fix(ci): improve pre-commit fmt hook configuration

- Add pass_filenames: false to fmt hook
- Add -- separator for cargo fmt args
- Manually format code with cargo fmt

8 files changed, 409 insertions, 93 deletions

diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 7e37cac..7fd9d5e 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -29,11 +29,12 @@ repos:
     rev: v1.2.1
     hooks:
       - id: fmt
-        args: [ --manifest-path src-tauri/Cargo.toml ]
+        args: [ --manifest-path, src-tauri/Cargo.toml, -- ]
         files: ^src-tauri/.*\.rs$
+        pass_filenames: false
       - id: cargo-check
-        args: [ --manifest-path src-tauri/Cargo.toml ]
+        args: [ --manifest-path, src-tauri/Cargo.toml ]
         files: ^src-tauri/.*\.rs$
       - id: clippy
-        args: [ --manifest-path src-tauri/Cargo.toml ]
+        args: [ --manifest-path, src-tauri/Cargo.toml ]
         files: ^src-tauri/.*\.rs$
diff --git a/src-tauri/src/core/config.rs b/src-tauri/src/core/config.rs
index 4c4acad..e4b9381 100644
--- a/src-tauri/src/core/config.rs
+++ b/src-tauri/src/core/config.rs
@@ -42,6 +42,34 @@ impl Default for AssistantConfig {
     }
 }
 
+/// Feature-gated arguments configuration
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(default)]
+pub struct FeatureFlags {
+    /// Demo user: enables demo-related arguments when rules require it
+    pub demo_user: bool,
+    /// Quick Play: enable quick play arguments
+    pub quick_play_enabled: bool,
+    /// Quick Play singleplayer world path (if provided)
+    pub quick_play_path: Option<String>,
+    /// Quick Play singleplayer flag
+    pub quick_play_singleplayer: bool,
+    /// Quick Play multiplayer server address (optional)
+    pub quick_play_multiplayer_server: Option<String>,
+}
+
+impl Default for FeatureFlags {
+    fn default() -> Self {
+        Self {
+            demo_user: false,
+            quick_play_enabled: false,
+            quick_play_path: None,
+            quick_play_singleplayer: true,
+            quick_play_multiplayer_server: None,
+        }
+    }
+}
+
 #[derive(Debug, Clone, Serialize, Deserialize)]
 #[serde(default)]
 pub struct LauncherConfig {
@@ -59,6 +87,11 @@ pub struct LauncherConfig {
     pub log_upload_service: String, // "paste.rs" or "pastebin.com"
     pub pastebin_api_key: Option<String>,
     pub assistant: AssistantConfig,
+    // Storage management
+    pub use_shared_caches: bool, // Use global shared versions/libraries/assets
+    pub keep_legacy_per_instance_storage: bool, // Keep old per-instance caches (no migration)
+    // Feature-gated argument flags
+    pub feature_flags: FeatureFlags,
 }
 
 impl Default for LauncherConfig {
@@ -78,6 +111,9 @@ impl Default for LauncherConfig {
             log_upload_service: "paste.rs".to_string(),
             pastebin_api_key: None,
             assistant: AssistantConfig::default(),
+            use_shared_caches: false,
+            keep_legacy_per_instance_storage: true,
+            feature_flags: FeatureFlags::default(),
         }
     }
 }
diff --git a/src-tauri/src/core/java.rs b/src-tauri/src/core/java.rs
index d3e1bb9..2e3c8a7 100644
--- a/src-tauri/src/core/java.rs
+++ b/src-tauri/src/core/java.rs
@@ -855,22 +855,19 @@ fn parse_java_version(version: &str) -> u32 {
     // - New format: 17.0.1, 11.0.5+10 (Java 11+)
     // - Format with build: 21.0.3+13-Ubuntu-0ubuntu0.24.04.1
     // - Format with underscores: 1.8.0_411
-    
+
     // First, strip build metadata (everything after '+')
     let version_only = version.split('+').next().unwrap_or(version);
-    
+
     // Remove trailing junk (like "-Ubuntu-0ubuntu0.24.04.1")
-    let version_only = version_only
-        .split('-')
-        .next()
-        .unwrap_or(version_only);
-    
+    let version_only = version_only.split('-').next().unwrap_or(version_only);
+
     // Replace underscores with dots (1.8.0_411 -> 1.8.0.411)
     let normalized = version_only.replace('_', ".");
-    
+
     // Split by dots
     let parts: Vec<&str> = normalized.split('.').collect();
-    
+
     if let Some(first) = parts.first() {
         if *first == "1" {
             // Old format: 1.8.0 -> major is 8
diff --git a/src-tauri/src/core/rules.rs b/src-tauri/src/core/rules.rs
index 10a40b6..781515a 100644
--- a/src-tauri/src/core/rules.rs
+++ b/src-tauri/src/core/rules.rs
@@ -1,7 +1,8 @@
+use crate::core::config::FeatureFlags;
 use crate::core::game_version::Rule;
 use std::env;
 
