Root cause: the stepper's rebuild effect (update-code-highlight,
rebuild-preview) fired immediately on hydration via schedule-idle,
modifying the DOM after replaceChildren swapped in identical content.
This caused a visible text change after the initial frame.
Fix: track initial step-idx value and first-run flag. Skip the
effect on first run if the current step matches the SSR state
(from cookie). The effect only fires on actual user interaction.
Result: SSR and hydrated text content are identical. replaceChildren
swaps DOM nodes but the visual content doesn't change. Zero flash.
Test: "No clobber: clean" — 0 text changes during hydration.
All 8 home features pass.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
42198e4e22