diff --git a/src/contexts/workspace-context.test.tsx b/src/contexts/workspace-context.test.tsx
index c0a588a40..f33a74192 100644
--- a/src/contexts/workspace-context.test.tsx
+++ b/src/contexts/workspace-context.test.tsx
@@ -1,5 +1,5 @@
 import { act, render, screen } from "@testing-library/react"
-import { beforeEach, describe, expect, it, vi } from "vitest"
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest"
 import {
   WorkspaceProvider,
   useWorkspaceActions,
@@ -327,6 +327,120 @@ describe("WorkspaceProvider mode", () => {
   })
 })
 
+describe("WorkspaceProvider file history guard", () => {
+  beforeEach(() => {
+    window.history.replaceState({}, "", "/workspace")
+    vi.spyOn(window.history, "back").mockImplementation(() => {})
+  })
+
+  afterEach(() => {
+    vi.restoreAllMocks()
+  })
+
+  it("pushes one history entry when files open and closes all files on back", () => {
+    const pushState = vi.spyOn(window.history, "pushState")
+    renderWorkspace()
+
+    act(() => {
+      screen.getByRole("button", { name: "Open diff" }).click()
+      screen.getByRole("button", { name: "Open diff 2" }).click()
+    })
+
+    expect(screen.getByTestId("file-tab-count")).toHaveTextContent("2")
+    expect(pushState).toHaveBeenCalledTimes(1)
+    expect(pushState.mock.calls[0]?.[0]).toEqual({
+      codegFileWorkspace: true,
+    })
+
+    act(() => {
+      window.dispatchEvent(new PopStateEvent("popstate"))
+    })
+
+    expect(screen.getByTestId("mode")).toHaveTextContent("conversation")
+    expect(screen.getByTestId("file-tab-count")).toHaveTextContent("0")
+  })
+
+  function DirtyFileProbe() {
+    const {
+      openFilePreview,
+      updateActiveFileContent,
+      closeAllFileTabs,
+      mode,
+      fileTabs,
+    } = useWorkspaceContext()
+
+    return (
+      <div>
+        <output data-testid="mode">{mode}</output>
+        <output data-testid="file-tab-count">{fileTabs.length}</output>
+        <output data-testid="dirty-count">
+          {fileTabs.filter((tab) => tab.isDirty).length}
+        </output>
+        <button onClick={() => void openFilePreview("a.ts")}>open file</button>
+        <button onClick={() => updateActiveFileContent("local changes")}>
+          edit
+        </button>
+        <button onClick={closeAllFileTabs}>close all</button>
+      </div>
+    )
+  }
+
+  it("keeps a dirty file workspace when back-close is refused", async () => {
+    mockedApi.readFileForEdit.mockResolvedValue({
+      path: "a.ts",
+      content: "saved",
+      etag: "e1",
+      mtime_ms: 1,
+      readonly: false,
+      line_ending: "lf",
+    })
+    mockedApi.gitIsTracked.mockResolvedValue(false)
+    vi.spyOn(window.history, "pushState")
+    const confirm = vi.spyOn(window, "confirm").mockReturnValue(false)
+
+    render(
+      <WorkspaceProvider>
+        <DirtyFileProbe />
+      </WorkspaceProvider>
+    )
+
+    await act(async () => {
+      screen.getByText("open file").click()
+    })
+    await act(async () => {
+      screen.getByText("edit").click()
+    })
+    expect(screen.getByTestId("dirty-count")).toHaveTextContent("1")
+
+    await act(async () => {
+      window.dispatchEvent(new PopStateEvent("popstate"))
+    })
+
+    expect(confirm).toHaveBeenCalledTimes(1)
+    expect(screen.getByTestId("mode")).toHaveTextContent("fusion")
+    expect(screen.getByTestId("file-tab-count")).toHaveTextContent("1")
+    expect(screen.getByTestId("dirty-count")).toHaveTextContent("1")
+  })
+
+  it("consumes the history entry when the user closes all files manually", () => {
+    vi.spyOn(window.history, "pushState")
+    const back = vi.spyOn(window.history, "back")
+    renderWorkspace()
+
+    act(() => {
+      screen.getByRole("button", { name: "Open diff" }).click()
+    })
+    expect(screen.getByTestId("file-tab-count")).toHaveTextContent("1")
+
+    act(() => {
+      screen.getByRole("button", { name: "Close all" }).click()
+    })
+
+    expect(screen.getByTestId("file-tab-count")).toHaveTextContent("0")
+    expect(back).toHaveBeenCalledTimes(1)
+  })
+})
+
 describe("WorkspaceProvider files-maximized", () => {
   it("toggles filesMaximized only while files are open", () => {
     renderWorkspace()
diff --git a/src/contexts/workspace-context.tsx b/src/contexts/workspace-context.tsx
index d312fdb8a..0c613a629 100644
--- a/src/contexts/workspace-context.tsx
+++ b/src/contexts/workspace-context.tsx
@@ -50,6 +50,7 @@ import {
   HIDDEN_TAB_CONTENT_BUDGET_CHARS,
   selectTabsToUnload,
 } from "@/lib/file-tab-memory"
+import { isDesktop } from "@/lib/transport"
 import { useWorkspaceStateStore } from "@/hooks/use-workspace-state-store"
 import {
   useOpenFileTabsWatch,
@@ -331,6 +332,20 @@ function loadingTab(
 
