`take_tiled_screenshot()` waited for the *absence* of `.loading` elements
visible in the viewport before capturing each tile. With
DashboardVirtualization on (default), a chart holder that has just scrolled
into view but hasn't fired its IntersectionObserver callback yet mounts
neither a spinner nor a chart, so the predicate passed vacuously and the
tile was captured blank. On top of that, a per-tile timeout was caught,
logged as a warning, and the tile was captured anyway -- delivering a
spinner screenshot to report recipients instead of failing the report.
Replace the absence-of-`.loading` predicate with a positive readiness
check: every chart holder (`data-test="dashboard-component-chart-holder"`)
intersecting the viewport must show a terminal state (a rendered chart via
`.slice_container`, or an error/empty state via `[role="alert"]` /
`.ant-empty` / `.missing-chart-container`) before a tile is captured. A
holder with nothing mounted no longer satisfies the wait.
A per-tile timeout is now logged at ERROR with the tile index, the
load_wait, and the identities of the still-unready chart holders, and
re-raises instead of being swallowed -- the report now fails
(ReportScheduleScreenshotFailedError) instead of silently shipping a
degraded screenshot.
Co-Authored-By: Claude <noreply@anthropic.com>
