fix: add macOS helper extension support

README.md

@@ -25,7 +25,7 @@ Wondering if your favorite Chrome extension works with Extendium? Check our offi
 1. Ensure you have **Millennium** installed on your Steam client.
 2. Download the **[latest release](https://github.com/BossSloth/Extendium/releases/latest)** from GitHub or install it from the **[Steambrew](https://steambrew.app/plugin?id=788ed8554492)** website.
 3. (Manual only) Place the plugin files into your Millennium plugins directory (typically a `plugins` folder inside your Steam installation).
-4. **Restart** your Steam client.
+4. **Restart** your Steam client using your normal Millennium launch method (on macOS, typically `Steam Millennium.app`).
 5. Open the Millennium plugin menu and **enable** the Extendium plugin.
 6. Click **Save Changes** at the top of the menu and **restart Steam** one more time.
 
@@ -85,6 +85,7 @@ If everything goes fully wrong (e.g. an extension breaks the client and you can'
 Don't worry, almost nothing is saved in these files, only extension settings and some browser state. If you want to be sure, back them up first.
 
 - **Windows**: `%localappdata%\Steam\htmlcache\Default`
+- **macOS**: `~/Library/Application Support/Steam/config/htmlcache/Default`
 - **Linux**: `~/.steam/steam/config/htmlcache/Default`
 
 After deleting these files, boot up Steam.
@@ -123,9 +124,14 @@ Follow the [Manual Extension Installation](#manual-extension-installation) steps
 
 - **Windows (Millennium < 3.0)**: `<Steam folder>/plugins/extendium/fake-header-extension`
 - **Windows (Millennium >= 3.0)**: `<Steam folder>/millennium/plugins/extendium/fake-header-extension`
+- **macOS**: `~/Library/Application Support/Millennium/plugins/extendium/fake-header-extension`
 - **Linux**: `~/.local/share/millennium/plugins/extendium/fake-header-extension`
 
-After loading it, restart Steam to make sure Extendium picks it up.
+After loading it, restart Steam using your normal Millennium launch method to make sure Extendium picks it up.
+
+If you previously selected **Ignore and don't show again**, close Steam, delete
+`install-state.json` from the `extendium` plugin directory listed above, and
+relaunch Steam to let Extendium retry the helper installation.
 
 ## Known Limitations
 

backend/install_extension/config.lua

@@ -12,6 +12,25 @@ function M.is_windows()
     return jit.os == "Windows"
 end
 
+function M.is_macos()
+    return jit.os == "OSX"
+end
+
+function M.is_linux()
+    return jit.os == "Linux"
+end
+
+function M.get_platform_name()
+    if M.is_windows() then
+        return "Windows"
+    elseif M.is_macos() then
+        return "macOS"
+    elseif M.is_linux() then
+        return "Linux"
+    end
+    return "Unsupported (" .. tostring(jit.os) .. ")"
+end
+
 function M.get_plugin_dir()
     local backend_path = utils.get_backend_path()
     if not backend_path then
@@ -32,17 +51,23 @@ function M.get_steam_config_dir()
     local steam_path = millennium.steam_path()
     logger:info("[install] Steam path: " .. tostring(steam_path))
 
-    local is_win = M.is_windows()
-    logger:info("[install] Platform: " .. (is_win and "Windows" or "Linux"))
+    logger:info("[install] Platform: " .. M.get_platform_name())
 
-    if is_win then
+    if M.is_windows() then
         -- Windows: %LOCALAPPDATA%\Steam\htmlcache\Default
         local appdata = utils.getenv("LOCALAPPDATA")
         if appdata then
             return fs.join(appdata, "Steam", "htmlcache", "Default")
         end
         return nil
-    else
+    elseif M.is_macos() then
+        -- macOS: ~/Library/Application Support/Steam/config/htmlcache/Default
+        local home = utils.getenv("HOME")
+        if home then
+            return fs.join(home, "Library", "Application Support", "Steam", "config", "htmlcache", "Default")
+        end
+        return nil
+    elseif M.is_linux() then
         -- Linux: ~/.local/share/Steam/config/htmlcache/Default
         -- Or symlink:  ~/.steam/steam/config/htmlcache/Default
         local home = utils.getenv("HOME")
@@ -51,6 +76,9 @@ function M.get_steam_config_dir()
         end
         return nil
     end
+
+    logger:error("[install] Unsupported platform: " .. tostring(jit.os))
+    return nil
 end
 
 -- Generic JSON file reader with logging

backend/install_extension/hmac.lua

@@ -5,18 +5,18 @@ local json_helpers = require("install_extension.json_helpers")
 local sha2 = require("install_extension.sha2")
 
 ---@class HmacContext
----@field sid string
+---@field device_id string
 ---@field seed_hex string
 ---@field seed_bytes string
 local HmacContext = {}
 HmacContext.__index = HmacContext
 
----@param sid string
+---@param device_id string
 ---@param seed_hex string
 ---@return HmacContext
-function HmacContext.new(sid, seed_hex)
+function HmacContext.new(device_id, seed_hex)
     local self = setmetatable({}, HmacContext)
-    self.sid = sid or ""
+    self.device_id = device_id or ""
     self.seed_hex = seed_hex or "" -- Empty for Steam CEF
     self.seed_bytes = sha2.hex_to_bin(seed_hex or "")
     return self
@@ -31,7 +31,7 @@ function HmacContext:compute_mac(json_path, value)
     local json_value = json_helpers.encode_sorted(cleaned)
     json_value = json_helpers.escape_for_hmac(json_value)
 
-    local message = self.sid .. json_path .. json_value
+    local message = self.device_id .. json_path .. json_value
     logger:info("[install] Computing MAC for path: " .. json_path)
     logger:info("[install] Message length: " .. #message)
     logger:info("[install] JSON preview: " .. json_value:sub(1, 100) .. "...")
@@ -48,9 +48,10 @@ end
 ---@param macs table
 ---@return string|nil
 function HmacContext:compute_super_mac(macs)
-    -- Use sorted JSON for consistent key ordering
-    local macs_json = json_helpers.encode_sorted(macs)
-    local message = self.sid .. macs_json
+    -- Chromium removes empty descendants before serializing tracked values.
+    local cleaned_macs = json_helpers.remove_empty_children(macs) or {}
+    local macs_json = json_helpers.encode_sorted(cleaned_macs)
+    local message = self.device_id .. macs_json
 
     logger:info("[install] Computing super MAC...")
     logger:info("[install] MACs JSON: " .. macs_json:sub(1, 100) .. "...")