diff --git a/packages/cli/src/commands/history.test.ts b/packages/cli/src/commands/history.test.ts
index 7dd8e4e8c9c..c6edea726b9 100644
--- a/packages/cli/src/commands/history.test.ts
+++ b/packages/cli/src/commands/history.test.ts
@@ -183,6 +183,27 @@ describe.each(["direct", "preview"])("hyperframes history (%s)", (mode) => {
     return { ...p, personWrites };
   }
 
+  it("refuses an empty start restore with exit 2 and leaves files intact", async () => {
+    const p = project();
+    rmSync(join(p.dir, "index.html"));
+    rmSync(join(p.dir, "notes.html"));
+    const history = await openProjectHistory({
+      projectDir: p.dir,
+      historyRoot: historyDeps.historyRoot,
+      now: () => clock.at,
+    });
+    p.write("index.html", "A");
+    p.write("notes.html", "N");
+    await history.close();
+    if (mode === "preview") await preview(p.dir);
+    const result = await p.hf("restore", "start");
+    expect(result.code).toBe(2);
+    expect(result.err).toBe(
+      "Restoring this point would remove every file in this project, so nothing was changed.",
+    );
+    expect(p.files()).toEqual(["A", "N"]);
+  });
+
   it("an agent's labelled turn, a person's edit after it: --since shows both, undo of the turn keeps the edit", async () => {
     const { json, hf, turn, personWrites, files } = await setup();
     const startedAt = new Date(clock.at - 1).toISOString();
diff --git a/packages/cli/src/commands/history.ts b/packages/cli/src/commands/history.ts
index bed3589e1f7..0dc5d03e4cf 100644
--- a/packages/cli/src/commands/history.ts
+++ b/packages/cli/src/commands/history.ts
@@ -16,6 +16,7 @@ import {
   HISTORY_START,
   HistoryBusyError,
   HistoryIdError,
+  HistoryRefusedError,
   type HistoryEntry,
   type HistoryListItem,
   type HistoryResult,
@@ -358,7 +359,8 @@ function guarded<A>(run: (args: A) => Promise<void>) {
         error instanceof Refusal ||
         error instanceof AmbiguousPreviewServerError ||
         error instanceof HistoryBusyError ||
-        error instanceof HistoryIdError;
+        error instanceof HistoryIdError ||
+        error instanceof HistoryRefusedError;
       if (!refused) throw error;
       setCommandExitCode(2);
       const message =
diff --git a/packages/studio-server/src/history/index.ts b/packages/studio-server/src/history/index.ts
index c048388de00..a3c0e58564e 100644
--- a/packages/studio-server/src/history/index.ts
+++ b/packages/studio-server/src/history/index.ts
@@ -13,6 +13,7 @@ export {
   type HistoryResult,
   type HistoryWindow,
   HistoryClosedError,
+  HistoryRefusedError,
 } from "./projectHistory.js";
 export { reclaimUncopiedBlobs, type ReclaimedHistory } from "./reclaimUncopied.js";
 export { HistoryBusyError } from "./ownerLock.js";
diff --git a/packages/studio-server/src/history/projectHistory.test.ts b/packages/studio-server/src/history/projectHistory.test.ts
index 9ee0f0fad00..e6199dffe94 100644
--- a/packages/studio-server/src/history/projectHistory.test.ts
+++ b/packages/studio-server/src/history/projectHistory.test.ts
@@ -25,6 +25,7 @@ import { HistoryBusyError } from "./ownerLock";
 import { HistoryIdError } from "./historyId";
 import {
   HistoryClosedError,
+  HistoryRefusedError,
   openProjectHistory,
   readProjectHistory,
   type ProjectHistory,
@@ -2652,3 +2653,72 @@ describe("the history's copy of a file", () => {
     },
   );
 });
+
+describe("restore refuses to empty a project", () => {
+  it.each(["restore", "back-to-before"])(
+    "refuses %s from an empty start without changing files",
+    async (action) => {
+      const { history, write, read } = await project({});
+      const files = { "index.html": "A", "compositions/a.html": "B", "assets/x.css": "C" };
+      const window = await history.beginWindow(you, "Add files");
+      for (const [path, content] of Object.entries(files)) write(path, content);
+      const entry = await window.close();
+      const restore =
+        action === "restore"
+          ? history.restore(START, you)
+          : history.undo(entry!.id, { who: you, mode: "back-to-before" });
+      await expect(restore).rejects.toThrow(HistoryRefusedError);
+      for (const [path, content] of Object.entries(files)) expect(read(path)).toBe(content);
+    },
+  );
+
+  it("refuses a start that holds only the media ledger", async () => {
+    const { history, write, read } = await project({ ".media/manifest.jsonl": "{}\n" });
+    expect(history.peek(START)).toHaveProperty([".media/manifest.jsonl"]);
+    const window = await history.beginWindow(you, "Add files");
+    write("index.html", "A");
+    write("compositions/a.html", "B");
+    await window.close();
+    await expect(history.restore(START, you)).rejects.toThrow(HistoryRefusedError);
+    expect([read("index.html"), read("compositions/a.html")]).toEqual(["A", "B"]);
+  });
+
+  it("refuses start while its media copy is still adopting", async () => {
+    let release = () => {};
+    mediaCopy.held = new Promise<void>((resolve) => (release = resolve));
+    const clip = Buffer.alloc(2 * 1024 ** 2, 7);
+    const { history, projectDir, read } = await project({ "index.html": "A", "clip.mp4": clip });
+    try {
+      await expect(history.restore(START, you)).rejects.toThrow(HistoryRefusedError);
+      expect(read("index.html")).toBe("A");
+      expect(readFileSync(join(projectDir, "clip.mp4")).equals(clip)).toBe(true);
+    } finally {
+      release();
+    }
+    await vi.waitFor(() => expect(history.peek(START)).toHaveProperty(["clip.mp4"]));
+    await expect(history.restore(START, you)).resolves.toBeNull();
+  });
+
+  it("restores an earlier entry and removes only files added later", async () => {
+    const { history, write, read, has } = await project({ "index.html": "A" });
+    const first = await history.beginWindow(you, "Edit index");
+    write("index.html", "B");
+    const entry = await first.close();
+    const later = await history.beginWindow(you, "Add file");
+    write("index.html", "C");
+    write("later.html", "later");
+    await later.close();
+    await history.restore(entry!.id, you);
+    expect(read("index.html")).toBe("B");
+    expect(has("later.html")).toBe(false);
+  });
+
+  it("allows normal undo to remove the only added file", async () => {
+    const { history, write, has } = await project({});
+    const window = await history.beginWindow(you, "Add index");
+    write("index.html", "A");
+    const entry = await window.close();
+    expect((await history.undo(entry!.id, { who: you })).ok).toBe(true);
+    expect(has("index.html")).toBe(false);
+  });
+});
diff --git a/packages/studio-server/src/history/projectHistory.ts b/packages/studio-server/src/history/projectHistory.ts
index a5eef2707d5..ec389369ef2 100644
--- a/packages/studio-server/src/history/projectHistory.ts
+++ b/packages/studio-server/src/history/projectHistory.ts
@@ -1238,6 +1238,18 @@ class Engine {
       [...this.tracked.keys()].map((path) => [path, null]),
     );
     for (const [path, hash] of files) target.set(path, hash);
+    if (point === START && this.adopting.size > 0) {
+      throw new HistoryRefusedError(
+        "The project's starting copy is still being saved; try again in a moment. Nothing was changed.",
+      );
+    }
+    const isProjectFile = (path: string) => !KEPT_HIDDEN_PATHS.has(path);
+    const keepsAny = [...target].some(([path, hash]) => hash !== null && isProjectFile(path));
+    if ([...this.tracked.keys()].some(isProjectFile) && !keepsAny) {
+      throw new HistoryRefusedError(
+        "Restoring this point would remove every file in this project, so nothing was changed.",
+      );
+    }
     return this.writeAs(who, label, target, { restoredTo: point });
   }
 
