Fixes hyperhive#2893: 'Element.attachShadow: Unable to re-attach to
existing ShadowDOM', crashing swarm.js's live-update render path.
A custom element's connectedCallback fires again on a same-document
*move* (insertBefore/append repositioning an already-connected node
runs the removal + insertion steps for its whole subtree), not just
on a fresh mount. swarm.js's row-fingerprint cache reuses + reorders
existing <li> subtrees on live updates -- reordering an unchanged,
cached row moves its already-initialised <hive-agent-menu>/<hive-menu>
without ever really detaching it from the document, so connectedCallback
re-runs full setup on an instance that's already set up. attachShadow()
throws unconditionally if the host already has a shadow root, and
HiveAgentMenu's unconditional child-menu creation would have appended a
second <hive-menu> on top of the first, doubling the dropdown, once the
shadow-attach crash itself was out of the way.
Both connectedCallbacks now bail early if already initialised
(shadowRoot present / _menu already built). Reproduced the crash and
duplicate-menu bug with an unguarded control copy of both files driven
via headless Chromium (simulating the exact row-reorder move), then
confirmed the guarded version throws nothing, keeps the same shadowRoot
object identity across the move, and doesn't duplicate the dropdown.
38aa5f77f4