From c1f230eeb76aaa50e98d3fe7d838573612b6e36f Mon Sep 17 00:00:00 2001
From: Tianren Dong <tianrendong.dtr@gmail.com>
Date: Wed, 9 Sep 2026 23:37:02 -0400
Subject: Enforce hard background and release 0.15.48

---
 test-suite/README.md                          |   9 +
 test-suite/challenges/43-hard-background.html |  42 +++
 test-suite/manifest.json                      |  75 ++++
 test-suite/unit/automation-target.test.mjs    |   2 +-
 test-suite/unit/background-policy.test.mjs    | 469 ++++++++++++++++++++++++++
 5 files changed, 596 insertions(+), 1 deletion(-)
 create mode 100644 test-suite/challenges/43-hard-background.html
 create mode 100644 test-suite/unit/background-policy.test.mjs

(limited to 'test-suite')

diff --git a/test-suite/README.md b/test-suite/README.md
index 47e737f..59d2388 100644
--- a/test-suite/README.md
+++ b/test-suite/README.md
@@ -176,6 +176,15 @@ The dashboard renders this from `manifest.json`. In brief:
 40. dynamic wait/readiness
 41. explicit tab lifecycle
 42. strict CSP eval/snapshot via CDP (regression guard for the CSP bypass)
+43. hard background: inactive-tab visibility and trusted input
+
+### Hard-background regression (43)
+
+Keep `/chrome background on`. Open challenge 43, then manually select a different tab in the **same window** and return to Pi. Target the challenge URL explicitly, arm its probe, and run its manifest recipe without selecting the target again. Inspect the saved screenshot for the colored target. The page detects visibility changes and synthetic input; it cannot establish OS focus or macOS Spaces behavior.
+
+Separately live-test with Chrome behind another app, a minimized window, multiple windows, and macOS Spaces. Confirm the foreground app/window and each active tab stay unchanged during background new-tab creation, viewport/full-page screenshots, and trusted input. Confirm `/chrome background off` permits explicit activation. Native prompts/page popups are outside this focus policy, not a zero-focus guarantee.
+
+`npm test` runs mocked regressions for every registered tool's policy, old-companion rejection, worker focus writes, CDP capture success/failure, trusted input, and full-page scroll restoration. No live Chrome is required; Node.js 22.13+ is required for TypeScript stripping.
 
 ## Design notes
 
diff --git a/test-suite/challenges/43-hard-background.html b/test-suite/challenges/43-hard-background.html
new file mode 100644
index 0000000..3fe9a34
--- /dev/null
+++ b/test-suite/challenges/43-hard-background.html
@@ -0,0 +1,42 @@
+<!doctype html>
+<meta charset="utf-8">
+<title>43 hard background</title>
+<link rel="stylesheet" href="../_style.css">
+<script src="../_lib.js"></script>
+<body>
+<main>
+  <h1>Hard-background target</h1>
+  <p>Setup: keep <code>/chrome background on</code>. Select another tab in this same Chrome window so this target is inactive, then return to Pi. Do not select this tab again until verification finishes.</p>
+  <p>Runner: target this URL explicitly. Evaluate <code>armBackgroundProbe()</code>, snapshot and screenshot with <code>background:false</code>, then click Verify with <code>domFallback:false</code> and <code>background:false</code>. These foreground requests must not activate this tab. Read <code>window.__verdict</code> without activating it.</p>
+  <p>This page grades tab visibility and trusted input, not OS focus or macOS Spaces. Inspect the screenshot for the colored target below; test OS focus separately. Reload to reset.</p>
+  <div style="background:#2463aa;color:white;padding:32px;border:16px solid #e5a323">SCREENSHOT TARGET: hard background</div>
+  <button id="verify">Verify hidden trusted click</button>
+</main>
+<script>
+Challenge.init({ id: "hard-background", instructions: "inactive tab → arm → snapshot/screenshot → trusted click; no activation" });
+let armed = false;
+window.armBackgroundProbe = () => {
+  if (armed) throw new Error("Already armed; reload to reset");
+  if (!document.hidden) throw new Error("Select another tab in this window before arming");
+  armed = true;
+  Challenge.log("armed", { visibility: document.visibilityState, focused: document.hasFocus() });
+  return { armed, visibility: document.visibilityState };
+};
+document.addEventListener("visibilitychange", () => {
+  Challenge.log("visibilitychange", { visibility: document.visibilityState, armed });
+  if (armed && !document.hidden) Challenge.fail("Target became visible after arming: background activation leaked");
+});
+for (const name of ["focus", "blur"]) {
+  window.addEventListener(name, () => Challenge.log(name, { visibility: document.visibilityState, focused: document.hasFocus() }));
+}
+document.getElementById("verify").addEventListener("click", (event) => {
+  Challenge.log("verify", { trusted: event.isTrusted, visibility: document.visibilityState, armed });
+  const failures = [];
+  if (!armed) failures.push("Probe was not armed while inactive");
+  if (!event.isTrusted) failures.push("Verify click isTrusted=false: synthetic input substituted");
+  if (!document.hidden) failures.push("Verify target is not hidden");
+  if (failures.length) Challenge.fail(...failures);
+  else Challenge.pass("Trusted click received while target remained hidden");
+});
+</script>
+</body>
diff --git a/test-suite/manifest.json b/test-suite/manifest.json
index 0ebb313..4f72c85 100644
--- a/test-suite/manifest.json
+++ b/test-suite/manifest.json
@@ -1565,6 +1565,9 @@
     "difficulty": "L2",
     "gate": "core",
     "goal": "Create a new tab, inspect it, close it, return to the parent tab, and verify tab lifecycle state.",
+    "prerequisites": [
+      "Ask the user to run /chrome background off for this explicit activation test. Background on intentionally blocks chrome_tab activate."
