feat: in-game theme store — server catalog + verified downloads + install UI

Phase 1+2 of the theme-store roadmap: a free catalog served by
solitaire_server and an in-app browse/install flow, making custom
themes installable on Android for the first time (the manual
drop-a-zip flow can't reach the app-private themes dir there).

- solitaire_sync: ThemeCatalogEntry/ThemeCatalogResponse wire types
  (additive module; SyncPayload and SyncProvider untouched)
- solitaire_server: THEME_STORE_DIR scan at startup (meta-only
  theme.ron parse, sha256, 20 MiB cap, best-effort per archive);
  public GET /api/themes, /api/themes/{id}/download, /{id}/preview;
  compose volume + README_SERVER docs
- solitaire_data: ThemeStoreClient — catalog fetch + download with
  mandatory size/sha256 verification before bytes are released
- solitaire_engine: ThemeStorePlugin — 'Browse theme store' button in
  Settings → Cosmetic, modal catalog (leaderboard-style rebuild),
  download on AsyncComputeTaskPool, atomic .tmp+rename write into
  user_theme_dir, then the existing hardened import_theme pipeline and
  an in-place registry refresh

New deps: sha2 (workspace, server+data); ron/zip reused in server;
serde_json added to solitaire_sync dev-deps for DTO round-trip tests.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Cargo.lock

@@ -7351,13 +7351,16 @@ dependencies = [
  "reqwest",
  "serde",
  "serde_json",
+ "sha2",
  "solitaire_core",
  "solitaire_server",
  "solitaire_sync",
  "sqlx",
+ "tempfile",
  "thiserror 2.0.18",
  "tokio",
  "uuid",
+ "zip",
 ]
 
 [[package]]
@@ -7402,10 +7405,13 @@ dependencies = [
  "chrono",
  "dotenvy",
  "jsonwebtoken",
+ "ron",
  "serde",
  "serde_json",
+ "sha2",
  "solitaire_sync",
  "sqlx",
+ "tempfile",
  "thiserror 2.0.18",
  "tokio",
  "tower",
@@ -7414,6 +7420,7 @@ dependencies = [
  "tracing",
  "tracing-subscriber",
  "uuid",
+ "zip",
 ]
 
 [[package]]
@@ -7422,6 +7429,7 @@ version = "0.1.0"
 dependencies = [
  "chrono",
  "serde",
+ "serde_json",
  "thiserror 2.0.18",
  "uuid",
 ]

Cargo.toml

@@ -47,6 +47,7 @@ dirs        = "6"
 keyring     = "4"
 keyring-core = "1"
 reqwest     = { version = "0.13", features = ["json", "rustls", "rustls-native-certs"], default-features = false }
+sha2        = "0.10"
 arboard     = { version = "3", default-features = false }
 jni         = { version = "0.21", default-features = false }
 

README_SERVER.md

@@ -44,6 +44,26 @@ docker compose up -d
 ```
 
 
+## Theme store
+
+The server can offer card-art themes for in-game download. Drop theme
+`.zip` archives (the same format the game's Settings → Import accepts:
+a `theme.ron` manifest plus 53 SVGs) into the directory named by
+`THEME_STORE_DIR` (default: `theme_store/` next to the binary), then
+restart the server — the catalog is scanned once at startup. An
+optional `<theme-id>.png` in the same directory becomes the theme's
+store preview.
+
+Endpoints (public, no auth):
+
+- `GET /api/themes` — catalog JSON (id, name, author, size, sha256)
+- `GET /api/themes/<id>/download` — the archive
+- `GET /api/themes/<id>/preview` — the preview PNG, if present
+
+Archives that are oversized (> 20 MiB), unreadable, or have a
+malformed `theme.ron` are skipped with a warning in the server log;
+they never fail startup.
+
 ## Admin — Password Reset
 
 If a player loses access to their account, the server binary includes a

docker-compose.yml

@@ -6,8 +6,13 @@ services:
       # Override DATABASE_URL so the DB always lands in the persistent volume,
       # regardless of what .env contains.
       DATABASE_URL: sqlite:///data/solitaire.db
+      # Theme-store catalog directory (scanned once at startup; the
+      # host ./theme_store folder is where the operator drops theme
+      # zips + preview PNGs).
+      THEME_STORE_DIR: /theme_store
     volumes:
       - ./data:/data
+      - ./theme_store:/theme_store:ro
     restart: unless-stopped
     expose:
       - "${SERVER_PORT:-8080}"

solitaire_data/Cargo.toml

@@ -24,6 +24,9 @@ uuid           = { workspace = true }
 dirs           = { workspace = true }
 reqwest        = { workspace = true }
 tokio          = { workspace = true }
+# Theme-store downloads are verified against the catalog's SHA-256
+# before the archive is handed to the engine's theme importer.
+sha2           = { workspace = true }
 
 # `keyring-core` is the typed Entry/Error API used by
 # `auth_tokens`. The crate's own dependency tree pulls in
@@ -47,6 +50,10 @@ sqlx             = { workspace = true }
 jsonwebtoken     = { workspace = true }
 uuid             = { workspace = true }
 chrono           = { workspace = true }
+# theme_store_round_trip builds a theme zip in a tempdir for the
+# in-process store server.
+zip              = { workspace = true }
+tempfile         = { workspace = true }
 
 [lints]
 workspace = true

solitaire_data/src/lib.rs

@@ -161,6 +161,11 @@ pub use sync_client::LocalOnlyProvider;
 #[cfg(not(target_arch = "wasm32"))]
 pub use sync_client::{SolitaireServerClient, provider_for_backend};
 
+#[cfg(not(target_arch = "wasm32"))]
+pub mod theme_store_client;
+#[cfg(not(target_arch = "wasm32"))]
+pub use theme_store_client::{ThemeStoreClient, ThemeStoreError};
+
 pub mod replay;
 pub use replay::{
     REPLAY_HISTORY_CAP, REPLAY_HISTORY_SCHEMA_VERSION, REPLAY_SCHEMA_VERSION, Replay,

solitaire_data/src/theme_store_client.rs

@@ -0,0 +1,200 @@
+//! HTTP client for the server's theme-store endpoints.
+//!
+//! Fetches the catalog (`GET /api/themes`) and downloads theme
+//! archives, verifying each download's size and SHA-256 against the
+//! catalog entry before returning the bytes. The caller (the engine's
+//! theme-store UI) hands verified bytes to the theme importer, which
+//! independently re-validates the archive's structure — the store
+//! pipeline never trusts a byte the importer hasn't checked.
+//!
+//! Native-only: gated out on wasm32 alongside the other `reqwest`
+//! consumers in this crate.
+
+use sha2::{Digest, Sha256};
+use solitaire_sync::{ThemeCatalogEntry, ThemeCatalogResponse};
+use thiserror::Error;
+
+/// Hard cap on a theme archive download, matching the engine
+/// importer's `MAX_ARCHIVE_BYTES` — anything larger can never import,
+/// so downloading it is pure waste.
+pub const MAX_THEME_DOWNLOAD_BYTES: u64 = 20 * 1024 * 1024;
+
+/// Errors surfaced by [`ThemeStoreClient`].
+#[derive(Debug, Error)]
+pub enum ThemeStoreError {
+    /// The request could not be sent or the response body not read.
+    #[error("network error: {0}")]
+    Network(String),
+    /// The server answered with a non-success status code.
+    #[error("server returned HTTP {0}")]
+    Http(u16),
+    /// The catalog JSON did not parse.
+    #[error("malformed catalog: {0}")]
+    MalformedCatalog(String),
+    /// The archive is larger than [`MAX_THEME_DOWNLOAD_BYTES`] or its
+    /// catalog-declared size.
+    #[error("archive size {got} exceeds the expected {expected} bytes")]
+    Oversized { expected: u64, got: u64 },
+    /// The downloaded bytes do not hash to the catalog's SHA-256 —
+    /// the file changed on the server or was corrupted in transit.
+    #[error("archive checksum mismatch (expected {expected}, got {got})")]
+    ChecksumMismatch { expected: String, got: String },
+}
+
+/// Client for one server's theme store.
+///
+/// Unauthenticated: the catalog and downloads are public endpoints,
+/// so unlike `SolitaireServerClient` there is no token handling.
+pub struct ThemeStoreClient {
+    /// Base URL of the server, trailing slash stripped.
+    base_url: String,
+    client: reqwest::Client,
+}
+
+impl ThemeStoreClient {
+    /// Construct a client for the server at `base_url`
+    /// (e.g. `"https://solitaire.example.com"`).
+    pub fn new(base_url: impl Into<String>) -> Self {
+        Self {
+            base_url: base_url.into().trim_end_matches('/').to_owned(),
+            client: reqwest::Client::new(),
+        }
+    }
+
+    /// Fetch the theme catalog, sorted by display name (server-side).
+    pub async fn fetch_catalog(&self) -> Result<Vec<ThemeCatalogEntry>, ThemeStoreError> {
+        let resp = self
+            .client
+            .get(format!("{}/api/themes", self.base_url))
+            .send()
+            .await
+            .map_err(|e| ThemeStoreError::Network(e.to_string()))?;
+        if !resp.status().is_success() {
+            return Err(ThemeStoreError::Http(resp.status().as_u16()));
+        }
+        let catalog: ThemeCatalogResponse = resp
+            .json()
+            .await
+            .map_err(|e| ThemeStoreError::MalformedCatalog(e.to_string()))?;
+        Ok(catalog.themes)
+    }
+
+    /// Download `entry`'s archive and verify it against the catalog's
+    /// size and SHA-256. Returns the verified `.zip` bytes, ready for
+    /// the engine's theme importer.
