance (Ctrl+K on desktop), and a sync dot with a
  label: synced, pending count, offline, unreachable.
- **Status bar** — the selected terminal's live dot and address, the vault's last status sentence, the sync
  label again, and the search hint.
- **Nav rail** — eight destinations: `HOSTS FILES KEYS PINS SNIPS LOGS TEAM PREFS`. Five characters is a
  desktop constraint, not a product one; the phone can use words.
- **Terminal strip** — always visible, above every screen. Tabs with a close cross *inside* each tab, a `+`,
  and a sentence when there are none. This is what makes a terminal a surface the window switches to rather
  than a screen you navigate away from, and it is the single most desktop-shaped idea in the product.
- **Quick connect** — a search palette over hosts that connects on Enter.

### The nine destinations

**1. Hosts** — the list of machines, and what is known about the selected one.

- *Sidebar:* filter box; group headings with a chevron and a count, **shown only when groups exist**; host
  rows carrying a connected dot, name, sync badge, address and one word for how it authenticates.
- *Editor* (doubles as "add"): name, hostname, port, username, notes, one authentication picker covering
  typed password / key / stored credential, a group picker, a relay checkbox with the sentence explaining
  that relay puts the address on the server in plain text, and **◆ forget host key** — the only way back from
  a legitimately rebuilt server.
- *Actions:* new / edit / delete, **replaced in place** by the delete confirmation rather than stacked under
  it.
- *Right column:* the connect banner — a password box only for a host that asks for one, a sentence in its
  place when it does not, and CONNECT.
- **◆ Unknown host key prompt** — fingerprint shown in full, TRUST AND CONNECT / CANCEL. Appears on first
  contact with any host.
- **◆ Changed host key refusal** — deliberately has *no* continue button. Presenting this as dismissible is
  the one design mistake that matters here.
- **◆ Conflict log** — what a merge overrode and what it discarded, scrollable, with DISMISS ALL. The merge
  is only allowed to pick a winner because this exists.
- *Groups panel:* the groups as chips with host counts, a name box that both adds and renames, delete with
  its own confirmation counting the affected hosts. Since groups gained a parent and the four defaults their
  hosts inherit, the panel is a small form rather than a box: a parent picker that excludes the group's own
  descendants, and a default port, username and binding beside the name.

**2. Files** — two panes and a queue.

- *Bar:* a HOST / BUCKET toggle, the matching picker, a password box for hosts that need one, CONNECT
  (or OPEN for a bucket), DISCONNECT, a connected chip, a status line.
- *Panes:* breadcrumb trail, drive roots on the local side, and a listing with name, size, modified and —
  remote only — POSIX permissions. Each pane has an empty state and a drop highlight in two flavours,
  accepting and refusing.
- *Queue:* direction arrow, name, the remote path, progress with bytes and rate, state, and RESUME / RETRY /
  stop per row.
- **◆ The host key prompts appear here too.** File transfer is a second, separate connection that makes its
  own trust decision.
- On Android this becomes one remote pane plus the document picker — see the decision above — but the queue,
  its states and the prompts are unchanged.

**3. Keychain** — everything that is not a host.

- *Categories:* ALL / SSH KEYS / PASSWORDS / BUCKETS, each with a count.
- *Table:* name, type, one line of detail, sync badge. The detail is what is *known about* an item and never
  the secret.
- *Four editors,* which are four different shapes: an SSH key (label, private key armour shown unmasked so a
  truncated paste is visible, passphrase, public key, notes); **generate a key** (algorithm choice, comment,
  and it fills the editor rather than saving); a password (label, username, password masked, notes); a bucket
  (label, bucket, access key id, secret access key masked, region, endpoint, **◆ a path-style checkbox with
  the sentence explaining why**, notes).
- **◆ Delete confirmations that count** — "three hosts authenticate with this key and will refuse to connect".
  The number is the difference between a sentence somebody reads and one they click past.

**4. Pins** — the host keys this keychain has approved.

- Filter that matches **fingerprints as well as names**, because the workflow is "the operator published
  SHA256:… — do I have that one?".
- Table: host, port, algorithm, **◆ fingerprint never truncated**, approved date.
- Detail pane with the fingerprint in full again, a "no host uses this" chip, the note that the date is
  derived from the item id and means first approval rather than last use, and FORGET THIS HOST KEY.

