perf(window): defer inspector NSHostingController content until first expansion

[datlechin]

Summary

Step 1A of the pure-SwiftUI scene migration (Phase C-2 in the perf refactor plan).

MainSplitViewController.viewDidLoad instantiates 3 NSHostingControllers (sidebar, detail, inspector) — one SwiftUI rendering root each. Each root negotiates intrinsic sizes via NSHostingView.SizeConstraints.update(from:) → ViewGraph.sizeThatFits(_:) during the window's first display cycle, contributing to the 1.19s connect-window-open spike captured in the Time Profiler trace.

The inspector starts collapsed by default (UserDefaults.bool(forKey: inspectorPresentedKey) = false), so its SwiftUI body (UnifiedRightPanelView with column inspector, query result summary, etc.) is built but never shown — pure waste at launch.

Fix

Apple-pattern lazy view-controller content. The inspector's NSHostingController is created with a placeholder Color.clear root view when collapsed; the heavy UnifiedRightPanelView body is materialized via inspectorHosting.rootView = AnyView(buildInspectorView()) only on first showInspector() call. If the user had inspector expanded last session (inspectorPresentedKey == true), content materializes immediately at launch — same as before.

NSHostingController.rootView is documented as get/set on Apple's docs, so this is the supported swap pattern. SwiftUI re-evaluates the view graph from scratch when the rootView is replaced.

private var hasMaterializedInspector = false

// viewDidLoad:
let initialInspectorContent: AnyView
if inspectorPresented {
    initialInspectorContent = AnyView(buildInspectorView())
    hasMaterializedInspector = true
} else {
    initialInspectorContent = AnyView(Color.clear)
}
inspectorHosting = NSHostingController(rootView: initialInspectorContent)
…

private func materializeInspectorIfNeeded() {
    guard !hasMaterializedInspector, let inspectorHosting else { return }
    hasMaterializedInspector = true
    inspectorHosting.rootView = AnyView(buildInspectorView())
}

func showInspector() {
    materializeInspectorIfNeeded()
    inspectorSplitItem?.animator().isCollapsed = false
    UserDefaults.standard.set(true, forKey: Self.inspectorPresentedKey)
}

This also establishes the lazy-rootView swap pattern that step 1B (toolbar move to SwiftUI) and step 1C (NavigationSplitView replacement) will reuse.

Test plan

• Cold launch with inspectorPresentedKey = false (default): main window opens, inspector pane shows nothing collapsed (same UX), Cmd+Option+I expands → content appears
• Cold launch with inspectorPresentedKey = true (had inspector open last session): inspector content visible immediately at launch (same as before)
• Toggle inspector via toolbar / menu / shortcut: works, content persists
• Multi-window: each window's inspector materializes independently on first expansion
• swiftlint --strict on changed file: 0 violations
• xcodebuild Debug arm64: BUILD SUCCEEDED

Why this is step 1A, not the full refactor

The full migration to pure SwiftUI scenes (NavigationSplitView + .toolbar + .inspector) replacing MainSplitViewController is a multi-week project. Per the planning discussion in this thread, the safer path is incremental: (1A) lazy inspector ← this PR, (1B) toolbar to SwiftUI .toolbar { ToolbarContent }, (1C) NavigationSplitView shell. Each step compiles, ships, and is independently reversible.

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.