diff --git a/desktop/src/features/channels/ui/MembersSidebar.revocationFence.test.mjs b/desktop/src/features/channels/ui/MembersSidebar.revocationFence.test.mjs
new file mode 100644
index 0000000000..c2c86d20e2
--- /dev/null
+++ b/desktop/src/features/channels/ui/MembersSidebar.revocationFence.test.mjs
@@ -0,0 +1,461 @@
+/**
+ * PR #6852 review: the pre-join read-only fence must also fail closed over
+ * mutation surfaces opened BEFORE membership was revoked. Membership
+ * notifications invalidate the channel queries live, so `channel.isMember`
+ * can flip to false while the sidebar — and the "Manage agent access" dialog
+ * it hosts — is open. The dialog's Save path dispatches the global
+ * `update_managed_agent` mutation with no channel-membership guard of its
+ * own, so the sidebar must close it on revocation and its Save must not be
+ * dispatchable afterwards.
+ *
+ * Mutation proof: revert the `respondToDialogAgent` clamp/reset hunk in
+ * MembersSidebar.tsx (pass `editRespondToAgent` straight through) and the
+ * revocation test goes RED — the dialog stays mounted across the
+ * isMember=false rerender.
+ */
+
+import assert from "node:assert/strict";
+import { after, afterEach, before, test } from "node:test";
+import { JSDOM } from "jsdom";
+
+const dom = new JSDOM("<!doctype html><html><body></body></html>", {
+  url: "http://localhost",
+});
+
+Object.assign(globalThis, {
+  HTMLElement: dom.window.HTMLElement,
+  HTMLIFrameElement: dom.window.HTMLIFrameElement,
+  IS_REACT_ACT_ENVIRONMENT: true,
+  MutationObserver: dom.window.MutationObserver,
+  ResizeObserver: class {
+    observe() {}
+    unobserve() {}
+    disconnect() {}
+  },
+  document: dom.window.document,
+  localStorage: dom.window.localStorage,
+  self: dom.window,
+  window: dom.window,
+});
+Object.defineProperty(globalThis, "navigator", {
+  configurable: true,
+  value: dom.window.navigator,
+});
+dom.window.requestAnimationFrame = (callback) => setTimeout(callback, 0);
+globalThis.requestAnimationFrame = dom.window.requestAnimationFrame;
+dom.window.ResizeObserver = globalThis.ResizeObserver;
+dom.window.matchMedia ??= (query) => ({
+  matches: false,
+  media: query,
+  onchange: null,
+  addListener: () => {},
+  removeListener: () => {},
+  addEventListener: () => {},
+  removeEventListener: () => {},
+  dispatchEvent: () => false,
+});
+globalThis.matchMedia = dom.window.matchMedia;
+// Copy all DOM-level globals from JSDOM that Radix Dialog/DropdownMenu
+// focus/dismiss machinery references without a window. prefix.
+for (const key of Object.getOwnPropertyNames(dom.window)) {
+  if (
+    !(key in globalThis) &&
+    (key.startsWith("HTML") ||
+      key.startsWith("SVG") ||
+      key.startsWith("CSS") ||
+      [
+        "Element",
+        "Document",
+        "ShadowRoot",
+        "DOMRect",
+        "DOMRectReadOnly",
+        "Node",
+        "NodeFilter",
+        "NodeList",
+        "NamedNodeMap",
+        "Event",
+        "CustomEvent",
+        "MouseEvent",
+        "KeyboardEvent",
+        "FocusEvent",
+        "InputEvent",
+        "PointerEvent",
+        "TouchEvent",
+        "WheelEvent",
+        "EventTarget",
+        "Text",
+        "Comment",
+        "DocumentFragment",
+        "Range",
+        "Selection",
+        "getComputedStyle",
+        "IntersectionObserver",
+        "ResizeObserver",
+      ].includes(key))
+  ) {
+    const val = dom.window[key];
+    if (val !== undefined) globalThis[key] = val;
+  }
+}
+// getComputedStyle must be bound to dom.window or it throws "Illegal invocation".
+globalThis.getComputedStyle = dom.window.getComputedStyle.bind(dom.window);
+// JSDOM has no layout; Radix roving focus scrolls highlighted items into view.
+dom.window.HTMLElement.prototype.scrollIntoView ??= () => {};
+
+// Radix DismissableLayer and FocusScope dispatch plain objects via
+// dispatchEvent for layer-coordination events. JSDOM's strict Event type
+// validation throws on these; silently drop non-Event objects.
