diff --git a/docs/dashboard-guide.md b/docs/dashboard-guide.md
index 1775102e9e..fc440823eb 100644
--- a/docs/dashboard-guide.md
+++ b/docs/dashboard-guide.md
@@ -74,9 +74,10 @@ The installed mobile/PWA home-screen icons are generated from `packages/dashboar
 
 The dashboard now handles browser back navigation consistently on desktop and mobile.
 Using Back will first dismiss open modals and then step back through in-app view changes before leaving the app.
-On mobile, an open navigation-bar **More** sheet or mailbox message detail is dismissed by one browser Back action, iOS edge-swipe, or Android Back action before the current dashboard view changes.
+On mobile, an open navigation-bar **More** sheet, mailbox message detail, or artifact viewer is dismissed by one browser Back action, iOS edge-swipe, or Android Back action before the current dashboard view changes.
 <!-- FNXC:MobileNavBackDocs 2026-07-16-14:45: The mobile More sheet registers as a navigation modal, so every Back delivery mechanism dismisses it before navigating away. -->
 <!-- FNXC:MailboxMobileBackDocs 2026-07-16-16:15: A mobile mailbox message detail registers as a navigation modal, so Back returns to the message list instead of navigating away. -->
+<!-- FNXC:ArtifactViewerMobileBackDocs 2026-07-16-17:15: Mobile artifact viewers register as navigation modals, so every Back delivery mechanism returns the operator to the artifact gallery before changing dashboard views. -->
 When task detail is open from a board card, task popup, mobile list row, right-dock/activity/onboarding link, deep link, or another task detail link, one browser, iOS edge-swipe, or Android Back action closes the current detail first and restores the prior dashboard context (for example, nested task detail → previous task detail, or task detail → board/list).
 <!-- FNXC:TaskDetailSwipeBackDocs 2026-07-15-10:36: Mobile task popups now register the same navigation entry as modal and full-panel task detail, so every Back delivery mechanism dismisses the popup before it can leave the originating Board or List. -->
 On mobile board-card detail, **Back to board** also restores the prior board/card scroll position so the same lane context remains visible.
diff --git a/packages/dashboard/app/components/ArtifactsGallery.tsx b/packages/dashboard/app/components/ArtifactsGallery.tsx
index 275ba15db6..9017187fd6 100644
--- a/packages/dashboard/app/components/ArtifactsGallery.tsx
+++ b/packages/dashboard/app/components/ArtifactsGallery.tsx
@@ -1,5 +1,5 @@
 import "./ArtifactsGallery.css";
-import { useCallback, useEffect, useMemo, useRef, useState, type KeyboardEvent } from "react";
+import { useCallback, useContext, useEffect, useMemo, useRef, useState, type KeyboardEvent } from "react";
 import { useTranslation } from "react-i18next";
 import type { TFunction } from "i18next";
 import {
@@ -22,6 +22,7 @@ import { artifactMediaUrl, artifactMediaUrlWithToken, fetchArtifact, updateArtif
 import { withTokenHeader } from "../auth";
 import { FileEditor } from "./FileEditor";
 import { FloatingWindow } from "./FloatingWindow";
+import { NavigationHistoryContext } from "../hooks/useNavigationHistory";
 
 /*
 FNXC:ArtifactRegistry 2026-07-10-15:40:
@@ -98,6 +99,7 @@ interface ViewerState {
 
 export function ArtifactsGallery({ artifacts, projectId, isMobile, addToast, onOpenTask, onArtifactUpdated }: ArtifactsGalleryProps) {
   const { t } = useTranslation("app");
+  const navigationHistory = useContext(NavigationHistoryContext);
   const [categoryFilter, setCategoryFilter] = useState<ArtifactCategoryFilter>("all");
   const [viewer, setViewer] = useState<ViewerState | null>(null);
   const viewerReturnFocusRef = useRef<HTMLElement | null>(null);
@@ -136,6 +138,22 @@ export function ArtifactsGallery({ artifacts, projectId, isMobile, addToast, onO
     viewerReturnFocusRef.current = null;
   }, []);
 
+  /*
+  FNXC:ArtifactViewerMobileBack 2026-07-16-17:00:
+  A mobile artifact viewer must dismiss before navigation on iOS swipe-back, Android native Back, and browser Back.
+  Register one stable modal closer for every viewer kind; nullable context keeps provider-less gallery renders working.
+  Programmatic close uses removeNav to consume its pushed entry, while popstate invokes closeViewer directly without a double-back.
+  */
+  useEffect(() => {
+    if (!isMobile || !viewer || !navigationHistory) return;
+    navigationHistory.pushNav({ type: "modal", close: closeViewer });
+  }, [closeViewer, isMobile, navigationHistory, viewer]);
+
+  const dismissViewer = useCallback(() => {
+    navigationHistory?.removeNav(closeViewer);
+    closeViewer();
+  }, [closeViewer, navigationHistory]);
+
   const visibleCategories = ARTIFACT_CATEGORY_ORDER.filter((category) =>
     grouped.has(category) && (categoryFilter === "all" || categoryFilter === category));
 
