Agents could set and clear the key object but not read it:
document.inspect, the control channel's ui.pointer reply and the
headless pointer_gesture reply left it out, and select.key returned
null. select.key with an id that was not selected, or with a value
that is not an id, such as "x", cleared the key without an error. A
compound-path member or an object inside a selected group could become
the key.
select.key now checks its id as select.set, select.add and
select.toggle do (#784). It returns an error for an id that is not a
selected top-level object and leaves the key as it was. Layers,
compound-path members and objects inside another selected object are
not top-level objects. select.key {id: null} used to clear the key and
is now an error; select.key {} still clears it. select.key returns
{key}, and document.inspect and both pointer replies include the key
object as "key".
In isolation mode a Selection-tool click can pick an object that
select.key does not accept as the key: a sublayer inside an isolated
layer, a member inside an isolated compound path, or an object in an
isolated group that is also selected. The tool no longer sends
select.key {id} for such an object. When the object is already the
key, the tool still sends select.key {}, which clears the key.
A recorded action whose select.key step names an object that is not a
selected top-level object when the action plays now fails and is
rolled back, as an action with a select.set step naming a deleted
object has failed since #784.
Docs: docs/mcp.md, docs/control-protocol.md, docs/target-app-parity.md.
845aa6848f