feat(tauri-app): Einladungscode im Client, Produktions-URLs als Default

Zwei Dinge, die einen ausgelieferten Client heute unbrauchbar gemacht
hätten.

Erstens: Seit die öffentliche Instanz Einladungscodes verlangt, bekam
jeder Registrierungsversuch aus dem Client 400 InvalidInviteCode, ohne
dass es ein Feld für einen Code gegeben hätte. auth_register und
create_account nehmen ihn jetzt entgegen, der LoginScreen zeigt das Feld
nur im Registrieren-Modus und leert es beim Moduswechsel — sonst würde
ein getippter Code im ausgeblendeten Feld überleben und beim nächsten
Versuch stillschweigend mitgehen.

Ein leeres Feld wird weggelassen, nicht abgelehnt: ob ein Code nötig
ist, entscheidet der Server (PDS_INVITE_REQUIRED), und eine lokale
Dev-PDS verlangt keinen. "Kein Code angegeben" und "mein Code ist der
Leerstring" sind zwei verschiedene Aussagen; nur die erste ist je wahr.
Deshalb fliegt der Schlüssel per skip_serializing_if ganz aus dem Body.

Der Server unterscheidet bei der Ablehnung bewusst nicht zwischen
fehlend, falsch, gesperrt und verbraucht — sonst wären Codes
enumerierbar. Die Meldung im Client nennt deshalb beide plausiblen
Auswege, statt einen zu raten.

Zweitens: Die Basis-URLs fielen ohne Umgebungsvariable auf
http://127.0.0.1:2583 bzw. :2584 zurück. Ein gebautes Paket hätte also
gegen nichts gesprochen. Beide zeigen jetzt auf
https://tweet.maarcade.com — dieselbe Origin für PDS und AppView, der
Proxy trennt nach Pfadpräfix. Die Variablen überschreiben weiterhin,
damit Entwicklung gegen localhost möglich bleibt; eine leer gesetzte
Variable gilt dabei als ungesetzt, weil eine leere Basis-URL sonst als
kryptischer Relative-URL-Fehler weit weg von der Ursache auftaucht.

Der Settings-View spiegelte dieselben alten Defaults und hätte falsche
Backends angezeigt — mitgezogen.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013HC9HLrUU1LNwkzp8nkDLX

crates/tauri-app/src-tauri/src/lib.rs

@@ -34,15 +34,32 @@ async fn pds_describe(state: tauri::State<'_, AppState>) -> Result<serde_json::V
     state.pds.describe_server().await.map_err(|e| e.to_string())
 }
 
+/// `auth_register(handle, password, inviteCode?)` — create an account
+/// on the configured PDS and store the resulting session.
+///
+/// `invite_code` arrives from the frontend as `inviteCode` (Tauri maps
+/// camelCase JS argument keys onto snake_case Rust parameters, the same
+/// way `mark_notifications_seen` receives `seenAt`). It is `Option`
+/// because the invite gate is a *server* setting
+/// (`PDS_INVITE_REQUIRED`): the public instance at
+/// `https://tweet.maarcade.com` demands a code, a locally run dev PDS
+/// usually does not, and the client has no business deciding which.
+/// When no code is given the field is dropped from the request body
+/// rather than sent empty — see [`pds_client::CreateAccountReq`].
+///
+/// A refused code surfaces as the PDS's `400
+/// {"error":"InvalidInviteCode", …}` inside the stringified error, and
+/// `errorMessage()` in `client.ts` turns that into German copy.
 #[tauri::command]
 async fn auth_register(
     state: tauri::State<'_, AppState>,
     handle: String,
     password: String,
+    invite_code: Option<String>,
 ) -> Result<AccountSession, String> {
     let sess = state
         .pds
-        .create_account(&handle, &password)
+        .create_account(&handle, &password, invite_code.as_deref())
         .await
         .map_err(|e| e.to_string())?;
     let s = AccountSession {
@@ -768,16 +785,74 @@ async fn show_notification(
     Ok(())
 }
 
