docs(android): bake the version gate, identity model + native build into the docs

ARCHITECTURE §2 (client-version gate + frozen wire contract + gate x offline),
§3 (local-guest / server-guest / reconciliation identity), §13 (native Capacitor
build). FUNCTIONAL (+_ru) a new "Native app (Android)" domain. TESTING (the
clientver/gate Go tests, the native/update e2e + retry mapping, and the manual
on-device Android smoke checklist). deploy/README (GATEWAY_MIN_CLIENT_VERSION +
the wire-break bump discipline + the Android build/release runbook). ui/README
native VITE_* vars. Mark F done in ANDROID_PLAN.md.

docs/ARCHITECTURE.md

@@ -140,6 +140,30 @@ dropped). Horizontal scaling is explicit future work.
   (your-turn, opponent-moved, chat, nudge). The gateway bridges them to the
   client's in-app stream while the app is open. Out-of-app delivery uses
   platform-native push via the platform side-service.
+- **Client-version gate** (native long-tail protection): a bundled native install (§13) can be
+  arbitrarily old, so the client stamps its build into an **`X-Client-Version`** request header (the app
+  version from `pkg/version` / `__APP_VERSION__`), read by the gateway **before it decodes the FlatBuffers
+  payload**. The version rides the **outermost stable layer** — an HTTP header, never the FBS payload —
+  because protobuf envelopes and headers are version-tolerant by design while the FBS payload is the layer
+  that breaks. Enforcement is **per-call, not a Hello RPC**: `Execute` and `Subscribe` compare the header to
+  `GATEWAY_MIN_CLIENT_VERSION` at the top (before registry lookup / auth / decode), so the first online call
+  an app makes is already gated. A too-old client gets the domain envelope `result_code = "update_required"`
+  (HTTP 200) on `Execute` and `CodeFailedPrecondition` on `Subscribe`, and makes **zero** successful
+  requests. The gate **fails open** (an absent or unparseable header passes) and is **dormant** until
+  `GATEWAY_MIN_CLIENT_VERSION` is deliberately set (empty ⇒ off, so web behaviour is unchanged). The client
+  raises a terminal *update* overlay — native → the store listing (`VITE_RUSTORE_URL`), web → reload.
+- **Frozen wire contract** (so any build, however old, can always recognise "update required"): three
+  things are permanent — (1) the protobuf envelope field numbers in `edge.proto` are never renumbered or
+  reused; (2) the `update_required` sentinel — the `result_code` string **and** the `FailedPrecondition`
+  code — never changes; (3) the FBS schema stays **additive** (append trailing fields; `(deprecated)`, never
+  delete — deleting shifts field IDs and breaks older readers). A breaking wire change happens only *inside*
+  the FBS payload, which is exactly what the gate guards. **Deploy discipline:** the production rollout that
+  ships an incompatible wire change **also** bumps `GATEWAY_MIN_CLIENT_VERSION` to that release, in the same
+  rollout (see [`../deploy/README.md`](../deploy/README.md)).
+- **Gate × offline** (UX rule): deliberate offline uses the network kill switch, so the gate never fires
+  while playing offline — an old install can always play local vs_ai / hotseat. The terminal *update*
+  overlay is raised **only on a user-initiated online action**; the silent background guest reconciliation
+  (§3) swallows an `update_required` and stays a local guest rather than interrupting local play.
 
 ## 3. Authentication & sessions
 
@@ -224,6 +248,19 @@ arrive from a platform rather than completing a mandatory registration).
   `BACKEND_GUEST_REAP_INTERVAL` sweep, so transient guest rows do not accumulate.
   Platform and email users are auto-provisioned **durable** accounts with an
   identity.
+- **Local guest vs. server guest** (native offline-first, §13). The **native** app splits the local-play
+  identity from the server account. A **local guest** is device-local with **no DB row**: a device-generated
+  id + the localized default name (*Guest* / *Гость*) persisted on the device, existing from the very first
+  launch with no network. It fills the human seat in a local vs_ai game and is the "you" for device-local
+  games; a purely-offline user never consumes a server row. The **server guest** is the durable `is_guest`
+  row above — minted **lazily** via `auth.guest` the first time the app reaches the network, its session
+  cached and reused (exactly one per device, guarded by the cached session so it never double-mints). It
+  unlocks online features (matchmaking, friends). **Reconciliation:** on gaining network with no server
+  session the native app silently `auth.guest`s in the background and adopts it — best-effort, swallowing an
+  `update_required` to stay a local guest rather than interrupting play (the gate × offline rule, §2).
+  **Local games stay device-only** (both local vs_ai and hotseat persist only on the device); an identity
+  transition never migrates them. Web/PWA/Telegram/VK are unchanged — they have no local guest and keep the
+  prior online-session rule.
 
 > **Decision (2026-06-20) — single bot, preference-based variant gating.** The former
 > two-bot model (one bot per service language, with `accounts.service_language`, a
@@ -1468,6 +1505,24 @@ Two contours, two secret/variable prefixes (`TEST_` / `PROD_`):
   client IPs). The `vpn`+`bot` pair is gated to a `telegram-local` compose profile the test
   contour activates; the prod main host omits it.
 
+**Native Android build (Capacitor).** The SPA is also packaged as a standalone **Android app** (Capacitor 8,
+appId `ru.eruditgame.app`, "Эрудит"; minSdk 24, compile/targetSdk 36, JDK 21), first for **RuStore**. It is
+a **bundle** model — the WebView loads the packaged `dist/` from app assets (**no `server.url`**), so there
+is no OTA: updates ship through the store, and the **client-version gate** (§2) turns away a build too old to
+speak the current wire contract. Because the packaged origin is `file://`, the native build talks to an
+**absolute** gateway origin (`VITE_GATEWAY_URL` = the production origin; `lib/origin.ts` centralises how absolute URLs are built), and the service worker is skipped (the bundle is
+the cache). It is **offline-first**:
+`ui/scripts/bundle-dicts.mjs` copies the versioned `scrabble-dictionary` release DAWGs into
+`dist/dict/<variant>@<version>.dawg` (keyed on `VITE_DICT_VERSION`), so a cold first launch with no network
+enters as a **local guest** (§3) and plays local vs_ai / hotseat from the bundled dictionaries. Purchases are
+hidden in the MVP (`VITE_PAYMENTS_DISABLED`). The APK is built by a **manual** `workflow_dispatch` workflow
+(`.gitea/workflows/android-build.yaml`, from `master`, `confirm=build`) that builds the native SPA, bundles
+the dicts, and assembles a **release APK** artifact — signed when the `ANDROID_KEYSTORE_*` secrets are
+present, unsigned otherwise. `versionCode`/`versionName` are deterministic from the release tag `vMA.MI.PA`
+(`versionCode = MA*1_000_000 + MI*1_000 + PA`, `versionName = "MA.MI.PA"`). The runner is a host-executor
+with a host-provisioned Android SDK; RuStore upload is manual. Full plan + runbook:
+[`../ANDROID_PLAN.md`](../ANDROID_PLAN.md), [`../deploy/README.md`](../deploy/README.md).
+
 ## 14. CI & branches
 
 - **Two long-lived branches**: **`development`** is the integration