New language feature: (cyst [:key id] body...) creates a DOM container
with its own island scope that persists across parent reactive re-renders.
On first render, the body is evaluated in a fresh with-island-scope and
the resulting DOM is cached. On subsequent renders, the cached DOM node
is returned if still connected to the document.
This solves the fundamental problem of nesting reactive islands inside
other islands' render trees — the child island's DOM (with its event
handlers and signal subscriptions) survives when the parent re-renders.
Implementation: *memo-cache* dict keyed by cyst id. render-dom checks
isConnected before returning cached node. Each cyst gets its own
disposer list via with-island-scope.
Usage in sx-tools: defisland render preview now wrapped in (cyst :key
full-name ...). Real mouse clicks work — counter increments, temperature
converts, computed signals update. Verified on both local and live site.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
giles
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