+/// Default PDS base URL — the public instance.
+///
+/// This is what a *shipped* build talks to. It used to be
+/// `http://127.0.0.1:2583`, which meant a packaged `.app` handed to
+/// anyone but the developer pointed at a server that does not exist on
+/// their machine: every call failed with a connection error and the
+/// login screen could not even render `describeServer`. A default is
+/// the configuration of the people who never set one, so it has to be
+/// the production deployment.
+///
+/// No trailing slash: [`PdsHttpClient`] builds its endpoints as
+/// `{base}/xrpc/com.atproto.…`, so the base must end at the host.
+const DEFAULT_PDS_URL: &str = "https://tweet.maarcade.com";
+
+/// Default AppView base URL. Same host as the PDS — the reverse proxy
+/// in front of `tweet.maarcade.com` routes by path prefix: `/xrpc/…`
+/// to the PDS, `/api/…` to the AppView. [`AppViewClient`] appends
+/// `/api/…` to this base (see the `format!("{}/api/…", self.base_url)`
+/// calls in `appview_client.rs`), so the two clients can and must
+/// share the one origin.
+const DEFAULT_APPVIEW_URL: &str = "https://tweet.maarcade.com";
+
+/// Resolve one base URL from its environment variable, falling back to
+/// the compiled-in default.
+///
+/// **The environment always wins.** Development runs against a local
+/// stack — `MAARCADETWEET_PDS_URL=http://127.0.0.1:2583` and
+/// `MAARCADETWEET_APPVIEW_URL=http://127.0.0.1:2584`, which is what
+/// `scripts/` and the dev docker-compose set up — and pointing the
+/// desktop client at it must stay a matter of exporting two variables,
+/// never of rebuilding. Only an *unset* variable takes the production
+/// default.
+///
+/// A variable set to whitespace (or the empty string) counts as unset:
+/// an empty base URL would silently produce request URLs like
+/// `/xrpc/…` with no host, and `reqwest` would reject them as a
+/// relative-URL error far away from the actual mistake. Trailing
+/// slashes are trimmed because both clients append an absolute path to
+/// this string, and `https://host//api/x` is not the same route to
+/// every proxy.
+///
+/// Takes the already-performed lookup rather than the variable name so
+/// it stays a pure function — testable without mutating the process
+/// environment, and without a Tauri runtime.
+fn base_url_or_default(from_env: Result<String, std::env::VarError>, default: &str) -> String {
+    let configured = from_env.ok();
+    let trimmed = configured
+        .as_deref()
+        .map(|v| v.trim().trim_end_matches('/'))
+        .filter(|v| !v.is_empty());
+    trimmed.unwrap_or(default).to_string()
+}
+
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
     tracing_subscriber::fmt()
         .with_env_filter(tracing_subscriber::EnvFilter::try_from_default_env().unwrap_or_else(|_| "info".into()))
         .init();
 
-    let pds_url = std::env::var("MAARCADETWEET_PDS_URL")
+    let pds_url = base_url_or_default(
-        .unwrap_or_else(|_| "http://127.0.0.1:2583".to_string());
+        std::env::var("MAARCADETWEET_PDS_URL"),
-    let appview_url = std::env::var("MAARCADETWEET_APPVIEW_URL")
+        DEFAULT_PDS_URL,
-        .unwrap_or_else(|_| "http://127.0.0.1:2584".to_string());
+    );
+    let appview_url = base_url_or_default(
+        std::env::var("MAARCADETWEET_APPVIEW_URL"),
+        DEFAULT_APPVIEW_URL,
+    );
+    tracing::info!(%pds_url, %appview_url, "resolved backend base URLs");
 
     let state = AppState {
         pds: PdsHttpClient::new(pds_url.clone()),
@@ -1056,3 +1131,75 @@ async fn profile_set(
         .map_err(|e| e.to_string())?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::env::VarError;
+
+    /// The whole point of the change: a build with nothing configured
+    /// must talk to the public instance, not to a loopback port that
+    /// only exists on a developer's laptop. Pinned as a literal so a
+    /// well-meant "let's default back to localhost for dev" has to
+    /// argue with a red test first.
+    #[test]
+    fn unset_env_falls_back_to_the_public_instance() {
+        assert_eq!(
+            base_url_or_default(Err(VarError::NotPresent), DEFAULT_PDS_URL),
+            "https://tweet.maarcade.com"
+        );
+        assert_eq!(
+            base_url_or_default(Err(VarError::NotPresent), DEFAULT_APPVIEW_URL),
+            "https://tweet.maarcade.com"
+        );
+        // Both services live behind the same origin — the proxy splits
+        // them by path prefix (`/xrpc/` vs `/api/`), which the clients
+        // append themselves.
+        assert_eq!(DEFAULT_PDS_URL, DEFAULT_APPVIEW_URL);
+        assert!(!DEFAULT_PDS_URL.ends_with('/'));
+    }
+
+    /// Development against a local stack has to keep working by
+    /// exporting a variable, so a set value always beats the default.
+    #[test]
+    fn env_var_overrides_the_default() {
+        assert_eq!(
+            base_url_or_default(Ok("http://127.0.0.1:2583".into()), DEFAULT_PDS_URL),
+            "http://127.0.0.1:2583"
+        );
+        assert_eq!(
+            base_url_or_default(Ok("http://127.0.0.1:2584".into()), DEFAULT_APPVIEW_URL),
+            "http://127.0.0.1:2584"
+        );
+    }
+
+    /// An empty or whitespace-only variable is a misconfiguration, not
+    /// a request for an empty base URL: `reqwest` would answer the
+    /// resulting host-less URL with a relative-URL error nowhere near
+    /// the cause. Trailing slashes go because both clients append an
+    /// absolute path (`{base}/xrpc/…`, `{base}/api/…`).
+    #[test]
+    fn blank_env_is_ignored_and_trailing_slashes_are_trimmed() {
+        assert_eq!(
+            base_url_or_default(Ok("".into()), DEFAULT_PDS_URL),
+            DEFAULT_PDS_URL
+        );
+        assert_eq!(
+            base_url_or_default(Ok("   ".into()), DEFAULT_PDS_URL),
+            DEFAULT_PDS_URL
+        );
+        assert_eq!(
+            base_url_or_default(Ok("http://127.0.0.1:2584/".into()), DEFAULT_APPVIEW_URL),
+            "http://127.0.0.1:2584"
+        );
+        assert_eq!(
+            base_url_or_default(Ok(" https://tweet.maarcade.com// ".into()), DEFAULT_PDS_URL),
+            "https://tweet.maarcade.com"
+        );
+        // A non-UTF-8 variable is as unusable as an unset one.
+        assert_eq!(
+            base_url_or_default(Err(VarError::NotUnicode("\u{fffd}".into())), DEFAULT_PDS_URL),
+            DEFAULT_PDS_URL
+        );
+    }
+}

