feat(onboarding): restrict display name to ASCII letters, digits, and spaces

Flipcash/Core/Screens/Onboarding/OnboardingNameViewModel.swift

@@ -28,7 +28,7 @@ final class OnboardingNameViewModel {
 
     @ObservationIgnored private let flipClient: FlipClient
     @ObservationIgnored private let owner: KeyPair
-    @ObservationIgnored private let validator = DisplayNameValidator()
+    @ObservationIgnored private let validator = DisplayNameValidator(asciiOnly: true)
 
     /// Fires once the name is saved; the onboarding flow advances from here.
     @ObservationIgnored var onComplete: (@MainActor () -> Void)?

FlipcashCore/Sources/FlipcashCore/Validation/DisplayNameValidator.swift

@@ -7,14 +7,20 @@ import Foundation
 
 /// Validates a profile display name: 1–64 Unicode scalars of any script.
 ///
-/// Returns the name trimmed of leading and trailing whitespace.
+/// Returns the name trimmed of leading and trailing whitespace. With `asciiOnly`,
+/// the trimmed name may also contain only `A-Z`, `a-z`, `0-9`, and U+0020.
 public struct DisplayNameValidator: Validator {
 
     /// PGV `max_len` from `FlipcashAPI/Core/proto/profile/v1/profile_service.proto`
     /// counts Unicode scalars, not grapheme clusters — one ZWJ emoji spends seven.
     public static let maxScalars = 64
 
-    public init() {}
+    private let asciiOnly: Bool
+
+    /// Creates a validator; `asciiOnly` restricts names to ASCII letters, digits, and spaces.
+    public init(asciiOnly: Bool = false) {
+        self.asciiOnly = asciiOnly
+    }
 
     public func validate(_ input: String) -> String? {
         let trimmed = input.trimmingCharacters(in: .whitespacesAndNewlines)
@@ -23,6 +29,10 @@ public struct DisplayNameValidator: Validator {
             return nil
         }
 
+        if asciiOnly, !trimmed.unicodeScalars.allSatisfy(Self.isASCIIAlphanumericOrSpace) {
+            return nil
+        }
+
         return trimmed
     }
 
@@ -32,4 +42,11 @@ public struct DisplayNameValidator: Validator {
         let trimmed = input.trimmingCharacters(in: .whitespacesAndNewlines)
         return Self.maxScalars - trimmed.unicodeScalars.count
     }
+
+    private static func isASCIIAlphanumericOrSpace(_ scalar: Unicode.Scalar) -> Bool {
+        switch scalar.value {
+        case 0x20, 0x30...0x39, 0x41...0x5A, 0x61...0x7A: true
+        default: false
+        }
+    }
 }

FlipcashCore/Tests/FlipcashCoreTests/DisplayNameValidatorTests.swift

@@ -88,4 +88,37 @@ struct DisplayNameValidatorTests {
     func remainingIgnoresSurroundingWhitespace() {
         #expect(validator.remaining(in: "  Ted  ") == DisplayNameValidator.maxScalars - 3)
     }
+
+    // MARK: - ASCII-only (onboarding) -
+
+    private let asciiValidator = DisplayNameValidator(asciiOnly: true)
+
+    @Test("ASCII-only accepts letters, digits, and spaces, trimmed",
+          arguments: [
+              (input: "Taylor Smith 2", expected: "Taylor Smith 2"),
+              (input: "  Taylor ", expected: "Taylor"),
+              (input: "A  B", expected: "A  B"),
+          ])
+    func asciiOnlyAccepts(input: String, expected: String) {
+        #expect(asciiValidator.validate(input) == expected)
+    }
+
+    @Test("ASCII-only rejects accents, punctuation, emoji, other whitespace, and over-limit",
+          arguments: [
+              "Jos\u{00E9}",
+              "Taylor!",
+              "\u{1F600}",
+              "Tay\tlor",
+              "Tay\u{00A0}lor",
+              "   ",
+              String(repeating: "a", count: 65),
+          ])
+    func asciiOnlyRejects(input: String) {
+        #expect(asciiValidator.validate(input) == nil)
+    }
+
+    @Test("Default validator still accepts accented names")
+    func defaultAcceptsAccents() {
+        #expect(validator.validate("Jos\u{00E9}") == "Jos\u{00E9}")
+    }
 }