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+# Follow Team Mode Design
+
+## Overview
+
+Add a 4th trip planning mode called "Follow Team" where users select a team, regions, and date range to build trips around that team's schedule (both home and away games).
+
+## User Flow
+
+1. Select "Follow Team" mode
+2. Pick a team (grouped by sport for browsing)
+3. Select regions (East/Central/West)
+4. Pick date range
+5. Choose whether to start/end from home location or fly-in/fly-out
+6. Plan trip
+
+## Scope
+
+**Included:**
+- Single team selection
+- Both home and away games
+- Region filtering (same as existing modes)
+- Date range filtering
+- Flexible start/end: home location OR first-game-to-last-game
+- Respect `allowRepeatCities` toggle
+
+**Not included (future):**
+- Multiple teams (rivalry trips)
+- Opponent filtering
+- Win/loss context display
+
+## Data Model Changes
+
+### PlanningMode Extension
+
+```swift
+enum PlanningMode: String, Codable, CaseIterable, Identifiable {
+    case dateRange      // Scenario A - dates first
+    case gameFirst      // Scenario B - pick games
+    case locations      // Scenario C - start/end cities
+    case followTeam     // Scenario D - follow one team
+
+    var displayName: String {
+        switch self {
+        case .dateRange: return "By Dates"
+        case .gameFirst: return "By Games"
+        case .locations: return "By Route"
+        case .followTeam: return "Follow Team"
+        }
+    }
+
+    var description: String {
+        switch self {
+        case .dateRange: return "Shows a curated sample of possible routes"
+        case .gameFirst: return "Build trip around specific games"
+        case .locations: return "Plan route between locations"
+        case .followTeam: return "Follow your team on the road"
+        }
+    }
+
+    var iconName: String {
+        switch self {
+        case .dateRange: return "calendar"
+        case .gameFirst: return "sportscourt"
+        case .locations: return "map"
+        case .followTeam: return "person.3.fill"
+        }
+    }
+}
+```
+
+### TripPreferences Addition
+
+```swift
+struct TripPreferences {
+    // ... existing properties ...
+
+    /// Team to follow (for Follow Team mode)
+    var followTeamId: UUID?
+
+    /// Whether to start/end from a home location (vs fly-in/fly-out)
+    var useHomeLocation: Bool = true
+}
+```
+
+### PlanningScenario Extension
+
+```swift
+enum PlanningScenario: Equatable {
+    case scenarioA  // Date range
+    case scenarioB  // Selected games
+    case scenarioC  // Start/end locations
+    case scenarioD  // Follow team
+}
+```
+
+## ScenarioDPlanner Logic
+
+### Core Algorithm
+
+```swift
+actor ScenarioDPlanner {
+    func plan(request: PlanningRequest) async throws -> ItineraryResult {
+        // 1. Filter games to selected team only
+        let teamGames = filterToTeam(
+            request.allGames,
+            teamId: request.preferences.followTeamId
+        )
+
+        // 2. Apply region filter
+        let regionalGames = filterByRegion(
+            teamGames,
+            regions: request.preferences.selectedRegions,
+            stadiums: request.stadiums
+        )
+
+        // 3. Apply date range
+        let dateFilteredGames = filterByDateRange(
+            regionalGames,
+            start: request.preferences.startDate,
+            end: request.preferences.endDate
+        )
+
+        // 4. Apply repeat city constraint
+        let finalGames = applyRepeatCityFilter(
+            dateFilteredGames,
+            allowRepeat: request.preferences.allowRepeatCities,
+            stadiums: request.stadiums
+        )
+
+        // 5. Build route (with or without home location)
+        if request.preferences.useHomeLocation,
+           let startLocation = request.startLocation {
+            // Round-trip from home
+            return buildRouteFromHome(finalGames, start: startLocation)
+        } else {
+            // Fly-in / fly-out (first game to last game)
+            return buildPointToPointRoute(finalGames)
+        }
+    }
+}
+```
+
+### Team Game Filtering
+
+A game belongs to the followed team if they're home OR away:
+
+```swift
+func filterToTeam(_ games: [Game], teamId: UUID?) -> [Game] {
+    guard let teamId else { return [] }
+    return games.filter { game in
+        game.homeTeamId == teamId || game.awayTeamId == teamId
