diff --git a/.claude-plugin/marketplace.json b/.claude-plugin/marketplace.json
index a9a7e84..d0e8f52 100644
--- a/.claude-plugin/marketplace.json
+++ b/.claude-plugin/marketplace.json
@@ -12,7 +12,7 @@
       "name": "pdat-swift-practice",
       "source": "./pdat-swift-practice",
       "description": "Curated Apple platform findings with sources, plus practices learned from production incidents.",
-      "version": "0.3.0",
+      "version": "0.4.0",
       "author": {
         "name": "PDAT s.r.o."
       },
diff --git a/pdat-swift-practice/.claude-plugin/plugin.json b/pdat-swift-practice/.claude-plugin/plugin.json
index 7b2d5ac..5ec5694 100644
--- a/pdat-swift-practice/.claude-plugin/plugin.json
+++ b/pdat-swift-practice/.claude-plugin/plugin.json
@@ -1,6 +1,6 @@
 {
   "name": "pdat-swift-practice",
-  "version": "0.3.0",
+  "version": "0.4.0",
   "description": "Curated Apple platform findings with sources, plus practices learned from production incidents.",
   "author": {
     "name": "PDAT s.r.o.",
diff --git a/pdat-swift-practice/skills/xcode-practice/SKILL.md b/pdat-swift-practice/skills/xcode-practice/SKILL.md
index fdedc3f..7fb3c2d 100644
--- a/pdat-swift-practice/skills/xcode-practice/SKILL.md
+++ b/pdat-swift-practice/skills/xcode-practice/SKILL.md
@@ -152,10 +152,55 @@ written down afterwards: a note recording a false cause is worse than no
 note, because the next person believes it.
 
 Corollary for UI tests: when one goes red without a code change, suspect
-what the test depends on but does not control — accumulated seed data,
-`@AppStorage` surviving between launches, a simulator location and the
-"nearby" sort order it drives, or an element scrolled out of a lazy
-container and therefore missing from the accessibility tree entirely.
+what the test depends on but does not control. In our case it was exactly
+that, and the two causes are worth naming.
+
+## UI tests inherit whatever the last test left behind
+
+`@AppStorage` is UserDefaults, and the simulator keeps those between
+tests, between runs, and between days. A test that switched the card list
+to its List layout left it that way; a different test, written for the
+grid, then failed — days later, with nobody having touched the code.
+
+Reset the state at launch. Do it with a **debug hook that writes to the
+normal domain**, not with launch arguments:
+
+```swift
+// in the app, under #if DEBUG
+if ProcessInfo.processInfo.arguments.contains("-resetUserState") {
+    UserDefaults.standard.removeObject(forKey: "cardTypeFilter")
+    UserDefaults.standard.set("cards", forKey: "cardLayoutStyle")
+}
+```
+
+Launch arguments look like the obvious answer and are a trap: they form
+`NSArgumentDomain`, which outranks anything the app writes at runtime. The
+setting can then be forced but never changed, so every test that toggles
+that setting fails. Trying it turned one failing test into five.
+
+While resetting, prefer values that don't depend on the environment. A
+"sort by distance" default makes card order a function of the simulator's
+location.
+
+## An element scrolled out of a lazy container does not exist
+
+`List`, `LazyVStack` and `LazyVGrid` only build what is visible, so
+`element.exists` is `false` for a row further down — indistinguishable
+from a genuine bug. Anything below the fold needs a helper that swipes
+until the element appears:
+
+```swift
+func scrollToStaticText(_ label: String, maxSwipes: Int = 8) -> XCUIElement {
+    let element = staticTexts[label]
+    if element.waitForExistence(timeout: 5) { return element }
+    for _ in 0..<maxSwipes where !element.exists { swipeUp() }
+    return element
+}
+```
+
+Watch for content whose position depends on grouping: ours groups cards by
+type with user-defined types last, which put exactly those cards off
+screen.
 
 ## Core Data in tests