* Record chat tab opens, closes and host-listed chats in main (dark, layout-owner build only)
A chat tab the window opens, closes, or adds and removes from a host
listing of this machine's chats now reaches main as openAgentSessionTab,
closeTabs or setTabProps under the window's ids, so the window's save no
longer teaches main a chat tab. openAgentSessionTab takes the window's
place, creation time and new split group, and the same open again
changes nothing. Switch-off builds are unchanged.
* test(layout): a paired server's chat tabs send nothing to main (dark)
* fix(layout): keep a windowless host's chat-tab saves as they were; send synced chat opens in tab order (dark)
Only a window's openAgentSessionTab (main marks it drawn on layout.apply)
takes the new rules: a repeat changes nothing, a taken id is refused, and
a workspace with no group takes the window's. A windowless host's own
saves mint a fresh group and keep a chat whose id another tab holds, as
before. A host listing's new chats are recorded in tab order, so each
open's anchor already reached main.
* refactor(layout): one rule set for a chat tab open; the windowless caller names only a group it holds (dark)
Drops the per-sender drawn flag. The windowless save passes its
remembered active group only when the workspace still holds it, so it
mints a fresh group as before. Refusing a taken chat tab id is gated on
the build switch: shipped builds still save the duplicate id.