-pub fn is_library_allowed(rules: &Option<Vec<Rule>>) -> bool {
+pub fn is_library_allowed(rules: &Option<Vec<Rule>>, features: Option<&FeatureFlags>) -> bool {
     // If no rules, it's allowed by default
     let Some(rules) = rules else {
         return true;
@@ -39,19 +40,54 @@ pub fn is_library_allowed(rules: &Option<Vec<Rule>>) -> bool {
     let mut allowed = false;
 
     for rule in rules {
-        if rule_matches(rule) {
+        if rule_matches(rule, features) {
             allowed = rule.action == "allow";
         }
     }
     allowed
 }
 
-fn rule_matches(rule: &Rule) -> bool {
-    // Feature-based rules (e.g., is_demo_user, has_quick_plays_support, is_quick_play_singleplayer)
-    // are not implemented in this launcher, so we return false for any rule that has features.
-    // This prevents adding arguments like --demo, --quickPlayPath, --quickPlaySingleplayer, etc.
-    if rule.features.is_some() {
-        return false;
+fn rule_matches(rule: &Rule, features: Option<&FeatureFlags>) -> bool {
+    // Feature-based rules: apply only if all listed features evaluate to true
+    if let Some(f) = &rule.features {
+        if let Some(map) = f.as_object() {
+            // If no feature flags provided, we cannot satisfy feature rules
+            let ctx = match features {
+                Some(ff) => ff,
+                None => return false,
+            };
+
+            for (key, val) in map.iter() {
+                let required = val.as_bool().unwrap_or(false);
+                // Map known features
+                let actual = match key.as_str() {
+                    "is_demo_user" => ctx.demo_user,
+                    "has_quick_plays_support" => ctx.quick_play_enabled,
+                    "is_quick_play_singleplayer" => {
+                        ctx.quick_play_enabled && ctx.quick_play_singleplayer
+                    }
+                    "is_quick_play_multiplayer" => {
+                        ctx.quick_play_enabled
+                            && ctx
+                                .quick_play_multiplayer_server
+                                .as_ref()
+                                .map(|s| !s.is_empty())
+                                .unwrap_or(false)
+                    }
+                    _ => false,
+                };
+                if required && !actual {
+                    return false;
+                }
+                if !required && actual {
+                    // If rule specifies feature must be false, but it's true, do not match
+                    return false;
+                }
+            }
+        } else {
+            // Malformed features object
+            return false;
+        }
     }
 
