diff --git a/packages/dashboard/app/components/ChatView.css b/packages/dashboard/app/components/ChatView.css
index b90e9efcdd..49751fec2f 100644
--- a/packages/dashboard/app/components/ChatView.css
+++ b/packages/dashboard/app/components/ChatView.css
@@ -37,6 +37,10 @@
 FNXC:ViewportChrome 2026-08-23-03:40:
 FN-9193 tablet-class touch devices can be 768 CSS pixels wide, so this scoped docked rule
 must override the mobile one-pane rule while phone mode remains unchanged.
+
+FNXC:ViewportChrome 2026-08-23-17:07:
+FN-9200 keeps the docked pane width exclusively in its inline width and min-width style because
+no docked-sidebar custom-property producer exists; the tablet cascade only restores its layout bounds.
 */
 .chat-view--docked-list .chat-sidebar--docked {
   flex: 0 0 auto;
@@ -69,7 +73,6 @@ must override the mobile one-pane rule while phone mode remains unchanged.
 }
 
 html[data-viewport-mode="tablet"] .chat-view--docked-list .chat-sidebar--docked {
-  width: var(--chat-docked-sidebar-width, auto);
   min-width: 0;
   max-width: none;
   height: auto;
diff --git a/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar-css.test.tsx b/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar-css.test.tsx
new file mode 100644
index 0000000000..7ef3866764
--- /dev/null
+++ b/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar-css.test.tsx
@@ -0,0 +1,52 @@
+/*
+FNXC:ViewportChrome 2026-08-23-17:07:
+FN-9200 verifies the rendered cascade because a 768px tablet-class device matches the mobile media
+query; without this proof, a mobile full-width rule could silently collapse the docked pane.
+*/
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { act, render, screen } from "@testing-library/react";
+import { ChatView } from "../ChatView";
+import { loadAllAppCss } from "../../test/cssFixture";
+import { installChatViewEnv, mockTabletClassTouchViewport, mockViewportMode, setupMockChat } from "./ChatView.test-harness";
+
+vi.mock("../../hooks/useChat");
+vi.mock("../../hooks/useChatRooms");
+vi.mock("../../hooks/useNavigationHistory", () => ({ useNavigationHistoryContext: () => ({ pushNav: vi.fn(), replaceCurrent: vi.fn() }) }));
+vi.mock("../../api", () => ({ fetchSettings: vi.fn().mockResolvedValue({}), fetchModels: vi.fn().mockResolvedValue({ models: [] }), fetchAgents: vi.fn().mockResolvedValue([]), fetchDiscoveredSkills: vi.fn().mockResolvedValue([]), fetchTasks: vi.fn().mockResolvedValue([]), searchFiles: vi.fn().mockResolvedValue({ files: [] }) }));
+
+installChatViewEnv();
+afterEach(() => { document.head.querySelector("#chat-docked-css")?.remove(); });
+const session = { id: "css-session", agentId: "agent-001", status: "active" as const, title: "CSS", createdAt: "2026-08-22T00:00:00.000Z", updatedAt: "2026-08-22T00:00:00.000Z" };
+
+async function renderCss() {
+  const style = document.createElement("style"); style.id = "chat-docked-css"; style.textContent = loadAllAppCss(); document.head.appendChild(style);
+  setupMockChat({ activeSession: session, sessions: [session], filteredSessions: [session] });
+  await act(async () => { render(<ChatView projectId="proj-123" addToast={vi.fn()} />); });
+}
+
+describe("ChatView docked sidebar tablet cascade", () => {
+  it("preserves inline docked width on a 768px tablet-class device", async () => {
+    const restore = mockTabletClassTouchViewport();
+    try {
+      await renderCss();
+      const sidebar = document.querySelector(".chat-sidebar") as HTMLElement;
+      const style = getComputedStyle(sidebar);
+      expect(sidebar.style.width).toBe("300px");
+      expect(style.minWidth).not.toBe("100%");
+      expect(style.maxWidth).not.toBe("100%");
+      expect(style.width).toBe("300px");
+    } finally { restore(); }
+  });
+
+  it("keeps the mobile one-pane sidebar full width", async () => {
+    const restore = mockViewportMode("mobile");
+    try {
+      await renderCss();
+      const sidebar = document.querySelector(".chat-sidebar") as HTMLElement;
+      const style = getComputedStyle(sidebar);
+      expect(document.querySelector(".chat-view")).not.toHaveClass("chat-view--docked-list");
+      expect(style.width).toBe("100%");
+      expect(style.minWidth).toBe("100%");
+    } finally { restore(); }
+  });
+});
diff --git a/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar.test.tsx b/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar.test.tsx
index 9f53998ae3..4e765ad027 100644
--- a/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar.test.tsx
+++ b/packages/dashboard/app/components/__tests__/ChatView.docked-sidebar.test.tsx
@@ -1,15 +1,17 @@
 /*
-FNXC:DashboardTests 2026-08-23-03:55:
-FN-9193 requires both tablet shapes to resolve through useViewportMode before docked-list
-assertions run. These tests also keep persistence and excluded hosts on the shared ChatView path.
