tabs: agent sessions share one window instead of opening one each

A session's first tab used chrome.windows.create, so every new session name (and
every Claude Code process) got its own window. It now goes into the window that
already holds any 'Pi Session:' group; a window is created only when none exists.
chrome_tab new for a session with no group also uses that window, not the user's
focused one. The primer and the chrome_tab description say so.

4 files changed, 113 insertions, 6 deletions

diff --git a/extensions/chrome-profile-bridge/browser-extension/service_worker.js b/extensions/chrome-profile-bridge/browser-extension/service_worker.js
index c62aff9..7fbbbba 100644
--- a/extensions/chrome-profile-bridge/browser-extension/service_worker.js
+++ b/extensions/chrome-profile-bridge/browser-extension/service_worker.js
@@ -226,11 +226,26 @@ function isPiChromeOwnedTarget(tabId, sessionKey) {
   return false;
 }
 
+// The window agents share. Every session has its own tab group and a group cannot span windows,
+// but sessions do not need their own windows: new tabs go to the window that already holds any
+// "Pi Session:" group, so agents stay together instead of opening one window each. Returns
+// undefined when no such window exists (the first session then creates one).
+async function sharedPiWindowId() {
+  if (!chrome.tabGroups || typeof chrome.windows?.get !== "function") return undefined;
+  const groups = await chrome.tabGroups.query({}).catch(() => []);
+  for (const group of groups) {
+    if (!/^pi session:/i.test((group.title || "").trim()) || typeof group.windowId !== "number") continue;
+    const win = await chrome.windows.get(group.windowId).catch(() => null);
+    if (win && (win.type === undefined || win.type === "normal")) return win.id ?? group.windowId;
+  }
+  return undefined;
+}
+
 // Create a fresh automation target for `sessionKey`. If this session already has a tab group,
 // create the tab inside that group's window so one Pi session keeps one Chrome tab group (Chrome
-// groups cannot span windows). If no group exists yet, prefer an isolated window; fall back to a
-// tab. When the tab is created in a pre-existing group window, leave windowId unset so cleanup only
-// closes our tab, never that whole window.
+// groups cannot span windows). If it has none, use the shared Pi window; only when there is no
+// Pi window yet, create one; fall back to a tab. When the tab is created in a pre-existing window,
+// leave windowId unset so cleanup only closes our tab, never that whole window.
 async function createAutomationTarget(sessionKey, groupTitle) {
   const existingGroup = groupTitle ? await findGroupRecordByTitle(groupTitle) : null;
   if (existingGroup && typeof existingGroup.windowId === "number") {
@@ -239,6 +254,14 @@ async function createAutomationTarget(sessionKey, groupTitle) {
     await persistAutomationTargets();
     return tab;
   }
+  const sharedWindowId = await sharedPiWindowId();
+  if (sharedWindowId !== undefined) {
+    // Someone else's window: leave windowId unset so cleanup only ever closes our tab.
+    const tab = await chrome.tabs.create({ url: "about:blank", active: false, windowId: sharedWindowId });
+    automationTargets.set(sessionKey, { windowId: undefined, tabId: typeof tab.id === "number" ? tab.id : undefined });
+    await persistAutomationTargets();
+    return tab;
+  }