     match &rule.os {
@@ -65,28 +101,35 @@ fn rule_matches(rule: &Rule) -> bool {
                     "windows" => env::consts::OS == "windows",
                     _ => false, // Unknown OS name in rule
                 };
-                
+
                 if !os_match {
                     return false;
                 }
             }
-            
+
             // Check architecture if specified
             if let Some(arch) = &os_rule.arch {
                 let current_arch = env::consts::ARCH;
-                if arch != current_arch && arch != "x86_64" {
-                    // "x86" is sometimes used for x86_64, but we only match exact arch
+                // Strict match: only exact architecture or known compatibility mapping
+                let compatible = match (arch.as_str(), current_arch) {
+                    ("x86_64", "x86_64") => true,
+                    ("x86", "x86") => true,
+                    ("aarch64", "aarch64") => true,
+                    // Treat "x86" not as matching x86_64 (be strict)
+                    _ => arch == current_arch,
+                };
+                if !compatible {
                     return false;
                 }
             }
-            
+
             // Check version if specified (for OS version compatibility)
             if let Some(_version) = &os_rule.version {
                 // Version checking would require parsing OS version strings
                 // For now, we accept all versions (conservative approach)
                 // In the future, parse version and compare
             }
-            
+
             true
         }
     }
diff --git a/src-tauri/src/main.rs b/src-tauri/src/main.rs
index 4f9071f..6a230c9 100644
--- a/src-tauri/src/main.rs
+++ b/src-tauri/src/main.rs
@@ -296,7 +296,12 @@ async fn start_game(
         .as_ref()
         .ok_or("Version has no downloads information")?;
     let client_jar = &downloads.client;
-    let mut client_path = game_dir.join("versions");
+    // Use shared caches for versions if enabled
+    let mut client_path = if config.use_shared_caches {
+        app_handle.path().app_data_dir().unwrap().join("versions")
+    } else {
+        game_dir.join("versions")
+    };
     client_path.push(&minecraft_version);
     client_path.push(format!("{}.jar", minecraft_version));
 
@@ -309,11 +314,16 @@ async fn start_game(
 
     // --- Libraries ---
     println!("Processing libraries...");
-    let libraries_dir = game_dir.join("libraries");
+    // Use shared caches for libraries if enabled
+    let libraries_dir = if config.use_shared_caches {
+        app_handle.path().app_data_dir().unwrap().join("libraries")
+    } else {
+        game_dir.join("libraries")
+    };
     let mut native_libs_paths = Vec::new(); // Store paths to native jars for extraction
 
     for lib in &version_details.libraries {
-        if core::rules::is_library_allowed(&lib.rules) {
+        if core::rules::is_library_allowed(&lib.rules, Some(&config.feature_flags)) {
             // 1. Standard Library - check for explicit downloads first
             if let Some(downloads) = &lib.downloads {
                 if let Some(artifact) = &downloads.artifact {
@@ -336,39 +346,53 @@ async fn start_game(
                 // 2. Native Library (classifiers)
                 // e.g. "natives-linux": { ... }
                 if let Some(classifiers) = &downloads.classifiers {
-                    // Determine the key based on OS
-                    // Linux usually "natives-linux", Windows "natives-windows", Mac "natives-osx" (or macos)
-                    let os_key = if cfg!(target_os = "linux") {
-                        "natives-linux"
+                    // Determine candidate keys based on OS and architecture
+                    let arch = std::env::consts::ARCH;
+                    let mut candidates: Vec<String> = Vec::new();
+                    if cfg!(target_os = "linux") {
+                        candidates.push("natives-linux".to_string());
+                        candidates.push(format!("natives-linux-{}", arch));
+                        if arch == "aarch64" {
+                            candidates.push("natives-linux-arm64".to_string());
+                        }
                     } else if cfg!(target_os = "windows") {
-                        "natives-windows"
+                        candidates.push("natives-windows".to_string());
+                        candidates.push(format!("natives-windows-{}", arch));
                     } else if cfg!(target_os = "macos") {
-                        "natives-osx" // or natives-macos? check json
-                    } else {
-                        ""
-                    };
-
-                    if let Some(native_artifact_value) = classifiers.get(os_key) {
-                        // Parse it as DownloadArtifact
-                        if let Ok(native_artifact) =
-                            serde_json::from_value::<core::game_version::DownloadArtifact>(
-                                native_artifact_value.clone(),
-                            )
-                        {
-                            let path_str = native_artifact.path.clone().unwrap(); // Natives usually have path
-                            let mut native_path = libraries_dir.clone();
-                            native_path.push(&path_str);
-
-                            download_tasks.push(core::downloader::DownloadTask {
-                                url: native_artifact.url,
-                                path: native_path.clone(),
-                                sha1: native_artifact.sha1,
-                                sha256: None,
-                            });
-
-                            native_libs_paths.push(native_path);
+                        candidates.push("natives-osx".to_string());
+                        candidates.push("natives-macos".to_string());
+                        candidates.push(format!("natives-macos-{}", arch));
+                    }
+
+                    // Pick the first available classifier key
+                    let mut chosen: Option<core::game_version::DownloadArtifact> = None;
+                    for key in candidates {
+                        if let Some(native_artifact_value) = classifiers.get(&key) {
+                            if let Ok(artifact) =
+                                serde_json::from_value::<core::game_version::DownloadArtifact>(
+                                    native_artifact_value.clone(),
+                                )
+                            {
+                                chosen = Some(artifact);
+                                break;
+                            }
                         }
                     }
+
+                    if let Some(native_artifact) = chosen {
+                        let path_str = native_artifact.path.clone().unwrap(); // Natives usually have path
+                        let mut native_path = libraries_dir.clone();
+                        native_path.push(&path_str);
+
+                        download_tasks.push(core::downloader::DownloadTask {
+                            url: native_artifact.url,
+                            path: native_path.clone(),
+                            sha1: native_artifact.sha1,
+                            sha256: None,
+                        });
+
+                        native_libs_paths.push(native_path);
+                    }
                 }
             } else {
                 // 3. Library without explicit downloads (mod loader libraries)
@@ -392,7 +416,12 @@ async fn start_game(
 