+FNXC:DashboardTests 2026-08-23-17:07:
+FN-9200 keeps docked-sidebar eligibility behavioral: all tablet variants must expose the pane and
+all embedded or floating hosts must retain the one-pane Back navigation.
 */
 import { describe, expect, it, vi } from "vitest";
 import { act, fireEvent, screen } from "@testing-library/react";
 import { ChatView, CHAT_DOCKED_SIDEBAR_DEFAULT_WIDTH, CHAT_DOCKED_SIDEBAR_MAX_WIDTH, CHAT_DOCKED_SIDEBAR_MIN_WIDTH, CHAT_DOCKED_SIDEBAR_OPEN_STORAGE_KEY, CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY, clampChatDockedSidebarWidth } from "../ChatView";
 import {
+  createRoomFixture,
   installChatViewEnv,
   mockTabletClassTouchViewport,
   mockViewportMode,
+  mockFetchModels,
   renderWithAct,
   setupMockChat,
   setupMockRooms,
@@ -38,36 +40,95 @@ const session = {
   createdAt: "2026-08-22T00:00:00.000Z", updatedAt: "2026-08-22T00:00:00.000Z",
 };
 
-async function renderSelected(props: Partial<React.ComponentProps<typeof ChatView>> = {}) {
+async function renderSelected(props: Partial<React.ComponentProps<typeof ChatView>> = {}, selected = session) {
   const selectSession = vi.fn();
-  setupMockChat({ activeSession: session, sessions: [session], filteredSessions: [session], selectSession });
+  setupMockChat({ activeSession: selected, sessions: [selected], filteredSessions: [selected], selectSession });
   const view = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} {...props} />);
-  await act(async () => { fireEvent.click(screen.getByTestId(`chat-session-${session.id}`)); });
+  await act(async () => { fireEvent.click(screen.getByTestId(`chat-session-${selected.id}`)); });
   return { view, selectSession };
 }
 
+function expectDocked() {
+  expect(document.querySelector(".chat-view")).toHaveClass("chat-view--docked-list");
+  const sidebar = document.querySelector(".chat-sidebar") as HTMLElement;
+  expect(sidebar).toHaveClass("chat-sidebar--docked");
+  expect(sidebar.style.width).toBeTruthy();
+  expect(screen.getByTestId("chat-docked-sidebar-toggle")).toBeInTheDocument();
+  return screen.getByTestId("chat-sidebar-resize-handle");
+}
+
+function expectOnePaneHost() {
+  expect(document.querySelector(".chat-view")).not.toHaveClass("chat-view--docked-list");
+  expect(screen.queryByTestId("chat-docked-sidebar-toggle")).toBeNull();
+  expect(screen.queryByTestId("chat-sidebar-resize-handle")).toBeNull();
+  expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
+}
+
 describe("ChatView docked conversation sidebar", () => {
-  it("proves mobile, desktop, and both tablet viewport shapes", async () => {
+  it.each([
+    ["desktop", () => mockViewportMode("desktop")],
+    ["769-1024 tablet", () => mockViewportMode("tablet")],
+    ["768px touch tablet", () => mockTabletClassTouchViewport()],
+  ])("renders a resizable docked pane on %s", async (_name, installViewport) => {
+    const restore = installViewport();
+    try {
+      const { view } = await renderSelected();
+      const handle = expectDocked();
+      expect(handle).toHaveAttribute("aria-valuenow", "300");
+      fireEvent.keyDown(handle, { key: "ArrowRight" });
+      expect(handle).toHaveAttribute("aria-valuenow", "316");
+      fireEvent.keyDown(handle, { key: "ArrowLeft" });
+      expect(handle).toHaveAttribute("aria-valuenow", "300");
+      view.unmount();
+    } finally { restore(); }
+  });
+
+  it.each([
+    ["mobile", { }, () => mockViewportMode("mobile")],
+    ["compact right dock", { compactLayout: true }, () => mockViewportMode("desktop")],
+    ["floating Quick Chat", { floating: true }, () => mockViewportMode("desktop")],
