fix(settings): harden persisted consumer state

- validate complete settings snapshots before replacing durable state
- sanitize malformed proxy, user-agent, sidebar, speed, and path values at native and renderer hydration boundaries
- add hostile persisted-settings regression coverage

src-tauri/src/lib.rs

@@ -10912,8 +10912,12 @@ fn db_save_settings(
         crate::db::preserve_legacy_pairing_token(existing.as_deref(), &sanitized)?
     };
     let merged = crate::settings::canonicalize_torrent_network_settings(&merged)?;
+    let decoded = crate::settings::decode_stored_settings(&serde_json::Value::String(merged.clone()))?;
+    // Validate the complete settings document before replacing the durable
+    // copy. A malformed renderer snapshot must not poison restart hydration or
+    // leave the previous valid settings unrecoverable after this command
+    // reports an error.
     crate::db::save_settings(&connection, &merged)?;
-    let decoded = crate::settings::decode_stored_settings(&serde_json::Value::String(merged))?;
     let prevent_system_sleep = decoded.prevents_sleep_while_downloading;
     let prevent_display_sleep = decoded.prevents_display_sleep_while_downloading;
     if let Ok(mut cached) = app_state.scheduler_settings.write() {

src-tauri/src/settings.rs

@@ -229,6 +229,19 @@ pub fn canonicalize_torrent_network_settings(stored: &str) -> Result<String, Str
             "IPv6 Torrent bind address requires IPv6 transport to remain enabled".to_string(),
         );
     }
+    // Renderer snapshots are also a persistence boundary. Remove malformed
+    // scalar values before the document is written so a recoverable default
+    // is not hidden behind a hostile value that will fail on the next save or
+    // restart. Keep the network canonicalization above first so invalid text
+    // fields retain their established empty-string representation.
+    let state_value = if document.get("state").is_some() {
+        document
+            .get_mut("state")
+            .ok_or_else(|| "persisted settings state is missing".to_string())?
+    } else {
+        &mut document
+    };
+    sanitize_persisted_setting_values(state_value);
     serde_json::to_string(&document)
         .map_err(|error| format!("failed to encode canonical settings: {error}"))
 }
@@ -441,6 +454,11 @@ fn sanitize_persisted_setting_values(state: &mut Value) {
     sanitize_integer_setting(state, "maxConcurrentDownloads", |value| value.as_u64().is_some());
     sanitize_integer_setting(state, "perServerConnections", |value| value.as_i64().is_some());
     sanitize_integer_setting(state, "maxAutomaticRetries", |value| value.as_i64().is_some());
+    sanitize_integer_setting(state, "proxyPort", |value| {
+        value
+            .as_u64()
+            .is_some_and(|value| (1..=u16::MAX as u64).contains(&value))
+    });
     sanitize_integer_setting(state, "torrentMaxOpenFiles", |value| {
         value
             .as_u64()
@@ -465,6 +483,7 @@ fn sanitize_persisted_setting_values(state: &mut Value) {
         })
     });
     for key in [
+        "isSidebarVisible",
         "torrentEnableDht",
         "torrentEnableDht6",
         "torrentEnablePex",
@@ -474,6 +493,9 @@ fn sanitize_persisted_setting_values(state: &mut Value) {
     ] {
         sanitize_boolean_setting(state, key);
     }
+    for key in ["proxyHost", "customUserAgent"] {
+        sanitize_string_setting(state, key);
+    }
     sanitize_torrent_network_string(state, "torrentListenPort", |value| {
         crate::queue::normalize_torrent_port_spec(Some(value), "TCP listen ports").is_ok()
     });
@@ -598,6 +620,12 @@ fn sanitize_boolean_setting(state: &mut serde_json::Map<String, Value>, key: &st
     }
 }
 
