Migration: Windowing evolution¶

Spec 054 intentionally removes a few legacy windowing fields in favor of more explicit shapes. The new APIs are additive except for the breaking changes below.

Removed / changed API	Replacement	Migration
`IsResizable` (bool)	`ResizeMode` (`WindowResizeMode`)	`IsResizable = false` → `ResizeMode = WindowResizeMode.NoResize`. The old default `true` is the new default `CanResize`.
`IsShownInSwitchers` (bool)	`ShowInTaskbar` + `ShowInSwitcher`	`IsShownInSwitchers = false` → `ShowInTaskbar = false, ShowInSwitcher = false`.
`IsAlwaysOnTop` (bool)	`Level` (`WindowLevel`)	`IsAlwaysOnTop = true` → `Level = WindowLevel.AlwaysOnTop`.
`WindowStartPosition.RestoreFromPersistence`	`.WithPersistence(id)` or `PersistPlacement = true`	Old: `StartPosition = WindowStartPosition.RestoreFromPersistence, PersistenceId = "main"`. New: `new WindowSpec { Title = "Main" }.WithPersistence("main")`.
`ExtendsContentIntoTitleBar` (`bool`)	`ExtendsContentIntoTitleBar` (`bool?`) plus `TitleBar(...)` inference	If a `TitleBar(...)` element is present, drop `ExtendsContentIntoTitleBar = true` and let Reactor infer it. Keep explicit `true` only for content-extension without a `TitleBar(...)`; keep explicit `false` to force system chrome.

Examples¶

// Before
// new WindowSpec
// {
//     Title = "Tools",
//     IsResizable = false,
//     IsShownInSwitchers = false,
//     IsAlwaysOnTop = true,
// };

// After
public static WindowSpec Tools { get; } = new()
{
    Title = "Tools",
    ResizeMode = WindowResizeMode.NoResize,
    ShowInTaskbar = false,
    ShowInSwitcher = false,
    Level = WindowLevel.AlwaysOnTop,
};

// Before
// new WindowSpec
// {
//     Title = "Main",
//     PersistenceId = "main",
//     StartPosition = WindowStartPosition.RestoreFromPersistence,
// };

// After
public static WindowSpec Main { get; } =
    new WindowSpec { Title = "Main" }.WithPersistence("main");

WindowPlacementCodec stores only monitor fingerprints and WINDOWPLACEMENT, not WindowStartPosition, so no on-disk placement migration is required.

Next Steps¶

Windows — The post-054 windowing surface in full: sizing, placement, z-order, chrome, taskbar, displays.
Advanced Windowing — Interop-heavy recipes that deliberately sit outside the WindowSpec contract.
Persistence — Persisted scopes beyond window placement.