crates/tauri-app/src-tauri/src/pds_client.rs

@@ -26,6 +26,27 @@ pub struct CreateAccountReq {
     pub handle: String,
     pub email: Option<String>,
     pub password: String,
+    /// Invite code, required by the PDS whenever it runs with
+    /// `PDS_INVITE_REQUIRED=true` (the public instance at
+    /// `https://tweet.maarcade.com` does). Rejected codes come back as
+    /// `400 {"error":"InvalidInviteCode", …}`.
+    ///
+    /// **Wire name.** The server's `CreateAccountReq`
+    /// (`crates/pds-server/src/routes/types.rs`) is snake_case with an
+    /// `#[serde(alias = "inviteCode")]` for off-the-shelf atproto
+    /// clients. We are not one of those: every body this client sends
+    /// is snake_case (`refresh_jwt` in `refresh_session`, `handle` /
+    /// `password` right here), so `invite_code` is the field name that
+    /// matches the rest of the file. The alias exists for other people.
+    ///
+    /// **Skipped when `None`.** Same reasoning as `validate` below —
+    /// a PDS with the invite gate *off* must keep accepting our
+    /// registrations, and sending `"invite_code": null` (let alone
+    /// `""`) would be claiming the user supplied something. Omitting
+    /// the key leaves the server's `Option` at `None`, which is exactly
+    /// "the user gave no code".
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub invite_code: Option<String>,
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -130,15 +151,31 @@ impl PdsHttpClient {
         Ok(r)
     }
 
+    /// `com.atproto.server.createAccount`.
+    ///
+    /// `invite_code` is `None` when the user left the field empty; the
+    /// key is then left out of the body entirely (see
+    /// [`CreateAccountReq::invite_code`]) so a PDS running without the
+    /// invite gate still registers the account. A code that only
+    /// contains whitespace is treated as absent for the same reason —
+    /// the server's `invite::normalize` trims before looking it up, so
+    /// `"  "` could never match a real code anyway, and passing it on
+    /// would only turn "you forgot the field" into "your code is
+    /// wrong".
     pub async fn create_account(
         &self,
         handle: &str,
         password: &str,
+        invite_code: Option<&str>,
     ) -> Result<AccountSession> {
         let body = CreateAccountReq {
             handle: handle.to_string(),
             email: None,
             password: password.to_string(),
+            invite_code: invite_code
+                .map(str::trim)
+                .filter(|c| !c.is_empty())
+                .map(str::to_string),
         };
         let r = self
             .client

