diff --git a/RewindTests/FavoritesModelTests.swift b/RewindTests/FavoritesModelTests.swift
new file mode 100644
index 0000000..51cd35c
--- /dev/null
+++ b/RewindTests/FavoritesModelTests.swift
@@ -0,0 +1,112 @@
+//
+//  FavoritesModelTests.swift
+//  RewindTests
+//
+//  FavoritesModel dedups add/remove by Model.Image's cid-only equality (Model.Image.== compares
+//  only `cid`, ignoring every other field). These tests pin that behavior with two DISTINCT
+//  instances sharing a cid but differing in every other field, so a port that widened equality to
+//  the full struct (or compared some other key) would fail: it would either grow a duplicate entry
+//  on re-favoriting the same photo from a different source screen, or fail to find/remove the
+//  stored entry when the caller only has a partially-populated instance (e.g. one rehydrated from
+//  persisted Storage.Image, which carries fewer fields than a freshly-fetched Model.Image).
+//
+
+import CoreLocation
+@testable import Rewind
+import Testing
+import VGSL
+
+@MainActor
+struct FavoritesModelTests {
+  /// Adding an image whose cid already exists in favorites is a no-op: the original entry is kept
+  /// (not replaced), and the synchronous storage effect is not re-invoked for the duplicate.
+  @Test func addToFavoritesDedupesByCidKeepingTheFirstEntry() {
+    let storage = StorageSpy()
+    let model = makeFavoritesModel(storage: storage.property)
+
+    let first = makeImage(cid: 1, title: "A", imagePath: "a.jpg", year: 1900)
+    let sameCidDifferentEverythingElse = makeImage(
+      cid: 1,
+      title: "B",
+      imagePath: "b.jpg",
+      year: 1950
+    )
+
+    model(.addToFavorites(first))
+    model(.addToFavorites(sameCidDifferentEverythingElse))
+
+    #expect(model.state.count == 1)
+    #expect(model.state.first?.title == "A")
+    #expect(model.state.first?.imagePath == "a.jpg")
+
+    // The second dispatch hit the `guard !state.contains(image)` and returned before enqueuing
+    // the persistence effect at all — not just "persisted the same thing twice".
+    #expect(storage.writes.count == 1)
+    #expect(storage.writes.last?.map(\.title) == ["A"])
+  }
+
+  /// Removing an image finds the stored entry by cid alone: an instance with the same cid but
+  /// different title/imagePath/coordinate still matches and is removed; an unrelated cid is a
+  /// no-op that neither changes state nor re-invokes the storage effect.
+  @Test func removeFromFavoritesMatchesStoredEntryByCidAlone() {
+    let toRemove = makeImage(cid: 1, title: "A", imagePath: "a.jpg", year: 1900)
+    let toKeep = makeImage(cid: 2, title: "B", imagePath: "b.jpg", year: 1950)
+    let storage = StorageSpy(initial: [toRemove, toKeep])
+    let model = makeFavoritesModel(storage: storage.property)
+
+    let differentInstanceSameCid = modified(
+      makeImage(cid: 1, title: "Z", imagePath: "z.jpg", year: 2020),
+    ) {
+      $0.coordinate = CLLocationCoordinate2D(latitude: 10, longitude: 20)
+    }
+    model(.removeFromFavorites(differentInstanceSameCid))
+
+    #expect(model.state.count == 1)
+    #expect(model.state.first?.cid == 2)
+    #expect(model.state.first?.title == "B")
+    #expect(storage.writes.count == 1)
+    #expect(storage.writes.last?.map(\.title) == ["B"])
+
+    // An unrelated cid finds no index (`firstIndex(of:)` returns nil) — state and storage are
+    // both left untouched, not just "unchanged after another identical write".
+    model(.removeFromFavorites(makeImage(cid: 99, title: "Nope", imagePath: "nope.jpg", year: 1)))
+    #expect(model.state.count == 1)
+    #expect(storage.writes.count == 1)
+  }
+}
+
+// MARK: - Fixtures
+
+private func makeImage(
+  cid: Int,
+  title: String,
+  imagePath: String,
+  year: Int,
+) -> Model.Image {
+  modified(Model.Image.mock) {
+    $0.cid = cid
+    $0.title = title
+    $0.imagePath = imagePath
+    $0.date = ImageDate(year: year, year2: year)
+  }
+}
+
+@MainActor
+private final class StorageSpy {
+  private(set) var writes: [[Model.Image]] = []
+  private var value: [Model.Image]
+
+  init(initial: [Model.Image] = []) {
+    value = initial
+  }
+
+  var property: Property<[Model.Image]> {
+    Property(
+      getter: { [weak self] in self?.value ?? [] },
+      setter: { [weak self] newValue in
+        self?.value = newValue
+        self?.writes.append(newValue)
+      },
+    )
+  }
+}
diff --git a/RewindTests/ImageDetailsModelTests.swift b/RewindTests/ImageDetailsModelTests.swift
new file mode 100644
index 0000000..12a1cf0
--- /dev/null
+++ b/RewindTests/ImageDetailsModelTests.swift
@@ -0,0 +1,109 @@
+//
+//  ImageDetailsModelTests.swift
+//  RewindTests
+//
+//  Tests the description-link routing in the ImageDetails reducer: a link to a pastvu photo
+//  (https://pastvu.com/p/<cid>) recurses into a nested ImageDetails screen loaded from the remote,
+//  while any other link (external host, or a non-photo pastvu path) is handed to the url opener.
