Add client-side length caps + truncation for Shop name/description

Ports nativeapptemplate/NativeAppTemplate-iOS#60.
Mirror the ItemTag pattern from PR #49 for Shop. Server has no caps on
Shop name/description; this is a client-only UX guard.

- Constants: maximumShopNameLength = 100, maximumShopDescriptionLength
  = 1_000. New strings: shopNameIsInvalid, shopDescriptionIsInvalid,
  plus shopNameHelp(maximumLength:) / shopDescriptionHelp(maximumLength:)
  parametric helpers.
- ShopCreateViewModel + ShopBasicSettingsViewModel: split hasInvalidData
  into hasInvalidDataName + hasInvalidDataDescription, expose
  maximumNameLength / maximumDescriptionLength, add validateNameLength()
  / validateDescriptionLength().
- ShopCreateView + ShopBasicSettingsView: wire .onChange truncation on
  Name and Description; switch to two-line footer (always-visible help
  + conditional red "is invalid" text), matching ItemTagCreateView.
- Tests: added maximumNameLength, maximumDescriptionLength, parametric
  nameValidation / descriptionValidation, and the two truncation tests
  on both viewmodel test suites; replaced the old simple
  hasInvalidData(name:) parametric test in ShopCreateViewModelTest.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dadachi

NativeAppTemplate/Constants.swift

@@ -72,6 +72,11 @@ enum NativeAppTemplateConstants {
         static let shadowRadius: CGFloat = 8
     }
 
+    // MARK: - Shop
+
+    static let maximumShopNameLength = 100
+    static let maximumShopDescriptionLength = 1_000
+
     // MARK: - ItemTag
 
     static let maximumItemTagNameLength = 100
@@ -146,6 +151,17 @@ extension String {
     static let addShopDescription = "Add a new shop."
     static let deleteShop = "Delete Shop"
     static let shopNameIsRequired = "Shop name is required."
+    static let shopNameIsInvalid = "Shop name is invalid."
+    static let shopDescriptionIsInvalid = "Shop description is too long."
+
+    static func shopNameHelp(maximumLength: Int) -> String {
+        "Name must be 1–\(maximumLength) characters."
+    }
+
+    static func shopDescriptionHelp(maximumLength: Int) -> String {
+        "Description can be up to \(maximumLength) characters."
+    }
+
     static let timeZone = "Time Zone"
     static let createShopsLabel = "Create shops"
     static let tapShopBelow = "Tap a shop below."

NativeAppTemplate/UI/Shop List/ShopCreateView.swift

@@ -36,14 +36,37 @@ struct ShopCreateView: View {
             Form {
                 Section {
                     TextField(String.name, text: $viewModel.name)
+                        .onChange(of: viewModel.name) {
+                            viewModel.validateNameLength()
+                        }
+                } header: {
+                    Text(String.shopName)
                 } footer: {
-                    Text(String.shopNameIsRequired)
-                        .foregroundStyle(viewModel.hasInvalidData ? .validationError : .clear)
+                    VStack(alignment: .leading) {
+                        Text(String.shopNameHelp(maximumLength: viewModel.maximumNameLength))
+                            .font(.uiFootnote)
+                        Text(String.shopNameIsInvalid)
+                            .font(.uiFootnote)
+                            .foregroundStyle(viewModel.hasInvalidDataName ? .validationError : .clear)
+                    }
                 }
 
                 Section {
                     TextField(String.descriptionString, text: $viewModel.description, axis: .vertical)
                         .lineLimit(10, reservesSpace: true)
+                        .onChange(of: viewModel.description) {
+                            viewModel.validateDescriptionLength()
+                        }
+                } header: {
+                    Text(String.descriptionString)
+                } footer: {
+                    VStack(alignment: .leading) {
+                        Text(String.shopDescriptionHelp(maximumLength: viewModel.maximumDescriptionLength))
+                            .font(.uiFootnote)
+                        Text(String.shopDescriptionIsInvalid)
+                            .font(.uiFootnote)
+                            .foregroundStyle(viewModel.hasInvalidDataDescription ? .validationError : .clear)
+                    }
                 }
 
                 Section {

NativeAppTemplate/UI/Shop List/ShopCreateViewModel.swift

@@ -31,7 +31,37 @@ final class ShopCreateViewModel {
     }
 
     var hasInvalidData: Bool {
-        Utility.isBlank(name)
+        hasInvalidDataName || hasInvalidDataDescription
+    }
+
+    var hasInvalidDataName: Bool {
+        if Utility.isBlank(name) {
+            return true
+        }
+        if name.count > maximumNameLength {
+            return true
+        }
+        return false
+    }
+
+    var hasInvalidDataDescription: Bool {
+        description.count > maximumDescriptionLength
+    }
+
+    var maximumNameLength: Int {
+        NativeAppTemplateConstants.maximumShopNameLength
+    }
+
+    var maximumDescriptionLength: Int {
+        NativeAppTemplateConstants.maximumShopDescriptionLength
+    }
+
+    func validateNameLength() {
+        name = String(name.prefix(maximumNameLength))
+    }
+
+    func validateDescriptionLength() {
+        description = String(description.prefix(maximumDescriptionLength))
     }
 
     func createShop() {

NativeAppTemplate/UI/Shop Settings/ShopBasicSettingsView.swift

@@ -45,19 +45,37 @@ private extension ShopBasicSettingsView {
         Form {
             Section {
                 TextField(String.shopName, text: $viewModel.name)
+                    .onChange(of: viewModel.name) {
+                        viewModel.validateNameLength()
+                    }
             } header: {
                 Text(String.shopName)
             } footer: {
-                Text(String.shopNameIsRequired)
-                    .font(.uiFootnote)
-                    .foregroundStyle(Utility.isBlank(viewModel.name) ? .validationError : .clear)
+                VStack(alignment: .leading) {
+                    Text(String.shopNameHelp(maximumLength: viewModel.maximumNameLength))
+                        .font(.uiFootnote)
+                    Text(String.shopNameIsInvalid)
+                        .font(.uiFootnote)
+                        .foregroundStyle(viewModel.hasInvalidDataName ? .validationError : .clear)
+                }
             }
 