+fn sanitize_string_setting(state: &mut serde_json::Map<String, Value>, key: &str) {
+    if state.get(key).is_some_and(|value| !value.is_string()) {
+        state.remove(key);
+    }
+}
+
 fn sanitize_torrent_network_string(
     state: &mut serde_json::Map<String, Value>,
     key: &str,
@@ -1347,6 +1375,27 @@ mod tests {
         assert_eq!(settings.site_logins[0].id, "valid");
     }
 
+    #[test]
+    fn malformed_proxy_and_user_agent_values_fall_back_to_safe_defaults() {
+        let stored = json!({
+            "state": {
+                "proxyMode": "custom",
+                "proxyHost": 123,
+                "proxyPort": 70000,
+                "customUserAgent": ["not-a-string"],
+                "isSidebarVisible": "yes"
+            }
+        });
+
+        let settings = decode_stored_settings(&Value::String(stored.to_string())).unwrap();
+
+        assert!(matches!(settings.proxy_mode, crate::ipc::ProxyMode::Custom));
+        assert!(settings.proxy_host.is_empty());
+        assert_eq!(settings.proxy_port, 8080);
+        assert!(settings.custom_user_agent.is_empty());
+        assert!(settings.is_sidebar_visible);
+    }
+
     #[test]
     fn preserves_valid_torrent_network_settings() {
         let stored = json!({
@@ -1386,7 +1435,10 @@ mod tests {
                 "torrentPeerAgent": " Firelink/1.3.1 ",
                 "torrentDhtMessageTimeout": 601,
                 "torrentMaxConcurrentSeeds": 65,
-                "torrentSeparateSeedSlots": "yes"
+                "torrentSeparateSeedSlots": "yes",
+                "proxyPort": 70000,
+                "proxyHost": 123,
+                "customUserAgent": ["not-a-string"]
             },
             "version": 6
         });
@@ -1406,6 +1458,9 @@ mod tests {
             crate::queue::DEFAULT_TORRENT_MAX_CONCURRENT_SEEDS
         );
         assert_eq!(canonical["state"]["torrentSeparateSeedSlots"], false);
+        assert!(canonical["state"].get("proxyPort").is_none());
+        assert!(canonical["state"].get("proxyHost").is_none());
+        assert!(canonical["state"].get("customUserAgent").is_none());
     }
 
     #[test]

src/store/useSettingsStore.test.ts

@@ -65,6 +65,32 @@ describe('durable main-window and sidebar preferences', () => {
       .toEqual({ width: 1440, height: 900 });
   });
 
+  it('rejects malformed consumer values during hydration', () => {
+    const merge = useSettingsStore.persist.getOptions().merge;
+    expect(merge).toBeTypeOf('function');
+    const current = useSettingsStore.getState();
+
+    expect(merge?.({
+      proxyMode: 'custom',
+      proxyHost: 123,
+      proxyPort: 70000,
+      customUserAgent: ['not-a-string'],
+      isSidebarVisible: 'yes',
+      lastCustomSpeedLimitKiB: Number.POSITIVE_INFINITY,
+      approvedDownloadRoots: ['/safe', 42],
+      speedLimitPresetValues: [1, '5', Number.NaN]
+    }, current)).toMatchObject({
+      proxyMode: 'custom',
+      proxyHost: current.proxyHost,
+      proxyPort: current.proxyPort,
+      customUserAgent: current.customUserAgent,
+      isSidebarVisible: current.isSidebarVisible,
+      lastCustomSpeedLimitKiB: current.lastCustomSpeedLimitKiB,
+      approvedDownloadRoots: ['/safe'],
+      speedLimitPresetValues: [1]
+    });
+  });
+
   it('uses the legacy localStorage value only when durable state is absent', () => {
     const originalWindow = globalThis.window;
     Object.defineProperty(globalThis, 'window', {

src/store/useSettingsStore.ts

@@ -162,6 +162,21 @@ const sanitizeSiteLogins = (value: unknown): SiteLogin[] => {
 const persistedBoolean = (value: unknown, fallback: boolean) =>
   typeof value === 'boolean' ? value : fallback;
 
