feat(studio-server): preview variable injection + render variables forwarding#2049
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This was referenced Jul 8, 2026
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…rwarding
Fourth PR of the template-variables Studio stack — the HTTP plumbing.
- preview routes (/preview and /preview/comp/*) accept
?variables=<url-encoded json> and inject
`window.__hfVariables = {...}` into <head>, before the runtime and any
composition script — the exact global the engine sets via
evaluateOnNewDocument at render time, so preview-with-values cannot
diverge from render output. Values are escaped against </script>
breakout, malformed payloads 400 instead of silently previewing
defaults, and the ETag is salted with a hash of the payload so cached
previews revalidate when values change.
- POST /projects/:id/render accepts variables ({variableId: value}) and
forwards them through StudioApiAdapter.startRender into the producer's
RenderConfig.variables — the same channel `hyperframes render
--variables` uses. Wired in both adapters (CLI embedded server + vite
dev adapter).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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What
Fourth PR of the template-variables stack: the HTTP plumbing.
/previewand/preview/comp/*) accept?variables=<url-encoded json>and injectwindow.__hfVariables = {...}before the runtime and any composition script — the exact global the engine sets viaevaluateOnNewDocumentat render time, so preview-with-values cannot diverge from render outputPOST /projects/:id/renderacceptsvariablesand forwards them throughStudioApiAdapter.startRenderinto the producer'sRenderConfig.variables— the same channelhyperframes render --variablesuses. Wired in both adapters (CLI embedded server + vite dev adapter)Why
Render-time injection existed; preview had no equivalent, so "preview with values" was impossible. Mirroring the engine's exact injection mechanism (rather than a bespoke postMessage protocol) is what makes the Studio preview render-truthful.
How
Safety/correctness details worth reviewing:
<-escaped against</script>breakout<head…>→<html…>→ after doctype → prepend (review fix — the original bare-<head>regex could land the tag before the doctype)helpers/variablesPayload.ts) used by both routesTest plan
variablesto this route🤖 Generated with Claude Code