+    pub async fn download_theme(
+        &self,
+        entry: &ThemeCatalogEntry,
+    ) -> Result<Vec<u8>, ThemeStoreError> {
+        // The catalog itself could name an absurd size; refuse before
+        // buffering anything.
+        if entry.size_bytes > MAX_THEME_DOWNLOAD_BYTES {
+            return Err(ThemeStoreError::Oversized {
+                expected: MAX_THEME_DOWNLOAD_BYTES,
+                got: entry.size_bytes,
+            });
+        }
+        let resp = self
+            .client
+            .get(format!("{}{}", self.base_url, entry.download_url))
+            .send()
+            .await
+            .map_err(|e| ThemeStoreError::Network(e.to_string()))?;
+        if !resp.status().is_success() {
+            return Err(ThemeStoreError::Http(resp.status().as_u16()));
+        }
+        let bytes = resp
+            .bytes()
+            .await
+            .map_err(|e| ThemeStoreError::Network(e.to_string()))?;
+        verify_archive(&bytes, entry)?;
+        Ok(bytes.to_vec())
+    }
+}
+
+/// Checks downloaded `bytes` against the catalog `entry`'s declared
+/// size and SHA-256. Pure so it can be unit-tested without a server.
+fn verify_archive(bytes: &[u8], entry: &ThemeCatalogEntry) -> Result<(), ThemeStoreError> {
+    if bytes.len() as u64 != entry.size_bytes {
+        return Err(ThemeStoreError::Oversized {
+            expected: entry.size_bytes,
+            got: bytes.len() as u64,
+        });
+    }
+    let got = hex_digest(bytes);
+    // Case-insensitive: the server emits lowercase hex, but a
+    // hand-authored catalog mirror shouldn't fail on case alone.
+    if !got.eq_ignore_ascii_case(&entry.sha256) {
+        return Err(ThemeStoreError::ChecksumMismatch {
+            expected: entry.sha256.clone(),
+            got,
+        });
+    }
+    Ok(())
+}
+
+/// Lowercase-hex SHA-256 of `bytes`. Mirrors the server's digest
+/// encoding in `solitaire_server::theme_store`.
+fn hex_digest(bytes: &[u8]) -> String {
+    let digest = Sha256::digest(bytes);
+    let mut out = String::with_capacity(digest.len() * 2);
+    for byte in digest {
+        out.push_str(&format!("{byte:02x}"));
+    }
+    out
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn entry_for(bytes: &[u8]) -> ThemeCatalogEntry {
+        ThemeCatalogEntry {
+            id: "neon".into(),
+            name: "Neon".into(),
+            author: "Test".into(),
+            version: "1.0.0".into(),
+            card_aspect: (2, 3),
+            size_bytes: bytes.len() as u64,
+            sha256: hex_digest(bytes),
+            download_url: "/api/themes/neon/download".into(),
+            preview_url: None,
+        }
+    }
+
+    #[test]
+    fn verify_accepts_matching_bytes() {
+        let bytes = b"theme archive bytes";
+        assert!(verify_archive(bytes, &entry_for(bytes)).is_ok());
+    }
+
+    #[test]
+    fn verify_accepts_uppercase_catalog_hash() {
+        let bytes = b"theme archive bytes";
+        let mut entry = entry_for(bytes);
+        entry.sha256 = entry.sha256.to_uppercase();
+        assert!(verify_archive(bytes, &entry).is_ok());
+    }
+
+    #[test]
+    fn verify_rejects_size_mismatch() {
+        let bytes = b"theme archive bytes";
+        let mut entry = entry_for(bytes);
+        entry.size_bytes += 1;
+        assert!(matches!(
+            verify_archive(bytes, &entry),
+            Err(ThemeStoreError::Oversized { .. })
+        ));
+    }
+
+    #[test]
+    fn verify_rejects_checksum_mismatch() {
+        let bytes = b"theme archive bytes";
+        let mut entry = entry_for(bytes);
+        entry.sha256 = "0".repeat(64);
+        assert!(matches!(
+            verify_archive(bytes, &entry),
+            Err(ThemeStoreError::ChecksumMismatch { .. })
+        ));
+    }
+}

solitaire_data/tests/theme_store_round_trip.rs

@@ -0,0 +1,118 @@
+//! End-to-end theme-store test: a real `solitaire_server` router
+//! serving a scanned catalog over a localhost TCP socket, consumed by
+//! [`solitaire_data::ThemeStoreClient`].
+//!
+//! Mirrors the `sync_round_trip` harness: `TcpListener` on port 0,
+//! router in a background `tokio::spawn`, no explicit shutdown.
+
+#![cfg(not(target_arch = "wasm32"))]
+
+use std::io::Write as _;
+use std::path::{Path, PathBuf};
+
+use solitaire_data::ThemeStoreClient;
+use solitaire_server::theme_store::ThemeStore;
+
+/// Minimal theme archive: the catalog scan only reads the `meta`
+/// block, so no face SVGs are needed.
+fn write_store_zip(dir: &Path, file_name: &str, id: &str, name: &str) -> PathBuf {
+    let manifest = format!(
+        r#"(
+    meta: (
+        id: "{id}",
+        name: "{name}",
+        author: "Round Trip",
+        version: "1.0.0",
+        card_aspect: (2, 3),
+    ),
+    faces: {{}},
+    back: "back.svg",
+)"#
+    );
+    let path = dir.join(file_name);
+    let file = std::fs::File::create(&path).expect("create zip");
+    let mut writer = zip::ZipWriter::new(file);
+    let options = zip::write::SimpleFileOptions::default();
+    writer.start_file("theme.ron", options).expect("start_file");
+    writer
+        .write_all(manifest.as_bytes())
+        .expect("write manifest");
+    writer.finish().expect("finish zip");
+    path
+}
+
+/// Spawn the test server with a theme store scanned from `store_dir`
+/// and return its base URL.
+async fn spawn_store_server(store_dir: &Path) -> String {
+    let listener = tokio::net::TcpListener::bind("127.0.0.1:0")
+        .await
+        .expect("failed to bind test listener");
+    let addr = listener.local_addr().expect("listener has no local addr");
+
+    let pool = solitaire_server::build_test_pool().await;
+    let app =
+        solitaire_server::build_test_router_with_theme_store(pool, ThemeStore::scan(store_dir));
+
+    tokio::spawn(async move {
+        if let Err(e) = axum::serve(listener, app).await {
+            eprintln!("test server crashed: {e}");
+        }
+    });
+
+    format!("http://{addr}")
+}
+
+/// Catalog fetch → download → verified bytes match the file the
+/// server scanned. This is the exact path the engine's store UI runs.
+#[tokio::test]
+async fn catalog_fetch_and_verified_download_round_trip() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let zip_path = write_store_zip(dir.path(), "neon.zip", "neon", "Neon");
+    let base_url = spawn_store_server(dir.path()).await;
+
+    let client = ThemeStoreClient::new(&base_url);
+    let catalog = client.fetch_catalog().await.expect("fetch catalog");
+    assert_eq!(catalog.len(), 1);
+    let entry = &catalog[0];
+    assert_eq!(entry.id, "neon");
+
+    let bytes = client.download_theme(entry).await.expect("download");
+    assert_eq!(bytes, std::fs::read(&zip_path).expect("read zip"));
+}
+
+/// A catalog entry whose hash no longer matches the served file must
+/// be rejected client-side — the importer never sees unverified bytes.
+#[tokio::test]
+async fn download_with_stale_catalog_hash_is_rejected() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    write_store_zip(dir.path(), "neon.zip", "neon", "Neon");
+    let base_url = spawn_store_server(dir.path()).await;
+
+    let client = ThemeStoreClient::new(&base_url);
+    let mut entry = client.fetch_catalog().await.expect("fetch catalog")[0].clone();
+    entry.sha256 = "0".repeat(64);
+
+    let err = client
+        .download_theme(&entry)
+        .await
+        .expect_err("mismatched hash must fail");
+    assert!(
+        matches!(
+            err,
+            solitaire_data::ThemeStoreError::ChecksumMismatch { .. }
+        ),
+        "expected ChecksumMismatch, got: {err:?}"
+    );
+}
+
+/// An empty (or absent) store directory serves an empty catalog — the
+/// client sees a store with nothing in it, not an error.
+#[tokio::test]
+async fn empty_store_yields_empty_catalog() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let base_url = spawn_store_server(dir.path()).await;
+
+    let client = ThemeStoreClient::new(&base_url);
+    let catalog = client.fetch_catalog().await.expect("fetch catalog");
+    assert!(catalog.is_empty());
+}

solitaire_engine/src/core_game_plugin.rs

@@ -25,6 +25,7 @@ use crate::{
 #[cfg(not(target_arch = "wasm32"))]
 use crate::{
     AnalyticsPlugin, AudioPlugin, AvatarPlugin, LeaderboardPlugin, SyncPlugin, SyncSetupPlugin,
+    ThemeStorePlugin,
 };
 
 /// Groups all Ferrous Solitaire gameplay plugins.
@@ -126,6 +127,7 @@ impl Plugin for CoreGamePlugin {
             .add_plugins(AudioPlugin)
             .add_plugins(SyncPlugin::new(sync_provider))
             .add_plugins(SyncSetupPlugin)
+            .add_plugins(ThemeStorePlugin)
             .add_plugins(AnalyticsPlugin)
             .add_plugins(LeaderboardPlugin);
     }

solitaire_engine/src/events.rs

@@ -134,6 +134,12 @@ pub struct ManualSyncRequestEvent;
 #[derive(Message, Debug, Clone, Copy, Default)]
 pub struct SyncConfigureRequestEvent;
 
+/// Request to open the in-game theme-store modal. Fired by the
+/// "Browse theme store" button in the Settings cosmetic section;
+/// handled by `theme_store_plugin`.