+    ["popped-out chat", { floating: true, persistChatPreferences: false }, () => mockViewportMode("desktop")],
+  ])("keeps %s in one-pane navigation", async (_name, props, installViewport) => {
+    const restore = installViewport();
+    // FN-9200 must prove the floating exclusion itself, not jsdom's zero-width narrow-host fallback.
+    const bounds = props.floating
+      ? vi.spyOn(HTMLElement.prototype, "getBoundingClientRect").mockReturnValue({ width: 1000 } as DOMRect)
+      : null;
+    try {
+      const { view } = await renderSelected(props);
+      expectOnePaneHost();
+      view.unmount();
+    } finally { bounds?.mockRestore(); restore(); }
+  });
+
+  it("hides Back without leaving a header shell while docked, and restores it when closed", async () => {
+    const { view } = await renderSelected();
+    expectDocked();
+    const header = document.querySelector(".chat-thread-header") as HTMLElement;
+    expect(header.querySelector('[aria-label="Back to conversations"]')).toBeNull();
+    expect(header.querySelector("button.btn, button.btn-icon")).toBeNull();
+    expect(screen.getByTestId("chat-thread-header-identity")).toBeInTheDocument();
+    fireEvent.click(screen.getByTestId("chat-docked-sidebar-toggle"));
+    expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
+    view.unmount();
+  });
+
+  it("keeps the Rooms scope inside the docked sidebar and removes its Back shell", async () => {
+    const room = createRoomFixture("docked");
+    localStorage.setItem("fusion:chat-scope", "rooms");
     setupMockChat({ sessions: [], filteredSessions: [] });
-    const desktop = mockViewportMode("desktop");
-    const desktopView = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
-    expect(document.documentElement.dataset.viewportMode).toBe("desktop");
-    desktopView.unmount(); desktop.mockRestore();
-
-    const tablet = mockViewportMode("tablet");
-    const tabletView = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
-    expect(document.documentElement.dataset.viewportMode).toBe("tablet");
-    tabletView.unmount(); tablet.mockRestore();
-
-    const restoreTouchTablet = mockTabletClassTouchViewport();
-    const touchTabletView = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
-    expect(document.documentElement.dataset.viewportMode).toBe("tablet");
-    touchTabletView.unmount(); restoreTouchTablet();
-
-    const mobile = mockViewportMode("mobile");
-    await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
-    expect(document.documentElement.dataset.viewportMode).toBe("mobile");
-    mobile.mockRestore();
+    setupMockRooms({ rooms: [room], activeRoom: room });
+    const view = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} experimentalFeatures={{ chatRooms: true }} />);
+    expectDocked();
+    const rooms = screen.getByTestId("chat-sidebar-rooms");
+    expect(rooms.closest(".chat-sidebar")).toHaveClass("chat-sidebar--docked");
+    fireEvent.click(screen.getByTestId(`chat-room-item-${room.slug}`));
+    const header = document.querySelector(".chat-room-thread-header") as HTMLElement;
+    expect(header.querySelector('[aria-label="Back to conversations"]')).toBeNull();
+    expect(header.querySelector("button.btn, button.btn-icon")).toBeNull();
+    fireEvent.click(screen.getByTestId("chat-docked-sidebar-toggle"));
+    expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
+    view.unmount();
   });
 
   it("clamps widths and restores valid stored preferences at first render", async () => {
@@ -76,23 +137,9 @@ describe("ChatView docked conversation sidebar", () => {
     expect(clampChatDockedSidebarWidth(300)).toBe(300);
     localStorage.setItem(CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY, "900");