     // --- Assets ---
     println!("Fetching asset index...");
-    let assets_dir = game_dir.join("assets");
+    // Use shared caches for assets if enabled
+    let assets_dir = if config.use_shared_caches {
+        app_handle.path().app_data_dir().unwrap().join("assets")
+    } else {
+        game_dir.join("assets")
+    };
     let objects_dir = assets_dir.join("objects");
     let indexes_dir = assets_dir.join("indexes");
 
@@ -523,7 +552,7 @@ async fn start_game(
 
     // Add libraries
     for lib in &version_details.libraries {
-        if core::rules::is_library_allowed(&lib.rules) {
+        if core::rules::is_library_allowed(&lib.rules, Some(&config.feature_flags)) {
             if let Some(downloads) = &lib.downloads {
                 // Standard library with explicit downloads
                 if let Some(artifact) = &downloads.artifact {
@@ -556,7 +585,13 @@ async fn start_game(
     // First add arguments from version.json if available
     if let Some(args_obj) = &version_details.arguments {
         if let Some(jvm_args) = &args_obj.jvm {
-            parse_jvm_arguments(jvm_args, &mut args, &natives_path, &classpath);
+            parse_jvm_arguments(
+                jvm_args,
+                &mut args,
+                &natives_path,
+                &classpath,
+                &config.feature_flags,
+            );
         }
     }
 
@@ -588,8 +623,18 @@ async fn start_game(
     replacements.insert("${assets_index_name}", asset_index.id.clone());
     replacements.insert("${auth_uuid}", account.uuid());
     replacements.insert("${auth_access_token}", account.access_token());
-    replacements.insert("${user_type}", "mojang".to_string());
-    replacements.insert("${version_type}", "release".to_string());
+    // Set user_type dynamically: "msa" for Microsoft accounts, "legacy" for offline
+    let user_type = match &account {
+        core::auth::Account::Microsoft(_) => "msa",
+        core::auth::Account::Offline(_) => "legacy",
+    };
+    replacements.insert("${user_type}", user_type.to_string());
+    // Use version_type from version JSON if available, fallback to "release"
+    let version_type_str = version_details
+        .version_type
+        .clone()
+        .unwrap_or_else(|| "release".to_string());
+    replacements.insert("${version_type}", version_type_str);
     replacements.insert("${user_properties}", "{}".to_string()); // Correctly pass empty JSON object for user properties
 
