Books — fix infinite render loop via value-based navigation

Opening a book chapter froze the app in an infinite render loop. Root
cause: the books screens used the eager `NavigationLink { destination }`
form inside `List`/`LazyVStack`. That form keeps the destination view
structurally parented to the source row, so `BookReaderView`'s ScrollView
got trapped inside a `List` row — a row sizes to intrinsic height, a
ScrollView has none, so the two never converge and re-measure forever.

Switch the whole books navigation chain to value-based navigation:
- practiceHomeView, BookLibraryView, BookChapterListView use
  NavigationLink(value:).
- PracticeView's NavigationStack declares the BooksRoute, Book, and
  BookChapter destinations once, at the stack root (mixing eager and
  value-based pushes in one path caused pushed screens to pop back).
- BookReaderView is built from just a BookChapter; it resolves its Book
  by slug via @Query.

Also:
- BookChapter gains a stored paragraphCount so the chapter list no longer
  decodes the full paragraph JSON on every render (bookDataVersion -> 6
  to re-seed).
- BookSpeechController builds its AVSpeechSynthesizer lazily.

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

Conjuga/Conjuga/Services/BookSpeechController.swift

@@ -25,7 +25,16 @@ final class BookSpeechController: NSObject, AVSpeechSynthesizerDelegate {
 
     // MARK: - Internals
 
-    private let synthesizer = AVSpeechSynthesizer()
+    /// Built on first use, not in `init`. `AVSpeechSynthesizer()` connects to
+    /// the system speech daemon, so allocating one per `BookReaderView` struct
+    /// construction (SwiftUI rebuilds the struct on every parent render) is a
+    /// real cost — deferring it keeps controller construction cheap.
+    @ObservationIgnored
+    private lazy var synthesizer: AVSpeechSynthesizer = {
+        let synth = AVSpeechSynthesizer()
+        synth.delegate = self
+        return synth
+    }()
     private var queue: [QueueEntry] = []
     private var queueCursor: Int = 0
     private var audioSessionConfigured = false
@@ -38,7 +47,6 @@ final class BookSpeechController: NSObject, AVSpeechSynthesizerDelegate {
 
     override init() {
         super.init()
-        synthesizer.delegate = self
     }
 
     // MARK: - Public control

Conjuga/Conjuga/Services/DataLoader.swift

@@ -9,7 +9,7 @@ actor DataLoader {
     static let textbookDataVersion = 14
     static let textbookDataKey = "textbookDataVersion"
 
-    static let bookDataVersion = 5  // bump: per-book glossary added
+    static let bookDataVersion = 6  // bump: BookChapter.paragraphCount added
     static let bookDataKey = "bookDataVersion"
 
     /// Quick check: does the DB need seeding or course data refresh?
@@ -632,6 +632,7 @@ actor DataLoader {
                     bookSlug: slug,
                     number: number,
                     title: chTitle,
+                    paragraphCount: paragraphsES.count,
                     paragraphsESJSON: esData,
                     paragraphsENJSON: enData
                 )

Conjuga/Conjuga/Views/Practice/Books/BookChapterListView.swift

@@ -19,9 +19,7 @@ struct BookChapterListView: View {
     var body: some View {
         List {
             ForEach(allChapters) { chapter in
-                NavigationLink {
+                NavigationLink(value: chapter) {
-                    BookReaderView(chapter: chapter, book: book)
-                } label: {
                     HStack(spacing: 12) {
                         Text("\(chapter.number)")
                             .font(.subheadline.weight(.bold).monospacedDigit())
@@ -31,7 +29,7 @@ struct BookChapterListView: View {
                         VStack(alignment: .leading, spacing: 2) {
                             Text(chapter.title)
                                 .font(.subheadline.weight(.medium))
-                            Text("\(chapter.paragraphsES().count) paragraph\(chapter.paragraphsES().count == 1 ? "" : "s")")
+                            Text("\(chapter.paragraphCount) paragraph\(chapter.paragraphCount == 1 ? "" : "s")")
                                 .font(.caption2)
                                 .foregroundStyle(.tertiary)
                         }

Conjuga/Conjuga/Views/Practice/Books/BookLibraryView.swift

@@ -2,6 +2,14 @@ import SwiftUI
 import SharedModels
 import SwiftData
 
+/// Route value for pushing the books library. Lets `PracticeView` use a
+/// value-based link so the entire books navigation chain is consistent —
+/// mixing a view-based push with value-based pushes deeper in the same
+/// NavigationStack made pushed screens pop back immediately.
+enum BooksRoute: Hashable {
+    case library
+}
+
 struct BookLibraryView: View {
     @Query(sort: \Book.title) private var books: [Book]
 