+const _origDispatch = dom.window.EventTarget.prototype.dispatchEvent;
+dom.window.EventTarget.prototype.dispatchEvent = function (event) {
+  if (!(event instanceof dom.window.Event)) return false;
+  return _origDispatch.call(this, event);
+};
+globalThis.EventTarget = dom.window.EventTarget;
+
+// ── Fixtures ─────────────────────────────────────────────────────────────────
+
+const VIEWER = "a".repeat(64);
+const BOT = "b".repeat(64);
+const CHANNEL_ID = "11111111-2222-3333-4444-555555555555";
+
+/** Raw snake_case managed agent as `list_managed_agents` returns over IPC. */
+const RAW_BOT_AGENT = {
+  pubkey: BOT,
+  name: "Nimbus",
+  persona_id: null,
+  relay_url: "wss://relay.example",
+  acp_command: "acp",
+  agent_command: "agent",
+  agent_args: [],
+  mcp_command: null,
+  turn_timeout_seconds: 60,
+  idle_timeout_seconds: 60,
+  max_turn_duration_seconds: 600,
+  parallelism: 1,
+  system_prompt: null,
+  model: null,
+  status: "stopped",
+  pid: null,
+  created_at: 1,
+  updated_at: 1,
+  last_started_at: null,
+  last_stopped_at: null,
+  last_exit_code: null,
+  last_error: null,
+  log_path: null,
+  start_on_app_launch: false,
+  backend: { type: "local" },
+  backend_agent_id: null,
+  respond_to: "owner-only",
+  respond_to_allowlist: [],
+};
+
+const RAW_MEMBERS = {
+  members: [
+    {
+      pubkey: VIEWER,
+      role: "member",
+      is_agent: false,
+      joined_at: 1,
+      display_name: "Viewer",
+    },
+    {
+      pubkey: BOT,
+      role: "bot",
+      is_agent: true,
+      joined_at: 1,
+      display_name: "Nimbus",
+    },
+  ],
+};
+
+function memberChannel(isMember) {
+  return {
+    id: CHANNEL_ID,
+    name: "orbit",
+    channelType: "channel",
+    visibility: "open",
+    isMember,
+    archivedAt: null,
+  };
+}
+
+// ── Tauri IPC stub ────────────────────────────────────────────────────────────
+
+let updateManagedAgentCalls = [];
+
+globalThis.__TAURI_INTERNALS__ = {
+  invoke: (command, args) => {
+    if (command.startsWith("plugin:")) return Promise.resolve(0);
+    switch (command) {
+      case "get_identity":
+        return Promise.resolve({ pubkey: VIEWER, display_name: "Viewer" });
+      case "get_channel_members":
+        return Promise.resolve(RAW_MEMBERS);
+      case "list_managed_agents":
+        return Promise.resolve([RAW_BOT_AGENT]);
+      case "list_relay_agents":
+        return Promise.resolve([]);
+      case "get_presence":
+        return Promise.resolve({});
+      case "get_users_batch":
+        return Promise.resolve({ profiles: {}, missing: [] });
+      case "search_users":
+        return Promise.resolve({ users: [], next_cursor: null });
+      case "list_archived_identities":
+        return Promise.resolve({ archived: [] });
+      case "get_my_relay_membership":
+        return Promise.reject(new Error("relay returned 404 Not Found"));
+      case "agent_access_owner_only":
+        return Promise.resolve(false);
+      case "update_managed_agent":
+        updateManagedAgentCalls.push(args);
+        return Promise.resolve({
+          agent: RAW_BOT_AGENT,
+          profile_sync_error: null,
+        });
+      default:
+        return Promise.resolve(null);
+    }
+  },
+  transformCallback: () => 1,
+};
+dom.window.__TAURI_INTERNALS__ = globalThis.__TAURI_INTERNALS__;
+
+// ── Deferred imports ──────────────────────────────────────────────────────────
+
+let React,
+  act,
+  createRoot,
+  QueryClient,
+  QueryClientProvider,
+  CommunitiesProvider,
+  ThemeProvider,
+  TooltipProvider,
+  MembersSidebar;
+
+before(async () => {
+  ({ default: React, act } = await import("react"));
+  ({ createRoot } = await import("react-dom/client"));
+  ({ QueryClient, QueryClientProvider } = await import(
+    "@tanstack/react-query"
+  ));
+  ({ CommunitiesProvider } = await import(
+    "@/features/communities/useCommunities.tsx"
+  ));
+  ({ ThemeProvider } = await import("@/shared/theme/ThemeProvider.tsx"));
