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>

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());
+}