@@ -17,9 +25,7 @@ struct BookLibraryView: View {
                 ScrollView {
                     LazyVStack(spacing: 12) {
                         ForEach(books) { book in
-                            NavigationLink {
+                            NavigationLink(value: book) {
-                                BookChapterListView(book: book)
-                            } label: {
                                 BookCard(book: book)
                             }
                             .tint(.primary)

Conjuga/Conjuga/Views/Practice/Books/BookReaderView.swift

@@ -1,10 +1,16 @@
 import SwiftUI
 import SharedModels
+import SwiftData
 import FoundationModels
 
 struct BookReaderView: View {
     let chapter: BookChapter
-    let book: Book
+
+    /// The book this chapter belongs to, resolved by slug — used for the
+    /// pre-computed glossary. A @Query is safe here because the reader is
+    /// built lazily by `navigationDestination`: one instance, when opened.
+    @Query private var bookMatches: [Book]
+    private var book: Book? { bookMatches.first }
 
     @Environment(DictionaryService.self) private var dictionary
     @State private var speech = BookSpeechController()
@@ -19,6 +25,12 @@ struct BookReaderView: View {
     @AppStorage("bookReaderVoiceId") private var storedVoiceId: String = ""
     @AppStorage("bookReaderRate") private var storedRate: Double = 0.45
 
+    init(chapter: BookChapter) {
+        self.chapter = chapter
+        let slug = chapter.bookSlug
+        _bookMatches = Query(filter: #Predicate<Book> { $0.slug == slug })
+    }
+
     private var paragraphsES: [String] { chapter.paragraphsES() }
     private var paragraphsEN: [String] { chapter.paragraphsEN() }
 
@@ -87,7 +99,7 @@ struct BookReaderView: View {
             speech.voiceIdentifier = storedVoiceId.isEmpty ? nil : storedVoiceId
             speech.rate = Float(storedRate)
             if glossary.isEmpty {
-                glossary = book.glossary()
+                glossary = book?.glossary() ?? [:]
             }
         }
         .onDisappear {

Conjuga/Conjuga/Views/Practice/PracticeView.swift

@@ -21,6 +21,19 @@ struct PracticeView: View {
                     practiceHomeView
                 }
             }
+            // Book navigation is value-based and declared once here, at the
+            // stack root. Eager `NavigationLink { destination }` forms inside
+            // the List/LazyVStack of the book screens caused an infinite
+            // render loop; value-based links build destinations lazily.
+            .navigationDestination(for: BooksRoute.self) { _ in
+                BookLibraryView()
+            }
+            .navigationDestination(for: Book.self) { book in
+                BookChapterListView(book: book)
+            }
+            .navigationDestination(for: BookChapter.self) { chapter in
+                BookReaderView(chapter: chapter)
+            }
             .navigationTitle("Practice")
             .navigationBarTitleDisplayMode(.inline)
             .onAppear(perform: loadProgress)
@@ -261,9 +274,7 @@ struct PracticeView: View {
                 .padding(.horizontal)
 
                 // Books
-                NavigationLink {
+                NavigationLink(value: BooksRoute.library) {
-                    BookLibraryView()
-                } label: {
                     HStack(spacing: 14) {
                         Image(systemName: "books.vertical.fill")
                             .font(.title3)

Conjuga/SharedModels/Sources/SharedModels/BookChapter.swift

@@ -10,6 +10,9 @@ public final class BookChapter {
     public var bookSlug: String = ""
     public var number: Int = 0
     public var title: String = ""
+    /// Spanish paragraph count, stored at seed time so chapter lists can show
+    /// it without decoding the full `paragraphsESJSON` blob on every render.
+    public var paragraphCount: Int = 0
     public var paragraphsESJSON: Data = Data()
     public var paragraphsENJSON: Data = Data()
 
@@ -18,6 +21,7 @@ public final class BookChapter {
         bookSlug: String,
         number: Int,
         title: String,
+        paragraphCount: Int,
         paragraphsESJSON: Data,
         paragraphsENJSON: Data
     ) {
@@ -25,6 +29,7 @@ public final class BookChapter {
         self.bookSlug = bookSlug
         self.number = number
         self.title = title
+        self.paragraphCount = paragraphCount
         self.paragraphsESJSON = paragraphsESJSON
         self.paragraphsENJSON = paragraphsENJSON
     }