+#[derive(Message, Debug, Clone, Copy, Default)]
+pub struct ThemeStoreOpenRequestEvent;
+
 /// Request to disconnect from the current sync backend, clear stored
 /// credentials, and reset to `SyncBackend::Local`. Fired by the "Disconnect"
 /// button in the Settings sync section.

solitaire_engine/src/lib.rs

@@ -54,6 +54,8 @@ pub mod sync_plugin;
 pub mod sync_setup_plugin;
 pub mod table_plugin;
 pub mod theme;
+#[cfg(not(target_arch = "wasm32"))]
+pub mod theme_store_plugin;
 pub mod time_attack_plugin;
 pub mod touch_selection_plugin;
 pub mod ui_focus;
@@ -176,6 +178,8 @@ pub use theme::{
     ActiveTheme, CardTheme, CardThemeLoader, ThemeEntry, ThemePlugin, ThemeRegistry,
     ThemeRegistryPlugin, set_theme,
 };
+#[cfg(not(target_arch = "wasm32"))]
+pub use theme_store_plugin::{ThemeStorePlugin, ThemeStoreScreen};
 pub use time_attack_plugin::{
     TIME_ATTACK_DURATION_SECS, TimeAttackEndedEvent, TimeAttackPlugin, TimeAttackResource,
 };

solitaire_engine/src/settings_plugin/input.rs

@@ -407,6 +407,10 @@ pub(super) fn handle_settings_buttons(
             | SettingsButton::DeleteAccount => {
                 // Handled by `handle_sync_buttons`.
             }
+            #[cfg(not(target_arch = "wasm32"))]
+            SettingsButton::OpenThemeStore => {
+                // Handled by `handle_sync_buttons`.
+            }
             SettingsButton::Done => {
                 screen.0 = false;
             }
@@ -423,6 +427,9 @@ pub(super) fn handle_sync_buttons(
     mut configure_sync: MessageWriter<SyncConfigureRequestEvent>,
     mut logout_sync: MessageWriter<SyncLogoutRequestEvent>,
     mut delete_account: MessageWriter<DeleteAccountRequestEvent>,
+    #[cfg(not(target_arch = "wasm32"))] mut open_theme_store: MessageWriter<
+        crate::events::ThemeStoreOpenRequestEvent,
+    >,
     mut screen: ResMut<SettingsScreen>,
 ) {
     for (interaction, button) in &interaction_query {
@@ -439,6 +446,13 @@ pub(super) fn handle_sync_buttons(
                 screen.0 = false;
                 configure_sync.write(SyncConfigureRequestEvent);
             }
+            #[cfg(not(target_arch = "wasm32"))]
+            SettingsButton::OpenThemeStore => {
+                // Same shape as ConnectSync: close settings first so the
+                // store modal's own-scrim guard doesn't block.
+                screen.0 = false;
+                open_theme_store.write(crate::events::ThemeStoreOpenRequestEvent);
+            }
             SettingsButton::DisconnectSync => {
                 logout_sync.write(SyncLogoutRequestEvent);
             }

solitaire_engine/src/settings_plugin/mod.rs

@@ -250,6 +250,9 @@ enum SettingsButton {
     /// Scan `user_theme_dir()` for new `.zip` files and import each one.
     #[cfg(not(target_arch = "wasm32"))]
     ScanThemes,
+    /// Open the in-game theme-store modal (closes Settings first).
+    #[cfg(not(target_arch = "wasm32"))]
+    OpenThemeStore,
     SyncNow,
     /// Open the sync-server Connect modal (shown when backend = Local).
     ConnectSync,
@@ -313,6 +316,8 @@ impl SettingsButton {
             SettingsButton::SelectTheme(_) => 85,
             #[cfg(not(target_arch = "wasm32"))]
             SettingsButton::ScanThemes => 86,
+            #[cfg(not(target_arch = "wasm32"))]
+            SettingsButton::OpenThemeStore => 87,
             // Sync section
             SettingsButton::SyncNow => 90,
             SettingsButton::ConnectSync => 91,
@@ -371,6 +376,7 @@ impl Plugin for SettingsPlugin {
             .add_message::<SyncLogoutRequestEvent>()
             .add_message::<DeleteAccountRequestEvent>()
             .add_message::<ToggleSettingsRequestEvent>()
+            .add_message::<crate::events::ThemeStoreOpenRequestEvent>()
             .add_message::<InfoToastEvent>()
             .add_message::<MouseWheel>()
             .add_message::<TouchInput>()

solitaire_engine/src/settings_plugin/ui.rs

@@ -239,6 +239,8 @@ pub(super) fn spawn_settings_panel(
             }
             #[cfg(not(target_arch = "wasm32"))]
             import_themes_row(body, font_res);
+            #[cfg(not(target_arch = "wasm32"))]
+            theme_store_row(body, font_res);
 
             // --- Privacy (only shown when a Matomo URL is configured) ---
             if settings.matomo_url.is_some() {
@@ -1193,6 +1195,31 @@ pub(super) fn import_themes_row(
         });
 }
 
+/// "Theme store" row: one pill button that closes Settings and opens
+/// the in-game theme-store modal (`theme_store_plugin`). Sits directly
+/// under the Import row so both install paths live together.
+#[cfg(not(target_arch = "wasm32"))]
+pub(super) fn theme_store_row(parent: &mut ChildSpawnerCommands, font_res: Option<&FontResource>) {
+    parent
+        .spawn((
+            FocusRow,
+            Node {
+                flex_direction: FlexDirection::Row,
+                align_items: AlignItems::Center,
+                ..default()
+            },
+        ))
+        .with_children(|row| {
+            pill_button(
+                row,
+                SettingsButton::OpenThemeStore,
+                "Browse theme store",
+                "Download themes from your sync server without leaving the game.",
+                font_res,
+            );
+        });
+}
+
 pub(super) fn icon_button(
     parent: &mut ChildSpawnerCommands,
     label: &str,

solitaire_engine/src/theme_store_plugin.rs

@@ -0,0 +1,657 @@
+//! In-game theme store: browse the sync server's theme catalog and
+//! install themes without leaving the app.
+//!
+//! Settings → Cosmetic → "Browse theme store" fires
+//! [`crate::events::ThemeStoreOpenRequestEvent`]; this plugin opens a
+//! modal listing the catalog (fetched on [`AsyncComputeTaskPool`]) and
+//! handles per-theme Install buttons. An install downloads the archive
+//! (SHA-256-verified by [`ThemeStoreClient`]), writes it atomically
+//! into `user_theme_dir()`, and runs it through the same hardened
+//! [`import_theme`] pipeline as a manually dropped zip — the store
+//! never bypasses the importer's validation.
+//!
+//! Native-only: downloads need `reqwest`/Tokio and the importer is
+//! filesystem-based; the plugin is gated out on wasm32 alongside
+//! `SyncPlugin`.
+
+use bevy::prelude::*;
+use bevy::tasks::{AsyncComputeTaskPool, Task, futures_lite::future};
+use thiserror::Error;
+
+use solitaire_data::theme_store_client::{ThemeStoreClient, ThemeStoreError};
+use solitaire_data::{Settings, SyncBackend};
+use solitaire_sync::ThemeCatalogEntry;
+
+use crate::assets::user_theme_dir;
+use crate::events::{InfoToastEvent, ThemeStoreOpenRequestEvent, WarningToastEvent};
+use crate::font_plugin::FontResource;
+use crate::resources::TokioRuntimeResource;
+use crate::settings_plugin::{SettingsPanel, SettingsResource};
+use crate::theme::{ImportError, ThemeRegistry, import_theme, refresh_registry};
+use crate::ui_modal::{
+    ButtonVariant, ModalScrim, ScrimDismissible, spawn_modal, spawn_modal_actions,
+    spawn_modal_button, spawn_modal_header,
+};
+use crate::ui_theme::{
+    BORDER_SUBTLE, TEXT_PRIMARY, TEXT_SECONDARY, TYPE_BODY, TYPE_CAPTION, VAL_SPACE_2, VAL_SPACE_3,
+    Z_MODAL_PANEL,
+};
+
+// ---------------------------------------------------------------------------
+// Errors
+// ---------------------------------------------------------------------------
+
+/// Everything that can go wrong between clicking Install and the theme
+/// appearing in the picker.
+#[derive(Debug, Error)]
+enum ThemeInstallError {
+    /// Catalog fetch or archive download failed (network, HTTP status,
+    /// size/checksum verification).
+    #[error(transparent)]
+    Download(#[from] ThemeStoreError),
+    /// The verified archive could not be written into the themes dir.
+    #[error("could not save archive: {0}")]
+    Io(#[from] std::io::Error),
+    /// The downloaded archive failed importer validation.
+    #[error(transparent)]
+    Import(#[from] ImportError),
+}
+
+// ---------------------------------------------------------------------------
+// Components & resources
+// ---------------------------------------------------------------------------
+
+/// Marker on the theme-store modal's scrim root.
+#[derive(Component)]
+pub struct ThemeStoreScreen;
+
+/// Marker on the modal's Close button.
+#[derive(Component)]
+struct ThemeStoreCloseButton;
+
+/// Per-row Install button carrying its catalog entry.
+#[derive(Component)]
+struct ThemeStoreInstallButton(ThemeCatalogEntry);
+
+/// Catalog fetch lifecycle. The modal renders directly from this state
+/// and is rebuilt (despawn + respawn, mirroring the leaderboard panel)
+/// whenever it changes.
+#[derive(Resource, Default)]
+enum CatalogState {
+    /// No fetch has run since the modal was last opened.