     setupMockChat({ sessions: [], filteredSessions: [] });
-    await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+    const view = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
     expect((document.querySelector(".chat-sidebar") as HTMLElement).style.width).toBe(`${CHAT_DOCKED_SIDEBAR_MAX_WIDTH}px`);
-  });
-
-  it("keeps selected desktop threads beside the list and supports toggle and keyboard resize", async () => {
-    const { selectSession } = await renderSelected();
-    expect(selectSession).toHaveBeenCalledWith(session.id);
-    expect(document.querySelector(".chat-sidebar")).toHaveClass("chat-sidebar--docked");
-    expect(screen.queryByTestId("chat-back-btn")).toBeNull();
-    const handle = screen.getByTestId("chat-sidebar-resize-handle");
-    fireEvent.keyDown(handle, { key: "ArrowRight" });
-    expect(handle).toHaveAttribute("aria-valuenow", "316");
-    expect(localStorage.getItem(CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY)).toBe("316");
-    fireEvent.click(screen.getByTestId("chat-docked-sidebar-toggle"));
-    expect(screen.queryByTestId("chat-sidebar-resize-handle")).toBeNull();
-    expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
-    expect(localStorage.getItem(CHAT_DOCKED_SIDEBAR_OPEN_STORAGE_KEY)).toBe("false");
+    view.unmount();
   });
 
   it("persists resize and open state across unmount/remount", async () => {
@@ -102,18 +149,87 @@ describe("ChatView docked conversation sidebar", () => {
     fireEvent.pointerMove(document, { pointerId: 1, clientX: 180 });
     fireEvent.pointerUp(document, { pointerId: 1, clientX: 180 });
     expect(localStorage.getItem(CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY)).toBe("380");
+    fireEvent.click(screen.getByTestId("chat-docked-sidebar-toggle"));
+    expect(localStorage.getItem(CHAT_DOCKED_SIDEBAR_OPEN_STORAGE_KEY)).toBe("false");
     view.unmount();
-    setupMockChat({ sessions: [], filteredSessions: [] });
-    await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+    const remount = await renderSelected();
+    expect(screen.queryByTestId("chat-sidebar-resize-handle")).toBeNull();
+    expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
+    fireEvent.click(screen.getByTestId("chat-docked-sidebar-toggle"));
     expect((document.querySelector(".chat-sidebar") as HTMLElement).style.width).toBe("380px");
+    remount.view.unmount();
   });
 
-  it("excludes mobile, compact dock, and floating hosts", async () => {
-    const mobile = mockViewportMode("mobile");
-    await renderSelected();
-    expect(screen.queryByTestId("chat-docked-sidebar-toggle")).toBeNull();
-    expect(screen.getByTestId("chat-back-btn")).toBeInTheDocument();
-    mobile.mockRestore();
+  it.each([[null, "300px"], ["340", "340px"], ["abc", "300px"], ["", "300px"], ["-5", "300px"], ["100", "220px"], ["900", "480px"]])("restores valid, corrupt, and bounded width preference %s", async (stored, expected) => {
+    if (stored !== null) localStorage.setItem(CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY, stored);
+    setupMockChat({ sessions: [], filteredSessions: [] });
+    const view = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+    expect((document.querySelector(".chat-sidebar") as HTMLElement).style.width).toBe(expected);
+    view.unmount();
+  });
+
+  it("round-trips both closed and default-open preferences", async () => {
+    localStorage.setItem(CHAT_DOCKED_SIDEBAR_OPEN_STORAGE_KEY, "false");
+    const closed = await renderSelected();
+    expect(screen.queryByTestId("chat-sidebar-resize-handle")).toBeNull();
+    closed.view.unmount();