crates/tauri-app/src/App.svelte

@@ -545,17 +545,23 @@
   // Used in the Settings view to show which backends the client is
   // talking to. Kept as plain helpers so they can be swapped for a
   // `pds_describe`/`appview_describe` Tauri command later.
+  // The fallbacks mirror `DEFAULT_PDS_URL` / `DEFAULT_APPVIEW_URL` in
+  // `src-tauri/src/lib.rs`: both services sit behind the one public
+  // origin, split by path prefix (`/xrpc/` → PDS, `/api/` → AppView).
+  // If those constants ever move, move these with them — a Settings
+  // pane that names the wrong backend is worse than one that names
+  // none.
   function pdsBase(): string {
     if (typeof import.meta !== "undefined" && (import.meta as any).env?.VITE_PDS_URL) {
       return (import.meta as any).env.VITE_PDS_URL as string;
     }
-    return "http://127.0.0.1:2583";
+    return "https://tweet.maarcade.com";
   }
   function appviewBase(): string {
     if (typeof import.meta !== "undefined" && (import.meta as any).env?.VITE_APPVIEW_URL) {
       return (import.meta as any).env.VITE_APPVIEW_URL as string;
     }
-    return "http://127.0.0.1:2584";
+    return "https://tweet.maarcade.com";
   }
 </script>
 

crates/tauri-app/src/lib/api/client.ts

@@ -142,6 +142,21 @@ export function isAuthFailure(e: unknown): boolean {
   );
 }
 
+/// True when the PDS refused a registration because of the invite
+/// code. The public instance runs with `PDS_INVITE_REQUIRED=true` and
+/// answers `400 {"error":"InvalidInviteCode","message":…}` — the same
+/// code for a missing, misspelled, disabled and already-spent code, on
+/// purpose: the server does not tell an unauthenticated caller which
+/// of those it was, since that would make invite codes enumerable.
+///
+/// Matched on the string for the same reason as [`isTokenInvalid`]:
+/// `pds_client.rs` bails with `createAccount failed: {status} {body}`
+/// and `lib.rs` stringifies that into the command's `Err(String)`, so
+/// the code travels verbatim across the IPC boundary.
+function isInvalidInviteCode(e: unknown): boolean {
+  return errorText(e).includes("InvalidInviteCode");
+}
+
 /// User-facing copy for a failed call, in the app's German UI voice.
 ///
 /// An auth failure gets a sentence naming the actual remedy. The raw
@@ -155,6 +170,18 @@ export function errorMessage(e: unknown): string {
   if (isAuthFailure(e)) {
     return "Sitzung abgelaufen oder abgelehnt — bitte neu anmelden.";
   }
+  if (isInvalidInviteCode(e)) {
+    // Deliberately covers "no code given" too: the raw body a user
+    // would otherwise read is `createAccount failed: 400 Bad Request
+    // {"error":"InvalidInviteCode","message":"a valid invite code is
+    // required to create an account on this server"}`. Since the
+    // server refuses to say *which* way the code was wrong, the copy
+    // names both plausible fixes rather than guessing one.
+    return (
+      "Einladungscode ungültig oder bereits verbraucht — " +
+      "bitte prüfen oder einen neuen Code anfordern."
+    );
+  }
   return String(e);
 }
 
@@ -208,11 +235,38 @@ function createSessionStore() {
       set(s);
       return s;
     },
-    async register(handle: string, password: string) {
+    /// Create an account on the configured PDS.
+    ///
+    /// `inviteCode` is optional because the invite gate lives on the
+    /// *server* (`PDS_INVITE_REQUIRED`): the public instance at
+    /// `https://tweet.maarcade.com` requires a code, a local dev PDS
+    /// normally does not. The client therefore never refuses a
+    /// registration for a missing code on its own — it would break
+    /// development against localhost — it just forwards what the user
+    /// typed and lets the PDS decide.
+    ///
+    /// An empty (or whitespace-only) field is *omitted*, not sent as
+    /// `""`. Those are two different statements: "I gave no code" vs.
+    /// "my code is the empty string". The first is legitimate against
+    /// an open server; the second is never true and would only turn
+    /// into a confusing `InvalidInviteCode` on a server that has the
+    /// gate switched off. Dropping the key leaves the Rust
+    /// `Option<String>` at `None`, and `create_account` then leaves
+    /// the field out of the JSON body entirely.
+    async register(handle: string, password: string, inviteCode?: string) {
       if (!isTauri()) {
         throw new Error("register requires the Tauri desktop runtime");
       }
-      const s = await safeInvoke<Session>("auth_register", { handle, password });
+      const code = inviteCode?.trim();
+      const s = await safeInvoke<Session>("auth_register", {
+        handle,
+        password,
+        // Explicit `null` rather than a dropped key, matching how
+        // `createPost` passes its optional `embed` / `reply`: it
+        // deserialises into the Rust `Option<String>` as `None`
+        // without depending on how `invoke` treats `undefined`.
+        inviteCode: code ? code : null,
+      });
       set(s);
       return s;
     },