+    #[default]
+    Idle,
+    Loading,
+    Loaded(Vec<ThemeCatalogEntry>),
+    Error(String),
+}
+
+/// In-flight catalog fetch, polled without blocking.
+#[derive(Resource, Default)]
+struct CatalogTask(Option<Task<Result<Vec<ThemeCatalogEntry>, ThemeStoreError>>>);
+
+/// Result of one download + import: `Ok(Some(id))` on a fresh install,
+/// `Ok(None)` when the theme was already installed (id collision) —
+/// informational, not an error.
+type InstallResult = Result<Option<String>, ThemeInstallError>;
+
+/// In-flight download + import. `String` is the theme id, for toasts.
+#[derive(Resource, Default)]
+struct InstallTask(Option<(String, Task<InstallResult>)>);
+
+/// Server base URL captured when the modal opens. Catalog
+/// `download_url`s are server-relative, so installs join them onto
+/// this. `None` while the modal has never been opened.
+#[derive(Resource, Default)]
+struct StoreBaseUrl(Option<String>);
+
+// ---------------------------------------------------------------------------
+// Plugin
+// ---------------------------------------------------------------------------
+
+/// Bevy plugin for the in-game theme store. See the module docs.
+pub struct ThemeStorePlugin;
+
+impl Plugin for ThemeStorePlugin {
+    fn build(&self, app: &mut App) {
+        app.init_resource::<CatalogState>()
+            .init_resource::<CatalogTask>()
+            .init_resource::<InstallTask>()
+            .init_resource::<StoreBaseUrl>()
+            .add_message::<ThemeStoreOpenRequestEvent>()
+            .add_message::<InfoToastEvent>()
+            .add_message::<WarningToastEvent>()
+            .add_systems(
+                Update,
+                (
+                    handle_open_request,
+                    poll_catalog_task,
+                    handle_install_buttons,
+                    poll_install_task,
+                    handle_close_button,
+                )
+                    .chain(),
+            );
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Systems
+// ---------------------------------------------------------------------------
+
+/// Resolves the store's server base URL from the player's sync
+/// backend. The store rides the same self-hosted server as sync;
+/// without one configured there is nothing to browse.
+fn store_base_url(settings: &Settings) -> Option<String> {
+    match &settings.sync_backend {
+        SyncBackend::SolitaireServer { url, .. } => Some(url.clone()),
+        _ => None,
+    }
+}
+
+/// Opens the store modal and kicks off the catalog fetch.
+///
+/// Mirrors `open_sync_setup_modal`: the Settings button closes the
+/// settings panel in the same frame it fires the event, and despawns
+/// are deferred, so the settings scrim is excluded from the
+/// another-modal-is-open guard.
+#[allow(clippy::type_complexity, clippy::too_many_arguments)]
+fn handle_open_request(
+    mut events: MessageReader<ThemeStoreOpenRequestEvent>,
+    existing: Query<(), With<ThemeStoreScreen>>,
+    other_modal_scrims: Query<
+        (),
+        (
+            With<ModalScrim>,
+            Without<ThemeStoreScreen>,
+            Without<SettingsPanel>,
+        ),
+    >,
+    settings: Option<Res<SettingsResource>>,
+    rt: Option<Res<TokioRuntimeResource>>,
+    mut catalog_state: ResMut<CatalogState>,
+    mut catalog_task: ResMut<CatalogTask>,
+    mut store_base: ResMut<StoreBaseUrl>,
+    mut warning_toast: MessageWriter<WarningToastEvent>,
+    mut commands: Commands,
+    font_res: Option<Res<FontResource>>,
+) {
+    if events.is_empty() {
+        return;
+    }
+    events.clear();
+    if !existing.is_empty() || !other_modal_scrims.is_empty() {
+        return;
+    }
+
+    let Some(base_url) = settings.as_deref().and_then(|s| store_base_url(&s.0)) else {
+        warning_toast.write(WarningToastEvent(
+            "Theme store needs a server — connect one in Settings → Sync.".to_string(),
+        ));
+        return;
+    };
+    let Some(rt) = rt else {
+        warning_toast.write(WarningToastEvent(
+            "Theme store unavailable — no network runtime.".to_string(),
+        ));
+        return;
+    };
+
+    store_base.0 = Some(base_url.clone());
+    *catalog_state = CatalogState::Loading;
+    let rt = rt.0.clone();
+    catalog_task.0 = Some(AsyncComputeTaskPool::get().spawn(async move {
+        rt.block_on(async { ThemeStoreClient::new(base_url).fetch_catalog().await })
+    }));
+
+    spawn_store_modal(&mut commands, &catalog_state, None, font_res.as_deref());
+}
+
+/// Polls the catalog fetch; on completion updates [`CatalogState`] and
+/// rebuilds the modal if it is still open.
+fn poll_catalog_task(
+    mut catalog_task: ResMut<CatalogTask>,
+    mut catalog_state: ResMut<CatalogState>,
+    screens: Query<Entity, With<ThemeStoreScreen>>,
+    registry: Option<Res<ThemeRegistry>>,
+    mut commands: Commands,
+    font_res: Option<Res<FontResource>>,
+) {
+    let Some(task) = catalog_task.0.as_mut() else {
+        return;
+    };
+    let Some(result) = future::block_on(future::poll_once(task)) else {
+        return;
+    };
+    catalog_task.0 = None;
+
+    *catalog_state = match result {
+        Ok(entries) => CatalogState::Loaded(entries),
+        Err(e) => {
+            warn!("theme store: catalog fetch failed: {e}");
+            CatalogState::Error(e.to_string())
+        }
+    };
+
+    rebuild_open_modal(
+        &screens,
+        &mut commands,
+        &catalog_state,
+        registry.as_deref(),
+        font_res.as_deref(),
+    );
+}
+
+/// Starts a download + import task when an Install button is pressed.
+/// One install at a time; repeat clicks while busy are ignored.
+fn handle_install_buttons(
+    interactions: Query<(&Interaction, &ThemeStoreInstallButton), Changed<Interaction>>,
+    rt: Option<Res<TokioRuntimeResource>>,
+    store_base: Res<StoreBaseUrl>,
+    mut install_task: ResMut<InstallTask>,
+    mut info_toast: MessageWriter<InfoToastEvent>,
+) {
+    for (interaction, button) in &interactions {
+        if *interaction != Interaction::Pressed || install_task.0.is_some() {
+            continue;
+        }
+        let (Some(rt), Some(base_url)) = (rt.as_ref(), store_base.0.clone()) else {
+            continue;
+        };
+        let entry = button.0.clone();
+        info_toast.write(InfoToastEvent(format!("Downloading '{}'…", entry.name)));
+        let rt = rt.0.clone();
+        let task = AsyncComputeTaskPool::get().spawn(async move {
+            let bytes = rt
+                .block_on(async { ThemeStoreClient::new(base_url).download_theme(&entry).await })?;
+            install_verified_archive(&entry.id, &bytes)
+        });
+        install_task.0 = Some((button.0.id.clone(), task));
+    }
+}
+
+/// Downloads land here (already SHA-256-verified): write the archive
+/// atomically into the user themes dir (`.tmp` + rename, §2.5), then
+/// run the standard importer. Returns `Ok(None)` when the theme was
+/// already installed.
+fn install_verified_archive(id: &str, bytes: &[u8]) -> Result<Option<String>, ThemeInstallError> {
+    let themes_dir = user_theme_dir();
+    std::fs::create_dir_all(&themes_dir)?;
+    let final_path = themes_dir.join(format!("{id}.zip"));
+    let tmp_path = themes_dir.join(format!("{id}.zip.tmp"));
+    std::fs::write(&tmp_path, bytes)?;
+    std::fs::rename(&tmp_path, &final_path)?;
+
+    match import_theme(&final_path) {
+        Ok(theme_id) => Ok(Some(theme_id.as_str().to_string())),
+        Err(ImportError::IdCollision { .. }) => Ok(None),
+        Err(e) => {
+            // Don't leave a zip that fails validation lying around for
+            // the folder-scan flow to re-try on every scan.
+            let _ = std::fs::remove_file(&final_path);
+            Err(e.into())
+        }
+    }
+}
+
+/// Polls the install task; on completion refreshes the theme registry,
+/// toasts the outcome, and rebuilds the modal so the row flips to
+/// "Installed".
+#[allow(clippy::too_many_arguments)]
+fn poll_install_task(
+    mut install_task: ResMut<InstallTask>,
+    mut registry: Option<ResMut<ThemeRegistry>>,
+    catalog_state: Res<CatalogState>,
+    screens: Query<Entity, With<ThemeStoreScreen>>,
+    mut info_toast: MessageWriter<InfoToastEvent>,
+    mut warning_toast: MessageWriter<WarningToastEvent>,
+    mut commands: Commands,
+    font_res: Option<Res<FontResource>>,
+) {
+    let Some((id, task)) = install_task.0.as_mut() else {
+        return;
+    };
+    let Some(result) = future::block_on(future::poll_once(task)) else {
+        return;
+    };
+    let id = id.clone();
+    install_task.0 = None;
+
+    match result {
+        Ok(Some(theme_id)) => {
+            if let Some(registry) = registry.as_deref_mut() {
+                refresh_registry(registry, &user_theme_dir());
+            }
+            info_toast.write(InfoToastEvent(format!(
+                "Theme '{theme_id}' installed — pick it in Settings → Cosmetic."
+            )));
+        }
+        Ok(None) => {
+            info_toast.write(InfoToastEvent(format!("Theme '{id}' already installed.")));
+        }
+        Err(e) => {
+            warn!("theme store: install of '{id}' failed: {e}");
+            warning_toast.write(WarningToastEvent(format!("Install failed: {e}")));
+        }
+    }
+
+    rebuild_open_modal(
+        &screens,
+        &mut commands,
+        &catalog_state,
+        registry.as_deref(),
+        font_res.as_deref(),
+    );
+}
+
+/// Despawns the store modal when Close is pressed.