@@ -195,10 +213,10 @@ export function ArtifactsGallery({ artifacts, projectId, isMobile, addToast, onO
       })}
 
       {viewer && viewer.kind === "media" && (
-        <MediaLightbox artifact={viewer.artifact} projectId={projectId} t={t} onClose={closeViewer} onOpenTask={onOpenTask} />
+        <MediaLightbox artifact={viewer.artifact} projectId={projectId} t={t} onClose={dismissViewer} onOpenTask={onOpenTask} />
       )}
       {viewer && viewer.kind === "pdf" && (
-        <PdfViewer artifact={viewer.artifact} projectId={projectId} t={t} onClose={closeViewer} onOpenTask={onOpenTask} />
+        <PdfViewer artifact={viewer.artifact} projectId={projectId} t={t} onClose={dismissViewer} onOpenTask={onOpenTask} />
       )}
       {viewer && viewer.kind === "doc" && (
         <DocViewer
@@ -206,7 +224,7 @@ export function ArtifactsGallery({ artifacts, projectId, isMobile, addToast, onO
           projectId={projectId}
           t={t}
           addToast={addToast}
-          onClose={closeViewer}
+          onClose={dismissViewer}
           onOpenTask={onOpenTask}
           onArtifactUpdated={onArtifactUpdated}
         />
diff --git a/packages/dashboard/app/components/__tests__/ArtifactsGallery.swipe-back.test.tsx b/packages/dashboard/app/components/__tests__/ArtifactsGallery.swipe-back.test.tsx
new file mode 100644
index 0000000000..661019cd2a
--- /dev/null
+++ b/packages/dashboard/app/components/__tests__/ArtifactsGallery.swipe-back.test.tsx
@@ -0,0 +1,170 @@
+import { act, cleanup, fireEvent, render, screen, waitFor } from "@testing-library/react";
+import { useEffect, type ReactNode } from "react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import type { ArtifactWithTask } from "@fusion/core";
+import { ArtifactsGallery } from "../ArtifactsGallery";
+import { NavigationHistoryProvider, useNavigationHistory, type UseNavigationHistoryResult } from "../../hooks/useNavigationHistory";
+
+vi.mock("../../api", () => ({
+  artifactMediaUrl: vi.fn((id: string) => `/api/artifacts/${id}/media`),
+  artifactMediaUrlWithToken: vi.fn((id: string) => `/api/artifacts/${id}/media?fn_token=test`),
+  fetchArtifact: vi.fn(() => Promise.resolve({})),
+  updateArtifact: vi.fn(),
+}));
+
+vi.mock("../FloatingWindow", () => ({
+  FloatingWindow: ({ children }: { children: ReactNode }) => <div>{children}</div>,
+}));
+
+const artifacts: ArtifactWithTask[] = [
+  {
+    id: "image-artifact",
+    type: "image",
+    title: "Image artifact",
+    mimeType: "image/png",
+    uri: "artifacts/image.png",
+    authorId: "agent",
+    authorType: "agent",
+    createdAt: "2026-07-16T12:00:00.000Z",
+    updatedAt: "2026-07-16T12:00:00.000Z",
+  },
+  {
+    id: "doc-artifact",
+    type: "document",
+    title: "Document artifact",
+    mimeType: "text/markdown",
+    content: "# Document",
+    authorId: "agent",
+    authorType: "agent",
+    createdAt: "2026-07-16T12:00:00.000Z",
+    updatedAt: "2026-07-16T12:00:00.000Z",
+  },
+];
+
+function HistoryHarness({ children, onReady }: { children: ReactNode; onReady: (history: UseNavigationHistoryResult) => void }) {
+  const history = useNavigationHistory({ enabled: true });
+  useEffect(() => onReady(history), [history, onReady]);
+  return <NavigationHistoryProvider value={history}>{children}</NavigationHistoryProvider>;
+}
+
+function dispatchPopState(navIndex: number) {
+  act(() => {
+    window.dispatchEvent(new PopStateEvent("popstate", { state: { navIndex } }));
+  });
+}
+
+const galleryProps = {
+  artifacts,
+  isMobile: true,
+  addToast: vi.fn(),
+  onOpenTask: vi.fn(),
+};
+
+function openImageViewer() {
+  fireEvent.click(screen.getByRole("button", { name: "Expand Image artifact" }));
+}
+
+function openDocumentViewer() {
+  fireEvent.click(screen.getByRole("button", { name: "Open Document artifact" }));
+}
+
+function expectViewerOpen(container: HTMLElement) {
+  expect(container.querySelector(".artifacts-gallery-viewer")).not.toBeNull();