+    ],
     "expected": {
       "synthetic": "CONDITIONAL",
       "trusted": "PASS",
@@ -1677,5 +1680,77 @@
     ],
     "manualBaseline": "unverified",
     "gradeSource": "page"
+  },
+  {
+    "id": "hard-background",
+    "file": "challenges/43-hard-background.html",
+    "category": "focus-keyboard",
+    "difficulty": "L2",
+    "gate": "conditional",
+    "goal": "Snapshot and screenshot an inactive target with background:false, then send a trusted click without activating it. Inspect the screenshot for the colored target.",
+    "expected": {
+      "synthetic": "FAIL",
+      "trusted": "PASS",
+      "manual": "FAIL"
+    },
+    "prerequisites": [
+      "Keep /chrome background on. Reload both Pi and the updated Chrome companion.",
+      "Open the target, manually select a different tab in the same window, then return to Pi before arming. Do not select the target until grading finishes."
+    ],
+    "recipe": [
+      {
+        "tool": "chrome_evaluate",
+        "params": {
+          "urlIncludes": "/43-hard-background.html",
+          "expression": "armBackgroundProbe()",
+          "background": true
+        }
+      },
+      {
+        "tool": "chrome_snapshot",
+        "params": {
+          "urlIncludes": "/43-hard-background.html",
+          "background": false
+        }
+      },
+      {
+        "tool": "chrome_screenshot",
+        "params": {
+          "urlIncludes": "/43-hard-background.html",
+          "path": ".pi/chrome-screenshots/hard-background.png",
+          "background": false
+        }
+      },
+      {
+        "tool": "chrome_click",
+        "params": {
+          "urlIncludes": "/43-hard-background.html",
+          "selector": "#verify",
+          "background": false,
+          "domFallback": false,
+          "includeSnapshot": true
+        }
+      },
+      {
+        "tool": "chrome_evaluate",
+        "params": {
+          "urlIncludes": "/43-hard-background.html",
+          "expression": "JSON.stringify({v:window.__verdict,r:window.__reason,e:window.__events})",
+          "background": true
+        }
+      }
+    ],
+    "requires": {
+      "cdp": true
+    },
+    "tags": ["background", "visibility", "screenshot", "trusted-input"],
+    "notes": [
+      "The page grades visibility and isTrusted, not OS focus or macOS Spaces. The runner must also inspect the screenshot for target fidelity.",
+      "Manual FAIL is intentional: a normal human click requires selecting the hidden tab. Synthetic FAIL detects replacing Chrome input with DOM events.",
+      "Selecting the target while armed causes sticky FAIL, including after PASS. Read results through background tools before returning to this tab."
+    ],
+    "flakeRisk": "medium",
+    "manualBaseline": "unverified",
+    "gradeSource": "both"
   }
 ]
diff --git a/test-suite/unit/automation-target.test.mjs b/test-suite/unit/automation-target.test.mjs
index f838fa6..7f46597 100644
--- a/test-suite/unit/automation-target.test.mjs
+++ b/test-suite/unit/automation-target.test.mjs
@@ -345,7 +345,7 @@ async function run() {
     ok(state.tabs.has(state.userArticle.id), "tab.close: user's active tab was NOT closed");
     ok(state.windows.size === windowsBefore && state.tabs.size === tabsBefore, "tab.close: did not spawn a throwaway tab/window");
 
-    await throwsWith(() => w.dispatch("tab.activate", { sessionKey: SK }), /no automation tab yet|Pass targetId/, "tab.activate: errors with no target/owned target");
+    await throwsWith(() => w.dispatch("tab.activate", { sessionKey: SK, foreground: true }), /no automation tab yet|Pass targetId/, "tab.activate: errors with no target/owned target");
 
     // Once an automation target exists, management actions operate on it (not on the user tab).
     const nav = await w.dispatch("page.navigate", { url: "https://pi.test/manage", waitUntilLoad: false, sessionKey: SK });
diff --git a/test-suite/unit/background-policy.test.mjs b/test-suite/unit/background-policy.test.mjs
new file mode 100644
index 0000000..e20d0ab
--- /dev/null
+++ b/test-suite/unit/background-policy.test.mjs
@@ -0,0 +1,469 @@
+// Runtime regressions for the Pi session policy and the real worker dispatch/input paths.