crates/tauri-app/src/lib/api/invite.test.ts

@@ -0,0 +1,138 @@
+// Unit tests for the invite-code half of the registration path.
+//
+// Same setup as `notifications.test.ts`: `@tauri-apps/api/core` is
+// mocked so no Tauri shell is needed, and every assertion is about the
+// exact command name + argument bag we hand the Rust IPC layer. That
+// argument bag is the contract — `invoke` maps camelCase JS keys onto
+// the snake_case Rust command parameters (`inviteCode` → `invite_code`
+// on `auth_register`), so a typo here surfaces at runtime as a null
+// argument, not at compile time.
+//
+// Covered:
+//   * `session.register` — the code is forwarded as `inviteCode`,
+//     alongside the unchanged `handle` / `password`;
+//   * the empty / whitespace-only field — must reach the shell as
+//     `null` ("no code given"), never as `""` ("my code is the empty
+//     string"), because a PDS without the invite gate has to keep
+//     accepting registrations;
+//   * `errorMessage` — the PDS's `InvalidInviteCode` body becomes
+//     German copy instead of the raw wire string.
+//
+// Run with:
+//   npx vitest run src/lib/api/invite.test.ts
+
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const invokeMock = vi.fn();
+
+vi.mock("@tauri-apps/api/core", () => ({
+  invoke: (...args: unknown[]) => invokeMock(...args),
+  isTauri: () => true,
+}));
+
+/// What the Rust `auth_register` command answers with on success.
+const SESSION = {
+  did: "did:plc:alice",
+  handle: "alice.tweet.maarcade.com",
+  access_jwt: "acc",
+  refresh_jwt: "ref",
+};
+
+beforeEach(() => {
+  invokeMock.mockReset();
+});
+
+describe("session.register", () => {
+  it("forwards the invite code as `inviteCode`", async () => {
+    const { session } = await import("./client");
+    invokeMock.mockResolvedValueOnce(SESSION);
+
+    const s = await session.register(
+      "alice.tweet.maarcade.com",
+      "hunter2hunter2",
+      "mt-7k3qw-z9d2m",
+    );
+
+    expect(invokeMock).toHaveBeenCalledTimes(1);
+    expect(invokeMock).toHaveBeenCalledWith("auth_register", {
+      handle: "alice.tweet.maarcade.com",
+      password: "hunter2hunter2",
+      inviteCode: "mt-7k3qw-z9d2m",
+    });
+    expect(s.did).toBe("did:plc:alice");
+  });
+
+  it("trims the surrounding whitespace off a pasted code", async () => {
+    const { session } = await import("./client");
+    invokeMock.mockResolvedValueOnce(SESSION);
+
+    // Copying a code out of a chat message routinely drags a space or
+    // a newline along. The server trims too (`invite::normalize`), but
+    // sending the untrimmed string would mean the *client* and the
+    // server disagree about whether the field is empty.
+    await session.register("alice.test", "pw", "  mt-7k3qw-z9d2m\n");
+
+    expect(invokeMock.mock.calls[0][1]).toMatchObject({
+      inviteCode: "mt-7k3qw-z9d2m",
+    });
+  });
+
+  it("sends null — never an empty string — when the field is blank", async () => {
+    const { session } = await import("./client");
+
+    // Three ways the UI can hand us "nothing": the argument omitted
+    // entirely (login-shaped call), an untouched input, and an input
+    // holding only whitespace. All three mean "the user gave no code"
+    // and must arrive at the Rust `Option<String>` as `None`, so that
+    // a PDS running without `PDS_INVITE_REQUIRED` still registers the
+    // account instead of rejecting a blank code.
+    for (const blank of [undefined, "", "   "]) {
+      invokeMock.mockReset();
+      invokeMock.mockResolvedValueOnce(SESSION);
+
+      await session.register("alice.test", "pw", blank);
+
+      const args = invokeMock.mock.calls[0][1] as Record<string, unknown>;
+      expect(args.inviteCode).toBeNull();
+      expect(args.inviteCode).not.toBe("");
+      // The rest of the bag is unaffected.
+      expect(args.handle).toBe("alice.test");
+      expect(args.password).toBe("pw");
+    }
+  });
+});
+
+describe("errorMessage for InvalidInviteCode", () => {
+  /// Exactly what crosses the IPC boundary when the PDS refuses the
+  /// code: `pds_client.rs` bails with `createAccount failed: {status}
+  /// {body}` and `lib.rs` stringifies that into `Err(String)`, which
+  /// `invoke` rejects with as a bare JS string.
+  const RAW =
+    'createAccount failed: 400 Bad Request {"error":"InvalidInviteCode",' +
+    '"message":"a valid invite code is required to create an account on this server"}';
+
+  it("replaces the raw 400 body with copy the user can act on", async () => {
+    const { errorMessage } = await import("./client");
+    const msg = errorMessage(RAW);
+
+    expect(msg).toContain("Einladungscode");
+    // None of the wire noise survives into the UI.
+    expect(msg).not.toContain("InvalidInviteCode");
+    expect(msg).not.toContain("400");
+    // Both shapes a rejected `invoke` can produce — a bare string and
+    // an Error — go through the same `errorText` normalisation.
+    expect(errorMessage(new Error(RAW))).toBe(msg);
+  });
+
+  it("leaves unrelated registration failures verbatim", async () => {
+    const { errorMessage } = await import("./client");
+    // A taken handle is a different 400 and has its own message worth
+    // showing; the invite branch must not swallow it.
+    expect(
+      errorMessage(
+        'createAccount failed: 400 Bad Request {"error":"HandleNotAvailable"}',
+      ),
+    ).toContain("HandleNotAvailable");
+    expect(errorMessage("createAccount failed: 500 db down")).toContain("500");
+  });
+});

