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Fix hydration flash: skip initial effect run when state matches SSR

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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>
This commit is contained in:
giles
2026-04-10 09:08:34 +00:00
parent e6def8b6cd
commit 42198e4e22
2 changed files with 27 additions and 7 deletions
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2
sx/sx/home-stepper.sx
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@@ -345,7 +345,7 @@
(build-code-tokens (first parsed) tokens step-ref 0)
(reset! code-tokens tokens)))))
(let
((_eff (effect (fn () (schedule-idle (fn () (build-code-dom) (rebuild-preview (deref step-idx)) (update-code-highlight) (run-post-render-hooks)))))))
((_eff (let ((initial-idx (deref step-idx)) (first-run (signal true))) (effect (fn () (let ((cur (deref step-idx))) (if (and (deref first-run) (= cur initial-idx)) (reset! first-run false) (do (reset! first-run false) (schedule-idle (fn () (build-code-dom) (rebuild-preview cur) (update-code-highlight) (run-post-render-hooks)))))))))))
(div
(~tw :tokens "space-y-4 text-center")
(div