+// Chrome APIs are mocked: these tests prove explicit focus calls, not OS/Spaces behavior.
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import vm from "node:vm";
+import path from "node:path";
+import { stripTypeScriptTypes } from "node:module";
+import { test } from "node:test";
+
+const indexSource = fs.readFileSync(new URL("../../extensions/chrome-profile-bridge/index.ts", import.meta.url), "utf8");
+const workerSource = fs.readFileSync(new URL("../../extensions/chrome-profile-bridge/browser-extension/service_worker.js", import.meta.url), "utf8");
+const clone = (value) => JSON.parse(JSON.stringify(value));
+function section(start, end) {
+  const from = indexSource.indexOf(start);
+  const to = indexSource.indexOf(end, from);
+  assert.ok(from >= 0 && to > from, `Missing source section: ${start}`);
+  return indexSource.slice(from, to);
+}
+
+// Load the shipped policy, existing command handler, and actual tool registrations. Only the
+// bridge/Pi UI/typebox/formatting/filesystem boundaries are replaced; no live server is opened.
+function piHarness({ session = "alpha", send } = {}) {
+  const calls = [], tools = new Map(), notices = [], writes = [];
+  let authorized = true;
+  const ctx = { key: `session:${session}`, title: `Pi Session: ${session}`, cwd: "/fixture", ui: { notify: (...args) => notices.push(args) } };
+  const bridge = {
+    connected: true, status: () => ({}),
+    async send(action, params, timeout, signal) {
+      calls.push({ action, params: clone(params), timeout, signal });
+      if (signal?.aborted) throw new Error("Chrome command aborted");
+      if (send) return send(action, params, timeout, signal);
+      if (action === "tab.version") return { capabilities: { hardBackground: true } };
+      if (action === "tab.list") return [];
+      if (action.startsWith("page.screenshot")) return { dataUrl: "data:image/png;base64,dGVzdA==", method: "cdp" };
+      return {};
+    },
+  };
+  const Type = new Proxy({}, { get: () => (value = {}) => value });
+  const sandbox = {
+    console, Buffer, Type,
+    Date,
+    DEFAULT_HOST: "127.0.0.1", DEFAULT_PORT: 17318, DEFAULT_TIMEOUT_MS: 30000, MAX_ELEMENTS: 80,
+    BACKGROUND_PARAM_DESCRIPTION: "background policy",
+    ChromeProfileBridge: function () { return bridge; },
+    requireChromeControlAuthorized() { if (!authorized) throw new Error("Chrome control locked"); },
+    sessionCtx: ctx, sessionKeyFor: (c) => c?.key, sessionGroupTitle: (c) => c.title,
+    chromeToolsRegistered: false, StringEnum: () => ({}),
+    tabActionValues: [], snapshotModeValues: [], waitForValues: [], imageFormatValues: [],
+    safeJson: JSON.stringify, truncateText: (s) => s, formatChromeSnapshot: JSON.stringify,
+    formatChromeInspect: JSON.stringify, summarizeActionResult: () => "", formatIncludedSnapshotText: (_r, text) => text,
+    workspaceCwd: () => ctx.cwd, ...path,
+    mkdir: async () => {}, writeFile: async (...args) => writes.push(args),
+  };
+  const registrations = indexSource.slice(indexSource.indexOf("function registerChromeTools(pi:"), indexSource.lastIndexOf("\n}"));
+  vm.runInNewContext(stripTypeScriptTypes([
+    section("const bridge = new ChromeProfileBridge(", "\n\tlet chromeAuthorizedUntil:"),
+    section("const authorizedBridgeSend =", '\n\tpi.on("session_start",'),
+    section("const BACKGROUND_DESC:", "\n\tconst authorizeFor ="),
+    registrations,
+    "globalThis.send = authorizedBridgeSend; globalThis.background = backgroundHandler;",
+  ].join("\n")), sandbox);
+  sandbox.registerChromeTools({ registerTool: (tool) => tools.set(tool.name, tool) });
+  return {
+    calls, tools, notices, writes, ctx,
+    send: async (...args) => sandbox.send(...args),
+    background: (arg) => sandbox.background(ctx, arg),
+    tool: (name, params = {}, signal) => tools.get(name).execute("test", params, signal, undefined, ctx),
+    authorize: (value) => { authorized = value; },
+  };
+}
+
+const flagCases = [
+  [{}, false], [{ background: false }, false], [{ background: true }, true],
+  [{ foreground: true }, false], [{ foreground: false }, true],
+  [{ background: false, foreground: false }, false], [{ background: true, foreground: true }, true],
+];
+
+test("session background on overrides all per-call/legacy foreground flags; off preserves per-call background", async () => {
+  const h = piHarness();
+  for (const mode of ["on", "off"]) {
+    await h.background(mode);
+    for (const [flags, requestedBackground] of flagCases) {
