Addresses the S7 mobile-fix code-review findings:
- (altitude) The header-height→content-pad contract lived across two files with
an implicit DOM coupling: Header measured itself and wrote --hdr-h onto
`el.parentElement`, assuming PageShell rendered it as a direct child of the
padded column. Move the whole contract into PageShell, which owns BOTH the
header slot and the padded content wrapper: Header is now forwardRef and
PageShell attaches a ref (via cloneElement), measures the header with a
ResizeObserver, and writes --hdr-h straight onto the content wrapper that
consumes it — no parent assumption, producer and consumer together.
- (simplification) The `+ 8` gap is now documented as the header's own gap-y-2
row gap reused below it, not a bare magic number.
- (test-coverage) PageShell.dom.test.tsx: stub ResizeObserver + the header's
offset metrics and assert --hdr-h is published onto the content wrapper (and
absent with no header).
Re-verified live at 440 (mobile, no overlap) and desktop (one row). FE gate:
tsc / knip / lint clean, 220 vitest pass.
peter
5c6172754a