crates/tauri-app/src/lib/components/LoginScreen.svelte

@@ -1,6 +1,11 @@
 <script lang="ts">
   import { onMount } from "svelte";
-  import { session, describeServer, type Session } from "../api/client";
+  import {
+    session,
+    describeServer,
+    errorMessage,
+    type Session,
+  } from "../api/client";
 
   let { onLogin }: { onLogin: (s: Session) => void } = $props();
 
@@ -10,6 +15,9 @@
   let mode: "login" | "register" = $state("login");
   let handle: string = $state("");
   let password: string = $state("");
+  // Only meaningful in "register" mode — the field below is rendered
+  // solely there, and `submit()` only forwards it on that branch.
+  let inviteCode: string = $state("");
   let busy = $state(false);
   let error: string | null = $state(null);
   let serverInfo: any = $state(null);
@@ -27,16 +35,40 @@
     busy = true;
     error = null;
     try {
+      // The invite code is deliberately *not* part of the guard above.
+      // Whether one is required is a server setting
+      // (`PDS_INVITE_REQUIRED`): the public instance demands a code, a
+      // dev PDS on localhost usually does not. Refusing to submit
+      // without one would make the client unusable against the second
+      // kind of server for a rule it cannot see. So we forward what
+      // the user typed — `session.register` drops an empty string
+      // instead of sending a blank code — and let the PDS answer.
       const s = mode === "register"
-        ? await session.register(handle, password)
+        ? await session.register(handle, password, inviteCode)
         : await session.login(handle, password);
       onLogin(s);
     } catch (e) {
-      error = String(e);
+      // `errorMessage` translates the failures worth naming — an
+      // expired session, and a rejected `InvalidInviteCode` — into
+      // German copy, and passes everything else through verbatim.
+      error = errorMessage(e);
     } finally {
       busy = false;
     }
   }
+
+  /// Clear the form's mode-specific state when switching sides.
+  ///
+  /// Without this, a code typed while registering would linger in the
+  /// hidden field: switch to login, switch back, and the stale value
+  /// is silently submitted again. The error goes too — the message
+  /// from a failed registration says nothing about the login the user
+  /// is now attempting.
+  function toggleMode() {
+    mode = mode === "register" ? "login" : "register";
+    inviteCode = "";
+    error = null;
+  }
 </script>
 
 <div class="login">
@@ -75,6 +107,30 @@
           autocomplete={mode === "register" ? "new-password" : "current-password"}
         />
       </label>
+      {#if mode === "register"}
+        <!--
+          Registration only. Logging in never carries a code, and a
+          field that is present but meaningless invites people to
+          fill it in. `{#if}` removes it from the DOM rather than
+          hiding it, so it also drops out of the tab order.
+        -->
+        <label class="field">
+          <span class="key">einladungscode</span>
+          <input
+            type="text"
+            bind:value={inviteCode}
+            placeholder="mt-xxxxx-xxxxx"
+            disabled={busy}
+            onkeydown={(e) => e.key === "Enter" && submit()}
+            autocomplete="off"
+            autocapitalize="none"
+            spellcheck="false"
+          />
+          <span class="hint">
+            // von dieser Instanz verlangt — ohne Code keine Registrierung
+          </span>
+        </label>
+      {/if}
     </form>
     {#if error}
       <div class="err">err: {error}</div>
@@ -83,7 +139,7 @@
       <button class="btn btn--primary" onclick={submit} disabled={busy || !handle || !password}>
         {busy ? "..." : mode === "register" ? "create account" : "log in"}
       </button>
-      <button class="btn btn--ghost" onclick={() => (mode = mode === "register" ? "login" : "register")} disabled={busy}>
+      <button class="btn btn--ghost" onclick={toggleMode} disabled={busy}>
         {mode === "register" ? "have an account? log in" : "no account? register"}
       </button>
     </div>
@@ -172,6 +228,15 @@
     font-size: var(--fs-50);
     letter-spacing: var(--tracking-label);
   }
+  /* Sub-label under the invite field. Same dim mono voice as the
+     `// pds: …` server meta line above the form, so it reads as a
+     comment on the field rather than as a second input label. */
+  .hint {
+    color: var(--text-dim);
+    font-family: var(--font-mono);
+    font-size: var(--fs-50);
+    opacity: 0.8;
+  }
   .form input {
     background: var(--bg);
     border: 1px solid var(--line-2);