+      const params = Object.freeze({ ...flags, targetId: "2" });
+      await h.send("page.snapshot", params);
+      const wire = h.calls.at(-1).params;
+      assert.equal(wire.background, mode === "on" || requestedBackground);
+      assert.equal(wire.foreground, !wire.background);
+      assert.equal(wire.sessionKey, "session:alpha");
+      assert.equal(wire.sessionGroupTitle, "Pi Session: alpha");
+      assert.equal(wire.joinSessionGroup, true);
+      assert.deepEqual(params, { ...flags, targetId: "2" }, "caller params not mutated");
+    }
+  }
+});
+
+test("every registered page tool, tab.new, and chrome_launch(url) use the central policy", async () => {
+  const h = piHarness();
+  const cases = [
+    ["chrome_launch", { url: "https://example.test" }, "tab.new"],
+    ["chrome_tab", { action: "new", group: false, groupTitle: "other" }, "tab.new"],
+    ["chrome_snapshot", {}, "page.snapshot"], ["chrome_find", { query: "button" }, "page.snapshot"],
+    ["chrome_inspect", { uid: "el-1" }, "page.inspect"], ["chrome_navigate", { url: "https://example.test" }, "page.navigate"],
+    ["chrome_evaluate", { expression: "1" }, "page.evaluate"], ["chrome_click", { uid: "el-1" }, "page.click"],
+    ["chrome_type", { text: "abc" }, "page.type"], ["chrome_fill", { text: "abc" }, "page.fill"],
+    ["chrome_key", { key: "Enter" }, "page.key"], ["chrome_wait_for", { kind: "expression", value: "true" }, "page.waitFor"],
+    ["chrome_list_console_messages", {}, "page.console.list"], ["chrome_list_network_requests", {}, "page.network.list"],
+    ["chrome_get_network_request", { requestId: "1" }, "page.network.get"], ["chrome_screenshot", {}, "page.screenshot"],
+    ["chrome_hover", {}, "page.hover"], ["chrome_drag", {}, "page.drag"], ["chrome_tap", {}, "page.tap"],
+    ["chrome_scroll", {}, "page.scroll"], ["chrome_upload_file", { paths: ["fixture.txt"] }, "page.upload"],
+  ];
+  for (const [name, params, action] of cases) {
+    await h.tool(name, { ...params, background: false, foreground: true });
+    const call = h.calls.at(-1);
+    assert.equal(call.action, action === "tab.new" || action === "page.screenshot" ? `${action}.background` : action, name);
+    assert.equal(call.params.foreground, false, name);
+    assert.equal(call.params.background, true, name);
+    if (action === "tab.new") assert.equal(call.params.groupTitle, "Pi Session: alpha");
+  }
+  assert.equal(h.writes[0][1].toString(), "test", "screenshot tool still writes decoded bytes");
+});
+
+test("activation is rejected before dispatch; existing on/off/toggle/status commands suffice", async () => {
+  const h = piHarness();
+  await assert.rejects(h.tool("chrome_tab", { action: "activate", targetId: "2", background: false }), /background mode.*\/chrome background off/);
+  assert.equal(h.calls.length, 0);
+  await h.background("off");
+  await h.tool("chrome_tab", { action: "activate", targetId: "2" });
+  assert.equal(h.calls.at(-1).params.foreground, true);
+  await h.background("toggle");
+  await h.background("status");
+  assert.match(h.notices.at(-1)[0], /on.*Hard background/);
+  for (const arg of ["lock", "unlock", "invalid"]) {
+    await h.background(arg);
+    assert.match(h.notices.at(-1)[0], /Unknown background setting/);
+    await assert.rejects(h.send("tab.activate", {}), /background mode/);
+  }
+  await h.background("");
+  await h.send("tab.activate", {});
+  for (const arg of ["true", "1", "on"]) {
+    await h.background(arg);
+    await assert.rejects(h.send("tab.activate", {}), /background mode/);
+  }
+  for (const arg of ["false", "0", "off"]) {
+    await h.background(arg);
+    await h.send("tab.activate", {});
+  }
+});
+
+test("older companions reject background-only wire actions; launch and screenshots never retry unsafe actions", async () => {
+  const h = piHarness({ send: async (action) => { throw new Error(`Unknown action: ${action}`); } });
+  for (const [tool, params] of [
+    ["chrome_tab", { action: "new" }], ["chrome_launch", { url: "https://example.test" }],
+    ["chrome_screenshot", {}], ["chrome_screenshot", { fullPage: true }],
+  ]) {
+    await assert.rejects(h.tool(tool, params), /Reload Pi Chrome Connector/);
+  }
+  assert.deepEqual(h.calls.map((c) => c.action), ["tab.new.background", "tab.new.background", "page.screenshot.background", "page.screenshot.background"]);
+});
+
+test("transport failures propagate without fallback; single dispatch preserves authorization/timeout/signal", async () => {