+const persistedString = (value: unknown, fallback: string): string =>
+  typeof value === 'string' ? value : fallback;
+
+const persistedFiniteInteger = (
+  value: unknown,
+  minimum: number,
+  maximum: number,
+  fallback: number
+): number => {
+  if (typeof value !== 'number' || !Number.isFinite(value) || !Number.isInteger(value)) {
+    return fallback;
+  }
+  return value >= minimum && value <= maximum ? value : fallback;
+};
+
 const tauriStorage: StateStorage = {
   getItem: async (name: string): Promise<string | null> => {
     if (name === 'firelink-settings') {
@@ -928,6 +943,10 @@ export const useSettingsStore = create<SettingsState>()(
             persisted.isFoldersCollapsed,
             foldersCollapsedFallback
           ),
+          isSidebarVisible: persistedBoolean(
+            persisted.isSidebarVisible,
+            currentState.isSidebarVisible
+          ),
           mainWindowSize: normalizeMainWindowSize(persisted.mainWindowSize)
             ?? currentState.mainWindowSize,
           appFontSize: isAllowedSetting(APP_FONT_SIZE_VALUES, persisted.appFontSize)
@@ -988,15 +1007,16 @@ export const useSettingsStore = create<SettingsState>()(
           torrentBindAddress: typeof persisted.torrentBindAddress === 'string'
             ? persisted.torrentBindAddress
             : currentState.torrentBindAddress,
-          aria2DiskCache: typeof persisted.aria2DiskCache === 'string'
+          aria2DiskCache: persistedString(persisted.aria2DiskCache, currentState.aria2DiskCache),
-            ? persisted.aria2DiskCache
+          customUserAgent: persistedString(persisted.customUserAgent, currentState.customUserAgent),
-            : currentState.aria2DiskCache,
           sidebarPosition: isAllowedSetting(SIDEBAR_POSITION_VALUES, persisted.sidebarPosition)
             ? persisted.sidebarPosition
             : currentState.sidebarPosition,
           proxyMode: isAllowedSetting(PROXY_MODE_VALUES, persisted.proxyMode)
             ? persisted.proxyMode
             : currentState.proxyMode,
+          proxyHost: persistedString(persisted.proxyHost, currentState.proxyHost),
+          proxyPort: persistedFiniteInteger(persisted.proxyPort, 1, 65_535, currentState.proxyPort),
           mediaCookieSource: isAllowedSetting(MEDIA_COOKIE_SOURCE_VALUES, persisted.mediaCookieSource)
             ? persisted.mediaCookieSource
             : 'none',
@@ -1078,15 +1098,23 @@ export const useSettingsStore = create<SettingsState>()(
             currentState.adaptiveMirrorSelection
           ),
           speedLimitPresetValues: Array.isArray(persisted.speedLimitPresetValues)
-            ? persisted.speedLimitPresetValues
+            ? persisted.speedLimitPresetValues.filter(
+              (value): value is number => typeof value === 'number' && Number.isFinite(value)
+            )
             : currentState.speedLimitPresetValues,
+          lastCustomSpeedLimitKiB: persistedFiniteInteger(
+            persisted.lastCustomSpeedLimitKiB,
+            1,
+            10_485_760,
+            currentState.lastCustomSpeedLimitKiB
+          ),
           lastCustomSpeedLimitUnit: persisted.lastCustomSpeedLimitUnit === 'KB/s'
             || persisted.lastCustomSpeedLimitUnit === 'MB/s'
             ? persisted.lastCustomSpeedLimitUnit
             : currentState.lastCustomSpeedLimitUnit,
           logsEnabled: persisted.logsEnabled === true,
           approvedDownloadRoots: Array.isArray(persisted.approvedDownloadRoots)
-            ? persisted.approvedDownloadRoots
+            ? persisted.approvedDownloadRoots.filter((root): root is string => typeof root === 'string')
             : currentState.approvedDownloadRoots,
         scheduler: {
           ...currentState.scheduler,