perf(keyboard): track KeyboardState per property with @Observable

- KeyboardState moves from ObservableObject/@Published to @Observable, so a view re-renders only for the properties it reads. Previously unpublished state and injected action hooks are @ObservationIgnored.
- KeyboardViewController replaces the $phase/$surface Combine sinks with Observations loops tied to the same cancellables.
- AIKeyboardView reads the 200 ms mic level and live ASR partials in small child views (AssistantWaveform, LiveTranscriptReader), so those ticks no longer rebuild the whole assistant surface.
- Tests observe changes with withObservationTracking instead of Combine publishers.

OSGKeyboardExt/KeyboardViewController.swift

@@ -778,28 +778,38 @@ public final class KeyboardViewController: UIInputViewController {
     }
 
     private func installSurfaceObservers() {
-        state.$phase
-            .receive(on: RunLoop.main)
-            .sink { [weak self] _ in
-                guard let self else { return }
-                if self.state.locksTypingSurface, self.state.surface == .typing {
-                    self.applySurface(.voice)
-                }
+        let state = state
+        // `Phase` is not Sendable; reading it only registers the dependency.
+        observe(Observations { _ = state.phase }) { [weak self] in
+            guard let self else { return }
+            if self.state.locksTypingSurface, self.state.surface == .typing {
+                self.applySurface(.voice)
             }
-            .store(in: &cancellables)
+        }
 
-        state.$surface
-            .receive(on: RunLoop.main)
-            .sink { [weak self] surface in
-                guard let self else { return }
-                if surface == .typing {
-                    self.activateTypingPresentationIfNeeded()
-                } else {
-                    self.deactivateTypingSurface()
-                }
-                self.refreshKeyboardHeight()
+        observe(Observations { state.surface }) { [weak self] surface in
+            guard let self else { return }
+            if surface == .typing {
+                self.activateTypingPresentationIfNeeded()
+            } else {
+                self.deactivateTypingSurface()
             }
-            .store(in: &cancellables)
+            self.refreshKeyboardHeight()
+        }
+    }
+
+    /// Runs `handler` for the current value and every later change. The loop
+    /// is cancelled together with `cancellables` when the controller goes away.
+    private func observe<Element: Sendable>(
+        _ values: Observations<Element, Never>,
+        handler: @escaping @MainActor (Element) -> Void
+    ) {
+        let task = Task { @MainActor in
+            for await value in values {
+                handler(value)
+            }
+        }
+        cancellables.insert(AnyCancellable { task.cancel() })
     }
 
     /// This App Group property is supplied by the parallel settings module.

OSGKeyboardExt/Typing/KeyboardSurfaceRoot.swift

@@ -10,7 +10,7 @@ struct KeyboardSurfaceRoot: View {
     @Environment(\.colorScheme) private var colorScheme
     @Namespace private var keyboardTabSelectionNamespace
 
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @ObservedObject var typing: TypingSessionController
 
     var onInsert: (String) -> Void

OSGKeyboardExt/Typing/TypingRootView.swift

@@ -38,7 +38,7 @@ enum TypingLayoutMetrics {
 
 struct TypingRootView: View {
     @Environment(\.colorScheme) private var colorScheme
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @ObservedObject var typing: TypingSessionController
 
     var onInsert: (String) -> Void

OSGKeyboardExt/Views/AIKeyboardView.swift

@@ -64,7 +64,7 @@ struct AIKeyboardView: View {
 
     @Environment(\.colorScheme) private var colorScheme
     @Environment(\.accessibilityReduceMotion) private var reduceMotion
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @ObservedObject var typing: TypingSessionController
     @ObservedObject private var clipboardHistory = ClipboardHistoryStore.shared
     @ObservedObject private var semanticRanking = ClipboardSemanticRankingStore.shared
@@ -604,9 +604,9 @@ struct AIKeyboardView: View {
     @ViewBuilder
     private var contextArea: some View {
         ZStack {
-            if showsOOBEClipboardSkill, activeStatus == nil {
+            if showsOOBEClipboardSkill, !hasActiveStatus {
                 clipboardSkillPager
-            } else if let onboardingPracticeHint, activeStatus == nil {
+            } else if let onboardingPracticeHint, !hasActiveStatus {
                 Text(onboardingPracticeHint)
                     .font(TypeStyle.footnote.weight(.semibold))
                     .foregroundStyle(palette.textPrimary)
@@ -636,8 +636,12 @@ struct AIKeyboardView: View {
                 }
             } else if let content = semanticBadgeContent {
                 semanticBadge(content)
-            } else if let status = activeStatus {
-                statusText(status.text, color: status.color)
+            } else if hasActiveStatus {
+                LiveTranscriptReader(state: state) { transcript in
+                    if let status = activeStatus(lastTranscript: transcript) {
+                        statusText(status.text, color: status.color)
+                    }
+                }
             } else if showsLongPressCoach {
                 Text(ExtL10n.string("keyboard.assistant.longPressCoach"))
                     .font(TypeStyle.footnote.weight(.medium))
@@ -720,7 +724,14 @@ struct AIKeyboardView: View {
         .frame(maxWidth: .infinity)
     }
 