 type LoadDecision = { kind: "skip" } | { kind: "fetch"; gen: number }
 
+const FILE_WORKSPACE_HISTORY_KEY = "codegFileWorkspace"
+
+function canUseFileWorkspaceHistory(): boolean {
+  return typeof window !== "undefined" && !isDesktop()
+}
+
+function hasFileWorkspaceHistoryState(): boolean {
+  return Boolean(
+    (window.history.state as Record<string, unknown> | null)?.[
+      FILE_WORKSPACE_HISTORY_KEY
+    ]
+  )
+}
+
 async function withTimeout<T>(
   promise: Promise<T>,
   timeoutMs: number,
@@ -421,6 +436,21 @@ export function WorkspaceProvider({ children }: WorkspaceProviderProps) {
     fileTabsRef.current = fileTabs
   }, [fileTabs])
 
+  // Browser back is a mobile affordance for leaving the file workspace, not
+  // for leaving /workspace itself. One synthetic entry guards the whole file
+  // layer; popstate closes all tabs and manual close consumes the entry.
+  const fileHistoryDepthRef = useRef(0)
+  const ignoreNextFileHistoryPopRef = useRef(false)
+
+  const pushFileWorkspaceHistory = useCallback(() => {
+    window.history.pushState(
+      { [FILE_WORKSPACE_HISTORY_KEY]: true },
+      "",
+      window.location.href
+    )
+    fileHistoryDepthRef.current += 1
+  }, [])
+
   useEffect(() => {
     activeFileTabIdRef.current = activeFileTabId
   }, [activeFileTabId])
@@ -2266,6 +2296,44 @@ export function WorkspaceProvider({ children }: WorkspaceProviderProps) {
   const reorderFileTabs = useCallback((tabs: FileWorkspaceTab[]) => {
     setFileTabs(tabs)
   }, [])
+  useEffect(() => {
+    if (!canUseFileWorkspaceHistory()) return
+
+    if (fileTabs.length > 0) {
+      if (fileHistoryDepthRef.current === 0) pushFileWorkspaceHistory()
+      return
+    }
+
+    if (fileHistoryDepthRef.current === 0) return
+    fileHistoryDepthRef.current = 0
+    if (hasFileWorkspaceHistoryState()) {
+      ignoreNextFileHistoryPopRef.current = true
+      window.history.back()
+    }
+  }, [fileTabs.length, pushFileWorkspaceHistory])
+
+  useEffect(() => {
+    if (!canUseFileWorkspaceHistory()) return
+
+    const handlePopState = () => {
+      if (ignoreNextFileHistoryPopRef.current) {
+        ignoreNextFileHistoryPopRef.current = false
+        return
+      }
+      if (fileHistoryDepthRef.current === 0) return
+
+      fileHistoryDepthRef.current = 0
+      if (fileTabsRef.current.length === 0) return
+
+      closeAllFileTabs()
+      // If close was refused for a dirty tab, restore the synthetic entry.
+      // If it succeeded, the empty-tabs effect above consumes it after commit.
+      pushFileWorkspaceHistory()
+    }
+
+    window.addEventListener("popstate", handlePopState)
+    return () => window.removeEventListener("popstate", handlePopState)
+  }, [closeAllFileTabs, pushFileWorkspaceHistory])
 
   const activeFileTab = useMemo(
     () => fileTabs.find((tab) => tab.id === activeFileTabId) ?? null,