+  ({ TooltipProvider } = await import("@/shared/ui/tooltip.tsx"));
+  ({ MembersSidebar } = await import("./MembersSidebar.tsx"));
+});
+
+afterEach(() => {
+  updateManagedAgentCalls = [];
+});
+
+after(() => dom.window.close());
+
+// ── Helpers ───────────────────────────────────────────────────────────────────
+
+function sidebarTree(queryClient, channel) {
+  return React.createElement(
+    QueryClientProvider,
+    { client: queryClient },
+    React.createElement(
+      ThemeProvider,
+      null,
+      React.createElement(
+        TooltipProvider,
+        null,
+        React.createElement(
+          CommunitiesProvider,
+          null,
+          React.createElement(MembersSidebar, {
+            channel,
+            currentPubkey: VIEWER,
+            onOpenChange: () => {},
+            open: true,
+          }),
+        ),
+      ),
+    ),
+  );
+}
+
+async function settle(ms = 50) {
+  await act(async () => {
+    await new Promise((r) => setTimeout(r, ms));
+  });
+}
+
+function findSaveAccessButton() {
+  return [...document.body.querySelectorAll("button")].find((button) =>
+    button.textContent?.includes("Save access"),
+  );
+}
+
+function accessDialogIsOpen() {
+  return [...document.body.querySelectorAll('[role="dialog"]')].some((el) =>
+    el.textContent?.includes("Manage agent access"),
+  );
+}
+
+/**
+ * Mount the sidebar as a joined member and open "Manage agent access" for the
+ * managed bot through the real row menu. Returns render handles for the
+ * caller to drive the membership transition.
+ */
+async function mountWithAccessDialogOpen() {
+  // gcTime 0: the default 5-minute garbage-collection timers outlive
+  // teardown and stall the node:test process for their full duration.
+  const queryClient = new QueryClient({
+    defaultOptions: {
+      queries: { retry: false, gcTime: 0 },
+      mutations: { gcTime: 0 },
+    },
+  });
+  const container = document.createElement("div");
+  document.body.appendChild(container);
+  const root = createRoot(container);
+
+  await act(async () => {
+    root.render(sidebarTree(queryClient, memberChannel(true)));
+  });
+  await settle();
+
+  // The member list virtualizes (zero-height in JSDOM), so filter by search —
+  // the search branch renders matching rows directly.
+  const searchInput = document.body.querySelector(
+    '[data-testid="channel-management-search-users"]',
+  );
+  assert.ok(searchInput, "members search input must render");
+  const setter = Object.getOwnPropertyDescriptor(
+    dom.window.HTMLInputElement.prototype,
+    "value",
+  ).set;
+  await act(async () => {
+    setter.call(searchInput, "nim");
+    searchInput.dispatchEvent(new dom.window.Event("input", { bubbles: true }));
+    await new Promise((r) => setTimeout(r, 0));
+  });
+  await settle();
+
+  const menuTrigger = document.body.querySelector(
+    `[data-testid="sidebar-member-menu-${BOT}"]`,
+  );
+  assert.ok(menuTrigger, "bot row actions menu must render for a member");
+  await act(async () => {
+    menuTrigger.dispatchEvent(
+      new dom.window.MouseEvent("pointerdown", { bubbles: true, button: 0 }),
+    );
+    await new Promise((r) => setTimeout(r, 0));
+  });
+  await settle();
+
+  const editItem = document.body.querySelector(
+    `[data-testid="sidebar-edit-respond-to-${BOT}"]`,
+  );
+  assert.ok(editItem, "Manage agent access menu item must render");
+  await act(async () => {
+    editItem.dispatchEvent(
+      new dom.window.MouseEvent("click", { bubbles: true }),
+    );
+    await new Promise((r) => setTimeout(r, 0));
+  });
+  await settle();
+
+  assert.ok(accessDialogIsOpen(), "Manage agent access dialog must open");
+
+  return {
+    queryClient,
+    container,
+    root,
+    async rerender(channel) {
+      await act(async () => {
+        root.render(sidebarTree(queryClient, channel));
+      });
+      await settle();
+    },
+    async teardown() {
+      await act(async () => {
+        root.unmount();
+      });
+      container.remove();