**5. Snippets** — saved commands.

- Filter matching the command text as well as the name.
- Rows: name, **◆ a "runs immediately" chip**, sync badge, and a one-line preview with newlines shown as `⏎`.
- Editor: name, a multi-line command box, notes, and **◆ a "press Enter after inserting this" checkbox with
  the paragraph explaining that leaving it off is the whole safety property**.
- Detail pane with the command in full and two buttons that **name the terminal they will type into** —
  `TYPE INTO prod-db` and, only for a snippet marked as running, `RUN IN prod-db`. Plus the "no terminal
  open" state, and the sentence saying whatever is in the terminal receives this.

**6. Logs** — two logs behind one screen.

- A CONNECTIONS / KEYCHAIN toggle and a refresh.
- *Connections:* live dot, host, address, **◆ "still open" rather than a dash for a session in progress**,
  kind (terminal or files), started, device, and a chip for a refused host key.
- *Keychain:* item, type, what happened, **the names of the fields that changed**, when.

**7. Preferences** — import `~/.ssh/config`, register or forget this device, sign out.

**8. Team** — nothing behind it, and the screen says so rather than being hidden from the rail.

**9. Import** — a preview before anything is written: tick per row, alias, resolved address, how it
authenticates, a warnings chip, an "already in the keychain" badge, TICK ALL / NONE, and IMPORT N HOSTS.
Nothing is stored until the button.

### States that cut across every screen

- **Empty states**, with copy written per screen — each says what the thing is *for*, not "no items".
- **A read-only item**, written by a newer client: shown, refused for editing, with a message saying to
  update. Re-encoding would silently drop a colleague's field.
- **Sync badges** per row: not synced yet, refused and waiting on a person, read-only.
- **Unreadable items** — a count of things that would not decrypt, which is the signal that new key grants
  are needed after a rekey.
- **Busy**, and **offline / unreachable**, which are different from each other and both different from
  "everything is synced".

### The five most likely to be lost on a phone

In the order I would worry about them, and all of them are full-width blocks today with nowhere obvious to
go at 360dp:

1. The changed-host-key refusal, which must not become dismissible.
2. The recovery code screen, which must not become skippable.
3. The counted delete confirmations, which are the difference between a decision and a reflex.
4. The unknown-host-key prompt, which is the one interruption that is genuinely load-bearing.
5. The conflict log, which is what makes the merge honest rather than last-writer-wins.

---

## The order of work

1. ~~Decide the product questions.~~ **Done** — see [Decisions](#decisions-taken).
2. ~~Move `WindowsDeviceKeyStore` into the desktop head.~~ **Done** — `DodoSSH.Client.Session` is now free
   of Windows APIs entirely.
3. ~~**The spike.**~~ **Done.** It came back clean — see the summary at the top. The throwaway screen has
   been deleted; what it proved is now load-bearing in the head itself.

   It also produced the one structural change the audit did not anticipate. The interface is a redesign, but
   *what survives it* — every view model, command and piece of state — had to be reachable from two heads,
   and it was sitting inside the desktop one. So **`DodoSSH.Client.Shell` is new**: the view models, the
   terminal renderer's files and the palette moved there, and both heads reference it. It is the one place
   the "everything except `App` is free of Avalonia" rule bends, and it bends narrowly — what it uses is
   `Dispatcher`, the asset loader and a resource dictionary, none of which imply a window.
4. ~~**Android device key store.**~~ **Done** — `AndroidDeviceKeyStore` plus `BiometricGate`. A StrongBox-backed
   AES-GCM key, generated with `setUserAuthenticationRequired`, wraps the X25519 scalar into a file beside
   the cache; the keystore will not perform the unwrap unless the prompt actually happened, because the
   cipher is bound to the prompt rather than merely following it.

   Two things worth knowing. StrongBox is asked for and fell back from, because refusing a TEE-backed key
   would cost a mid-range phone the whole feature to buy a distinction the threat model does not draw. And
   `setInvalidatedByBiometricEnrollment` is on, which is what stops somebody who can add a fingerprint to an
   unlocked phone from inheriting the vault — the cost being that re-enrolment permanently destroys the key,
   which the load path treats as ordinary rather than exceptional.