crates/tauri-app/src/lib/components/LoginScreen.test.ts

@@ -0,0 +1,231 @@
+// Regression guard for the invite-code field on the login screen.
+//
+// The public instance runs the PDS with `PDS_INVITE_REQUIRED=true`, so
+// `createAccount` without a code is refused with `400
+// {"error":"InvalidInviteCode", …}`. Three things have to hold for the
+// screen to be usable against it:
+//
+//   1. the field exists in "register" mode and *not* in "login" mode —
+//      a code is meaningless when signing in, and an input that is
+//      present but ignored invites people to fill it in;
+//   2. what the user typed reaches `session.register` as its third
+//      argument, and an untouched field does not become a blank code;
+//   3. a rejected code renders as German copy, not as the raw wire
+//      body, which is where the user would otherwise read
+//      `createAccount failed: 400 Bad Request {"error":…}`.
+//
+// Setup follows `NotificationsView.test.ts`: the component is mounted
+// against jsdom with `../api/client` partially mocked — the real
+// `errorMessage` is kept, since the error copy is part of what we are
+// asserting on, and only the calls that would need a Tauri runtime are
+// stubbed.
+
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { mount, unmount, tick } from "svelte";
+
+const registerMock = vi.fn();
+const loginMock = vi.fn();
+const describeServerMock = vi.fn();
+
+vi.mock("../api/client", async () => {
+  const actual =
+    await vi.importActual<typeof import("../api/client")>("../api/client");
+  return {
+    ...actual,
+    // Keep the real `errorMessage` from `actual` — the German copy for
+    // `InvalidInviteCode` is exactly what test 3 checks.
+    describeServer: (...args: unknown[]) => describeServerMock(...args),
+    session: {
+      ...actual.session,
+      register: (...args: unknown[]) => registerMock(...args),
+      login: (...args: unknown[]) => loginMock(...args),
+    },
+  };
+});
+
+import LoginScreen from "./LoginScreen.svelte";
+
+let target: HTMLDivElement;
+let app: ReturnType<typeof mount> | null = null;
+
+const SESSION = {
+  did: "did:plc:alice",
+  handle: "alice.tweet.maarcade.com",
+  access_jwt: "acc",
+  refresh_jwt: "ref",
+};
+
+beforeEach(() => {
+  target = document.createElement("div");
+  document.body.appendChild(target);
+  registerMock.mockReset();
+  loginMock.mockReset();
+  describeServerMock.mockReset();
+  // `onMount` calls this; a resolved stub keeps the meta line quiet.
+  describeServerMock.mockResolvedValue({ did: "did:web:tweet.maarcade.com" });
+});
+
+afterEach(() => {
+  if (app) unmount(app);
+  app = null;
+  target.remove();
+});
+
+/// Let `onMount`, the mocked promises and Svelte's flush settle.
+async function flush(turns = 6) {
+  for (let i = 0; i < turns; i++) {
+    await Promise.resolve();
+    await tick();
+  }
+}
+
+/// The screen has no test ids; the inputs are addressed the way a user
+/// would, by the label text beside them.
+function fieldByLabel(label: string): HTMLInputElement | null {
+  for (const el of target.querySelectorAll("label.field")) {
+    if (el.querySelector(".key")?.textContent?.trim() === label) {
+      return el.querySelector("input");
+    }
+  }
+  return null;
+}
+
+function typeInto(input: HTMLInputElement, value: string) {
+  input.value = value;
+  input.dispatchEvent(new Event("input", { bubbles: true }));
+}
+
+/// Flip login ⇄ register via the ghost button under the form.
+async function toggleMode() {
+  const buttons = [...target.querySelectorAll("button.btn--ghost")];
+  buttons[buttons.length - 1].dispatchEvent(
+    new MouseEvent("click", { bubbles: true }),
+  );
+  await tick();
+}
+
+async function submitForm() {
+  target
+    .querySelector("button.btn--primary")!
+    .dispatchEvent(new MouseEvent("click", { bubbles: true }));
+  await flush();
+}
+
+async function mountScreen() {
+  app = mount(LoginScreen, { target, props: { onLogin: vi.fn() } });
+  await flush();
+}
+
+describe("LoginScreen invite field", () => {
+  it("shows the code field only while registering", async () => {
+    await mountScreen();
+
+    // "login" is the default mode — no invite field, and nothing in
