Stabilize iOS UI test foundation and fix flaky suites

Tests iOS/Helpers/BaseUITestCase.swift

@@ -32,10 +32,7 @@ class BaseUITestCase: XCTestCase {
         super.setUp()
         continueAfterFailure = false
 
-        app = XCUIApplication()
-        app.launchArguments = buildLaunchArguments()
-        app.launchEnvironment = buildLaunchEnvironment()
-        app.launch()
+        app = launchApp(resetState: true)
     }
 
     override func tearDown() {
@@ -48,8 +45,11 @@ class BaseUITestCase: XCTestCase {
 
     // MARK: - Launch Configuration
 
-    private func buildLaunchArguments() -> [String] {
-        var args = ["--ui-testing", "--reset-state", "--disable-animations"]
+    private func buildLaunchArguments(resetState: Bool) -> [String] {
+        var args = ["--ui-testing", "--disable-animations", "-AppleLanguages", "(en)", "-AppleLocale", "en_US"]
+        if resetState {
+            args.append("--reset-state")
+        }
         if bypassSubscription {
             args.append("--bypass-subscription")
         }
@@ -78,4 +78,29 @@ class BaseUITestCase: XCTestCase {
         screenshot.lifetime = .keepAlways
         add(screenshot)
     }
+
+    // MARK: - Shared Test Utilities
+
+    @discardableResult
+    func launchApp(resetState: Bool) -> XCUIApplication {
+        let application = XCUIApplication()
+        application.launchArguments = buildLaunchArguments(resetState: resetState)
+        application.launchEnvironment = buildLaunchEnvironment()
+        application.launch()
+        return application
+    }
+
+    @discardableResult
+    func relaunchPreservingState() -> XCUIApplication {
+        app.terminate()
+        let relaunched = launchApp(resetState: false)
+        app = relaunched
+        return relaunched
+    }
+
+    func assertDayContentVisible(timeout: TimeInterval = 8, file: StaticString = #file, line: UInt = #line) {
+        let hasEntry = app.firstEntryRow.waitForExistence(timeout: timeout)
+        let hasMoodHeader = app.element(UITestID.Day.moodHeader).waitForExistence(timeout: 2)
+        XCTAssertTrue(hasEntry || hasMoodHeader, "Day view should show entry list or mood header", file: file, line: line)
+    }
 }