     if let Some(minecraft_arguments) = &version_details.minecraft_arguments {
@@ -622,7 +667,10 @@ async fn start_game(
                             if let Ok(rules) = serde_json::from_value::<Vec<core::game_version::Rule>>(
                                 rules_val.clone(),
                             ) {
-                                core::rules::is_library_allowed(&Some(rules))
+                                core::rules::is_library_allowed(
+                                    &Some(rules),
+                                    Some(&config.feature_flags),
+                                )
                             } else {
                                 true // Parse error, assume allow? or disallow.
                             }
@@ -815,6 +863,7 @@ fn parse_jvm_arguments(
     args: &mut Vec<String>,
     natives_path: &str,
     classpath: &str,
+    feature_flags: &core::config::FeatureFlags,
 ) {
     let mut replacements = std::collections::HashMap::new();
     replacements.insert("${natives_directory}", natives_path.to_string());
@@ -840,7 +889,7 @@ fn parse_jvm_arguments(
                     if let Ok(rules) =
                         serde_json::from_value::<Vec<core::game_version::Rule>>(rules_val.clone())
                     {
-                        core::rules::is_library_allowed(&Some(rules))
+                        core::rules::is_library_allowed(&Some(rules), Some(feature_flags))
                     } else {
                         false
                     }
@@ -1049,7 +1098,17 @@ async fn install_version(
         .as_ref()
         .ok_or("Version has no downloads information")?;
     let client_jar = &downloads.client;
-    let mut client_path = game_dir.join("versions");
+    // Use shared caches for versions if enabled
+    let mut client_path = if config.use_shared_caches {
+        window
+            .app_handle()
+            .path()
+            .app_data_dir()
+            .unwrap()
+            .join("versions")
+    } else {
+        game_dir.join("versions")
+    };
     client_path.push(&minecraft_version);
     client_path.push(format!("{}.jar", minecraft_version));
 
@@ -1061,10 +1120,20 @@ async fn install_version(
     });
 
     // --- Libraries ---
-    let libraries_dir = game_dir.join("libraries");
+    // Use shared caches for libraries if enabled
+    let libraries_dir = if config.use_shared_caches {
+        window
+            .app_handle()
+            .path()
+            .app_data_dir()
+            .unwrap()
+            .join("libraries")
+    } else {
+        game_dir.join("libraries")
+    };
 
     for lib in &version_details.libraries {
-        if core::rules::is_library_allowed(&lib.rules) {
+        if core::rules::is_library_allowed(&lib.rules, Some(&config.feature_flags)) {
             if let Some(downloads) = &lib.downloads {
                 if let Some(artifact) = &downloads.artifact {
                     let path_str = artifact
@@ -1085,34 +1154,51 @@ async fn install_version(
 
                 // Native Library (classifiers)
                 if let Some(classifiers) = &downloads.classifiers {
-                    let os_key = if cfg!(target_os = "linux") {
-                        "natives-linux"
+                    // Determine candidate keys based on OS and architecture
+                    let arch = std::env::consts::ARCH;
+                    let mut candidates: Vec<String> = Vec::new();
+                    if cfg!(target_os = "linux") {
+                        candidates.push("natives-linux".to_string());
+                        candidates.push(format!("natives-linux-{}", arch));
+                        if arch == "aarch64" {
+                            candidates.push("natives-linux-arm64".to_string());
+                        }
                     } else if cfg!(target_os = "windows") {
-                        "natives-windows"
+                        candidates.push("natives-windows".to_string());
+                        candidates.push(format!("natives-windows-{}", arch));
                     } else if cfg!(target_os = "macos") {
-                        "natives-osx"
-                    } else {
-                        ""
-                    };
-
-                    if let Some(native_artifact_value) = classifiers.get(os_key) {
-                        if let Ok(native_artifact) =
-                            serde_json::from_value::<core::game_version::DownloadArtifact>(
-                                native_artifact_value.clone(),
-                            )
-                        {
-                            let path_str = native_artifact.path.clone().unwrap();
-                            let mut native_path = libraries_dir.clone();
-                            native_path.push(&path_str);
-
-                            download_tasks.push(core::downloader::DownloadTask {
-                                url: native_artifact.url,
-                                path: native_path.clone(),
-                                sha1: native_artifact.sha1,
-                                sha256: None,
-                            });
+                        candidates.push("natives-osx".to_string());
+                        candidates.push("natives-macos".to_string());
+                        candidates.push(format!("natives-macos-{}", arch));
+                    }
+
+                    // Pick the first available classifier key
+                    let mut chosen: Option<core::game_version::DownloadArtifact> = None;
+                    for key in candidates {
+                        if let Some(native_artifact_value) = classifiers.get(&key) {
+                            if let Ok(artifact) =
+                                serde_json::from_value::<core::game_version::DownloadArtifact>(
+                                    native_artifact_value.clone(),
+                                )
+                            {
+                                chosen = Some(artifact);
+                                break;
+                            }
                         }
                     }
+
+                    if let Some(native_artifact) = chosen {
+                        let path_str = native_artifact.path.clone().unwrap();
+                        let mut native_path = libraries_dir.clone();
+                        native_path.push(&path_str);
+
+                        download_tasks.push(core::downloader::DownloadTask {
+                            url: native_artifact.url,
+                            path: native_path.clone(),
+                            sha1: native_artifact.sha1,
+                            sha256: None,
+                        });
+                    }
                 }
             } else {
                 // Library without explicit downloads (mod loader libraries)
@@ -1134,7 +1220,17 @@ async fn install_version(
     }
 