+  const offline = piHarness({ send: async () => { throw new Error("offline"); } });
+  await assert.rejects(offline.send("tab.new", {}), /offline/);
+  assert.equal(offline.calls.length, 1);
+  const h = piHarness(), controller = new AbortController();
+  await h.send("tab.new", {}, 900, controller.signal);
+  assert.equal(h.calls.length, 1);
+  assert.equal(h.calls[0].timeout, 900);
+  assert.equal(h.calls[0].signal, controller.signal);
+  controller.abort();
+  await assert.rejects(h.send("tab.new", {}, 900, controller.signal), /Chrome command aborted/);
+  h.authorize(false);
+  await assert.rejects(h.send("tab.new", {}), /Chrome control locked/);
+  assert.equal(h.calls.length, 2, "locked call does not reach bridge");
+});
+
+test("shared-owner sessions retain independent policies; per-call background still works with mode off", async () => {
+  const sharedCalls = [];
+  const send = async (action, params) => { sharedCalls.push({ action, params }); return {}; };
+  const a = piHarness({ session: "A", send }), b = piHarness({ session: "B", send });
+  await b.background("off");
+  await a.send("tab.new", { background: false });
+  await b.send("tab.new", {});
+  assert.equal(sharedCalls[0].params.sessionKey, "session:A");
+  assert.equal(sharedCalls[0].params.foreground, false);
+  assert.equal(sharedCalls[0].action, "tab.new.background");
+  assert.equal(sharedCalls[1].params.sessionKey, "session:B");
+  assert.equal(sharedCalls[1].params.foreground, true);
+  assert.equal(sharedCalls[1].action, "tab.new");
+  await b.send("tab.new", { background: true });
+  assert.equal(sharedCalls[2].action, "tab.new.background");
+  assert.equal(sharedCalls[2].params.foreground, false);
+});
+
+function workerHarness({ withWindows = true } = {}) {
+  const calls = [];
+  const tabs = new Map([
+    [1, { id: 1, windowId: 1, active: true, groupId: -1, url: "https://user.test/", title: "User" }],
+    [2, { id: 2, windowId: 1, active: false, groupId: -1, url: "https://target.test/", title: "Target" }],
+  ]);
+  let focusedWindow = 1, nextTab = 3, nextWindow = 2;
+  const storage = {}, groups = new Map();
+  const listener = { addListener() {}, removeListener() {} };
+  const chrome = {
+    runtime: { id: "test", getManifest: () => ({ version: "0.0.0" }), onInstalled: listener, onStartup: listener },
+    alarms: { onAlarm: listener, create() {} }, action: { onClicked: listener }, webNavigation: { onCommitted: listener },
+    storage: { session: { get: async (key) => ({ [key]: storage[key] }), set: async (value) => Object.assign(storage, value) } },
+    tabs: {
+      onUpdated: listener,
+      query: async (query = {}) => [...tabs.values()].filter((t) => (!query.active || t.active) && (query.windowId === undefined || query.windowId === t.windowId)).map(clone),
+      get: async (id) => { if (!tabs.has(id)) throw new Error("No tab"); return clone(tabs.get(id)); },
+      create: async (params) => {
+        calls.push({ action: "tabs.create", params });
+        const tab = { id: nextTab++, windowId: params.windowId ?? 1, active: params.active, url: params.url, groupId: -1 };
+        if (tab.active) for (const t of tabs.values()) if (t.windowId === tab.windowId) t.active = false;
+        tabs.set(tab.id, tab);
+        return clone(tab);
+      },
+      update: async (id, params) => {
+        calls.push({ action: "tabs.update", id, params });
+        const tab = tabs.get(id);
+        if (params.active) for (const t of tabs.values()) if (t.windowId === tab.windowId) t.active = false;
+        Object.assign(tab, params);
+        return clone(tab);
+      },
+      remove: async (id) => tabs.delete(id),
+      group: async ({ groupId, tabIds }) => {
+        const id = groupId ?? groups.size + 1;
+        if (!groups.has(id)) groups.set(id, { id, windowId: tabs.get(tabIds[0]).windowId });
+        for (const tid of tabIds) tabs.get(tid).groupId = id;
+        return id;
+      },
+      ungroup: async (id) => { tabs.get(id).groupId = -1; },
+      captureVisibleTab: async () => { calls.push({ action: "captureVisibleTab" }); throw new Error("activation-based capture forbidden"); },
+    },
+    tabGroups: {
+      query: async ({ windowId } = {}) => [...groups.values()].filter((g) => windowId === undefined || g.windowId === windowId).map(clone),
+      get: async (id) => groups.get(id),
+      update: async (id, props) => Object.assign(groups.get(id), props),
+    },
+    windows: {
