Guide — bidirectional cross-link chips between tense guides & grammar notes

After the full enrichment pass, both the Tenses and Grammar surfaces of
the Guide tab cover overlapping material — WEIRDO appears in both
"Subjuntivo Presente" and "Subjunctive Triggers", preterite↔imperfect
contrast in three places, etc. Instead of trimming either body and
losing content, add a small chip row at the top of each detail view
linking directly across.

GuideCrossLinks.swift (new) — curated tense→[noteId] map covering 18 of
the 20 tenses. The two without aligned notes (ind_pluscuamperfecto,
ind_preterito_anterior) don't show chips. The reverse map (noteId→
[tenseId]) is derived once at static init and sorted by canonical tense
order so chips appear in conjugation-table order.

GuideDetailView — "Related grammar" indigo chip row directly under the
header. Tap a chip → switch to the Grammar segment with that note
selected.

GrammarNoteDetailView — "Used in tenses" orange chip row directly under
the title. Tap a chip → switch to the Tenses segment with that tense
selected.

The GuideView segment-change handler now only clears the *other* tab's
selection so programmatic jumps keep their destination intact; manual
segment swipes still feel "fresh" like before.

No content is removed. Users get a deeper-dive path one tap away in
either direction, and the redundancy becomes a feature instead of a
maintenance hazard.

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

Conjuga/Conjuga.xcodeproj/project.pbxproj

@@ -96,6 +96,7 @@
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 		C2B3D97F119EFCE97E3CB1CE /* ConjugaApp.swift in Sources */ = {isa = PBXBuildFile; fileRef = 1EB4830F9289AACC82D753F8 /* ConjugaApp.swift */; };
 		C3851F960C1162239DC2F935 /* CourseQuizView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 143D06606AE10DCA30A140C2 /* CourseQuizView.swift */; };
+		C3F567971CE8379CCC0AA9ED /* GuideCrossLinks.swift in Sources */ = {isa = PBXBuildFile; fileRef = A3FCE2E42939FB4CF491B9F1 /* GuideCrossLinks.swift */; };
 		C8C3880535008764B7117049 /* DataLoader.swift in Sources */ = {isa = PBXBuildFile; fileRef = DADCA82DDD34DF36D59BB283 /* DataLoader.swift */; };
 		CAC69045B74249F121643E88 /* AnswerReviewView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 83A8C1A048627C8DEB83C12D /* AnswerReviewView.swift */; };
 		CC886125F8ECE72D1AAD4861 /* StoryReaderView.swift in Sources */ = {isa = PBXBuildFile; fileRef = 6A48474D969CEF5F573DF09B /* StoryReaderView.swift */; };
@@ -230,6 +231,7 @@
 		9708FF3CF33E4765DB225F93 /* ConjugaWidgetExtension.appex */ = {isa = PBXFileReference; includeInIndex = 0; lastKnownFileType = "wrapper.app-extension"; path = ConjugaWidgetExtension.appex; sourceTree = BUILT_PRODUCTS_DIR; };
 		9E1FB35614B709E6B1D1D017 /* Conjuga.entitlements */ = {isa = PBXFileReference; lastKnownFileType = text.plist.entitlements; path = Conjuga.entitlements; sourceTree = "<group>"; };
 		A014EEC3EE08E945FBBA5335 /* Assets.xcassets */ = {isa = PBXFileReference; lastKnownFileType = folder.assetcatalog; path = Assets.xcassets; sourceTree = "<group>"; };
+		A3FCE2E42939FB4CF491B9F1 /* GuideCrossLinks.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = GuideCrossLinks.swift; sourceTree = "<group>"; };
 		A4B95B276C054DBFE508C4D1 /* StartupCoordinator.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = StartupCoordinator.swift; sourceTree = "<group>"; };
 		A63061BBC8998DF33E3DCA2B /* VerbListView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = VerbListView.swift; sourceTree = "<group>"; };
 		A661ADF1141176EE96774138 /* BookSpeechController.swift */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = sourcecode.swift; path = BookSpeechController.swift; sourceTree = "<group>"; };
@@ -382,6 +384,7 @@
 				3BC3247457109FC6BF00D85B /* TenseInfo.swift */,
 				DAFE27F29412021AEC57E728 /* TestResult.swift */,
 				E536AD1180FE10576EAC884A /* UserProgress.swift */,
+				A3FCE2E42939FB4CF491B9F1 /* GuideCrossLinks.swift */,
 			);
 			path = Models;
 			sourceTree = "<group>";
@@ -774,6 +777,7 @@
 				64E08FBC4B188B332F8039FD /* BookReaderView.swift in Sources */,
 				33BFEC0F0DEFC8A0E1FD8009 /* BookSpeechController.swift in Sources */,
 				2CB1E7454C1C04C2A9A06D57 /* BookVoicePickerSheet.swift in Sources */,
+				C3F567971CE8379CCC0AA9ED /* GuideCrossLinks.swift in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