     // --- Assets ---
-    let assets_dir = game_dir.join("assets");
+    // Use shared caches for assets if enabled
+    let assets_dir = if config.use_shared_caches {
+        window
+            .app_handle()
+            .path()
+            .app_data_dir()
+            .unwrap()
+            .join("assets")
+    } else {
+        game_dir.join("assets")
+    };
     let objects_dir = assets_dir.join("objects");
     let indexes_dir = assets_dir.join("indexes");
 
diff --git a/ui/src/components/SettingsView.svelte b/ui/src/components/SettingsView.svelte
index 4de18b3..0e89e25 100644
--- a/ui/src/components/SettingsView.svelte
+++ b/ui/src/components/SettingsView.svelte
@@ -123,6 +123,15 @@
     settingsState.settings.custom_background_path = undefined;
     settingsState.saveSettings();
   }
+
+  async function runMigrationToSharedCaches() {
+    try {
+      await (await import("@tauri-apps/api/core")).invoke("migrate_shared_caches");
+      settingsState.loadSettings();
+    } catch (e) {
+      console.error("Migration failed:", e);
+    }
+  }
 </script>
 
 <div class="h-full flex flex-col p-6 overflow-hidden">
@@ -398,6 +407,118 @@
         </div>
     </div>
 
+    <!-- Storage & Caches -->
+    <div class="dark:bg-[#09090b] bg-white p-6 rounded-sm border dark:border-white/10 border-gray-200 shadow-sm">
+      <h3 class="text-xs font-bold uppercase tracking-widest text-white/40 mb-6 flex items-center gap-2">Storage & Version Caches</h3>
+      <div class="space-y-4">
+        <div class="flex items-center justify-between">
+          <div>
+            <h4 class="text-sm font-medium text-white/90" id="shared-caches-label">Use Shared Caches</h4>
+            <p class="text-xs text-white/40 mt-1">Store versions/libraries/assets in a global cache shared by all instances.</p>
+          </div>
+          <button
+            aria-labelledby="shared-caches-label"
+            onclick={() => { settingsState.settings.use_shared_caches = !settingsState.settings.use_shared_caches; settingsState.saveSettings(); }}
+            class="w-11 h-6 rounded-full transition-colors duration-200 ease-in-out relative focus:outline-none {settingsState.settings.use_shared_caches ? 'bg-indigo-500' : 'bg-white/10'}"
+          >
+            <div class="absolute top-1 left-1 bg-white w-4 h-4 rounded-full shadow-sm transition-transform duration-200 ease-in-out {settingsState.settings.use_shared_caches ? 'translate-x-5' : 'translate-x-0'}"></div>
+          </button>
+        </div>
+
+        <div class="flex items-center justify-between">
+          <div>
+            <h4 class="text-sm font-medium text-white/90" id="legacy-storage-label">Keep Legacy Per-Instance Storage</h4>
+            <p class="text-xs text-white/40 mt-1">Do not migrate existing instance caches; keep current layout.</p>
+          </div>
+          <button
+            aria-labelledby="legacy-storage-label"
+            onclick={() => { settingsState.settings.keep_legacy_per_instance_storage = !settingsState.settings.keep_legacy_per_instance_storage; settingsState.saveSettings(); }}
+            class="w-11 h-6 rounded-full transition-colors duration-200 ease-in-out relative focus:outline-none {settingsState.settings.keep_legacy_per_instance_storage ? 'bg-indigo-500' : 'bg-white/10'}"
+          >
+            <div class="absolute top-1 left-1 bg-white w-4 h-4 rounded-full shadow-sm transition-transform duration-200 ease-in-out {settingsState.settings.keep_legacy_per_instance_storage ? 'translate-x-5' : 'translate-x-0'}"></div>