   **The prompt is raised on arrival at the lock screen** rather than waiting for the button, which is still
   there and still says what it does. Two rules shape it, both in `PhoneShell.TryOfferDeviceUnlock`. It
   happens **only at launch**: a lock the user asked for is not answered with a request to unlock, because
   that makes LOCK look inert and trains the reflex of authenticating at a prompt nobody asked for. And it
   happens **once**: a declined gesture leaves the passphrase box exactly where it was, which is the whole
   fallback, and a prompt that came back after being dismissed would be a modal you cannot get out of to
   type into it. It watches three properties rather than one because startup sets the state to `Locked`
   before it has asked the keystore whether there is a key to offer, and does both inside the busy wrapper.

   **Enrolling one is on PREFERENCES**, and until it was, none of the above could ever happen on a phone:
   the store, the gate and the lock screen's button all shipped, and nothing in this head could create the
   key they are about — so `CanUnlockWithDevice` was false on every launch of every phone. Registering needs
   an unlocked keychain and a reachable server (the vault has to be open to seal the bundle, and the wrap has
   to reach the account or a lost phone could never be revoked), which is why the offer is on a screen behind
   SETTINGS rather than beside the button it turns on.
5. ~~**Android sign-in.**~~ **Done**, and the seam it needed turned out to be worth more than the
   implementation. `IAuthorizationCallback` now sits between `OidcClient` and the loopback listener, so the
   two heads differ in *where the response arrives* and in nothing else — PKCE, the state check, discovery,
   the token exchange and the key binding are one implementation, which is the point. A second OIDC client
   would have been a second place for a security bug to live.

   The system browser by `ACTION_VIEW` rather than a Custom Tab: a Custom Tab is the nicer surface and
   shares the same cookie jar, but it needs `androidx.browser` and this needs nothing. Worth revisiting when
   something else pulls AndroidX in.

   **A private-use scheme, not an App Link**, and the difference is worth writing down rather than
   discovering. The redirect is `dev.dodotech.dodossh:/callback` — the reversed package name, which RFC 8252
   §7.1 recommends. Another application *can* also declare that scheme, and Android will show a chooser
   rather than refuse; what stops that being a compromise is PKCE, since the code is useless without a
   verifier that never leaves the process. An App Link would close it properly, at the cost of an
   `assetlinks.json` on the DodoSSH server's own domain — a server change, and the natural upgrade.
6. ~~**The foreground service.**~~ **Done** — `SessionForegroundService`, with `SessionKeepAlive` starting and
   stopping it from a count rather than a lifecycle. `TerminalWorkspace.LiveSessionCount` is the source of
   truth deliberately: it already knows that a session whose shell exited is not live, which a counter
   incremented on open would not, and a phone showing "1 shell connected" over nothing would be exactly the
   dishonesty the unlock screen's count exists to prevent.
7. ~~**The interface**, phone-first.~~ **Done for the decided scope** — all seven screens of the design,
   plus the two states the design does not draw because it starts at an enrolled phone (naming a server, and
   choosing a passphrase).

   All five of the ◆ states this document worried about are built and none of them softened:

   - the changed-key refusal has no continue button, and is a full-screen panel rather than a bottom sheet
     precisely because a sheet is swipe-to-dismiss by convention;
   - the recovery code cannot be skipped, and `FLAG_SECURE` is raised for that state alone so the screen's
     claim about screenshots is true rather than decorative;
   - the delete confirmations keep their counts and replace the row in place;
   - the unknown-key prompt shows the fingerprint in full, wrapping rather than clipping;
   - the conflict log is a banner on the host list rather than a screen nobody opens.