+      update: async (id, params) => { calls.push({ action: "windows.update", id, params }); if (params.focused) focusedWindow = id; },
+    },
+    debugger: {
+      onDetach: listener, getTargets: (cb) => cb([]), attach: async () => {}, detach: async () => {},
+      sendCommand: (target, method, params, callback) => {
+        calls.push({ action: "cdp", target, method, params });
+        try { callback(h.cdpResult(method, params)); }
+        catch (error) { chrome.runtime.lastError = { message: error.message }; callback(); chrome.runtime.lastError = undefined; }
+      },
+    },
+    scripting: { executeScript: async () => [{ result: { ok: true, value: { elements: [], url: "https://target.test/" } } }] },
+  };
+  if (withWindows) chrome.windows.create = async (params) => {
+    calls.push({ action: "windows.create", params });
+    const id = nextWindow++;
+    if (params.focused) focusedWindow = id;
+    const tab = { id: nextTab++, windowId: id, active: true, url: params.url, groupId: -1 };
+    tabs.set(tab.id, tab);
+    return { id, tabs: [clone(tab)] };
+  };
+  const w = {
+    chrome, console, setTimeout, clearTimeout, setInterval: () => 0, clearInterval() {},
+    fetch: async () => { throw new Error("no network in unit tests"); }, navigator: { userAgent: "unit-test" },
+  };
+  w.self = w;
+  vm.runInNewContext(workerSource, w);
+  w.sleep = async () => {}; // Skip human timing, not CDP dispatch.
+  w.resolveTargetInTab = async () => ({ found: true, x: 40, y: 50, tag: "BUTTON" });
+  const h = {
+    w, chrome, calls, tabs, focusedWindow: () => focusedWindow,
+    cdpResult: (method) => method === "Page.captureScreenshot" ? { data: "c2NyZWVuc2hvdA==" }
+      : method === "DOM.requestNode" ? { nodeId: 1 }
+      : { result: { type: "boolean", value: true, objectId: "file-input" } },
+  };
+  return h;
+}
+function assertNoFocus(h) {
+  assert.equal(h.focusedWindow(), 1);
+  assert.equal(h.tabs.get(1).active, true);
+  assert.ok(!h.calls.some((c) => c.action === "windows.update" || c.action === "captureVisibleTab" || (c.action === "tabs.update" && c.params.active) || (c.action === "tabs.create" && c.params.active)));
+}
+
+test("Pi-to-worker background aliases preserve grouping, screenshot output, and ownership-aware cleanup", async () => {
+  const h = workerHarness();
+  const pi = piHarness({ send: (action, params) => h.w.dispatch(action, params) });
+  const opened = await pi.tool("chrome_tab", { action: "new", group: false, groupTitle: "wrong", background: false });
+  assert.equal(opened.details.result.group.title, "Pi Session: alpha");
+  const launched = await pi.tool("chrome_launch", { url: "https://fixture.test" });
+  const shot = await pi.tool("chrome_screenshot", { targetId: "2", background: false });
+  assert.equal(shot.details.method, "cdp");
+  assert.equal(pi.writes[0][1].toString(), "screenshot");
+  assertNoFocus(h);
+  await h.w.dispatch("automation.cleanup", { sessionKey: "session:alpha" });
+  assert.ok(!h.tabs.has(opened.details.result.tab.id));
+  assert.ok(!h.tabs.has(launched.details.result.tab.id));
+  assert.ok(h.tabs.has(1) && h.tabs.has(2), "user/adopted tabs survive cleanup");
+  assert.equal(h.tabs.get(2).groupId, -1, "adopted tab is safely ungrouped");
+});
+
+test("worker advertises support, keeps new tabs inactive, and rejects activation before target resolution", async () => {
+  const h = workerHarness();
+  assert.equal((await h.w.dispatch("tab.version", {})).capabilities.hardBackground, true);
+  for (const flags of [{}, { foreground: false }, { background: true, foreground: true }]) {
+    const result = await h.w.dispatch("tab.new", { ...flags, sessionKey: "alpha", groupTitle: "Pi Session: alpha" });
+    assert.equal(result.tab.active, false);
+    await assert.rejects(h.w.dispatch("tab.activate", { ...flags, targetId: "missing" }), /background mode/);
+  }
+  assertNoFocus(h);
+  const active = await h.w.dispatch("tab.activate", { targetId: "2", foreground: true, background: false });
+  assert.equal(active.id, 2);
+  assert.equal(active.active, true);
+  const opened = await h.w.dispatch("tab.new", { foreground: true });
+  assert.equal(opened.tab.active, true);
+});
+
+test("background-only worker aliases force safe behavior even with foreground flags", async () => {
+  const h = workerHarness();
+  const opened = await h.w.dispatch("tab.new.background", { foreground: true, background: false });
+  assert.equal(opened.tab.active, false);