+          </button>
+        </div>
+
+        <div class="flex items-center justify-between pt-2 border-t border-white/10">
+          <div>
+            <h4 class="text-sm font-medium text-white/90">Run Migration</h4>
+            <p class="text-xs text-white/40 mt-1">Hard-link or copy existing per-instance caches into the shared cache.</p>
+          </div>
+          <button onclick={runMigrationToSharedCaches} class="px-4 py-2 rounded-lg bg-indigo-600 hover:bg-indigo-500 text-white text-sm">Migrate Now</button>
+        </div>
+      </div>
+    </div>
+
+    <!-- Feature Flags -->
+    <div class="dark:bg-[#09090b] bg-white p-6 rounded-sm border dark:border-white/10 border-gray-200 shadow-sm">
+      <h3 class="text-xs font-bold uppercase tracking-widest text-white/40 mb-6 flex items-center gap-2">Feature Flags (Launcher Arguments)</h3>
+      <div class="space-y-4">
+        <div class="flex items-center justify-between">
+          <div>
+            <h4 class="text-sm font-medium text-white/90" id="demo-user-label">Demo User</h4>
+            <p class="text-xs text-white/40 mt-1">Enable demo-related arguments when rules require them.</p>
+          </div>
+          <button
+            aria-labelledby="demo-user-label"
+            onclick={() => { settingsState.settings.feature_flags.demo_user = !settingsState.settings.feature_flags.demo_user; settingsState.saveSettings(); }}
+            class="w-11 h-6 rounded-full transition-colors duration-200 ease-in-out relative focus:outline-none {settingsState.settings.feature_flags.demo_user ? 'bg-indigo-500' : 'bg-white/10'}"
+          >
+            <div class="absolute top-1 left-1 bg-white w-4 h-4 rounded-full shadow-sm transition-transform duration-200 ease-in-out {settingsState.settings.feature_flags.demo_user ? 'translate-x-5' : 'translate-x-0'}"></div>
+          </button>
+        </div>
+
+        <div class="flex items-center justify-between">
+          <div>
+            <h4 class="text-sm font-medium text-white/90" id="quick-play-label">Quick Play</h4>
+            <p class="text-xs text-white/40 mt-1">Enable quick play singleplayer/multiplayer arguments.</p>
+          </div>
+          <button
+            aria-labelledby="quick-play-label"
+            onclick={() => { settingsState.settings.feature_flags.quick_play_enabled = !settingsState.settings.feature_flags.quick_play_enabled; settingsState.saveSettings(); }}
+            class="w-11 h-6 rounded-full transition-colors duration-200 ease-in-out relative focus:outline-none {settingsState.settings.feature_flags.quick_play_enabled ? 'bg-indigo-500' : 'bg-white/10'}"
+          >
+            <div class="absolute top-1 left-1 bg-white w-4 h-4 rounded-full shadow-sm transition-transform duration-200 ease-in-out {settingsState.settings.feature_flags.quick_play_enabled ? 'translate-x-5' : 'translate-x-0'}"></div>
+          </button>
+        </div>
+
+        {#if settingsState.settings.feature_flags.quick_play_enabled}
+          <div class="grid grid-cols-1 md:grid-cols-2 gap-4 pl-2 border-l-2 border-white/10">
+            <div>
+              <label class="block text-sm font-medium text-white/70 mb-2">Singleplayer World Path</label>
+              <input
+                type="text"
+                bind:value={settingsState.settings.feature_flags.quick_play_path}
+                placeholder="/path/to/saves/MyWorld"