+    }
+}
+```
+
+### Repeat City Handling
+
+When `allowRepeatCities = false`, keep only one game per city:
+
+```swift
+func applyRepeatCityFilter(_ games: [Game], allowRepeat: Bool, stadiums: [UUID: Stadium]) -> [Game] {
+    guard !allowRepeat else { return games }
+
+    var seenCities: Set<String> = []
+    return games.filter { game in
+        guard let stadium = stadiums[game.stadiumId] else { return false }
+        if seenCities.contains(stadium.city) { return false }
+        seenCities.insert(stadium.city)
+        return true
+    }
+}
+```
+
+## UI Changes
+
+### Mode Selector
+
+Expand to 4 modes in a 2x2 grid:
+
+```swift
+var planningModeSection: some View {
+    LazyVGrid(columns: [GridItem(.flexible()), GridItem(.flexible())], spacing: 12) {
+        ForEach(PlanningMode.allCases) { mode in
+            PlanningModeCard(
+                mode: mode,
+                isSelected: viewModel.planningMode == mode,
+                action: { viewModel.planningMode = mode }
+            )
+        }
+    }
+}
+```
+
+### Follow Team Mode Sections
+
+```swift
+case .followTeam:
+    teamPickerSection      // Select team (grouped by sport)
+    regionSection          // East/Central/West
+    datesSection           // Start/end dates
+    homeLocationToggle     // "Start from home?" toggle
+    locationSection        // Conditional: Only if toggle is on
+```
+
+### Team Picker Section
+
+```swift
+var teamPickerSection: some View {
+    Section("Select Team") {
+        Picker("Team", selection: $viewModel.followTeamId) {
+            Text("Choose a team").tag(nil as UUID?)
+            ForEach(teamsByLeague) { league in
+                Section(league.name) {
+                    ForEach(league.teams) { team in
+                        Text(team.name).tag(team.id as UUID?)
+                    }
+                }
+            }
+        }
+    }
+}
+```
+
+### Home Location Toggle
+
+```swift
+var homeLocationToggle: some View {
+    Toggle("Start and end from home", isOn: $viewModel.useHomeLocation)
+        .toggleStyle(.switch)
+}
+```
+
+## Validation Rules
+
+```swift
+var followTeamValidation: String? {
+    guard viewModel.followTeamId != nil else {
+        return "Select a team to follow"
+    }
+
+    guard viewModel.endDate > viewModel.startDate else {
+        return "End date must be after start date"
+    }
+
+    if viewModel.useHomeLocation && viewModel.startLocation == nil {
+        return "Enter your home location"
+    }
+
+    return nil
+}
+```
+
+## Edge Cases
+
+| Case | Behavior |
+|------|----------|
+| No games in range | Show: "No [Team] games found in [Region] between [dates]" |
+| All games in one city | Valid single-stop trip |
+| Repeat city + toggle off | Keep first game in each city, skip duplicates |
+| Back-to-back different cities | Existing driving constraints handle feasibility |
+| No start location but toggle on | Block submission with validation message |
+
+## Planning Failures
+
+Reuse existing `PlanningFailure` reasons:
+- `.noGamesInRange` — No team games in date/region
+- `.noValidRoutes` — Can't build feasible route
+- `.repeatCityViolation` — Would require repeat city but toggle is off
+
+## Implementation Plan
+
+### Files to Create
+
+```
+SportsTime/Planning/Engine/ScenarioDPlanner.swift
+SportsTimeTests/Planning/ScenarioDPlannerTests.swift
+```
+
+### Files to Modify
+
+```
+SportsTime/Core/Models/Domain/TripPreferences.swift
+SportsTime/Planning/Models/PlanningModels.swift
+SportsTime/Planning/Engine/TripPlanningEngine.swift
+SportsTime/Features/Trip/Views/TripCreationView.swift
+SportsTime/Features/Trip/ViewModels/TripCreationViewModel.swift
+```
+
+### Implementation Order
+
+1. Data model — Add properties to `TripPreferences`, add `scenarioD`
+2. Planner — Create `ScenarioDPlanner`
+3. Engine routing — Update `TripPlanningEngine` to route to Scenario D
+4. ViewModel — Add state and validation
+5. UI — Add team picker, toggle, mode card
+6. Tests — Cover all edge cases
+
+### Test Cases
+
+- Happy path: Team with 5 games in region → valid route
+- No games: Team has no games in range → proper failure
+- Single city: All home games, repeat allowed → valid single-stop
+- Repeat city blocked: Multiple home games, repeat off → keeps one
+- With home location: Round-trip from user's city
+- Without home location: Point-to-point first to last game