+      queryClient.clear();
+    },
+  };
+}
+
+// ── Tests ─────────────────────────────────────────────────────────────────────
+
+test("control: Save dispatches update_managed_agent while still a member", async () => {
+  const surface = await mountWithAccessDialogOpen();
+
+  const saveButton = findSaveAccessButton();
+  assert.ok(saveButton, "Save access button must render for a member");
+  await act(async () => {
+    saveButton.dispatchEvent(
+      new dom.window.MouseEvent("click", { bubbles: true }),
+    );
+    await new Promise((r) => setTimeout(r, 0));
+  });
+  await settle();
+
+  assert.equal(
+    updateManagedAgentCalls.length,
+    1,
+    "Save must dispatch exactly one update_managed_agent while a member",
+  );
+
+  await surface.teardown();
+});
+
+test("membership revocation closes the open access dialog and Save cannot dispatch", async () => {
+  const surface = await mountWithAccessDialogOpen();
+
+  const staleSaveButton = findSaveAccessButton();
+  assert.ok(
+    staleSaveButton,
+    "Save access button must render before revocation",
+  );
+
+  // Membership revoked mid-session: notifications invalidate the channel
+  // queries and isMember flips to false with the sidebar still open.
+  await surface.rerender(memberChannel(false));
+
+  assert.equal(
+    accessDialogIsOpen(),
+    false,
+    "revocation must close the already-open Manage agent access dialog",
+  );
+  assert.equal(
+    findSaveAccessButton(),
+    undefined,
+    "no Save access button may remain reachable after revocation",
+  );
+
+  // Even a click landing on the stale pre-revocation button must not reach
+  // the mutation.
+  await act(async () => {
+    staleSaveButton.dispatchEvent(
+      new dom.window.MouseEvent("click", { bubbles: true }),
+    );
+    await new Promise((r) => setTimeout(r, 0));
+  });
+  await settle();
+  assert.equal(
+    updateManagedAgentCalls.length,
+    0,
+    "update_managed_agent must not fire after revocation",
+  );
+
+  // The stale selection is cleared, not merely hidden: re-joining later must
+  // not spontaneously reopen the dialog.
+  await surface.rerender(memberChannel(true));
+  assert.equal(
+    accessDialogIsOpen(),
+    false,
+    "re-join must not resurrect the pre-revocation dialog",
+  );
+
+  await surface.teardown();
+});
diff --git a/desktop/src/features/channels/ui/MembersSidebar.tsx b/desktop/src/features/channels/ui/MembersSidebar.tsx
index 3564bcdbf0..8f62ad0e23 100644
--- a/desktop/src/features/channels/ui/MembersSidebar.tsx
+++ b/desktop/src/features/channels/ui/MembersSidebar.tsx
@@ -562,6 +562,19 @@ export function MembersSidebar({
 
   const [editRespondToAgent, setEditRespondToAgent] =
     React.useState<ManagedAgent | null>(null);
+  // Membership can be revoked while the sidebar is open (member-removed
+  // notifications invalidate the channel queries live) and the roster
+  // deliberately stays visible afterwards, so the read-only fence must also
+  // fail closed over mutation surfaces opened BEFORE revocation. Clamp the
+  // agent-access dialog at render — an effect-only reset would leave its Save
+  // dispatchable for a frame — and clear the stale selection so a later
+  // re-join cannot spontaneously reopen the dialog.
+  const respondToDialogAgent = isReadOnlyRoster ? null : editRespondToAgent;
+  React.useEffect(() => {
+    if (isReadOnlyRoster) {
+      setEditRespondToAgent(null);
+    }
+  }, [isReadOnlyRoster]);
 
   React.useEffect(() => {
     if (!open) {
@@ -923,12 +936,12 @@ export function MembersSidebar({
         </DialogContent>
       </Dialog>
       <EditRespondToDialog
-        agent={editRespondToAgent}
+        agent={respondToDialogAgent}
         currentPubkey={currentPubkey}
         onOpenChange={(dialogOpen) => {
           if (!dialogOpen) setEditRespondToAgent(null);
         }}
-        open={editRespondToAgent !== null}
+        open={respondToDialogAgent !== null}
       />
     </>
   );