On mobile the dialog was rendering with its top hidden behind the in-page
\"Agents\" header. The dialog wasn't actually positioned wrong — its overlay
is `position: fixed; inset: 0`. The problem was that NewAgentDialog
rendered as a child of `.agents-view` (which has `overflow: hidden` and
`position: relative`), and an ancestor stacking context combined with the
relative+overflow parent prevented the fixed overlay from escaping above
the page header in the painter's order.
Render the dialog through `createPortal(..., document.body)` so the
overlay attaches at the document root, escaping every parent stacking
context. This is the standard React modal pattern.
All 9639 dashboard tests still pass — React Testing Library queries
traverse portals transparently.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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