-    private var activeStatus: (text: String, color: Color)? {
+    /// Whether a status line replaces the idle content. Never depends on the
+    /// transcript text, so this surface does not re-render per ASR partial.
+    private var hasActiveStatus: Bool {
+        activeStatus(lastTranscript: "") != nil
+    }
+
+    /// `lastTranscript` is passed in so only `LiveTranscriptReader` tracks it.
+    private func activeStatus(lastTranscript: String) -> (text: String, color: Color)? {
         if let error = state.aiSession.errorMessage,
            !error.isEmpty,
            !ordinaryPipelineIsActive {
@@ -757,18 +768,18 @@ struct AIKeyboardView: View {
             return nil
         case .requestingPermissions:
             return (
-                state.lastTranscript.isEmpty
+                lastTranscript.isEmpty
                     ? ExtL10n.string("keyboard.placeholder.preparing")
-                    : state.lastTranscript,
+                    : lastTranscript,
                 palette.textSecondary
             )
         case .recording:
-            return (state.lastTranscript.isEmpty ? " " : state.lastTranscript, palette.textPrimary)
+            return (lastTranscript.isEmpty ? " " : lastTranscript, palette.textPrimary)
         case .processing:
             return (
-                state.lastTranscript.isEmpty
+                lastTranscript.isEmpty
                     ? ExtL10n.string("keyboard.placeholder.processing")
-                    : state.lastTranscript,
+                    : lastTranscript,
                 palette.textSecondary
             )
         case .error(_, let message):
@@ -1149,14 +1160,7 @@ struct AIKeyboardView: View {
     }
 
     private func waveform(color: Color) -> some View {
-        WaveformView(
-            level: state.level,
-            barCount: 7,
-            color: color,
-            active: true
-        )
-        .frame(width: 38, height: 26)
-        .clipped()
+        AssistantWaveform(state: state, color: color)
     }
 
     private var microphoneTint: Color {
@@ -1562,6 +1566,35 @@ struct AIKeyboardView: View {
 /// Uses a subview's intrinsic width until it reaches a visual cap. Unlike
 /// `frame(maxWidth:)`, this layout does not expand short labels to the cap,
 /// so each capsule and its complete hit target follow the actual content.
+/// Reads `state.level` in its own body so the 200 ms mic level tick re-renders
+/// only these bars instead of the whole assistant surface.
+private struct AssistantWaveform: View {
+    let state: KeyboardState
+    let color: Color
+
+    var body: some View {
+        WaveformView(
+            level: state.level,
+            barCount: 7,
+            color: color,
+            active: true
+        )
+        .frame(width: 38, height: 26)
+        .clipped()
+    }
+}
+
+/// Reads `state.lastTranscript` in its own body so per-word ASR partials
+/// re-render only the status line.
+private struct LiveTranscriptReader<Content: View>: View {
+    let state: KeyboardState
+    @ViewBuilder let content: (String) -> Content
+
+    var body: some View {
+        content(state.lastTranscript)
+    }
+}
+
 private struct IntrinsicWidthCap: Layout {
     let maxWidth: CGFloat
 

OSGKeyboardExt/Views/GlobeInputModeButton.swift

@@ -12,7 +12,7 @@ import SwiftUI
 import UIKit
 
 struct GlobeInputModeButton: UIViewRepresentable {
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @Binding var isPressed: Bool
 
     func makeUIView(context: Context) -> GlobeInputModeButtonView {
@@ -41,7 +41,7 @@ struct GlobeInputModeButton: UIViewRepresentable {
 struct SystemGlobeKey: View {
     @Environment(\.colorScheme) private var colorScheme
     @Environment(\.themePalette) private var palette
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @State private var isPressed = false
 
     var width: CGFloat = 44

OSGKeyboardExt/Views/KeyboardTopControls.swift

@@ -112,7 +112,7 @@ struct KeyboardTopControls: View {
     @Environment(\.keyboardTabSelectionNamespace) private var sharedSelectionNamespace
     @Namespace private var fallbackSelectionNamespace
 
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @ObservedObject var typing: TypingSessionController
 
     let palette: ThemePalette

OSGKeyboardExt/Views/LastInputEditView.swift

@@ -12,7 +12,7 @@ struct LastInputEditView: View {
 
     @Environment(\.colorScheme) private var colorScheme
     @Environment(\.accessibilityReduceMotion) private var reduceMotion
-    @ObservedObject var state: KeyboardState
+    var state: KeyboardState
     @State private var selectedPage: Int? = 0
 
     private var palette: ThemePalette {