+fn handle_close_button(
+    interactions: Query<&Interaction, (Changed<Interaction>, With<ThemeStoreCloseButton>)>,
+    screens: Query<Entity, With<ThemeStoreScreen>>,
+    mut commands: Commands,
+) {
+    for interaction in &interactions {
+        if *interaction != Interaction::Pressed {
+            continue;
+        }
+        for entity in &screens {
+            commands.entity(entity).despawn();
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Modal rendering
+// ---------------------------------------------------------------------------
+
+/// Despawn + respawn the modal for every open screen (Bevy despawns
+/// are deferred, so this is safe within one frame).
+fn rebuild_open_modal(
+    screens: &Query<Entity, With<ThemeStoreScreen>>,
+    commands: &mut Commands,
+    catalog_state: &CatalogState,
+    registry: Option<&ThemeRegistry>,
+    font_res: Option<&FontResource>,
+) {
+    for entity in screens {
+        commands.entity(entity).despawn();
+        spawn_store_modal(commands, catalog_state, registry, font_res);
+    }
+}
+
+/// Spawns the store modal for the current catalog state.
+fn spawn_store_modal(
+    commands: &mut Commands,
+    catalog_state: &CatalogState,
+    registry: Option<&ThemeRegistry>,
+    font_res: Option<&FontResource>,
+) {
+    let body_font = TextFont {
+        font: font_res.map(|f| f.0.clone()).unwrap_or_default(),
+        font_size: TYPE_BODY,
+        ..default()
+    };
+    let caption_font = TextFont {
+        font: font_res.map(|f| f.0.clone()).unwrap_or_default(),
+        font_size: TYPE_CAPTION,
+        ..default()
+    };
+
+    let scrim = spawn_modal(commands, ThemeStoreScreen, Z_MODAL_PANEL + 1, |card| {
+        spawn_modal_header(card, "Theme Store", font_res);
+
+        match catalog_state {
+            CatalogState::Idle | CatalogState::Loading => {
+                card.spawn((
+                    Text::new("Loading catalog…"),
+                    body_font.clone(),
+                    TextColor(TEXT_SECONDARY),
+                ));
+            }
+            CatalogState::Error(msg) => {
+                card.spawn((
+                    Text::new(format!("Could not load the catalog: {msg}")),
+                    body_font.clone(),
+                    TextColor(TEXT_SECONDARY),
+                ));
+            }
+            CatalogState::Loaded(entries) if entries.is_empty() => {
+                card.spawn((
+                    Text::new("The server has no themes yet."),
+                    body_font.clone(),
+                    TextColor(TEXT_SECONDARY),
+                ));
+            }
+            CatalogState::Loaded(entries) => {
+                for entry in entries {
+                    let installed =
+                        registry.is_some_and(|registry| registry.find(&entry.id).is_some());
+                    spawn_store_row(card, entry, installed, &body_font, &caption_font, font_res);
+                }
+            }
+        }
+
+        spawn_modal_actions(card, |actions| {
+            spawn_modal_button(
+                actions,
+                ThemeStoreCloseButton,
+                "Close",
+                None,
+                ButtonVariant::Primary,
+                font_res,
+            );
+        });
+    });
+    commands.entity(scrim).insert(ScrimDismissible);
+}
+
+/// One catalog row: name + author/size caption on the left, Install
+/// button (or "Installed" caption) on the right.
+fn spawn_store_row(
+    parent: &mut ChildSpawnerCommands,
+    entry: &ThemeCatalogEntry,
+    installed: bool,
+    body_font: &TextFont,
+    caption_font: &TextFont,
+    font_res: Option<&FontResource>,
+) {
+    parent
+        .spawn((
+            Node {
+                flex_direction: FlexDirection::Row,
+                justify_content: JustifyContent::SpaceBetween,
+                align_items: AlignItems::Center,
+                column_gap: VAL_SPACE_3,
+                padding: UiRect::vertical(VAL_SPACE_2),
+                border: UiRect::bottom(Val::Px(1.0)),
+                ..default()
+            },
+            BorderColor::all(BORDER_SUBTLE),
+        ))
+        .with_children(|row| {
+            row.spawn(Node {
+                flex_direction: FlexDirection::Column,
+                row_gap: VAL_SPACE_2,
+                ..default()
+            })
+            .with_children(|col| {
+                col.spawn((
+                    Text::new(entry.name.clone()),
+                    body_font.clone(),
+                    TextColor(TEXT_PRIMARY),
+                ));
+                col.spawn((
+                    Text::new(format!(
+                        "by {} — {} KB",
+                        entry.author,
+                        entry.size_bytes.div_ceil(1024)
+                    )),
+                    caption_font.clone(),
+                    TextColor(TEXT_SECONDARY),
+                ));
+            });
+            if installed {
+                row.spawn((
+                    Text::new("Installed"),
+                    caption_font.clone(),
+                    TextColor(TEXT_SECONDARY),
+                ));
+            } else {
+                spawn_modal_button(
+                    row,
+                    ThemeStoreInstallButton(entry.clone()),
+                    "Install",
+                    None,
+                    ButtonVariant::Secondary,
+                    font_res,
+                );
+            }
+        });
+}
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use bevy::ecs::message::Messages;
+
+    fn headless_app() -> App {
+        let mut app = App::new();
+        app.add_plugins(MinimalPlugins)
+            .add_plugins(ThemeStorePlugin);
+        app.update();
+        app
+    }
+
+    fn settings_with_server() -> SettingsResource {
+        SettingsResource(Settings {
+            sync_backend: SyncBackend::SolitaireServer {
+                url: "http://127.0.0.1:1".to_string(),
+                username: "tester".to_string(),
+                avatar_url: None,
+            },
+            ..Settings::default()
+        })
+    }
+
+    fn screen_count(app: &mut App) -> usize {
+        app.world_mut()
+            .query::<&ThemeStoreScreen>()
+            .iter(app.world())
+            .count()
+    }
+
+    #[test]
+    fn store_base_url_requires_server_backend() {
+        assert_eq!(store_base_url(&Settings::default()), None);
+        assert_eq!(
+            store_base_url(&settings_with_server().0).as_deref(),
+            Some("http://127.0.0.1:1")
+        );
+    }
+
+    #[test]
+    fn open_request_without_server_warns_and_spawns_nothing() {
+        let mut app = headless_app();
+        // Default settings → SyncBackend::Local → no store.
+        app.insert_resource(SettingsResource(Settings::default()));
+        app.world_mut()
+            .resource_mut::<Messages<ThemeStoreOpenRequestEvent>>()
+            .write(ThemeStoreOpenRequestEvent);
+        app.update();
+
+        assert_eq!(screen_count(&mut app), 0);
+        assert!(
+            !app.world()
+                .resource::<Messages<WarningToastEvent>>()
+                .is_empty(),
+            "player must be told why the store did not open"
+        );
+    }
+
+    #[test]
+    fn open_request_without_runtime_warns_and_spawns_nothing() {
+        let mut app = headless_app();
+        app.insert_resource(settings_with_server());
+        // No TokioRuntimeResource inserted.
+        app.world_mut()
+            .resource_mut::<Messages<ThemeStoreOpenRequestEvent>>()
+            .write(ThemeStoreOpenRequestEvent);
+        app.update();
+
+        assert_eq!(screen_count(&mut app), 0);
+        assert!(
+            !app.world()
+                .resource::<Messages<WarningToastEvent>>()
+                .is_empty()
+        );
+    }
+
+    #[test]
+    fn open_request_with_server_spawns_modal_in_loading_state() {
+        let mut app = headless_app();
+        app.insert_resource(settings_with_server());
+        app.insert_resource(TokioRuntimeResource::new().expect("test runtime"));
+        app.world_mut()
+            .resource_mut::<Messages<ThemeStoreOpenRequestEvent>>()
+            .write(ThemeStoreOpenRequestEvent);
+        app.update();
+
+        assert_eq!(screen_count(&mut app), 1);
+        assert!(matches!(
+            *app.world().resource::<CatalogState>(),
+            CatalogState::Loading | CatalogState::Error(_)
+        ));
+        assert_eq!(
+            app.world().resource::<StoreBaseUrl>().0.as_deref(),
+            Some("http://127.0.0.1:1")
+        );
+    }
+
+    #[test]
+    fn second_open_request_does_not_stack_a_second_modal() {
+        let mut app = headless_app();
+        app.insert_resource(settings_with_server());
+        app.insert_resource(TokioRuntimeResource::new().expect("test runtime"));
+        for _ in 0..2 {
+            app.world_mut()
+                .resource_mut::<Messages<ThemeStoreOpenRequestEvent>>()
+                .write(ThemeStoreOpenRequestEvent);
+            app.update();
+        }
+        assert_eq!(screen_count(&mut app), 1);
+    }
+
+    #[test]
+    fn failed_catalog_fetch_rebuilds_modal_with_error_state() {
+        let mut app = headless_app();
+        app.insert_resource(settings_with_server());
+        app.insert_resource(TokioRuntimeResource::new().expect("test runtime"));
+        app.world_mut()
+            .resource_mut::<Messages<ThemeStoreOpenRequestEvent>>()
+            .write(ThemeStoreOpenRequestEvent);
+        app.update();
+
+        // 127.0.0.1:1 refuses connections; the fetch task must resolve
+        // to an error within a bounded number of frames and the modal
+        // must survive the rebuild.
