diff --git a/src/client/App.tsx b/src/client/App.tsx
index e86b361..e93cbe4 100644
--- a/src/client/App.tsx
+++ b/src/client/App.tsx
@@ -19,7 +19,7 @@ import { useProgress } from "./state/useProgress.ts";
 import { useDailyLog, type DailyLogMap } from "./state/useDailyLog.ts";
 import { useTasks } from "./state/useTasks.ts";
 import { useAmounts } from "./state/useAmounts.ts";
-import { adoptNewLanes, usePrefs, type Prefs } from "./state/usePrefs.ts";
+import { adoptNewLanes, firstRunPrefs, usePrefs, type Prefs } from "./state/usePrefs.ts";
 import { buildExportData, parseImportData, triggerDownload } from "./state/export.ts";
 import { snapDayWidth } from "./state/zoom.ts";
 import { useCustom, type EventDraft } from "./state/useCustom.ts";
@@ -487,11 +487,7 @@ export function App() {
           <Welcome
             available={ordered}
             onConfirm={(chosen, chosenView) =>
-              update({
-                onboarded: true,
-                hiddenGames: games.filter((g) => !chosen.includes(g)),
-                view: chosenView,
-              })
+              update(firstRunPrefs(games, chosen, chosenView))
             }
           />
         </Shell>
diff --git a/src/client/state/usePrefs.ts b/src/client/state/usePrefs.ts
index 44a9555..d03bdb0 100644
--- a/src/client/state/usePrefs.ts
+++ b/src/client/state/usePrefs.ts
@@ -7,6 +7,7 @@ import { KEYS, readJson, writeJson } from "./storage.ts";
 import type { TimelineGroup } from "./lanes.ts";
 import { DEFAULT_THEME_CHOICE, type ThemeChoice } from "./theme.ts";
 import { DEFAULT_DAY_WIDTH, snapDayWidth } from "./zoom.ts";
+import { ENTRIES, newestId } from "../../shared/changelog.ts";
 
 /**
  * Which of the two views the reader is looking at.
@@ -192,6 +193,30 @@ export interface Prefs {
   routineGames?: LaneId[] | undefined;
   /** Games already asked "track its weekly tasks?", so the question is asked once. */
   routinesAsked?: LaneId[] | undefined;
+  /**
+   * The newest changelog entry the reader dismissed (PRD F18). Absent means
+   * unrecorded, not "seen nothing": first-run setup sets it, so an absent value
+   * is an install from before the changelog, shown the launch window once.
+   */
+  changelogSeen?: string | undefined;
+}
+
+/**
+ * What finishing first-run setup writes. A new reader is marked up to date
+ * with the changelog: a list of changes means nothing before you've used the
+ * thing it changes.
+ */
+export function firstRunPrefs(
+  games: readonly LaneId[],
+  chosen: readonly LaneId[],
+  view: View,
+): Partial<Prefs> {
+  return {
+    onboarded: true,
+    hiddenGames: games.filter((g) => !chosen.includes(g)),
+    view,
+    changelogSeen: newestId(ENTRIES),
+  };
 }
 
 export function defaults(): Prefs {
@@ -321,6 +346,10 @@ export function restorePrefsValue(incoming: unknown): Prefs {
     }
   }
 
+  if (result.changelogSeen !== undefined && typeof result.changelogSeen !== "string") {
+    result.changelogSeen = undefined;
+  }
+
   // Built-in tasks: string arrays, or absent.
   for (const key of ["routineGames", "routinesAsked"] as const) {
     const value: unknown = result[key];
diff --git a/test/changelog.test.ts b/test/changelog.test.ts
index 7d96ed2..85911a2 100644
--- a/test/changelog.test.ts
+++ b/test/changelog.test.ts
@@ -63,3 +63,22 @@ describe("what a reader has not seen", () => {
     expect(compareUrl("https://r", "a1b2c3d", "e4f5a6b")).toBe("https://r/compare/a1b2c3d...e4f5a6b");
   });
 });
+
+describe("the seen marker in prefs", () => {
+  test("restore keeps a string and drops anything else", async () => {
+    const { restorePrefsValue } = await import("../src/client/state/usePrefs.ts");
+    expect(restorePrefsValue({ changelogSeen: "check-in-goals" }).changelogSeen).toBe("check-in-goals");
+    expect(restorePrefsValue({ changelogSeen: 7 }).changelogSeen).toBeUndefined();
+    expect(restorePrefsValue({}).changelogSeen).toBeUndefined();
+  });
+
+  test("first-run setup marks everything seen", async () => {
+    const { firstRunPrefs } = await import("../src/client/state/usePrefs.ts");
+    expect(firstRunPrefs(["genshin", "hsr"], ["hsr"], "soon")).toEqual({
+      onboarded: true,
+      hiddenGames: ["genshin"],
+      view: "soon",
+      changelogSeen: newestId(ENTRIES),
+    });
+  });
+});