@@ -1372,6 +1384,13 @@ export class HistoryClosedError extends Error {
   }
 }
 
+export class HistoryRefusedError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = "HistoryRefusedError";
+  }
+}
+
 /** Opens a project's history: every write to its files becomes an entry that can be undone or restored. */
 export async function openProjectHistory(options: ProjectHistoryOptions): Promise<ProjectHistory> {
   if (!existsSync(options.projectDir))
diff --git a/packages/studio-server/src/routes/history.test.ts b/packages/studio-server/src/routes/history.test.ts
index f1823cb6087..4b5d8c16d9b 100644
--- a/packages/studio-server/src/routes/history.test.ts
+++ b/packages/studio-server/src/routes/history.test.ts
@@ -645,3 +645,23 @@ it("checkpoints pending writes without closing an agent window", async () => {
   expect(history.list()).toHaveLength(2);
   expect(history.list().at(-1)?.who).toEqual(who);
 });
+
+it("refuses an empty start restore with 409 and leaves files intact", async () => {
+  const projectDir = tempDir("hf-history-empty-start-");
+  const history = await openProjectHistory({
+    projectDir,
+    historyRoot: tempDir("hf-history-root-"),
+  });
+  cleanup.push(() => history.close());
+  const call = apiFor(projectDir, history);
+  writeFileSync(join(projectDir, "index.html"), "A");
+  writeFileSync(join(projectDir, "notes.html"), "N");
+  await history.checkpoint();
+  const response = await call("/restore", { point: "start" });
+  expect(response.status).toBe(409);
+  expect(await response.json()).toEqual({
+    error: "Restoring this point would remove every file in this project, so nothing was changed.",
+  });
+  expect(readFileSync(join(projectDir, "index.html"), "utf-8")).toBe("A");
+  expect(readFileSync(join(projectDir, "notes.html"), "utf-8")).toBe("N");
+});
diff --git a/scripts/package-size-budgets.json b/scripts/package-size-budgets.json
index 8194a4a9155..1e5ae92bcd9 100644
--- a/scripts/package-size-budgets.json
+++ b/scripts/package-size-budgets.json
@@ -52,7 +52,7 @@
     "unpacked": 24360208
   },
   "@hyperframes/studio-server": {
-    "packed": 142100,
+    "packed": 143700,
     "unpacked": 559199
   }
 }