umputun / agterm / 33928854654

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fix(titlebar): read the window title in child views, not WindowContentView.body (#548)

PR B for #516, after #547. `WindowContentView.body` read the active session's `displayName` twice, for the OS title token and for the visible title row, so every OSC title tick invalidated the whole body and re-ran SwiftUI's graph and layout for the window. `WindowAccessor.updateNSView` then ran the full `WindowAppearance.sync` when only `NSWindow.title` had changed.

two child views now own those reads. `WindowTitleSync` resolves the OS title in its own body and hosts `WindowAccessor`; `TitlebarLabel` resolves `TitlebarComposition` for the visible row, and the zoom titlebar reuses it. The parent passes the store and ids and no title. `WindowAccessor` writes `window.title` on a token change and keeps the blend on attach, key, main, fullscreen, appearance and accessibility changes, which already carry every other blend input. The custom window name lookup moved into `WindowLibrary` next to `windowName(for:)`, and the dashboard title uses it.

tests: hosted, a `TitleProbeView` title write leaves a separator sentinel the full blend would reset, a title set before attach survives attachment, and `WindowTitleSync` hosted in `NSHostingView` follows an OSC title, a session rename and a window rename to `NSWindow.title`. Host-free, the `customWindowName(for:)` cases.

profile, Time Profiler, Debug builds of a8bbaa5a and this branch, isolated state, sidebar hidden, one session printing numbered OSC 2 titles at about 10 Hz, two recordings of about 20 s each, main thread only. Values are inclusive main-thread sample weight in ms:

| symbol | a8bbaa5a | this branch |
| --- | --- | --- |
| `WindowContentView.body.getter` | 212 | 0 |
| `WindowTitleSync.body` / `TitlebarLabel.body` | absent | 6 / 28 |
| `WindowAppearance.sync` | 70 | 0 |
| `-[NSWindow _dosetTitle:andDefeatWrap:]` | 187 | 213 |
| `GraphHost.flushTransactions` | 1086 | 539 |
| main thread, all samples | 1774 | 978 ... (continued)

4 of 4 new or added lines in 1 file covered. (100.0%)

9661 of 9931 relevant lines covered (97.28%)

4108896.47 hits per line