+    localStorage.removeItem(CHAT_DOCKED_SIDEBAR_OPEN_STORAGE_KEY);
+    const open = await renderSelected();
+    expectDocked();
+    open.view.unmount();
+  });
+
+  it("cleans up a pointer resize when unmounted mid-drag", async () => {
+    const setItem = vi.spyOn(Storage.prototype, "setItem");
+    const { view } = await renderSelected();
+    const handle = screen.getByTestId("chat-sidebar-resize-handle");
+    fireEvent.pointerDown(handle, { pointerId: 1, clientX: 100 });
+    fireEvent.pointerMove(document, { pointerId: 1, clientX: 140 });
+    view.unmount();
+    const writes = setItem.mock.calls.filter(([key]) => key === CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY).length;
+    fireEvent.pointerMove(document, { pointerId: 1, clientX: 300 });
+    fireEvent.pointerUp(document, { pointerId: 1, clientX: 300 });
+    expect(setItem.mock.calls.filter(([key]) => key === CHAT_DOCKED_SIDEBAR_WIDTH_STORAGE_KEY)).toHaveLength(writes);
+    setItem.mockRestore();
+  });
+
+  it("renders conversation row fallbacks, populated selection, and the docked empty state", async () => {
+    mockFetchModels.mockResolvedValueOnce({ models: [], favoriteProviders: [], favoriteModels: [] });
+    const untitled = { ...session, id: "session-untitled", title: "", lastMessagePreview: "", modelProvider: undefined, modelId: undefined };
+    const selectSession = vi.fn();
+    setupMockChat({ activeSession: session, sessions: [session, untitled], filteredSessions: [session, untitled], selectSession });
+    const view = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+    const populatedRow = screen.getByTestId(`chat-session-${session.id}`);
+    expect(populatedRow.querySelector(".chat-session-title")).toHaveTextContent(session.title);
+    expect(populatedRow.querySelector(".chat-session-preview")).toHaveTextContent(session.lastMessagePreview);
+    expect(populatedRow.querySelector(".chat-session-meta-model [data-provider='anthropic']")).toBeInTheDocument();
+    const untitledRow = screen.getByTestId(`chat-session-${untitled.id}`);
+    expect(untitledRow.querySelector(".chat-session-title")).toHaveTextContent("Untitled");
+    expect(untitledRow.querySelector(".chat-session-preview")).toHaveTextContent("No messages");
+    expect(untitledRow.querySelector(".chat-session-meta-model [data-provider]")).toBeNull();
+    expect(screen.getByTestId(`chat-session-model-tag-${untitled.id}`)).toHaveTextContent("Fusion");
+    fireEvent.click(untitledRow);
+    expect(selectSession).toHaveBeenCalledWith(untitled.id);
+    expectDocked();
+    view.unmount();
+    setupMockChat({ sessions: [], filteredSessions: [] });
+    const empty = await renderWithAct(<ChatView projectId="proj-123" addToast={vi.fn()} />);
+    expectDocked();
+    expect(screen.getByText("No conversations yet")).toBeInTheDocument();
+    empty.unmount();
+  });
+
+  it("keeps the conversation-row contract on mobile", async () => {
+    const restore = mockViewportMode("mobile");
+    try {
+      const { view } = await renderSelected();
+      const row = screen.getByTestId(`chat-session-${session.id}`);
+      expect(row.querySelector(".chat-session-title")).toHaveTextContent(session.title);
+      expect(row.querySelector(".chat-session-preview")).toHaveTextContent(session.lastMessagePreview);
+      expect(row.querySelector(".chat-session-meta-model [data-provider='anthropic']")).toBeInTheDocument();
+      expect(screen.getByTestId(`chat-session-model-tag-${session.id}`)).toHaveTextContent("Claude Sonnet 4.5");
+      view.unmount();
+    } finally { restore(); }
   });
 
   it("does not persist preferences for ephemeral hosts", async () => {