diff --git a/Cotabby/App/Core/AppDelegate.swift b/Cotabby/App/Core/AppDelegate.swift
index d5c6587..19fd153 100644
--- a/Cotabby/App/Core/AppDelegate.swift
+++ b/Cotabby/App/Core/AppDelegate.swift
@@ -31,6 +31,11 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
 
     private let activationIndicatorController: ActivationIndicatorController
     private let focusDebugOverlayController: FocusDebugOverlayController?
+    /// Retained for the app's lifetime because the environment owns its own `cancellables` (the only
+    /// subscriptions wiring the focus-poll-interval setting and the global-toggle hotkey rebind to the
+    /// runtime). If the environment deallocated when `init` returned, those subscriptions would be
+    /// cancelled and both settings would silently stop working until the next relaunch.
+    private let environment: CotabbyAppEnvironment
     private var cancellables = Set<AnyCancellable>()
     private var didStartServices = false
 
@@ -38,9 +43,9 @@ final class AppDelegate: NSObject, NSApplicationDelegate {
         CotabbyLogger.bootstrap()
 
         // Build the dependency graph once up front so every scene/view observes the same
-        // long-lived objects for the entire app session. `CotabbyAppEnvironment` is a composition
-        // helper here; the app delegate retains the root objects it needs directly.
+        // long-lived objects for the entire app session.
         let environment = CotabbyAppEnvironment()
+        self.environment = environment
         permissionManager = environment.permissionManager
         runtimeModel = environment.runtimeModel
         modelDownloadManager = environment.modelDownloadManager
diff --git a/Cotabby/Services/UI/OverlayController.swift b/Cotabby/Services/UI/OverlayController.swift
index d8ed617..2b0791b 100644
--- a/Cotabby/Services/UI/OverlayController.swift
+++ b/Cotabby/Services/UI/OverlayController.swift
@@ -1,5 +1,6 @@
 import AppKit
 import Foundation
+import Logging
 import SwiftUI
 
 /// File overview:
@@ -183,6 +184,13 @@ final class OverlayController: SuggestionOverlayControlling {
 
         let frame = layout.panelFrame(for: contentSize, caretRect: geometry.caretRect)
 
+        // Last-resort guard: AppKit raises on a non-finite frame. The AX ingest boundary already
+        // rejects NaN/Inf rects, so reaching here means the layout math produced one; skip the show
+        // rather than crash on the hottest path.
+        guard AXHelper.rectHasFiniteComponents(frame) else {
+            CotabbyLogger.suggestion.warning("Skipped inline overlay: computed a non-finite frame")
+            return
+        }
         panel.setFrame(frame.integral, display: true)
         panel.orderFrontRegardless()
     }
@@ -231,7 +239,12 @@ final class OverlayController: SuggestionOverlayControlling {
             panel.contentView = contentView
         }
 
-        panel.setFrame(layout.panelFrame, display: true)
+        let panelFrame = layout.panelFrame
+        guard AXHelper.rectHasFiniteComponents(panelFrame) else {
+            CotabbyLogger.suggestion.warning("Skipped mirror overlay: computed a non-finite frame")
+            return
+        }
+        panel.setFrame(panelFrame, display: true)
         panel.orderFrontRegardless()
     }
 
diff --git a/Cotabby/Support/AXHelper.swift b/Cotabby/Support/AXHelper.swift
index fccb3fd..c78a35c 100644
--- a/Cotabby/Support/AXHelper.swift
+++ b/Cotabby/Support/AXHelper.swift
@@ -590,6 +590,9 @@ enum AXHelper {
     /// Use this for element-level rects (AXFrame) that are reliably in Cocoa points.
     /// For text-range rects (BoundsForRange, TextMarker), use `validatedCocoaTextRect` instead.
     static func cocoaRect(fromAccessibilityRect rect: CGRect) -> CGRect {
+        guard rectHasFiniteComponents(rect) else {
+            return .zero
+        }
         guard !rect.isNull, rect != .zero else {
             return rect
         }
@@ -605,6 +608,15 @@ enum AXHelper {
         return legacyDesktopUnionFlip(rect)
     }
 
+    /// True only when every component of `rect` is a finite number. Some host AX implementations
+    /// (Chromium/Electron, especially mid-scroll or under load) return NaN/Inf bounds; AppKit raises
+    /// on a non-finite window frame and `Int(.nan)` traps, so such rects are rejected here at the AX
+    /// ingest boundary before they can reach geometry math or `NSWindow.setFrame`.
+    static func rectHasFiniteComponents(_ rect: CGRect) -> Bool {
+        rect.origin.x.isFinite && rect.origin.y.isFinite
+            && rect.size.width.isFinite && rect.size.height.isFinite
+    }
+
     /// Converts a text-range AX rect to Cocoa coordinates, using the element's AXFrame (already
     /// in Cocoa coordinates) as a ground-truth anchor to detect whether pixel-to-point scaling
     /// is needed. This replaces the old bundle-ID heuristic with empirical geometric validation:
@@ -615,6 +627,9 @@ enum AXHelper {
         fromAccessibilityRect textRect: CGRect,
         anchorFrame cocoaAnchorFrame: CGRect?
     ) -> CGRect {
+        guard rectHasFiniteComponents(textRect) else {
+            return .zero
+        }
         guard !textRect.isNull, textRect != .zero else {
             return textRect
         }
diff --git a/CotabbyTests/AXTextGeometryResolverTests.swift b/CotabbyTests/AXTextGeometryResolverTests.swift
index 6fd8458..c34fc75 100644
--- a/CotabbyTests/AXTextGeometryResolverTests.swift
+++ b/CotabbyTests/AXTextGeometryResolverTests.swift
@@ -146,4 +146,20 @@ final class AXTextGeometryResolverTests: XCTestCase {
         XCTAssertTrue(resolver.rectIsNearAnchor(rect, anchor: nil))
         XCTAssertTrue(resolver.rectIsNearAnchor(rect, anchor: .zero))
     }
+
+    // MARK: - Non-finite AX rect rejection (crash guard)
+
+    func test_rectHasFiniteComponents_rejectsNaNAndInfinity() {
+        XCTAssertTrue(AXHelper.rectHasFiniteComponents(CGRect(x: 1, y: 2, width: 3, height: 4)))
+        XCTAssertFalse(AXHelper.rectHasFiniteComponents(CGRect(x: CGFloat.nan, y: 0, width: 10, height: 10)))
+        XCTAssertFalse(AXHelper.rectHasFiniteComponents(CGRect(x: 0, y: 0, width: CGFloat.infinity, height: 10)))
+        XCTAssertFalse(AXHelper.rectHasFiniteComponents(CGRect(x: 0, y: CGFloat.nan, width: 10, height: CGFloat.nan)))
+    }
+
+    func test_validatedCocoaTextRect_collapsesNonFiniteRectToZero() {
+        // A NaN/Inf AX rect must collapse to .zero, never propagate toward NSWindow.setFrame (a crash).
+        let nan = CGRect(x: CGFloat.nan, y: 10, width: 20, height: 14)
+        XCTAssertEqual(AXHelper.validatedCocoaTextRect(fromAccessibilityRect: nan, anchorFrame: nil), .zero)
+        XCTAssertEqual(AXHelper.cocoaRect(fromAccessibilityRect: nan), .zero)
+    }
 }