feat(sys): expose canGoBack for the chrome that offers the control

lua/api/core/sys.lua

@@ -36,19 +36,23 @@ function sys.getAppDataPath() end
 ---@param title string
 function sys.setAppTitle(title) end
 
----Launches /.lua/apps/<path>/main.lua and pushes the current route.
----@param path string App-relative directory path; traversal is rejected.
----@param arg? string Passed to init(arg).
+---Launches a route, which main.lua resolves, and pushes the current one.
+---@param path string App-relative route; traversal is rejected.
+---@param arg? string Passed to main.start(route, arg).
 function sys.launch(path, arg) end
 
----Launches an app path without retaining the current route.
----@param path string App-relative directory path; traversal is rejected.
----@param arg? string Passed to init(arg).
+---Launches a route without retaining the current one.
+---@param path string App-relative route; traversal is rejected.
+---@param arg? string Passed to main.start(route, arg).
 function sys.replace(path, arg) end
 
 ---Returns to the previous app, or the launcher when history is empty.
 function sys.back() end
 
+---Whether sys.back() would return somewhere rather than land on the launcher, which is what chrome needs to decide whether to offer a back control.
+---@return boolean
+function sys.canGoBack() end
+
 ---Returns heap statistics.
 ---@return integer freeBytes
 ---@return integer totalBytes