+        for _ in 0..200 {
+            app.update();
+            if matches!(
+                *app.world().resource::<CatalogState>(),
+                CatalogState::Error(_)
+            ) {
+                break;
+            }
+            std::thread::sleep(std::time::Duration::from_millis(10));
+        }
+        assert!(matches!(
+            *app.world().resource::<CatalogState>(),
+            CatalogState::Error(_)
+        ));
+        assert_eq!(screen_count(&mut app), 1);
+    }
+}

solitaire_server/Cargo.toml

@@ -29,9 +29,15 @@ tower-http         = { version = "0.6", features = ["fs"] }
 tracing            = { workspace = true }
 tracing-subscriber = { workspace = true }
 dotenvy            = { workspace = true }
+# Theme store: scans a directory of theme .zip archives at startup,
+# reading each archive's theme.ron manifest and hashing the bytes.
+ron                = { workspace = true }
+zip                = { workspace = true }
+sha2               = { workspace = true }
 
 [dev-dependencies]
 tower    = { version = "0.5", features = ["util"] }
+tempfile = { workspace = true }
 
 [lints]
 workspace = true

solitaire_server/src/lib.rs

@@ -11,6 +11,7 @@ pub mod leaderboard;
 pub mod middleware;
 pub mod replays;
 pub mod sync;
+pub mod theme_store;
 
 pub use auth::reset_password;
 
@@ -86,6 +87,10 @@ pub struct AppState {
     pub pool: SqlitePool,
     /// HS256 signing secret for JWT access and refresh tokens.
     pub jwt_secret: String,
+    /// Theme-store catalog scanned once at startup.
+    /// [`theme_store::ThemeStore::empty`] when the server runs without
+    /// a store directory.
+    pub theme_store: Arc<theme_store::ThemeStore>,
 }
 
 /// Construct the full Axum [`Router`].
@@ -125,9 +130,20 @@ pub async fn build_test_pool() -> SqlitePool {
 /// integration tests do not need to set `JWT_SECRET` in the environment.
 #[doc(hidden)]
 pub fn build_test_router(pool: SqlitePool) -> Router {
+    build_test_router_with_theme_store(pool, theme_store::ThemeStore::empty())
+}
+
+/// [`build_test_router`] with a caller-supplied theme store, for
+/// integration tests exercising the theme endpoints.
+#[doc(hidden)]
+pub fn build_test_router_with_theme_store(
+    pool: SqlitePool,
+    theme_store: theme_store::ThemeStore,
+) -> Router {
     let state = AppState {
         pool,
         jwt_secret: "test_secret_32_chars_minimum_ok!".to_string(),
+        theme_store: Arc::new(theme_store),
     };
     build_router_inner(state, false)
 }
@@ -195,6 +211,9 @@ fn build_router_inner(state: AppState, rate_limit: bool) -> Router {
         .route("/api/daily-challenge", get(challenge::daily_challenge))
         .route("/api/replays/recent", get(replays::recent))
         .route("/api/replays/{id}", get(replays::get_by_id))
+        .route("/api/themes", get(theme_store::list))
+        .route("/api/themes/{id}/download", get(theme_store::download))
+        .route("/api/themes/{id}/preview", get(theme_store::preview))
         .route("/health", get(health))
         .nest_service("/avatars", ServeDir::new("avatars"));
 

solitaire_server/src/main.rs

@@ -31,12 +31,13 @@
 //! echo "new_password" | ./solitaire_server --reset-password alice
 //! ```
 
-use solitaire_server::{AppState, build_router};
+use solitaire_server::{AppState, build_router, theme_store};
 use sqlx::{SqlitePool, sqlite::SqliteConnectOptions};
 use std::{
     io::{self, BufRead},
     net::SocketAddr,
     str::FromStr,
+    sync::Arc,
 };
 
 const JWT_SECRET_MIN_BYTES: usize = 32;
@@ -142,7 +143,19 @@ async fn run_server() {
 
     tracing::info!("database ready at {db_url}");
 
-    let state = AppState { pool, jwt_secret };
+    // Theme store: optional; a missing directory just means an empty
+    // catalog. Scanned once — add themes, then restart to publish.
+    let theme_store_dir = std::env::var(theme_store::THEME_STORE_DIR_ENV)
+        .unwrap_or_else(|_| theme_store::DEFAULT_THEME_STORE_DIR.into());
+    let theme_store = Arc::new(theme_store::ThemeStore::scan(std::path::Path::new(
+        &theme_store_dir,
+    )));
+
+    let state = AppState {
+        pool,
+        jwt_secret,
+        theme_store,
+    };
     let app = build_router(state);
 
     let addr = SocketAddr::from(([0, 0, 0, 0], port));

solitaire_server/src/theme_store.rs

@@ -0,0 +1,366 @@
+//! Theme-store catalog and file-serving endpoints.
+//!
+//! The store is filesystem-driven: the operator drops theme `.zip`
+//! archives (the same format the engine's theme importer consumes)
+//! into the directory named by the `THEME_STORE_DIR` environment
+//! variable (default `theme_store/`), plus an optional `<id>.png`
+//! preview per theme. [`ThemeStore::scan`] runs once at startup —
+//! adding a theme means dropping the files and restarting the server.
+//!
+//! Endpoints (all public, no auth — the catalog is free):
+//!
+//! - `GET /api/themes` — [`ThemeCatalogResponse`] JSON
+//! - `GET /api/themes/{id}/download` — the theme `.zip`
+//! - `GET /api/themes/{id}/preview` — the preview PNG (404 when absent)
+
+use std::collections::HashMap;
+use std::io::{Cursor, Read};
+use std::path::{Path, PathBuf};
+
+use axum::Json;
+use axum::extract::{Path as UrlPath, State};
+use axum::http::header;
+use axum::response::{IntoResponse, Response};
+use serde::Deserialize;
+use sha2::{Digest, Sha256};
+use solitaire_sync::{ThemeCatalogEntry, ThemeCatalogResponse};
+use tracing::{info, warn};
+
+use crate::AppState;
+use crate::error::AppError;
+
+/// Environment variable naming the theme-store directory.
+pub const THEME_STORE_DIR_ENV: &str = "THEME_STORE_DIR";
+
+/// Default theme-store directory, relative to the server working dir —
+/// same convention as the `avatars/` upload directory.
+pub const DEFAULT_THEME_STORE_DIR: &str = "theme_store";
+
+/// Archives larger than this are skipped at scan time with a warning.
+/// Mirrors the engine importer's `MAX_ARCHIVE_BYTES` (20 MiB) — a zip
+/// whose *compressed* size already exceeds the client's uncompressed
+/// limit can never import, so serving it only wastes bandwidth.
+pub const MAX_STORE_ARCHIVE_BYTES: u64 = 20 * 1024 * 1024;
+
+/// Upper bound on the bytes read out of an archive's `theme.ron`
+/// entry at scan time, guarding the catalog scan against a
+/// zip-bombed manifest. Real manifests are a few KB.
+const MAX_MANIFEST_BYTES: u64 = 1024 * 1024;
+
+/// `theme.ron`'s outer shape, `meta` block only — the 53 face entries
+/// are irrelevant to the catalog and are validated client-side by the
+/// importer at install time.
+#[derive(Debug, Deserialize)]
+struct ManifestMetaOnly {
+    meta: StoreThemeMeta,
+}
+
+/// Mirror of the `meta` block of a theme manifest. The canonical
+/// definition is `solitaire_engine::theme::ThemeMeta`; the server
+/// cannot depend on the engine crate (it links Bevy), so the shape is
+/// re-declared here. Keep the two in lockstep.
+#[derive(Debug, Deserialize)]
+struct StoreThemeMeta {
+    id: String,
+    name: String,
+    author: String,
+    version: String,
+    card_aspect: (u32, u32),
+}
+
+/// In-memory catalog built by scanning the theme-store directory once
+/// at startup. Shared via [`AppState`].
+#[derive(Debug, Default)]
+pub struct ThemeStore {
+    entries: Vec<ThemeCatalogEntry>,
+    zip_paths: HashMap<String, PathBuf>,
+    preview_paths: HashMap<String, PathBuf>,
+}
+
+impl ThemeStore {
+    /// An empty store — used by tests and when the store directory is
+    /// absent (the server runs fine without a theme store).
+    pub fn empty() -> Self {
+        Self::default()
+    }
+
+    /// Scans `dir` for `*.zip` theme archives and builds the catalog.
+    ///
+    /// Best-effort per archive: unreadable files, oversized archives,
+    /// missing/malformed manifests, and duplicate ids are skipped with
+    /// a warning rather than failing startup — one bad upload must not
+    /// take the store (or the server) down.
+    pub fn scan(dir: &Path) -> Self {
+        let mut store = Self::default();
+        let read_dir = match std::fs::read_dir(dir) {
+            Ok(read_dir) => read_dir,
+            Err(e) => {
+                info!(
+                    "theme store: directory {} not readable ({e}); serving an empty catalog",
+                    dir.display()
+                );
+                return store;
+            }
+        };
+
+        let mut zips: Vec<PathBuf> = read_dir
+            .flatten()
+            .map(|entry| entry.path())
+            .filter(|path| path.extension().is_some_and(|ext| ext == "zip"))
+            .collect();
+        // Deterministic catalog regardless of directory iteration order.