   if (chrome.windows && typeof chrome.windows.create === "function") {
     try {
       const win = await chrome.windows.create({ url: "about:blank", focused: false });
@@ -1825,6 +1848,11 @@ async function dispatch(action, params) {
       const existingGroup = await findGroupRecordByTitle(groupTitle);
       const createParams = { url: params.url || "about:blank", active: foregroundRequested(params) };
       if (existingGroup && typeof existingGroup.windowId === "number") createParams.windowId = existingGroup.windowId;
+      else {
+        // No group of this session yet: use the shared Pi window, never the user's focused one.
+        const sharedWindowId = await sharedPiWindowId();
+        if (sharedWindowId !== undefined) createParams.windowId = sharedWindowId;
+      }
       // Register the creation as in flight until the tab is tracked, so early capture (which only
       // runs in tracked tabs) waits for it instead of skipping the new tab's first page load.
       const creation = (async () => {
diff --git a/extensions/chrome-profile-bridge/index.ts b/extensions/chrome-profile-bridge/index.ts
index 90f080e..32ae79f 100644
--- a/extensions/chrome-profile-bridge/index.ts
+++ b/extensions/chrome-profile-bridge/index.ts
@@ -1276,7 +1276,8 @@ Usage rules:
 6. /chrome background on (default) is a hard policy: per-call \`background=false\` cannot override it, new tabs stay inactive, and \`chrome_tab activate\` is blocked. Ask the user to run /chrome background off when they want foreground/watch mode. With background off, per-call \`background=true\` still avoids explicit focus/tab activation. Screenshots use CDP without activating background tabs; debugger failures never fall back to tab activation. Page scripts, trusted input, native prompts, and Chrome/OS behavior can still affect focus.
 7. If you hit a native file-picker or privileged browser prompt gate, tell the user; generic clicks/typing/CSP gates are handled by Chrome input.
 8. Run /chrome doctor when in doubt about connectivity or capabilities.
-9. A page can open dialogs you cannot see: alert, confirm, prompt, and the \"Leave site? Changes you made may not be saved\" prompt of a page with unsaved changes. They are dismissed for you (stay, cancel). \`chrome_navigate\` reports one by failing, and \`leaveIfAsked: true\` leaves anyway; use that only when you know nothing unsaved matters, and ask the user when unsure. If a click or key press that should have navigated did nothing, a Leave-site prompt may have stopped it: check the page, then ask the user before discarding anything.`;
+9. A page can open dialogs you cannot see: alert, confirm, prompt, and the \"Leave site? Changes you made may not be saved\" prompt of a page with unsaved changes. They are dismissed for you (stay, cancel). \`chrome_navigate\` reports one by failing, and \`leaveIfAsked: true\` leaves anyway; use that only when you know nothing unsaved matters, and ask the user when unsure. If a click or key press that should have navigated did nothing, a Leave-site prompt may have stopped it: check the page, then ask the user before discarding anything.
+10. All agent sessions share one browser window; your tabs sit in your own colored tab group inside it. Reuse a tab you already have (navigate it) rather than opening new ones, and open a new tab only when you need two pages at once. Do not open new windows unless the user asks.`;
 
