tabs: one window for every agent; inactive tabs take input; background off by defaultHEADmaster

Measured in Brave on 2026-11-14: an inactive tab takes trusted CDP clicks,
key presses, text and mouse moves, and Page.captureScreenshot renders it
live. Only mouseWheel hangs, waiting for a frame. The upstream guard that
refused input to every hidden page was wrong for inactive tabs, and it is
what made a window per session look necessary.

- New sessions' tabs open inactive in the user's last focused window, in
  the session's tab group; a window is created only when none is open.
- New groups start collapsed, unless their tab is the one showing, and
  expand when a tab in them is brought forward. Existing groups keep the
  user's setting.
- Input is refused up front only in a minimized window (untested there).
- chrome_scroll scrolls hidden pages by script instead of the wheel.
- Focus emulation on attach, so blur-sensitive menus stay open.
- Background mode is off by default. Calls still default to background;
  background:false or chrome_tab activate brings a tab forward.
- Agent guidance, tool descriptions and docs say so.

1 files changed, 119 insertions, 0 deletions

diff --git a/test-suite/unit/user-window.test.mjs b/test-suite/unit/user-window.test.mjs
new file mode 100644
index 0000000..af4e939
--- /dev/null
+++ b/test-suite/unit/user-window.test.mjs
@@ -0,0 +1,119 @@
+// Agents' tabs go in the user's window, inactive, in per-session tab groups that start collapsed.
+// An inactive tab takes trusted input and renders screenshots (measured 2026-11-14), so there is no
+// need for a window per session. A window is created only when Brave has none.
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import vm from "node:vm";
+import { test } from "node:test";
+
+const workerSource = fs.readFileSync(new URL("../../extensions/chrome-profile-bridge/browser-extension/service_worker.js", import.meta.url), "utf8");
+
+function worker({ groups = [], windows = { 5: { id: 5, type: "normal" } }, lastFocused = 5, tabs = {} } = {}) {
+  const calls = [];
+  const listener = { addListener() {}, removeListener() {} };
+  let nextTab = 100;
+  const w = {
+    console, setTimeout, clearTimeout, setInterval: () => 0, navigator: { userAgent: "unit-test" }, fetch: async () => { throw new Error("offline"); },
+    chrome: {
+      runtime: { id: "test", getManifest: () => ({ version: "0.0.0" }), onInstalled: listener, onStartup: listener },
+      alarms: { create() {}, onAlarm: listener }, action: { onClicked: listener }, webNavigation: { onCommitted: listener },
+      debugger: { onDetach: listener, onEvent: listener, getTargets: (cb) => cb([]) },
+      storage: { session: { get: async () => ({}), set: async (v) => { calls.push({ method: 'storage.set', json: JSON.stringify(v) }); } } },
+      tabGroups: { query: async () => groups, update: async (id, props) => { calls.push({ method: "tabGroups.update", id, props }); return { id, ...props }; } },
+      windows: {
+        get: async (id) => windows[id] ?? Promise.reject(new Error("No window")),
+        getLastFocused: async () => (lastFocused === null ? Promise.reject(new Error("No window")) : windows[lastFocused]),
+        getAll: async () => Object.values(windows),
+        update: async (id, props) => { calls.push({ method: "windows.update", id, props }); return { id }; },
+        create: async (props) => { calls.push({ method: "windows.create", props }); return { id: 9, tabs: [{ id: 900, windowId: 9 }] }; },
+      },
+      tabs: {
+        create: async (props) => { calls.push({ method: "tabs.create", props }); return { id: nextTab++, windowId: props.windowId }; },
+        query: async () => [], get: async (id) => tabs[id] ?? null, onUpdated: listener,
+        group: async () => 77,
+        update: async (id, props) => { calls.push({ method: "tabs.update", id, props }); return { id, ...props }; },
+      },
+    },
+  };
+  w.self = w;
+  vm.runInNewContext(workerSource, w);
+  return { w, calls };
+}
+
+const piGroup = (windowId, name = "Pi Session: claude-code 1 other") => ({ id: 1, windowId, title: name });