+        zips.sort();
+
+        for zip_path in zips {
+            match scan_archive(&zip_path) {
+                Ok((meta, size_bytes, sha256)) => {
+                    if store.zip_paths.contains_key(&meta.id) {
+                        warn!(
+                            "theme store: skipping {} — duplicate theme id {:?}",
+                            zip_path.display(),
+                            meta.id
+                        );
+                        continue;
+                    }
+                    let preview_path = dir.join(format!("{}.png", meta.id));
+                    let preview_url = if preview_path.is_file() {
+                        store.preview_paths.insert(meta.id.clone(), preview_path);
+                        Some(format!("/api/themes/{}/preview", meta.id))
+                    } else {
+                        None
+                    };
+                    store.entries.push(ThemeCatalogEntry {
+                        download_url: format!("/api/themes/{}/download", meta.id),
+                        preview_url,
+                        id: meta.id.clone(),
+                        name: meta.name,
+                        author: meta.author,
+                        version: meta.version,
+                        card_aspect: meta.card_aspect,
+                        size_bytes,
+                        sha256,
+                    });
+                    store.zip_paths.insert(meta.id, zip_path);
+                }
+                Err(reason) => {
+                    warn!("theme store: skipping {} — {reason}", zip_path.display());
+                }
+            }
+        }
+
+        store.entries.sort_by(|a, b| a.name.cmp(&b.name));
+        info!("theme store: serving {} theme(s)", store.entries.len());
+        store
+    }
+
+    /// Catalog entries, sorted by display name.
+    pub fn entries(&self) -> &[ThemeCatalogEntry] {
+        &self.entries
+    }
+}
+
+/// Reads one archive: enforces the size cap, hashes the bytes, and
+/// extracts + validates the manifest's `meta` block.
+fn scan_archive(zip_path: &Path) -> Result<(StoreThemeMeta, u64, String), String> {
+    let size_bytes = std::fs::metadata(zip_path)
+        .map_err(|e| format!("cannot stat: {e}"))?
+        .len();
+    if size_bytes > MAX_STORE_ARCHIVE_BYTES {
+        return Err(format!(
+            "{size_bytes} bytes exceeds the {MAX_STORE_ARCHIVE_BYTES}-byte store limit"
+        ));
+    }
+
+    let bytes = std::fs::read(zip_path).map_err(|e| format!("cannot read: {e}"))?;
+    let sha256 = hex_digest(&bytes);
+
+    let mut archive =
+        zip::ZipArchive::new(Cursor::new(bytes)).map_err(|e| format!("not a zip archive: {e}"))?;
+    let manifest_bytes = {
+        let entry = archive
+            .by_name("theme.ron")
+            .map_err(|e| format!("no theme.ron in archive: {e}"))?;
+        let mut buf = Vec::new();
+        entry
+            .take(MAX_MANIFEST_BYTES)
+            .read_to_end(&mut buf)
+            .map_err(|e| format!("cannot read theme.ron: {e}"))?;
+        buf
+    };
+
+    let parsed: ManifestMetaOnly =
+        ron::de::from_bytes(&manifest_bytes).map_err(|e| format!("malformed theme.ron: {e}"))?;
+    let meta = parsed.meta;
+    if meta.id.is_empty() {
+        return Err("theme id is empty".to_string());
+    }
+    if meta.id.contains('/') || meta.id.contains('\\') || meta.id.contains("..") {
+        return Err(format!("theme id {:?} is not filesystem-safe", meta.id));
+    }
+    if meta.card_aspect.0 == 0 || meta.card_aspect.1 == 0 {
+        return Err("card_aspect contains a zero".to_string());
+    }
+    Ok((meta, size_bytes, sha256))
+}
+
+/// Lowercase-hex SHA-256 of `bytes`.
+fn hex_digest(bytes: &[u8]) -> String {
+    let digest = Sha256::digest(bytes);
+    let mut out = String::with_capacity(digest.len() * 2);
+    for byte in digest {
+        out.push_str(&format!("{byte:02x}"));
+    }
+    out
+}
+
+/// `GET /api/themes` — the full catalog.
+pub async fn list(State(state): State<AppState>) -> Json<ThemeCatalogResponse> {
+    Json(ThemeCatalogResponse {
+        themes: state.theme_store.entries().to_vec(),
+    })
+}
+
+/// `GET /api/themes/{id}/download` — the theme archive bytes.
+pub async fn download(
+    State(state): State<AppState>,
+    UrlPath(id): UrlPath<String>,
+) -> Result<Response, AppError> {
+    let path = state
+        .theme_store
+        .zip_paths
+        .get(&id)
+        .ok_or_else(|| AppError::NotFound("theme not found".into()))?;
+    let bytes = tokio::fs::read(path)
+        .await
+        .map_err(|e| AppError::Internal(format!("theme archive unreadable: {e}")))?;
+    Ok((
+        [
+            (header::CONTENT_TYPE, "application/zip".to_string()),
+            (
+                header::CONTENT_DISPOSITION,
+                format!("attachment; filename=\"{id}.zip\""),
+            ),
+        ],
+        bytes,
+    )
+        .into_response())
+}
+
+/// `GET /api/themes/{id}/preview` — the preview PNG, when the store
+/// ships one for this theme.
+pub async fn preview(
+    State(state): State<AppState>,
+    UrlPath(id): UrlPath<String>,
+) -> Result<Response, AppError> {
+    let path = state
+        .theme_store
+        .preview_paths
+        .get(&id)
+        .ok_or_else(|| AppError::NotFound("theme preview not found".into()))?;
+    let bytes = tokio::fs::read(path)
+        .await
+        .map_err(|e| AppError::Internal(format!("theme preview unreadable: {e}")))?;
+    Ok(([(header::CONTENT_TYPE, "image/png".to_string())], bytes).into_response())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Write;
+
+    /// Minimal valid manifest for id/name pairs — the scan only reads
+    /// the `meta` block, so no face entries are needed.
+    fn manifest(id: &str, name: &str) -> String {
+        format!(
+            r#"(
+    meta: (
+        id: "{id}",
+        name: "{name}",
+        author: "Test Author",
+        version: "1.0.0",
+        card_aspect: (2, 3),
+    ),
+    faces: {{}},
+    back: "back.svg",
+)"#
+        )
+    }
+
+    fn write_zip(dir: &Path, file_name: &str, manifest: &str) -> PathBuf {
+        let path = dir.join(file_name);
+        let file = std::fs::File::create(&path).expect("create zip");
+        let mut writer = zip::ZipWriter::new(file);
+        let options = zip::write::SimpleFileOptions::default();
+        writer.start_file("theme.ron", options).expect("start");
+        writer.write_all(manifest.as_bytes()).expect("write");
+        writer.finish().expect("finish");
+        path
+    }
+
+    #[test]
+    fn scan_of_missing_dir_yields_empty_catalog() {
+        let store = ThemeStore::scan(Path::new("/nonexistent/theme/store"));
+        assert!(store.entries().is_empty());
+    }
+
+    #[test]
+    fn scan_builds_sorted_catalog_with_hashes() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        let zebra = write_zip(dir.path(), "b.zip", &manifest("zebra", "Zebra"));
+        write_zip(dir.path(), "a.zip", &manifest("aurora", "Aurora"));
+
+        let store = ThemeStore::scan(dir.path());
+        let entries = store.entries();
+        assert_eq!(entries.len(), 2);
+        // Sorted by display name, not filename.
+        assert_eq!(entries[0].id, "aurora");
+        assert_eq!(entries[1].id, "zebra");
+        assert_eq!(entries[1].download_url, "/api/themes/zebra/download");
+        assert_eq!(entries[1].preview_url, None);
+
+        let zebra_bytes = std::fs::read(&zebra).expect("read zip");
+        assert_eq!(entries[1].sha256, hex_digest(&zebra_bytes));
+        assert_eq!(entries[1].size_bytes, zebra_bytes.len() as u64);
+    }
+
+    #[test]
+    fn scan_picks_up_preview_png_keyed_by_theme_id() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        write_zip(dir.path(), "neon.zip", &manifest("neon", "Neon"));
+        std::fs::write(dir.path().join("neon.png"), b"png-bytes").expect("write png");
+
+        let store = ThemeStore::scan(dir.path());
+        assert_eq!(
+            store.entries()[0].preview_url.as_deref(),
+            Some("/api/themes/neon/preview")
+        );
+        assert!(store.preview_paths.contains_key("neon"));
+    }
+
+    #[test]
+    fn scan_skips_duplicate_ids_and_keeps_first() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        write_zip(dir.path(), "1_first.zip", &manifest("dupe", "First"));
+        write_zip(dir.path(), "2_second.zip", &manifest("dupe", "Second"));
+
+        let store = ThemeStore::scan(dir.path());
+        assert_eq!(store.entries().len(), 1);
+        assert_eq!(store.entries()[0].name, "First");
+    }
+
+    #[test]
+    fn scan_skips_malformed_and_unsafe_manifests() {
+        let dir = tempfile::tempdir().expect("tempdir");
+        // Not a zip at all.
+        std::fs::write(dir.path().join("junk.zip"), b"not a zip").expect("write");
+        // Path-separator id must be rejected — it would become a URL
+        // path segment and a client install directory name.
+        write_zip(dir.path(), "evil.zip", &manifest("../evil", "Evil"));
+        // Valid one to prove the scan carries on past failures.
+        write_zip(dir.path(), "ok.zip", &manifest("ok", "Ok"));
+
+        let store = ThemeStore::scan(dir.path());
+        assert_eq!(store.entries().len(), 1);
+        assert_eq!(store.entries()[0].id, "ok");
+    }
+}

solitaire_server/tests/server_tests.rs

@@ -1614,6 +1614,7 @@ async fn auth_rate_limit_returns_429_on_11th_request() {
     let state = solitaire_server::AppState {
         pool: test_pool().await,
         jwt_secret: TEST_SECRET.to_string(),
+        theme_store: std::sync::Arc::new(solitaire_server::theme_store::ThemeStore::empty()),
     };
     let app = solitaire_server::build_router(state);
 
@@ -1675,6 +1676,7 @@ async fn sync_push_rate_limit_returns_429_on_11th_request() {
     let state = solitaire_server::AppState {
         pool: test_pool().await,
         jwt_secret: TEST_SECRET.to_string(),
+        theme_store: std::sync::Arc::new(solitaire_server::theme_store::ThemeStore::empty()),
     };
     let app = solitaire_server::build_router(state);
 
@@ -1879,3 +1881,125 @@ async fn replay_upload_malformed_body_returns_400() {
     let resp = post_authed(app, "/api/replays", &token, bad).await;
     assert_eq!(resp.status(), StatusCode::BAD_REQUEST);
 }
+
+// ---------------------------------------------------------------------------
+// Theme store
+// ---------------------------------------------------------------------------
+
+/// Writes a minimal theme zip (manifest only — the catalog scan reads
+/// just the `meta` block) into `dir` and returns its path.
