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, 1 insertions, 1 deletions

diff --git a/docs/FAQ.md b/docs/FAQ.md
index bf46a51..cfa2cfa 100644
--- a/docs/FAQ.md
+++ b/docs/FAQ.md
@@ -36,7 +36,7 @@ Subagent sessions that run inside an authorized Pi process (for example with pi-
 
 ## Does pi-chrome navigate my current tab?
 
-No. The first chrome_* action that has no explicit target opens a **dedicated automation window** that pi-chrome owns (falling back to a dedicated tab only if a separate window can't be created), and reuses it for the rest of the session. Your existing tabs and windows are never reused or overwritten. Pass `targetId`/`urlIncludes`/`titleIncludes` to deliberately act on a tab you already have open.
+No. The first chrome_* action that has no explicit target opens a **dedicated automation tab** that pi-chrome owns, inactive, in your window and in the session's own (collapsed) tab group, and reuses it for the rest of the session. A window is created only when none is open. Your existing tabs and windows are never reused or overwritten. Pass `targetId`/`urlIncludes`/`titleIncludes` to deliberately act on a tab you already have open.
 
 The window survives `/reload` and Chrome service-worker restarts because ownership is tracked by id and mirrored to `chrome.storage.session`. It is closed when you run `/chrome revoke` and on real session end (not on `/reload`); cleanup only ever closes that session's own window/tab.