   The nav rail's eight destinations became four. Pins, snippets, logs, import and teams are not built here:
   import has no meaning under scoped storage, and the other four are list screens whose view models already
   exist — they are additive rather than structural. *(Snippets, logs and teams have since been built, behind
   MORE. Pins and import have not, and import still cannot be.)*

   **Superseded by v2.** A second design — *DodoSSH Android v2* — is what this head now draws, and it took
   the "additive rather than structural" claim at its word: snippets, logs, SFTP and S3 are built, over the
   view models that were already shared, behind a hub that holds the destinations the bottom bar has no room
   for. `ShellScreen` gained `More` and `Buckets`. The palette went blue and the two heads moved together,
   because it is shared. What v2 asked for and did not get is in
   [`docs/design-import-gaps.md`](design-import-gaps.md) — the short version being that port forwarding is
   named as absent rather than drawn, because nothing in the SSH layer forwards anything.

   **The bar has since gone from four entries to three.** The keychain joined the hub, which is now called
   SETTINGS rather than MORE and wears a gear: a bottom bar is for the places a session moves between, and
   managing keys is not one of them. `IsMoreSurface` gained `ShellScreen.Vault`, which is the whole of it —
   the membership test, the tab that lights and the back gesture's first case all read that one property.
   The desktop keeps its Keychain rail entry, so this is the second thing the two heads arrange
   deliberately differently, after the hub itself.
8. ~~**The terminal.**~~ **Done** — one `NativeWebView` for every session, as on the desktop and for the
   same reason, with the tab strip scrolling horizontally rather than wrapping so that opening a tab never
   reflows a terminal while output is arriving.

   The accessory key row needed one addition to the shared layer: `TerminalWorkspace.SendInputAsync`, since
   ordinary typing goes from the renderer straight down the socket and there was no way in for input that
   has no key to produce it. Ctrl latches rather than being held — one thumb cannot chord — and the latch is
   drawn, because a modifier that is on and does not look on is how somebody sends `^L` to a database prompt
   believing they typed an `l`.

   **The surface has since taken the whole screen.** `PhoneShell` collapses the header, the session strip
   and the bottom bar while a terminal is showing — one binding on `IsShowingPages` each — and the screen
   draws a 35-pixel bar in their place: back, the session pills, and a `+` raising a sheet with the three
   connections there are. That sheet is the head's first control that could be drawn over the renderer, so
   it collapses it rather than covering it, exactly as the desktop's palette does; whether Android's
   WebView actually composites above Avalonia content is still the unverified question recorded below, and
   collapsing is correct under either answer.

   **The + also puts the software keyboard away, and that needed the platform.** `TopLevel.InputPane`
   reports the keyboard and cannot close one — Avalonia's model is that it belongs to whatever has focus, so
   the supported dismissal is to move focus — and the keyboard over a terminal was raised by the `WebView`'s
   own text input, by a native view Avalonia's focus manager never owned. Clearing Avalonia's focus does
   nothing to it. `Platform/SoftKeyboard.cs` asks `InputMethodManager` directly, off the decor view's window
   token, and every step of it is allowed to be absent. Without it the sheet arrives under a keyboard
   covering the half of the screen the sheet is on — and worse, laid out into what is left, since the
   keyboard's inset shortens everything this head draws.

   **With nothing open the surface is a connect screen rather than an empty state**, which is why the bar
   calls it Connections. It offers a `user@host[:port]` box with a password and the machines most recently
   connected to, out of the vault's connection log. The connect path in `VaultViewModel` was shaped like
   `HostRowViewModel` all the way down; it now hangs off a four-field `ConnectionTarget`, so the ladder of
   refusals, the host-key question, the log entry and the tab's lifecycle are shared rather than copied. The
   host-key retry replays the attempt that raised the question instead of re-running whichever host was
   selected — which was correct while a selected host was the only way to connect, and would now dial the
   wrong machine.

All eight are done for the decided scope, and v2 has since gone past it — see the note under step 7.

What is left, in the order it matters:

- **Running any of it on a device.** Still the one that is not optional, and still true: nothing here has
  ever been launched on hardware or an emulator. Everything below is reasoning from the code.
- ~~**The save picker — the other half of file transfer.**~~ **Built**, along with the half before it: both
  pickers go through Avalonia's storage provider and both stage through the cache. See the correction under
  the decision above for the shape and for the one thing about it a person will notice — an empty file where
  a failed download was pointed. What is *not* built is a folder picker for several downloads at once: the
  save picker names one destination, so SAVE FILE takes the selected row.
- **Editors.** There is no host editor and no keychain item editor on the phone, so both are create-on-
  desktop-and-sync. That is why the v2 design's `+` buttons on HOSTS and on the keychain are not drawn.
- **Pins and import**, which v2 does not draw either. Teams *is* drawn, behind MORE — it was the one of
  the three whose view model needed nothing new on the phone, because none of that screen is vault content.
- **The App Link upgrade**, unchanged from step 5.