Conjuga/Conjuga/Models/GuideCrossLinks.swift

@@ -0,0 +1,108 @@
+import Foundation
+
+/// Maps tense guides ↔ grammar notes for the Guide tab's cross-link chips.
+/// The forward map is the curated source; the reverse map is derived once.
+///
+/// A tense ID appears here only if at least one grammar note in
+/// `GrammarNote.allNotesIncludingGenerated` covers a concept directly tied
+/// to that tense (forms, contrast, triggers, choice). Two tenses currently
+/// have no aligned notes and don't appear: `ind_pluscuamperfecto` and
+/// `ind_preterito_anterior`.
+enum GuideCrossLinks {
+    /// Tense ID → ordered grammar note IDs that go deeper on this tense.
+    /// Order matters — the first chip is the most-relevant note for the
+    /// tense's primary teaching point.
+    static let relatedNotes: [String: [String]] = [
+        "ind_presente": [
+            "present-indicative-conjugation",
+            "irregular-yo-verbs",
+            "stem-changing-verbs",
+            "estar-gerund-progressive",
+        ],
+        "ind_preterito": [
+            "preterite-vs-imperfect",
+            "stem-changing-verbs",
+        ],
+        "ind_imperfecto": [
+            "preterite-vs-imperfect",
+        ],
+        "ind_futuro": [
+            "future-vs-ir-a",
+        ],
+        "ind_perfecto": [
+            "present-perfect-tense",
+        ],
+        "ind_futuro_perfecto": [
+            "future-perfect-tense",
+        ],
+        "cond_presente": [
+            "conditional-if-clauses",
+        ],
+        "cond_perfecto": [
+            "conditional-if-clauses",
+        ],
+        "subj_presente": [
+            "subjunctive-triggers",
+            "irregular-yo-verbs",
+            "stem-changing-verbs",
+        ],
+        "subj_imperfecto_1": [
+            "subjunctive-triggers",
+            "conditional-if-clauses",
+        ],
+        "subj_imperfecto_2": [
+            "subjunctive-triggers",
+            "conditional-if-clauses",
+        ],
+        "subj_perfecto": [
+            "subjunctive-triggers",
+        ],
+        "subj_pluscuamperfecto_1": [
+            "subjunctive-triggers",
+            "conditional-if-clauses",
+        ],
+        "subj_pluscuamperfecto_2": [
+            "subjunctive-triggers",
+            "conditional-if-clauses",
+        ],
+        "subj_futuro": [
+            "subjunctive-triggers",
+        ],
+        "subj_futuro_perfecto": [
+            "subjunctive-triggers",
+        ],
+        "imp_afirmativo": [
+            "commands-imperative",
+        ],
+        "imp_negativo": [
+            "commands-imperative",
+            "subjunctive-triggers",
+        ],
+    ]
+
+    /// Grammar note ID → tense IDs that point at this note, ordered by the
+    /// shared `TenseInfo.order` so chips appear in canonical conjugation
+    /// order.
+    static let relatedTenses: [String: [String]] = {
+        var inverse: [String: [String]] = [:]
+        for (tenseId, noteIds) in relatedNotes {
+            for noteId in noteIds {
+                inverse[noteId, default: []].append(tenseId)
+            }
+        }
+        for key in inverse.keys {
+            inverse[key]?.sort { lhs, rhs in
+                (TenseInfo.find(lhs)?.order ?? 999) < (TenseInfo.find(rhs)?.order ?? 999)
+            }
+        }
+        return inverse
+    }()
+
+    static func noteIds(forTense tenseId: String) -> [String] {
+        relatedNotes[tenseId] ?? []
+    }
+
+    static func tenseIds(forNote noteId: String) -> [String] {
+        relatedTenses[noteId] ?? []
+    }
+}

Conjuga/Conjuga/Views/Guide/GrammarNotesView.swift

@@ -1,4 +1,6 @@
 import SwiftUI
+import SwiftData
+import SharedModels
 
 /// Standalone grammar notes view with its own NavigationStack (used outside GuideView).
 struct GrammarNotesView: View {
@@ -67,12 +69,25 @@ private struct GrammarNoteRow: View {
 
 struct GrammarNoteDetailView: View {
     let note: GrammarNote
+    var onJumpToTense: ((TenseGuide) -> Void)? = nil
     @Environment(YouTubeVideoStore.self) private var videoStore
+    @State private var relatedTenses: [TenseGuide] = []
 
     private var curatedVideo: YouTubeVideoStore.VideoEntry? {
         videoStore.video(forGrammarNoteId: note.id)
     }
 
+    private func loadRelatedTenses() {
+        guard let container = SharedStore.localContainer else {
+            relatedTenses = []
+            return
+        }
+        let context = ModelContext(container)
+        let guides = ReferenceStore(context: context).fetchGuides()
+        let byId = Dictionary(uniqueKeysWithValues: guides.map { ($0.tenseId, $0) })
+        relatedTenses = GuideCrossLinks.tenseIds(forNote: note.id).compactMap { byId[$0] }
+    }
+
     var body: some View {
         ScrollView {
             VStack(alignment: .leading, spacing: 20) {
@@ -88,6 +103,10 @@ struct GrammarNoteDetailView: View {
                         .background(.fill.tertiary, in: Capsule())
                 }
 
+                if !relatedTenses.isEmpty {
+                    relatedTensesSection
+                }
+
                 videoSection
 
