feat(desktop): cover the channel with the agent activity drawer

desktop/playwright.config.ts

@@ -92,6 +92,7 @@ export default defineConfig({
         "**/thread-reply-anchor-roleplay.spec.ts",
         "**/threadpane-ultrawide.spec.ts",
         "**/thread-focus-mode.spec.ts",
+        "**/agent-activity-cover.spec.ts",
         "**/animated-avatar.spec.ts",
         "**/reminders.spec.ts",
         "**/reminder-click-repro.spec.ts",

desktop/src/app/AppShell.tsx

@@ -75,7 +75,7 @@ import {
 import { useDueReminderBadgeCount } from "@/features/reminders/hooks";
 import { useReminderNotifications } from "@/features/reminders/useReminderNotifications";
 import { AppSidebar } from "@/features/sidebar/ui/AppSidebar";
-import { requestFocusedThreadClose } from "@/features/channels/focusedThreadCloseRequest";
+import { requestCoverDrawerClose } from "@/features/channels/coverDrawerCloseRequest";
 import { CommunityRail } from "@/features/sidebar/ui/CommunityRail";
 import { useChannelMutes } from "@/features/sidebar/lib/useChannelMutes";
 import { useChannelStars } from "@/features/sidebar/lib/useChannelStars";
@@ -846,7 +846,7 @@ export function AppShell() {
                             addCommunityDialog.onOpenChange
                           }
                           onNewMessage={goNewMessage}
-                          onBackgroundClick={requestFocusedThreadClose}
+                          onBackgroundClick={requestCoverDrawerClose}
                           onCreateChannelOpenChange={setIsCreateChannelOpen}
                           onOpenAddCommunity={addCommunityDialog.openDialog}
                           onSendFeedback={() => setIsSendFeedbackOpen(true)}

desktop/src/features/channels/coverDrawerCloseRequest.test.mjs

@@ -0,0 +1,21 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import {
+  requestCoverDrawerClose,
+  subscribeToCoverDrawerCloseRequest,
+} from "./coverDrawerCloseRequest.ts";
+
+test("cover drawer close requests reach active subscribers only", () => {
+  let calls = 0;
+  const unsubscribe = subscribeToCoverDrawerCloseRequest(() => {
+    calls += 1;
+  });
+
+  requestCoverDrawerClose();
+  assert.equal(calls, 1);
+
+  unsubscribe();
+  requestCoverDrawerClose();
+  assert.equal(calls, 1);
+});

desktop/src/features/channels/coverDrawerCloseRequest.ts

@@ -0,0 +1,22 @@
+const listeners = new Set<() => void>();
+
+/**
+ * Request dismissal of the channel's open cover drawer.
+ *
+ * One channel of a channel pane is covered at a time (focus-mode thread or
+ * agent activity), so this needs no discriminator — whichever drawer is open
+ * subscribes and closes.
+ */
+export function requestCoverDrawerClose(): void {
+  for (const listener of listeners) {
+    listener();
+  }
+}
+
+/** Subscribe the active cover drawer to external dismissal requests. */
+export function subscribeToCoverDrawerCloseRequest(
+  listener: () => void,
+): () => void {
+  listeners.add(listener);
+  return () => listeners.delete(listener);
+}

desktop/src/features/channels/lib/agentSessionPanelPresentation.test.mjs

@@ -0,0 +1,54 @@
+import assert from "node:assert/strict";
+import test from "node:test";
+
+import { getAgentSessionPanelPresentation } from "./agentSessionPanelPresentation.ts";
+
+test("the cover drawer owns motion and gets standalone, opaque chrome", () => {
+  assert.deepEqual(
+    getAgentSessionPanelPresentation({
+      isCoverDrawer: true,
+      isSinglePanelView: false,
+      useSplitAuxiliaryPane: true,
+    }),
+    {
+      enterMotion: false,
+      isSinglePanelView: true,
+      layout: "standalone",
+      transparentChrome: false,
+    },
+  );
+});
+
+test("the split pane keeps docked chrome and its own enter motion", () => {
+  assert.deepEqual(
+    getAgentSessionPanelPresentation({
+      isCoverDrawer: false,
+      isSinglePanelView: false,
+      useSplitAuxiliaryPane: true,
+    }),
+    {
+      enterMotion: true,
+      isSinglePanelView: false,
+      layout: "split",
+      transparentChrome: true,
+    },
+  );
+});
+
+test("narrow viewports keep today's overlay and single-panel presentations", () => {
+  for (const isSinglePanelView of [false, true]) {
+    assert.deepEqual(
+      getAgentSessionPanelPresentation({
+        isCoverDrawer: false,
+        isSinglePanelView,
+        useSplitAuxiliaryPane: false,
+      }),
+      {
+        enterMotion: true,
+        isSinglePanelView,
+        layout: "standalone",
+        transparentChrome: false,
+      },
+    );
+  }
+});

desktop/src/features/channels/lib/agentSessionPanelPresentation.ts

@@ -0,0 +1,57 @@
+/**
+ * `AnimatePresence` key shared by every agent activity presentation.
+ *
+ * The split pane and the cover drawer are two containers for one session, so
+ * presence is a property of the session, not of either container — crossing the
+ * viewport breakpoint changes how it is shown, not whether it is open.
+ */
+export const AGENT_SESSION_SURFACE_KEY = "agent-session-surface";
+
+export type AgentSessionPanelPresentation = {
+  enterMotion: boolean;
+  isSinglePanelView: boolean;
+  layout: "standalone" | "split";
+  transparentChrome: boolean;
+};
+
+type AgentSessionPanelPresentationOptions = {
+  /** The panel is rendered inside the agent activity cover drawer. */
+  isCoverDrawer: boolean;
+  isSinglePanelView: boolean;
+  useSplitAuxiliaryPane: boolean;
+};
+
+/**
+ * Maps channel presentation into the agent session panel's layout props.
+ *
+ * TODO(#6538): once the `conversation` transcript variant lands on main, this
+ * should also return `transcriptVariant: "conversation"` for the cover drawer
+ * and `undefined` otherwise, so the reading view is pinned by presentation
+ * rather than inferred from panel width. The variant does not exist on main
+ * yet, so the prop is deliberately not set here.
+ */
+export function getAgentSessionPanelPresentation({
+  isCoverDrawer,
+  isSinglePanelView,
+  useSplitAuxiliaryPane,
+}: AgentSessionPanelPresentationOptions): AgentSessionPanelPresentation {
+  if (isCoverDrawer) {
+    return {
+      // The drawer animates itself; a second slide inside it would compound.
+      enterMotion: false,
+      // Fills the drawer, and selects the standalone header chrome that owns
+      // its own backdrop — the drawer is not sharing the channel's header, and
+      // it has no resizable neighbour to draw a resize border against.
+      isSinglePanelView: true,
+      layout: "standalone",
+      transparentChrome: false,
+    };
+  }
+
+  return {
+    enterMotion: true,
+    isSinglePanelView: useSplitAuxiliaryPane ? false : isSinglePanelView,
+    layout: useSplitAuxiliaryPane ? "split" : "standalone",
+    transparentChrome: useSplitAuxiliaryPane,
+  };
+}