---

## Still open

Neither of these blocked the spike, and both wanted answering before there was anything to release. Both
now have answers, kept here under the questions that produced them — the heading stays because what is
worth reading is which way each went and why, not that the list is empty.

- ~~**Which Android versions.**~~ **✅ Settled: minSdk 28, targetSdk 36**, and the reasoning divided in two.

  The ceiling is not a choice at all, which the audit had slightly wrong. `Avalonia.Controls.WebView` ships
  **only** a `net10.0-android36.0` assembly — there is no lower Android target in the package — so a project
  below `targetSdk` 36 cannot resolve it and therefore cannot have a terminal. That is a hard constraint
  rather than a preference, and it also means the API 36 platform must be installed to build this head at
  all.

  The floor *was* a real choice, and 28 is where the three platform APIs the device key store depends on all
  exist in the framework rather than behind an AndroidX shim: `BiometricPrompt`, StrongBox-backed keys, and
  `setInvalidatedByBiometricEnrollment`. Going lower would mean carrying `androidx.biometric` to reach
  devices that mostly cannot hold a hardware-backed key anyway — which is the one thing the store is for.
  API 28 and 29 still cost one branch each in `BiometricGate`, because allowed-authenticator lists arrived
  in 30.
- ~~**How it is distributed, and what that does to the supply-chain story.**~~ **✅ Settled in
  [ADR 0011](adr/0011-android-distribution.md): the project holds the release key, the deployment never
  serves the client, and Play is deferred.** The question was whether Play App Signing — Google generating
  and holding the release key — is a change to the security property ADR 0001 documents. It is, and the ADR
  takes it as a one-way door rather than a setting: a new Play app must use App Bundles and therefore Play
  App Signing, an installed app can only be updated by a package signed with the same key, so the first
  release picks one identity for good.

  Two things follow for this head *now*, before there is anything to release. CI keeps signing with the
  debug key and must never gain a keystore secret. And no download link for the APK may ever be served by a
  DodoSSH deployment — that hands the client binary to the party the threat model is about, which is a
  worse arrangement than either of the two the question was originally between.

## Smaller things, decided by default

Recorded so they are choices rather than accidents. Any of them is cheap to revisit.

- **`ClientPaths`** gets the app's own `filesDir`, injected by the head rather than branched for inside the
  record — which already takes an explicit directory for exactly this reason. It satisfies the
  local-and-non-roaming requirement more cleanly than any desktop platform does.
- **The device name** on log entries comes from the head, not `Environment.MachineName`, which returns
  something like `localhost` on Android and would make every entry from a phone indistinguishable.
- **`NativeKeyboardFocus` is not ported.** It exists for a documented Win32 asymmetry — focus crosses into
  WebView2 but does not come back — and Android's focus model is different enough that the problem should be
  confirmed to exist before anything is written to solve it.
- **The software keyboard is kept off the interface in one place, and by two mechanisms.** `PhoneShell`
  owns it rather than each screen, because everything the phone draws is inside that one control and a
  screen added later would otherwise have to remember. The two mechanisms are not a belt and braces: before
  Android 15 the activity's `AdjustResize` has the platform shorten the window and the reported keyboard
  inset arrives already consumed, and from Android 15 edge-to-edge is enforced, the window is no longer
  resized for the keyboard, and the inset is what there is. Each is dead where the other applies, which is
  why the margin is taken from the inset alone — the two added together would strand the interface an
  entire keyboard too high. See `docs/manual-checks.md` phase 10, which is the only way either is verified.
- **A box that takes a secret says so twice.** `PasswordChar` is what the screen draws and
  `TextInputOptions.ContentType` is what the software keyboard is told, and only the second one turns off
  the suggestion strip and keeps the passphrase out of the IME's learning dictionary. The desktop head
  needs only the first, which is why the phone's `TextBox.secret` class carries both rather than the two
  being set per box.