+  const shot = await h.w.dispatch("page.screenshot.background", { targetId: "2", foreground: true, background: false });
+  assert.equal(shot.method, "cdp");
+  assertNoFocus(h);
+});
+
+test("implicit automation windows stay unfocused; tab fallback stays inactive", async () => {
+  for (const withWindows of [true, false]) {
+    const h = workerHarness({ withWindows });
+    const tab = await h.w.dispatch("page.navigate", { url: "https://fixture.test", waitUntilLoad: false, background: true, foreground: true, sessionKey: "alpha" });
+    assert.notEqual(tab.id, 1);
+    assertNoFocus(h);
+    assert.ok(h.calls.filter((c) => c.action === "windows.create").every((c) => c.params.focused === false));
+  }
+});
+
+test("all worker page/input paths veto conflicting foreground flags without replacing trusted input", async () => {
+  const h = workerHarness();
+  const actions = [
+    ["navigate", { url: "https://target.test/", waitUntilLoad: false }], ["snapshot", {}], ["inspect", { uid: "el-1" }],
+    ["evaluate", { expression: "true" }], ["waitFor", { kind: "expression", value: "true" }],
+    ["console.list", {}], ["network.list", {}], ["network.get", { requestId: "1" }],
+    ["click", { x: 40, y: 50, includeSnapshot: true }], ["fill", { selector: "input", text: "a", submit: true }],
+    ["type", { selector: "input", text: "a", pressEnter: true }], ["key", { key: "Enter" }], ["hover", { x: 40, y: 50 }],
+    ["drag", { fromX: 40, fromY: 50, toX: 80, toY: 90 }], ["tap", { x: 40, y: 50 }],
+    ["scroll", { deltaY: 10 }], ["upload", { selector: "input", paths: ["/fixture.txt"] }],
+  ];
+  for (const [action, params] of actions) {
+    const result = await h.w.dispatch(`page.${action}`, { targetId: "2", ...params, background: true, foreground: true, domFallback: false });
+    if (["click", "fill", "type", "key", "hover", "drag", "tap", "scroll"].includes(action)) assert.equal((result.result ?? result).input, "chrome", action);
+    assertNoFocus(h);
+  }
+  const methods = new Set(h.calls.filter((c) => c.action === "cdp").map((c) => c.method));
+  for (const method of ["Input.dispatchMouseEvent", "Input.dispatchKeyEvent", "Input.dispatchTouchEvent", "DOM.setFileInputFiles"]) assert.ok(methods.has(method), method);
+  h.chrome.debugger = undefined;
+  for (const action of ["click", "fill"]) {
+    await assert.rejects(h.w.dispatch(`page.${action}`, { targetId: "2", selector: "input", text: "a", background: true, domFallback: false }), /chrome.debugger API unavailable/);
+  }
+  assertNoFocus(h);
+});
+
+test("CDP PNG/JPEG screenshots preserve active tabs and pass viewport/quality options", async () => {
+  for (const targetId of ["1", "2"]) {
+    for (const options of [{}, { format: "png", quality: 70 }, { format: "jpeg", quality: 0 }, { format: "jpeg", quality: 83 }]) {
+      const h = workerHarness();
+      const result = await h.w.dispatch("page.screenshot", { targetId, background: true, foreground: true, ...options });
+      const capture = h.calls.find((c) => c.method === "Page.captureScreenshot");
+      const format = options.format ?? "png";
+      assert.equal(result.dataUrl, `data:image/${format};base64,c2NyZWVuc2hvdA==`);
+      assert.equal(result.method, "cdp");
+      assert.equal(result.tab.id, Number(targetId));
+      assert.equal(capture.target.tabId, Number(targetId));
+      assert.deepEqual(clone(capture.params), { format, fromSurface: true, captureBeyondViewport: false, ...(format === "jpeg" ? { quality: options.quality } : {}) });
+      assertNoFocus(h);
+    }
+  }
+});
+
+test("screenshot failures never fall back to activation/visible-tab capture", async () => {
+  for (const failure of ["attach", "capture", "empty", "missing"]) {
+    const h = workerHarness();
+    if (failure === "attach") h.chrome.debugger.attach = async () => { throw new Error("permission denied"); };
+    else h.cdpResult = () => {
+      if (failure === "capture") throw new Error("capture failed");
+      return failure === "empty" ? { data: "" } : undefined;
+    };
+    await assert.rejects(h.w.dispatch("page.screenshot", { targetId: "2", background: true }), /no tab-activation fallback/);
+    assertNoFocus(h);
+  }
+});
+
+test("screenshot does not restore/override a user tab switch during capture; watch mode explicitly activates", async () => {
+  const h = workerHarness();
+  h.cdpResult = () => {
+    h.tabs.get(1).active = false;
+    h.tabs.get(2).active = true; // Human selection while CDP is pending.