+    // the tab order either, since `{#if}` removes it from the DOM.
+    expect(fieldByLabel("einladungscode")).toBeNull();
+
+    await toggleMode();
+    expect(fieldByLabel("einladungscode")).not.toBeNull();
+
+    await toggleMode();
+    expect(fieldByLabel("einladungscode")).toBeNull();
+  });
+
+  it("passes the typed code to session.register as the third argument", async () => {
+    registerMock.mockResolvedValue(SESSION);
+    await mountScreen();
+    await toggleMode();
+
+    typeInto(fieldByLabel("handle")!, "alice.tweet.maarcade.com");
+    typeInto(fieldByLabel("password")!, "hunter2hunter2");
+    typeInto(fieldByLabel("einladungscode")!, "mt-7k3qw-z9d2m");
+    await submitForm();
+
+    expect(loginMock).not.toHaveBeenCalled();
+    expect(registerMock).toHaveBeenCalledTimes(1);
+    expect(registerMock).toHaveBeenCalledWith(
+      "alice.tweet.maarcade.com",
+      "hunter2hunter2",
+      "mt-7k3qw-z9d2m",
+    );
+  });
+
+  it("does not turn an untouched field into a blank code", async () => {
+    registerMock.mockResolvedValue(SESSION);
+    await mountScreen();
+    await toggleMode();
+
+    typeInto(fieldByLabel("handle")!, "alice.test");
+    typeInto(fieldByLabel("password")!, "hunter2hunter2");
+    // Invite field deliberately left alone. The submit must still go
+    // through: whether a code is required is the *server's* call
+    // (`PDS_INVITE_REQUIRED`), and a dev PDS on localhost runs without
+    // the gate. What must not happen is a blank code travelling on as
+    // if the user had entered one.
+    await submitForm();
+
+    expect(registerMock).toHaveBeenCalledTimes(1);
+    const code = registerMock.mock.calls[0][2];
+    expect(code === "" || code === undefined).toBe(true);
+    expect(code?.trim?.() ?? "").toBe("");
+  });
+
+  it("clears a typed code when switching back to login", async () => {
+    loginMock.mockResolvedValue(SESSION);
+    await mountScreen();
+    await toggleMode();
+
+    typeInto(fieldByLabel("handle")!, "alice.test");
+    typeInto(fieldByLabel("password")!, "hunter2hunter2");
+    typeInto(fieldByLabel("einladungscode")!, "mt-stale-code0");
+
+    // Back to login, then to register again: a stale code lingering in
+    // the hidden field would be submitted silently on the next try.
+    await toggleMode();
+    await toggleMode();
+    expect(fieldByLabel("einladungscode")!.value).toBe("");
+  });
+
+  it("renders German copy when the PDS rejects the code", async () => {
+    // Verbatim what reaches the component: `pds_client.rs` bails with
+    // `createAccount failed: {status} {body}`, `lib.rs` stringifies it
+    // into the command's `Err(String)`, and `invoke` rejects with that
+    // bare string.
+    registerMock.mockRejectedValue(
+      'createAccount failed: 400 Bad Request {"error":"InvalidInviteCode",' +
+        '"message":"a valid invite code is required to create an account on this server"}',
+    );
+    await mountScreen();
+    await toggleMode();
+
+    typeInto(fieldByLabel("handle")!, "alice.test");
+    typeInto(fieldByLabel("password")!, "hunter2hunter2");
+    typeInto(fieldByLabel("einladungscode")!, "mt-wrong-code0");
+    await submitForm();
+
+    const err = target.querySelector(".err");
+    expect(err).not.toBeNull();
+    expect(err!.textContent).toContain("Einladungscode");
+    // The wire noise the user would otherwise be shown is gone.
+    expect(err!.textContent).not.toContain("InvalidInviteCode");
+    expect(err!.textContent).not.toContain("400 Bad Request");
+  });
+
+  it("still shows an unrelated failure verbatim", async () => {
+    // The invite branch must not swallow every registration error —
+    // a taken handle has its own message worth reading.
+    registerMock.mockRejectedValue(
+      'createAccount failed: 400 Bad Request {"error":"HandleNotAvailable"}',
+    );
+    await mountScreen();
+    await toggleMode();
+
+    typeInto(fieldByLabel("handle")!, "alice.test");
+    typeInto(fieldByLabel("password")!, "hunter2hunter2");
+    await submitForm();
+
+    expect(target.querySelector(".err")!.textContent).toContain(
+      "HandleNotAvailable",
+    );
+  });
+});