             Section {
                 TextField(String.descriptionString, text: $viewModel.description, axis: .vertical)
                     .lineLimit(10, reservesSpace: true)
+                    .onChange(of: viewModel.description) {
+                        viewModel.validateDescriptionLength()
+                    }
             } header: {
                 Text(String.descriptionString)
+            } footer: {
+                VStack(alignment: .leading) {
+                    Text(String.shopDescriptionHelp(maximumLength: viewModel.maximumDescriptionLength))
+                        .font(.uiFootnote)
+                    Text(String.shopDescriptionIsInvalid)
+                        .font(.uiFootnote)
+                        .foregroundStyle(viewModel.hasInvalidDataDescription ? .validationError : .clear)
+                }
             }
 
             Section {

NativeAppTemplate/UI/Shop Settings/ShopBasicSettingsViewModel.swift

@@ -39,7 +39,11 @@ final class ShopBasicSettingsViewModel {
     }
 
     var hasInvalidData: Bool {
-        if Utility.isBlank(name) {
+        if hasInvalidDataName {
+            return true
+        }
+
+        if hasInvalidDataDescription {
             return true
         }
 
@@ -54,6 +58,36 @@ final class ShopBasicSettingsViewModel {
         return false
     }
 
+    var hasInvalidDataName: Bool {
+        if Utility.isBlank(name) {
+            return true
+        }
+        if name.count > maximumNameLength {
+            return true
+        }
+        return false
+    }
+
+    var hasInvalidDataDescription: Bool {
+        description.count > maximumDescriptionLength
+    }
+
+    var maximumNameLength: Int {
+        NativeAppTemplateConstants.maximumShopNameLength
+    }
+
+    var maximumDescriptionLength: Int {
+        NativeAppTemplateConstants.maximumShopDescriptionLength
+    }
+
+    func validateNameLength() {
+        name = String(name.prefix(maximumNameLength))
+    }
+
+    func validateDescriptionLength() {
+        description = String(description.prefix(maximumDescriptionLength))
+    }
+
     func reload() {
         Task { @MainActor in
             isFetching = true

NativeAppTemplateTests/UI/Shop List/ShopCreateViewModelTest.swift

@@ -27,16 +27,91 @@ struct ShopCreateViewModelTest {
         #expect(viewModel.isCreating == false)
     }
 
-    @Test("Has invalid data", arguments: ["", "Shop Name 1"])
-    func hasInvalidData(name: String) {
+    @Test
+    func maximumNameLength() {
+        let viewModel = ShopCreateViewModel(
+            sessionController: sessionController,
+            shopRepository: shopRepository,
+            messageBus: messageBus
+        )
+
+        #expect(viewModel.maximumNameLength == 100)
+    }
+
+    @Test
+    func maximumDescriptionLength() {
+        let viewModel = ShopCreateViewModel(
+            sessionController: sessionController,
+            shopRepository: shopRepository,
+            messageBus: messageBus
+        )
+
+        #expect(viewModel.maximumDescriptionLength == 1_000)
+    }
+
+    @Test("Name validation", arguments: [
+        ("", true),                                  // blank → invalid
+        ("a", false),                                // 1 char → valid
+        ("Shop Name 1", false),                      // normal → valid
+        (String(repeating: "a", count: 100), false), // exactly 100 → valid
+        (String(repeating: "a", count: 101), true)   // 101 → invalid
+    ])
+    func nameValidation(name: String, shouldBeInvalid: Bool) {
         let viewModel = ShopCreateViewModel(
             sessionController: sessionController,
             shopRepository: shopRepository,
             messageBus: messageBus
         )
 
         viewModel.name = name
-        #expect(viewModel.hasInvalidData == (name == "" ? true : false))
+
+        #expect(viewModel.hasInvalidDataName == shouldBeInvalid)
+    }
+
+    @Test("Description validation", arguments: [
+        ("", false),                                  // empty → valid
+        ("Short note.", false),                       // short → valid
+        (String(repeating: "x", count: 1000), false), // exactly 1000 → valid
+        (String(repeating: "x", count: 1001), true)   // 1001 → invalid
+    ])
+    func descriptionValidation(description: String, shouldBeInvalid: Bool) {
+        let viewModel = ShopCreateViewModel(
+            sessionController: sessionController,
+            shopRepository: shopRepository,
+            messageBus: messageBus
+        )
+
+        viewModel.description = description
+
+        #expect(viewModel.hasInvalidDataDescription == shouldBeInvalid)
+    }
+
+    @Test
+    func validateNameLengthTruncatesCorrectly() {
+        let viewModel = ShopCreateViewModel(
+            sessionController: sessionController,
+            shopRepository: shopRepository,
+            messageBus: messageBus
+        )
+
+        viewModel.name = String(repeating: "a", count: 100) + "EXTRA"
+        viewModel.validateNameLength()
+
+        #expect(viewModel.name == String(repeating: "a", count: 100))
+    }
+
+    @Test
+    func validateDescriptionLengthTruncatesCorrectly() {
+        let viewModel = ShopCreateViewModel(
+            sessionController: sessionController,
+            shopRepository: shopRepository,
+            messageBus: messageBus
+        )
+
+        viewModel.description = String(repeating: "x", count: 1500)
+        viewModel.validateDescriptionLength()
+
+        #expect(viewModel.description.count == 1_000)
     }
 
     @Test