 	// Shared handlers, dispatched by the unified /chrome command below.
 	const doctorHandler = async (ctx: ExtensionContext) => {
@@ -1651,7 +1652,7 @@ Usage rules:
 	pi.registerTool({
 		name: "chrome_tab",
 		label: "Chrome Tab",
-		description: "List, create, activate, close, group, ungroup, or inspect tabs in the user's existing Chrome profile via the companion extension. New/grouped tabs always use this session's Pi tab group. Background mode keeps new tabs inactive and blocks activate; ask the user to run /chrome background off for foreground/watch mode. activate/close/group/ungroup require a target (targetId/urlIncludes/titleIncludes); with no target they act on this session's pi-chrome automation tab if one exists, and otherwise error rather than touching the user's active tab.",
+		description: "List, create, activate, close, group, ungroup, or inspect tabs in the user's existing Chrome profile via the companion extension. New/grouped tabs always use this session's Pi tab group, inside the one window all agent sessions share; prefer navigating a tab you already have to opening another. Background mode keeps new tabs inactive and blocks activate; ask the user to run /chrome background off for foreground/watch mode. activate/close/group/ungroup require a target (targetId/urlIncludes/titleIncludes); with no target they act on this session's pi-chrome automation tab if one exists, and otherwise error rather than touching the user's active tab.",
 		promptSnippet: "List/open/activate/close/group existing Chrome tabs through the companion extension.",
 		parameters: Type.Object({
 			action: StringEnum(tabActionValues),
diff --git a/package.json b/package.json
index de5cabb..c9b422b 100644
--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
 	"name": "pi-chrome",
 	"version": "0.15.57",
 	"scripts": {
-		"test": "node test-suite/unit/csp-eval.test.mjs && node test-suite/unit/automation-target.test.mjs && node test-suite/unit/session-cleanup.test.mjs && node test-suite/unit/background-policy.test.mjs && node test-suite/unit/input-reliability.test.mjs && node test-suite/unit/chrome-command.test.mjs && node test-suite/unit/bridge-resilience.test.mjs && node test-suite/unit/cdp-passthrough.test.mjs && node test-suite/unit/type-evidence.test.mjs && node test-suite/unit/hidden-input.test.mjs && node test-suite/unit/console-capture.test.mjs && node test-suite/unit/prompt-section.test.mjs && node test-suite/unit/upload-guard.test.mjs && node test-suite/unit/grant-scope.test.mjs && node test-suite/unit/leave-site-prompt.test.mjs",
+		"test": "node test-suite/unit/csp-eval.test.mjs && node test-suite/unit/automation-target.test.mjs && node test-suite/unit/session-cleanup.test.mjs && node test-suite/unit/background-policy.test.mjs && node test-suite/unit/input-reliability.test.mjs && node test-suite/unit/chrome-command.test.mjs && node test-suite/unit/bridge-resilience.test.mjs && node test-suite/unit/cdp-passthrough.test.mjs && node test-suite/unit/type-evidence.test.mjs && node test-suite/unit/hidden-input.test.mjs && node test-suite/unit/console-capture.test.mjs && node test-suite/unit/prompt-section.test.mjs && node test-suite/unit/upload-guard.test.mjs && node test-suite/unit/grant-scope.test.mjs && node test-suite/unit/leave-site-prompt.test.mjs && node test-suite/unit/shared-window.test.mjs",
 		"version": "node scripts/sync-manifest-version.js",
 		"prepublishOnly": "node scripts/sync-manifest-version.js"
 	},
diff --git a/test-suite/unit/shared-window.test.mjs b/test-suite/unit/shared-window.test.mjs
new file mode 100644
index 0000000..7afeb77
--- /dev/null
+++ b/test-suite/unit/shared-window.test.mjs
@@ -0,0 +1,78 @@
+// Agent sessions share one window: a new session's tab goes into the window that already holds a
+// "Pi Session:" group, and a window is created only when there is 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" } } } = {}) {
+  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 },
+      windows: {
+        get: async (id) => windows[id] ?? Promise.reject(new Error("No window")),
+        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 () => null, onUpdated: listener,
+      },
+    },
+  };
+  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 });
+
+test("a new session's tab goes into the window that already holds another Pi session", async () => {
+  const { w, calls } = worker({ groups: [piGroup(5)] });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(calls.filter((c) => c.method !== "storage.set").map((c) => c.method), ["tabs.create"]);
+  assert.equal(calls[0].props.windowId, 5);
+});
+
+test("with no Pi window yet, the first session creates one", async () => {
+  const { w, calls } = worker({ groups: [] });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(calls.filter((c) => c.method !== "storage.set").map((c) => c.method), ["windows.create"]);
+});
+
+test("groups that are not Pi sessions do not attract agent tabs", async () => {
+  const { w, calls } = worker({ groups: [{ id: 2, windowId: 5, title: "Work" }] });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(calls.filter((c) => c.method !== "storage.set").map((c) => c.method), ["windows.create"]);
+});
+
+test("a Pi group whose window is gone, or is not a normal window, is skipped", async () => {
+  const { w, calls } = worker({ groups: [piGroup(7), piGroup(8)], windows: { 8: { id: 8, type: "popup" } } });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  assert.deepEqual(calls.filter((c) => c.method !== "storage.set").map((c) => c.method), ["windows.create"]);
+});
+
+test("the shared window is never recorded as ours, so cleanup cannot close it", async () => {
+  const { w, calls } = worker({ groups: [piGroup(5)] });
+  await w.createAutomationTarget("claude-code 2 mine", "Pi Session: claude-code 2 mine");
+  const stored = calls.filter((c) => c.method === "storage.set").map((c) => c.json).join("");
+  assert.doesNotMatch(stored, /"windowId":5/);
+});
+
+test("chrome_tab new for a session with no group uses the shared window, not the focused one", async () => {
+  const { w, calls } = worker({ groups: [piGroup(5)] });
+  w.groupTab = async (tab) => tab;
+  w.bringToFront = async () => {};
+  await w.dispatch("tab.new", { url: "about:blank", groupTitle: "Pi Session: claude-code 2 mine", sessionKey: "claude-code 2 mine" });
+  const created = calls.find((c) => c.method === "tabs.create");
+  assert.equal(created.props.windowId, 5);
+});