+                class="bg-black/40 text-white w-full px-4 py-3 rounded-xl border border-white/10 focus:border-indigo-500/50 outline-none font-mono text-xs transition-colors"
+              />
+            </div>
+            <div class="flex items-center justify-between">
+              <div>
+                <h4 class="text-sm font-medium text-white/90" id="qp-singleplayer-label">Prefer Singleplayer</h4>
+                <p class="text-xs text-white/40 mt-1">If enabled, use singleplayer quick play path.</p>
+              </div>
+              <button
+                aria-labelledby="qp-singleplayer-label"
+                onclick={() => { settingsState.settings.feature_flags.quick_play_singleplayer = !settingsState.settings.feature_flags.quick_play_singleplayer; settingsState.saveSettings(); }}
+                class="w-11 h-6 rounded-full transition-colors duration-200 ease-in-out relative focus:outline-none {settingsState.settings.feature_flags.quick_play_singleplayer ? 'bg-indigo-500' : 'bg-white/10'}"
+              >
+                <div class="absolute top-1 left-1 bg-white w-4 h-4 rounded-full shadow-sm transition-transform duration-200 ease-in-out {settingsState.settings.feature_flags.quick_play_singleplayer ? 'translate-x-5' : 'translate-x-0'}"></div>
+              </button>
+            </div>
+            <div>
+              <label class="block text-sm font-medium text-white/70 mb-2">Multiplayer Server Address</label>
+              <input
+                type="text"
+                bind:value={settingsState.settings.feature_flags.quick_play_multiplayer_server}
+                placeholder="example.org:25565"
+                class="bg-black/40 text-white w-full px-4 py-3 rounded-xl border border-white/10 focus:border-indigo-500/50 outline-none font-mono text-xs transition-colors"
+              />
+            </div>
+          </div>
+        {/if}
+      </div>
+    </div>
+
     <!-- Debug / Logs -->
     <div class="dark:bg-[#09090b] bg-white p-6 rounded-sm border dark:border-white/10 border-gray-200 shadow-sm">
         <h3 class="text-xs font-bold uppercase tracking-widest text-white/40 mb-6 flex items-center gap-2">
diff --git a/ui/src/stores/settings.svelte.ts b/ui/src/stores/settings.svelte.ts
index 8a90736..5d20050 100644
--- a/ui/src/stores/settings.svelte.ts
+++ b/ui/src/stores/settings.svelte.ts
@@ -42,6 +42,15 @@ export class SettingsState {
       tts_enabled: false,
       tts_provider: "disabled",
     },
+    use_shared_caches: false,
+    keep_legacy_per_instance_storage: true,
+    feature_flags: {
+      demo_user: false,
+      quick_play_enabled: false,
+      quick_play_path: undefined,
+      quick_play_singleplayer: true,
+      quick_play_multiplayer_server: undefined,
+    },
   });
 
   // Convert background path to proper asset URL
diff --git a/ui/src/types/index.ts b/ui/src/types/index.ts
index a5b336e..858ee43 100644
--- a/ui/src/types/index.ts
+++ b/ui/src/types/index.ts
@@ -68,6 +68,19 @@ export interface LauncherConfig {
   log_upload_service: "paste.rs" | "pastebin.com";
   pastebin_api_key?: string;
   assistant: AssistantConfig;
+  // Storage management
+  use_shared_caches: boolean;
+  keep_legacy_per_instance_storage: boolean;
+  // Feature-gated argument flags
+  feature_flags: FeatureFlags;
+}
+
+export interface FeatureFlags {
+  demo_user: boolean;
+  quick_play_enabled: boolean;
+  quick_play_path?: string;
+  quick_play_singleplayer: boolean;
+  quick_play_multiplayer_server?: string;
 }
 
 export interface JavaInstallation {