+const ops = (calls) => calls.filter((c) => c.method !== "storage.set").map((c) => c.method);
+const noWindows = { windows: {}, lastFocused: null };
+
+test("a new session's tab goes in the user's window, inactive", async () => {
+  const { w, calls } = worker({ groups: [piGroup(5)] });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(ops(calls), ["tabs.create"]);
+  const props = calls.find((c) => c.method === "tabs.create").props;
+  assert.equal(props.windowId, 5);
+  assert.equal(props.active, false);
+});
+
+test("a window is created only when Brave has none", async () => {
+  const { w, calls } = worker(noWindows);
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(ops(calls), ["windows.create"]);
+  assert.equal(calls[0].props.focused, false);
+});
+
+test("a session that already has a group adds its tab to that group's window", async () => {
+  const { w, calls } = worker({ groups: [piGroup(7, "Pi Session: claude-code 2 mine")], windows: { 5: { id: 5 }, 7: { id: 7 } } });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(ops(calls), ["tabs.create"]);
+  assert.equal(calls.find((c) => c.method === "tabs.create").props.windowId, 7);
+});
+
+test("chrome_tab new for a session with no group goes in the user's window, inactive", async () => {
+  const { w, calls } = worker({ groups: [piGroup(5)] });
+  w.groupTab = async (tab) => tab;
+  w.bringToFront = async () => {};
+  await w.dispatch("tab.new", { url: "https://x.test/", groupTitle: "Pi Session: claude-code 2 mine", sessionKey: "claude-code 2 mine" });
+  assert.deepEqual(ops(calls), ["tabs.create"]);
+  assert.equal(calls[0].props.windowId, 5);
+  assert.equal(calls[0].props.active, false);
+});
+
+test("chrome_tab new with no window open creates an unfocused one", async () => {
+  const { w, calls } = worker(noWindows);
+  w.groupTab = async (tab) => tab;
+  w.bringToFront = async () => {};
+  await w.dispatch("tab.new", { url: "https://x.test/", groupTitle: "Pi Session: claude-code 2 mine", sessionKey: "claude-code 2 mine" });
+  assert.deepEqual(ops(calls), ["windows.create"]);
+  assert.equal(calls[0].props.focused, false);
+});
+
+test("a new group starts collapsed; an existing group keeps the user's setting", async () => {
+  const { w, calls } = worker({ tabs: { 300: { id: 300, windowId: 5, active: false, groupId: -1 }, 301: { id: 301, windowId: 5, active: false, groupId: 77 } } });
+  w.groupRecord = async (id) => ({ id });
+  w.formatTab = async (t) => t;
+  await w.groupTab({ id: 300, windowId: 5, groupId: -1 }, "Pi Session: x", "blue");
+  await w.groupTab({ id: 301, windowId: 5, groupId: 77 }, "Pi Session: x", "blue");
+  const updates = calls.filter((c) => c.method === "tabGroups.update").map((c) => c.props.collapsed);
+  assert.deepEqual(updates, [true, undefined]);
+});
+
+test("a new group holding the tab that is showing is not collapsed", async () => {
+  const { w, calls } = worker({ tabs: { 300: { id: 300, windowId: 5, active: true, groupId: -1 } } });
+  w.groupRecord = async (id) => ({ id });
+  w.formatTab = async (t) => t;
+  await w.groupTab({ id: 300, windowId: 5, groupId: -1 }, "Pi Session: x", "blue");
+  assert.equal(calls.find((c) => c.method === "tabGroups.update").props.collapsed, false);
+});
+
+test("bringing a tab forward expands its group", async () => {
+  const { w, calls } = worker();
+  await w.bringToFront({ id: 300, windowId: 5, groupId: 77 }, { foreground: true, background: false });
+  assert.deepEqual(ops(calls), ["windows.update", "tabGroups.update", "tabs.update"]);
+  assert.equal(calls[1].props.collapsed, false);
+});
+
+test("input is sent to an inactive tab; only a minimized window refuses it", async () => {
+  const { w } = worker({ windows: { 5: { id: 5, state: "normal" }, 6: { id: 6, state: "minimized" } }, tabs: { 300: { id: 300, windowId: 5, active: false }, 301: { id: 301, windowId: 6, active: true } } });
+  w.pageVisibilityState = async () => "hidden";
+  await w.assertTabVisibleForInput({ id: 300, windowId: 5 }, {}, "chrome.click");
+  await assert.rejects(w.assertTabVisibleForInput({ id: 301, windowId: 6 }, {}, "chrome.click"), /minimized/);
+});