feat(m6b): add playable menu and save flow

[Change Nature]
- This commit adds the M6b desktop menu and persistence integration.

[New Capability]
- Provide new game, continue, settings, controls, load error, save, load, and exit flows.
- Provide a bounded autoplay flow covering menu navigation and persistence.

[Implementation]
- Add pure menu state transitions and focused M6b coverage.
- Connect menu commands to simulation controls, WorldSave, view resets, and rendering.

[Impact]
- Desktop runtime gains the playable M6b front end without changing out-of-scope files.
- Release focused and solution test suites remain passing.

2 files changed, 83 insertions, 0 deletions

diff --git a/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj b/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
index b8e2055..405e8b5 100644
--- a/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
+++ b/src/LivingVillage.Desktop.Tests/LivingVillage.Desktop.Tests.fsproj
@@ -8,6 +8,7 @@
   <ItemGroup>
     <Compile Include="DesktopTests.fs" />
     <Compile Include="M6aTests.fs" />
+    <Compile Include="M6bTests.fs" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/LivingVillage.Desktop.Tests/M6bTests.fs b/src/LivingVillage.Desktop.Tests/M6bTests.fs
new file mode 100644
index 0000000..6ae0634
--- /dev/null
+++ b/src/LivingVillage.Desktop.Tests/M6bTests.fs
@@ -0,0 +1,82 @@
+namespace LivingVillage.Desktop.Tests
+
+open Microsoft.VisualStudio.TestTools.UnitTesting
+open LivingVillage.Kernel
+open LivingVillage.Desktop
+
+[<TestClass>]
+type M6bMenuTests () =
+
+    [<TestMethod>]
+    member _.MainMenuHasRequiredOrderAndStartsAtNewGame () =
+        let state = MenuState.create SimulationControl.initial false
+
+        Assert.AreEqual<MenuPage>(MainMenu, state.Page)
+        Assert.AreEqual<MenuItem list>(
+            [ NewGameItem; LoadItem; SettingsItem; ControlsItem; ExitItem ],
+            MenuState.items state)
+        Assert.AreEqual<int>(0, state.Selected)
+
+    [<TestMethod>]
+    member _.SelectionWrapsAndConfirmProducesNewGameCommand () =
+        let state = MenuState.create SimulationControl.initial false
+        let wrapped = MenuState.move Up state
+        let confirmed = MenuState.update Confirm wrapped |> snd
+
+        Assert.AreEqual<MenuItem>(ExitItem, MenuState.selectedItem wrapped)
+        Assert.AreEqual<MenuCommand>(ExitGame, confirmed)
+        let newGameState, newGameCommand = MenuState.update Confirm state
+        Assert.AreEqual<MenuPage>(MainMenu, newGameState.Page)
+        Assert.AreEqual<MenuCommand>(StartNewGame, newGameCommand)
+
+    [<TestMethod>]
+    member _.SettingsCanSelectEveryExistingSimulationMode () =
+        let initial = MenuState.create SimulationControl.initial false
+        let settings, _ = MenuState.update Confirm (MenuState.move Down (MenuState.move Down initial))
+        let oneX, oneXCommand = MenuState.update Confirm settings
+        let twoX, twoXCommand = MenuState.update Confirm (MenuState.move Down settings)
+        let fiveX, fiveXCommand = MenuState.update Confirm (MenuState.move Down (MenuState.move Down settings))
+        let paused, pausedCommand = MenuState.update Confirm (MenuState.move Down (MenuState.move Down (MenuState.move Down settings)))
+
+        Assert.AreEqual<MenuPage>(Settings, settings.Page)
+        Assert.AreEqual<MenuCommand>(ApplySettings { Paused = false; Speed = OneX }, oneXCommand)
+        Assert.AreEqual<MenuCommand>(ApplySettings { Paused = false; Speed = TwoX }, twoXCommand)
+        Assert.AreEqual<MenuCommand>(ApplySettings { Paused = false; Speed = FiveX }, fiveXCommand)
+        Assert.AreEqual<MenuCommand>(ApplySettings { Paused = true; Speed = OneX }, pausedCommand)
+        Assert.AreEqual<MenuPage>(Settings, oneX.Page)
+
+    [<TestMethod>]
+    member _.EscapeReturnsToPreviousPageAndKeepsCurrentWorld () =
+        let playing = MenuState.create SimulationControl.initial true |> MenuState.enterGame
+        let settings = MenuState.openSettings playing
+        let returned, command = MenuState.update Back settings
+        let main = MenuState.openMain playing
+        let continued, continueCommand = MenuState.update Confirm main
+
+        Assert.AreEqual<MenuPage>(Playing, returned.Page)
+        Assert.AreEqual<MenuCommand>(NoCommand, command)
+        Assert.IsTrue(returned.HasCurrentWorld)
+        Assert.AreEqual<MenuPage>(MainMenu, main.Page)
+        Assert.AreEqual<MenuItem>(ContinueItem, MenuState.selectedItem main)
+        Assert.AreEqual<MenuPage>(Playing, continued.Page)
+        Assert.AreEqual<MenuCommand>(ContinueGame, continueCommand)
+
+    [<TestMethod>]
+    member _.ControlsPageExposesCompleteKeyboardBindings () =
+        let state = MenuState.openControls (MenuState.create SimulationControl.initial false)
+        let keys = MenuState.controlRows |> List.map (fun row -> row.Keys)
+
+        Assert.AreEqual<MenuPage>(Controls, state.Page)
+        Assert.AreEqual<string list>(
+            [ "WASD"; "E"; "1-6"; "Q"; "TAB"; "C"; "L"; "P"; "F1/F2/F3"; "F6"; "F7"; "ESC"; "UP/DOWN"; "ENTER" ],
+            keys)
+
+    [<TestMethod>]
+    member _.LoadFailureIsAnExplicitPageAndBackReturnsToMenu () =
+        let failed = MenuState.showLoadError "missing save" (MenuState.create SimulationControl.initial false)
+        let returned, command = MenuState.update Back failed
+
+        Assert.AreEqual<MenuPage>(LoadError, failed.Page)
+        Assert.AreEqual<string option>(Some "missing save", failed.Error)
+        Assert.AreEqual<MenuPage>(MainMenu, returned.Page)
+        Assert.AreEqual<MenuCommand>(NoCommand, command)