+//  The routing hinges on a branchy URL parse (host + /p/ path + integer cid), which is exactly the
+//  kind of quirk worth pinning; the raw button/url string tables are not tested.
+//
+
+import Foundation
+@testable import Rewind
+import Testing
+import VGSL
+
+@MainActor
+struct ImageDetailsModelTests {
+  /// A link to a pastvu photo loads that photo's details from the remote and presents them as a
+  /// nested details screen; loadingAnotherImage flips true while the load is in flight, and the
+  /// external url opener is never called.
+  @Test func pastvuPhotoLinkOpensNestedDetails() async {
+    let harness = Harness()
+    let model = harness.makeModel()
+
+    let linkedCid = 2_223_969
+    model(.descriptionLink(pastvuPhotoURL(linkedCid)))
+    #expect(model.state.loadingAnotherImage) // set synchronously, before the load returns
+
+    #expect(await eventually { model.state.anotherImageModel != nil })
+    #expect(!model.state.loadingAnotherImage) // cleared once the nested model is presented
+    #expect(harness.requestedCids == [linkedCid]) // the remote was asked for the linked photo
+    #expect(harness.openedURLs.isEmpty) // recursion, not a browser hand-off
+  }
+
+  /// A link to an external host is opened in the browser rather than recursing.
+  @Test func externalLinkOpensInBrowser() async throws {
+    let harness = Harness()
+    let model = harness.makeModel()
+
+    let external = try #require(URL(string: "https://example.com/gallery"))
+    model(.descriptionLink(external))
+
+    #expect(await eventually { harness.openedURLs == [external] })
+    #expect(!model.state.loadingAnotherImage)
+    #expect(model.state.anotherImageModel == nil)
+    #expect(harness.requestedCids.isEmpty)
+  }
+
+  /// A pastvu link that is not a photo page (e.g. a user profile) is opened in the browser, not
+  /// mistaken for a photo to recurse into.
+  @Test func nonPhotoPastvuLinkOpensInBrowser() async throws {
+    let harness = Harness()
+    let model = harness.makeModel()
+
+    let userPage = try #require(URL(string: "https://pastvu.com/u/someone"))
+    model(.descriptionLink(userPage))
+
+    #expect(await eventually { harness.openedURLs == [userPage] })
+    #expect(model.state.anotherImageModel == nil)
+    #expect(harness.requestedCids.isEmpty)
+  }
+}
+
+private func pastvuPhotoURL(_ cid: Int) -> URL {
+  URL(string: "https://pastvu.com/p/\(cid)")!
+}
+
+@MainActor
+private final class Harness {
+  private(set) var openedURLs: [URL] = []
+  private(set) var requestedCids: [Int] = []
+
+  // Both closures below are non-Sendable and formed in this @MainActor context, so they inherit
+  // main-actor isolation — their bodies hop back to the main actor before touching harness state.
+  func makeModel() -> ImageDetailsModel {
+    makeImageDetailsModel(
+      modelImage: .mock,
+      remote: Remote { [weak self] cid in
+        self?.requestedCids.append(cid)
+        return modified(.mock) { $0.cid = cid }
+      },
+      openSource: "",
+      favoritesModel: .mock,
+      showOnMap: { _ in },
+      canOpenURL: { _ in true },
+      urlOpener: { [weak self] in self?.openedURLs.append($0) },
+      setOrientationLock: { _ in },
+      streetViewAvailability: .mock(.unavailable),
+      translate: .mock("translated"),
+      extractModelImage: { _ in .mock },
+    )
+  }
+}
+
+// MARK: - Async helpers (mirrors MapModelTests: async effects run in a Task we can't await)
+
+@MainActor
+private func eventually(
+  timeout: Duration = .seconds(2),
+  _ condition: () -> Bool,
+) async -> Bool {
+  let deadline = ContinuousClock().now.advanced(by: timeout)
+  while !condition() {
+    if ContinuousClock().now >= deadline { return false }
+    try? await Task.sleep(for: .milliseconds(5))
+  }
+  return true
+}