                 Divider()
@@ -114,6 +133,35 @@ struct GrammarNoteDetailView: View {
         }
         .navigationTitle(note.title)
         .navigationBarTitleDisplayMode(.inline)
+        .onAppear(perform: loadRelatedTenses)
+        .onChange(of: note.id) { _, _ in loadRelatedTenses() }
+    }
+
+    private var relatedTensesSection: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Label("Used in tenses", systemImage: "clock.arrow.circlepath")
+                .font(.caption.weight(.semibold))
+                .foregroundStyle(.secondary)
+                .textCase(.uppercase)
+
+            ScrollView(.horizontal, showsIndicators: false) {
+                HStack(spacing: 8) {
+                    ForEach(relatedTenses, id: \.tenseId) { guide in
+                        Button {
+                            onJumpToTense?(guide)
+                        } label: {
+                            Text(TenseInfo.find(guide.tenseId)?.english ?? guide.title)
+                                .font(.caption.weight(.semibold))
+                                .padding(.horizontal, 12)
+                                .padding(.vertical, 7)
+                                .background(.orange.opacity(0.12), in: Capsule())
+                                .foregroundStyle(.orange)
+                        }
+                        .buttonStyle(.plain)
+                    }
+                }
+            }
+        }
     }
 
     @ViewBuilder

Conjuga/Conjuga/Views/Guide/GuideView.swift

@@ -41,15 +41,20 @@ struct GuideView: View {
             .navigationTitle("Guide")
             .task { loadGuides() }
             .onAppear(perform: loadGuides)
-            .onChange(of: selectedTab) { _, _ in
+            .onChange(of: selectedTab) { _, newTab in
-                selectedGuide = nil
+                // Only clear the *other* tab's selection so programmatic
-                selectedNote = nil
+                // cross-link jumps (chip taps in the detail pane) can keep
+                // their newly-set selection on the destination tab.
+                switch newTab {
+                case .tenses: selectedNote = nil
+                case .grammar: selectedGuide = nil
+                }
             }
         } detail: {
             if let guide = selectedGuide {
-                GuideDetailView(guide: guide)
+                GuideDetailView(guide: guide, onJumpToNote: jumpToNote)
             } else if let note = selectedNote {
-                GrammarNoteDetailView(note: note)
+                GrammarNoteDetailView(note: note, onJumpToTense: jumpToTense)
             } else {
                 ContentUnavailableView("Select a Topic", systemImage: "book", description: Text("Choose a tense or grammar topic to learn more."))
             }
@@ -79,6 +84,16 @@ struct GuideView: View {
         GrammarNotesListView(selectedNote: $selectedNote)
     }
 
+    private func jumpToNote(_ note: GrammarNote) {
+        selectedTab = .grammar
+        selectedNote = note
+    }
+
+    private func jumpToTense(_ guide: TenseGuide) {
+        selectedTab = .tenses
+        selectedGuide = guide
+    }
+
     private func loadGuides() {
         // Hit the shared local container directly, bypassing @Environment.
         guard let container = SharedStore.localContainer else {
@@ -127,8 +142,15 @@ private struct TenseRowView: View {
 
 struct GuideDetailView: View {
     let guide: TenseGuide
+    var onJumpToNote: ((GrammarNote) -> Void)? = nil
     @Environment(YouTubeVideoStore.self) private var videoStore
 
+    private var relatedNotes: [GrammarNote] {
+        GuideCrossLinks.noteIds(forTense: guide.tenseId).compactMap { id in
+            GrammarNote.allNotesIncludingGenerated.first { $0.id == id }
+        }
+    }
+
     private var tenseInfo: TenseInfo? {
         TenseInfo.find(guide.tenseId)
     }
@@ -151,6 +173,11 @@ struct GuideDetailView: View {
                 // Header
                 headerSection
 
+                // Related grammar notes — cross-links into the Grammar tab
+                if !relatedNotes.isEmpty {
+                    relatedNotesSection
+                }
+
                 // Video section (Issue #21)
                 videoSection
 
@@ -188,6 +215,35 @@ struct GuideDetailView: View {
         .navigationBarTitleDisplayMode(.inline)
     }
 
+    // MARK: - Related grammar notes
+
+    private var relatedNotesSection: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Label("Related grammar", systemImage: "book")
+                .font(.caption.weight(.semibold))
+                .foregroundStyle(.secondary)
+                .textCase(.uppercase)
+
+            ScrollView(.horizontal, showsIndicators: false) {
+                HStack(spacing: 8) {
+                    ForEach(relatedNotes, id: \.id) { note in
+                        Button {
+                            onJumpToNote?(note)
+                        } label: {
+                            Text(note.title)
+                                .font(.caption.weight(.semibold))
+                                .padding(.horizontal, 12)
+                                .padding(.vertical, 7)
+                                .background(.indigo.opacity(0.12), in: Capsule())
+                                .foregroundStyle(.indigo)
+                        }
+                        .buttonStyle(.plain)
+                    }
+                }
+            }
+        }
+    }
+
     // MARK: - Video (Issue #21)
 
     @ViewBuilder