+}
+
+describe("ArtifactsGallery mobile viewer navigation history", () => {
+  let navigationHistory: UseNavigationHistoryResult | null = null;
+
+  beforeEach(() => {
+    navigationHistory = null;
+    window.history.replaceState({ navIndex: 0 }, "");
+    vi.spyOn(window.history, "back").mockImplementation(() => {});
+  });
+
+  afterEach(() => {
+    cleanup();
+    vi.restoreAllMocks();
+  });
+
+  function renderWithHistory(isMobile = true) {
+    return render(
+      <HistoryHarness onReady={(history) => { navigationHistory = history; }}>
+        <ArtifactsGallery {...galleryProps} isMobile={isMobile} />
+      </HistoryHarness>,
+    );
+  }
+
+  it("dismisses the media viewer on browser Back and drains its nav entry", async () => {
+    const { container } = renderWithHistory();
+    openImageViewer();
+    expectViewerOpen(container);
+
+    dispatchPopState(0);
+
+    await waitFor(() => expect(container.querySelector(".artifacts-gallery-viewer")).toBeNull());
+    expect(screen.getByRole("button", { name: "Expand Image artifact" })).toBeInTheDocument();
+    dispatchPopState(0);
+    expect(container.querySelector(".artifacts-gallery-viewer")).toBeNull();
+  });
+
+  it("routes Android native Back through popstate before dismissing the document viewer", async () => {
+    const { container } = renderWithHistory();
+    openDocumentViewer();
+    expectViewerOpen(container);
+
+    const nativeBack = new CustomEvent("fusion:native-back", { cancelable: true });
+    expect(window.dispatchEvent(nativeBack)).toBe(false);
+    expect(window.history.back).toHaveBeenCalledOnce();
+    expectViewerOpen(container);
+
+    dispatchPopState(0);
+    await waitFor(() => expect(container.querySelector(".artifacts-gallery-viewer")).toBeNull());
+    expect(screen.getByRole("button", { name: "Open Document artifact" })).toBeInTheDocument();
+  });
+
+  async function expectProgrammaticCloseConsumesViewerEntry(close: () => void) {
+    const { container } = renderWithHistory();
+    await waitFor(() => expect(navigationHistory).not.toBeNull());
+    const sentinelClose = vi.fn();
+    navigationHistory?.pushNav({ type: "modal", close: sentinelClose });
+    openImageViewer();
+    expectViewerOpen(container);
+
+    close();
+    await waitFor(() => expect(container.querySelector(".artifacts-gallery-viewer")).toBeNull());
+    expect(window.history.back).toHaveBeenCalledOnce();
+
+    // The first pop is removeNav's self-pop; exactly one more pop reaches the lower entry.
+    dispatchPopState(1);
+    expect(sentinelClose).not.toHaveBeenCalled();
+    dispatchPopState(0);
+    expect(sentinelClose).toHaveBeenCalledOnce();
+  }
+
+  it("consumes the viewer entry when the header close button dismisses it", async () => {
+    await expectProgrammaticCloseConsumesViewerEntry(() => fireEvent.click(screen.getByRole("button", { name: "Close artifact preview" })));
+  });
+
+  it("consumes the viewer entry when Escape dismisses it", async () => {
+    await expectProgrammaticCloseConsumesViewerEntry(() => fireEvent.keyDown(document, { key: "Escape" }));
+  });
+
+  it("keeps provider-less gallery renders functional", async () => {
+    const { container } = render(<ArtifactsGallery {...galleryProps} />);
+    openImageViewer();
+    expectViewerOpen(container);
+    fireEvent.click(screen.getByRole("button", { name: "Close artifact preview" }));
+    await waitFor(() => expect(container.querySelector(".artifacts-gallery-viewer")).toBeNull());
+  });
+
+  it("does not push a viewer entry on desktop", async () => {
+    renderWithHistory(false);
+    await waitFor(() => expect(navigationHistory).not.toBeNull());
+    const sentinelClose = vi.fn();
+    navigationHistory?.pushNav({ type: "modal", close: sentinelClose });
+    openImageViewer();
+
+    dispatchPopState(0);
+    expect(sentinelClose).toHaveBeenCalledOnce();
+  });
+});