+fn write_store_zip(
+    dir: &std::path::Path,
+    file_name: &str,
+    id: &str,
+    name: &str,
+) -> std::path::PathBuf {
+    use std::io::Write as _;
+    let manifest = format!(
+        r#"(
+    meta: (
+        id: "{id}",
+        name: "{name}",
+        author: "Test Author",
+        version: "1.0.0",
+        card_aspect: (2, 3),
+    ),
+    faces: {{}},
+    back: "back.svg",
+)"#
+    );
+    let path = dir.join(file_name);
+    let file = std::fs::File::create(&path).expect("create zip");
+    let mut writer = zip::ZipWriter::new(file);
+    let options = zip::write::SimpleFileOptions::default();
+    writer.start_file("theme.ron", options).expect("start_file");
+    writer
+        .write_all(manifest.as_bytes())
+        .expect("write manifest");
+    writer.finish().expect("finish zip");
+    path
+}
+
+/// `GET /api/themes` returns the scanned catalog as JSON, no auth needed.
+#[tokio::test]
+async fn theme_catalog_lists_scanned_themes() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let zip_path = write_store_zip(dir.path(), "neon.zip", "neon", "Neon");
+    let store = solitaire_server::theme_store::ThemeStore::scan(dir.path());
+    let app = solitaire_server::build_test_router_with_theme_store(test_pool().await, store);
+
+    let req = Request::builder()
+        .uri("/api/themes")
+        .body(Body::empty())
+        .expect("build request");
+    let resp = app.oneshot(req).await.expect("oneshot");
+    assert_eq!(resp.status(), StatusCode::OK);
+
+    let body = axum::body::to_bytes(resp.into_body(), usize::MAX)
+        .await
+        .expect("read body");
+    let catalog: solitaire_sync::ThemeCatalogResponse =
+        serde_json::from_slice(&body).expect("parse catalog");
+    assert_eq!(catalog.themes.len(), 1);
+    let entry = &catalog.themes[0];
+    assert_eq!(entry.id, "neon");
+    assert_eq!(entry.name, "Neon");
+    assert_eq!(entry.download_url, "/api/themes/neon/download");
+    assert_eq!(entry.preview_url, None);
+    let zip_bytes = std::fs::read(&zip_path).expect("read zip");
+    assert_eq!(entry.size_bytes, zip_bytes.len() as u64);
+}
+
+/// The download endpoint streams back exactly the bytes on disk, so a
+/// client hashing the response gets the catalog's sha256.
+#[tokio::test]
+async fn theme_download_returns_archive_bytes() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let zip_path = write_store_zip(dir.path(), "neon.zip", "neon", "Neon");
+    let store = solitaire_server::theme_store::ThemeStore::scan(dir.path());
+    let app = solitaire_server::build_test_router_with_theme_store(test_pool().await, store);
+
+    let req = Request::builder()
+        .uri("/api/themes/neon/download")
+        .body(Body::empty())
+        .expect("build request");
+    let resp = app.oneshot(req).await.expect("oneshot");
+    assert_eq!(resp.status(), StatusCode::OK);
+    assert_eq!(
+        resp.headers()
+            .get("content-type")
+            .and_then(|v| v.to_str().ok()),
+        Some("application/zip")
+    );
+    let body = axum::body::to_bytes(resp.into_body(), usize::MAX)
+        .await
+        .expect("read body");
+    assert_eq!(&body[..], &std::fs::read(&zip_path).expect("read zip")[..]);
+}
+
+/// Unknown ids 404 on both file endpoints; a theme without preview art
+/// 404s on `/preview` while still serving its download.
+#[tokio::test]
+async fn theme_unknown_id_and_missing_preview_return_404() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    write_store_zip(dir.path(), "neon.zip", "neon", "Neon");
+    let store = solitaire_server::theme_store::ThemeStore::scan(dir.path());
+    let app = solitaire_server::build_test_router_with_theme_store(test_pool().await, store);
+
+    for uri in [
+        "/api/themes/nope/download",
+        "/api/themes/nope/preview",
+        "/api/themes/neon/preview",
+    ] {
+        let req = Request::builder()
+            .uri(uri)
+            .body(Body::empty())
+            .expect("build request");
+        let resp = app.clone().oneshot(req).await.expect("oneshot");
+        assert_eq!(
+            resp.status(),
+            StatusCode::NOT_FOUND,
+            "expected 404 for {uri}"
+        );
+    }
+}

solitaire_sync/Cargo.toml

@@ -10,5 +10,8 @@ uuid       = { workspace = true }
 chrono     = { workspace = true }
 thiserror  = { workspace = true }
 
+[dev-dependencies]
+serde_json = { workspace = true }
+
 [lints]
 workspace = true

solitaire_sync/src/lib.rs

@@ -10,11 +10,13 @@ pub mod achievements;
 pub mod merge;
 pub mod progress;
 pub mod stats;
+pub mod theme_store;
 
 pub use achievements::AchievementRecord;
 pub use merge::{merge, merge_at};
 pub use progress::{PlayerProgress, level_for_xp};
 pub use stats::StatsSnapshot;
+pub use theme_store::{ThemeCatalogEntry, ThemeCatalogResponse};
 
 use chrono::{DateTime, Utc};
 use serde::{Deserialize, Serialize};

solitaire_sync/src/theme_store.rs

@@ -0,0 +1,102 @@
+//! Theme-store catalog wire types.
+//!
+//! Shared between `solitaire_server` (which builds the catalog by
+//! scanning its theme-store directory) and `solitaire_data` (which
+//! fetches it and downloads theme archives). These are **additive**
+//! API types: they do not participate in [`crate::SyncPayload`] and
+//! changing them cannot break the sync wire format.
+//!
+//! Store entries describe downloadable card-art theme archives — the
+//! same `.zip` format consumed by the engine's theme importer (a
+//! `theme.ron` manifest plus 53 SVGs).
+
+use serde::{Deserialize, Serialize};
+
+/// One downloadable theme in the server's catalog.
+///
+/// URLs are server-relative (e.g. `/api/themes/neon/download`) so a
+/// client can join them onto whichever base URL it is configured with.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct ThemeCatalogEntry {
+    /// Unique theme id — `meta.id` from the archive's `theme.ron`.
+    /// Also the id the theme installs under on the client.
+    pub id: String,
+    /// Display name shown in the store UI.
+    pub name: String,
+    /// Author attribution (free-form text).
+    pub author: String,
+    /// Version string (conventionally semver).
+    pub version: String,
+    /// Card aspect ratio as `(numerator, denominator)`.
+    pub card_aspect: (u32, u32),
+    /// Size of the `.zip` archive in bytes. Clients use this for
+    /// display and as a pre-download sanity bound.
+    pub size_bytes: u64,
+    /// Lowercase-hex SHA-256 of the `.zip` archive. Clients MUST
+    /// verify the downloaded bytes against this digest before handing
+    /// the archive to the theme importer.
+    pub sha256: String,
+    /// Server-relative URL of the theme archive.
+    pub download_url: String,
+    /// Server-relative URL of a PNG preview, when the store ships one.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub preview_url: Option<String>,
+}
+
+/// Response body of the catalog listing endpoint (`GET /api/themes`).
+///
+/// Wrapped in a struct (rather than a bare `Vec`) so future additive
+/// fields — pagination, store revision, purchase metadata — don't
+/// break existing clients.
+#[derive(Debug, Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct ThemeCatalogResponse {
+    /// Every theme currently offered by the server, sorted by name.
+    pub themes: Vec<ThemeCatalogEntry>,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn entry() -> ThemeCatalogEntry {
+        ThemeCatalogEntry {
+            id: "neon".into(),
+            name: "Neon".into(),
+            author: "Rusty Solitaire".into(),
+            version: "1.0.0".into(),
+            card_aspect: (2, 3),
+            size_bytes: 123_456,
+            sha256: "ab".repeat(32),
+            download_url: "/api/themes/neon/download".into(),
+            preview_url: Some("/api/themes/neon/preview".into()),
+        }
+    }
+
+    #[test]
+    fn catalog_round_trips_through_json() {
+        let response = ThemeCatalogResponse {
+            themes: vec![entry()],
+        };
+        let json = serde_json::to_string(&response).expect("serialize");
+        let back: ThemeCatalogResponse = serde_json::from_str(&json).expect("deserialize");
+        assert_eq!(back, response);
+    }
+
+    #[test]
+    fn missing_preview_url_deserializes_to_none() {
+        // Older servers (or themes without preview art) omit the key
+        // entirely; the field must default rather than error.
+        let json = r#"{
+            "id": "neon",
+            "name": "Neon",
+            "author": "Rusty Solitaire",
+            "version": "1.0.0",
+            "card_aspect": [2, 3],
+            "size_bytes": 1,
+            "sha256": "00",
+            "download_url": "/api/themes/neon/download"
+        }"#;
+        let entry: ThemeCatalogEntry = serde_json::from_str(json).expect("deserialize");
+        assert_eq!(entry.preview_url, None);
+    }
+}