diff --git a/supacode/Features/Canvas/Models/CanvasCardLayout.swift b/supacode/Features/Canvas/Models/CanvasCardLayout.swift
index 131e50cd4..b8e3a20a5 100644
--- a/supacode/Features/Canvas/Models/CanvasCardLayout.swift
+++ b/supacode/Features/Canvas/Models/CanvasCardLayout.swift
@@ -388,6 +388,10 @@ final class CanvasLayoutStore {
     initiallyLoadedCardKeys = Set(stored.cardLayouts.keys)
   }
 
+  // No actor-bound cleanup is needed. Avoid inferred isolated deinit, which can
+  // hit the TaskLocal invalid-free bug in older system Swift runtimes (swiftlang/swift#85204).
+  nonisolated deinit {}
+
   func shouldAutoArrangeOnInitialEntry(for cardKeys: [String]) -> Bool {
     guard !cardKeys.isEmpty else { return false }
     return !cardKeys.contains { initiallyLoadedCardKeys.contains($0) }
diff --git a/supacodeTests/CanvasLayoutStoreTests.swift b/supacodeTests/CanvasLayoutStoreTests.swift
index 09febcca1..26b579197 100644
--- a/supacodeTests/CanvasLayoutStoreTests.swift
+++ b/supacodeTests/CanvasLayoutStoreTests.swift
@@ -6,6 +6,35 @@ import Testing
 
 @MainActor
 struct CanvasLayoutStoreTests {
+  @Test func releasesSynchronouslyWithTaskLocalStorageOutsideATask() async {
+    // Swift Testing runs in a Task. A main-queue callback reproduces synchronous
+    // UI teardown with thread-local TaskLocal storage instead of task-owned storage.
+    await withCheckedContinuation { continuation in
+      DispatchQueue.main.async {
+        MainActor.assumeIsolated {
+          #expect(Thread.isMainThread)
+          withUnsafeCurrentTask { #expect($0 == nil) }
+          let defaults = makeDefaults()
+          defer { defaults.removePersistentDomain(forName: defaultsSuiteName(defaults)) }
+          let layouts = ["tab-a": CanvasCardLayout(position: CGPoint(x: 10, y: 20))]
+
+          CanvasLayoutStoreTestLocal.$marker.withValue(1) {
+            var store: CanvasLayoutStore? = CanvasLayoutStore(defaults: defaults)
+            weak let releasedStore = store
+            store?.setCardLayouts(layouts)
+            store = nil
+
+            #expect(releasedStore == nil)
+            #expect(CanvasLayoutStoreTestLocal.marker == 1)
+            #expect(CanvasLayoutStore(defaults: defaults).cardLayouts == layouts)
+          }
+          #expect(CanvasLayoutStoreTestLocal.marker == 0)
+          continuation.resume()
+        }
+      }
+    }
+  }
+
   @Test func loadsLegacyCardLayoutDictionary() throws {
     let defaults = makeDefaults()
     defer { defaults.removePersistentDomain(forName: defaultsSuiteName(defaults)) }
@@ -76,6 +105,10 @@ struct CanvasLayoutStoreTests {
   }
 }
 
+private enum CanvasLayoutStoreTestLocal {
+  @TaskLocal static var marker = 0
+}
+
 private func makeDefaults() -> UserDefaults {
   let suiteName = "CanvasLayoutStoreTests-\(UUID().uuidString)"
   let defaults = UserDefaults(suiteName: suiteName)!