+    return { data: "dGVzdA==" };
+  };
+  const result = await h.w.dispatch("page.screenshot", { targetId: "1", background: true });
+  assert.equal(result.tab.id, 1);
+  assert.equal(h.tabs.get(2).active, true);
+  assert.ok(!h.calls.some((c) => c.action === "tabs.update" || c.action === "windows.update"));
+
+  const watch = workerHarness();
+  const shot = await watch.w.dispatch("page.screenshot", { targetId: "2", foreground: true, background: false });
+  assert.equal(shot.tab.active, true);
+  assert.equal(watch.calls.filter((c) => c.action === "tabs.update" && c.params.active).length, 1);
+  assert.equal(watch.calls.filter((c) => c.action === "windows.update").length, 1);
+  assert.ok(!watch.calls.some((c) => c.action === "captureVisibleTab"));
+});
+
+test("challenge 43 grader rejects activation/synthetic input and retains sticky failures", () => {
+  const lib = fs.readFileSync(new URL("../_lib.js", import.meta.url), "utf8");
+  const html = fs.readFileSync(new URL("../challenges/43-hard-background.html", import.meta.url), "utf8");
+  const script = html.match(/<script>([\s\S]*?)<\/script>/)[1];
+  function page() {
+    const listeners = new Map();
+    const add = (name, fn) => listeners.set(name, fn);
+    const document = {
+      hidden: true, get visibilityState() { return this.hidden ? "hidden" : "visible"; }, hasFocus: () => false,
+      body: { insertBefore() {} }, createElement: () => ({ style: {} }),
+      getElementById: (id) => id === "verify" ? { addEventListener: add } : null,
+      addEventListener: add,
+    };
+    const p = { document, addEventListener: add, location: { search: "" }, URLSearchParams,
+      performance: { now: () => 1 }, localStorage: { setItem() {} } };
+    p.window = p;
+    vm.runInNewContext(`${lib}\n${script}`, p);
+    return { p, document, fire: (name, event = {}) => listeners.get(name)(event) };
+  }
+  const visible = page();
+  visible.document.hidden = false;
+  assert.throws(() => visible.p.armBackgroundProbe(), /Select another tab/);
+  const good = page();
+  good.p.armBackgroundProbe();
+  assert.throws(() => good.p.armBackgroundProbe(), /Already armed/);
+  good.fire("click", { isTrusted: true });
+  assert.equal(good.p.__verdict, "PASS");
+  good.document.hidden = false;
+  good.fire("visibilitychange");
+  assert.equal(good.p.__verdict, "FAIL", "late activation must invalidate an earlier pass");
+  const synthetic = page();
+  synthetic.p.armBackgroundProbe();
+  synthetic.fire("click", { isTrusted: false });
+  synthetic.fire("click", { isTrusted: true });
+  assert.equal(synthetic.p.__verdict, "FAIL", "trusted retry cannot hide synthetic input");
+});
+
+test("full-page tiles remain CDP-only, pin the resolved target, and restore both scroll axes after success/failure", async () => {
+  for (const fail of [false, true]) {
+    const h = workerHarness(), scrolls = [];
+    h.w.executeInTab = async (params, fn, args) => {
+      assert.equal(params.targetId, 2);
+      assert.equal(params.foreground, false);
+      if (fn.name === "captureFullPageTiles") return { width: 800, height: 1200, viewportHeight: 600, dpr: 2, originalScrollY: 73, originalScrollX: 31, tiles: [{ y: 0, scrollY: 0 }, { y: 600, scrollY: 600 }] };
+      scrolls.push(clone(args));
+    };
+    let captures = 0;
+    h.cdpResult = () => { if (++captures === 2 && fail) throw new Error("tile failed"); return { data: "dGlsZQ==" }; };
+    const shot = h.w.dispatch("page.screenshot", { urlIncludes: "target.test", fullPage: true, background: true, foreground: true });
+    if (fail) await assert.rejects(shot, /tile failed/);
+    else {
+      const result = await shot;
+      assert.equal(result.method, "cdp");
+      assert.equal(result.tiles.length, 2);
+      assert.equal(result.dimensions.dpr, 2);
+    }
+    assert.deepEqual(scrolls, [[0], [600], [73, 31]]);
+    assertNoFocus(h);
+  }
+});
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