Phase 5 item #6: screenshot_responsive renders per breakpoint#13
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Before: HTML rendered once at `max(breakpoints).{width,height}`; puppeteer
just retargeted its viewport for each shot. The viewport change alone
already let @media rules fire (the responsive: "stack" verification from
PR #6 worked) but the body scaffold stayed sized for the largest
breakpoint — body.max-width = 1440 and body.min-height = 1024 on every
shot, even the 390-wide mobile one.
`takeResponsiveScreenshots` now takes a per-breakpoint render callback
instead of a single pre-built HTML string. The handler in src/index.ts
passes a closure that calls `renderToHtml(resolved, bp.width, bp.height, canvas)`
per shot, so the body scaffold matches the viewport for every breakpoint.
The viewer side of item #6 was already true reflow — on breakpoint
toggle, JS sets the iframe src to `/canvas/:id/html?w=...&h=...` and the
server route at viewer.ts:75-88 re-renders. This PR brings the
screenshot side up to the same standard.
`test-responsive-reflow.ts` asserts at each preset breakpoint that the
runtime body box (max-width, min-height, width) matches the viewport and
that the `responsive: "stack"` rule fires when expected — 12/12 pass.
The other five smokes still pass — no regression on PRs #6-12.
Found in passing: at exactly 768px the `responsive: "stack"` rule fires
because the `@media` is `max-width: 768px`. Matches Bootstrap/Tailwind
convention (768 is the start of the desktop band, not the end of mobile)
but the labelled tablet preset of 768 lands in the mobile rule. Worth a
separate PR if we want 768 to be desktop-side; out of scope here.
This was referenced May 16, 2026
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Summary
The viewer side of item #6 was already true reflow: on breakpoint toggle, JS sets the iframe src to
/canvas/:id/html?w=...&h=...and the server route atviewer.ts:75-88re-renders the HTML with the new dimensions.screenshot_responsivewas the half still doing the iframe-resize equivalent: HTML was rendered once at the largest breakpoint and puppeteer just retargeted its viewport per shot. The viewport change alone let@mediarules fire (PR #6's responsive: "stack" worked end-to-end), but the body scaffold stayed sized for the largest breakpoint —body.max-width = 1440andbody.min-height = 1024even on the 390-wide mobile shot.This change makes
screenshot_responsiverender per breakpoint so the scaffold matches each viewport.What lands
src/screenshot.ts—takeResponsiveScreenshotsnow takes(bp) => stringinstead of a pre-builthtml: string. The function renders inside the loop, so the body scaffold matches the viewport.src/index.ts— the handler passes(bp) => renderToHtml(resolved, bp.width, bp.height, canvas)instead of computingmax(breakpoints)and rendering once.test-responsive-reflow.ts— exercises the same closure shape the handler uses. For each preset breakpoint (mobile/tablet/desktop) assertsbody.max-width,body.min-height, runtimebody.width, and therowflex direction (column whenresponsive: "stack"fires, row otherwise). 12/12 pass.VISION.md— item Phase 5: responsive hint API + renderer mapping (items #1+#2) #6 ticked.Found in passing (separable, not fixing here)
At exactly 768px the
responsive: "stack"rule fires because the rule is@media (max-width: 768px)—max-widthis inclusive in CSS. That matches Bootstrap/Tailwind convention (768 is the start of the desktop band, so anything ≤ 767 is mobile, ≤ 1023 is tablet, etc.), but the labelledtabletpreset at exactly 768 lands in the mobile rule. If we want 768 to be desktop-side, change the renderer'sMOBILE_BREAKPOINTto 767 — but that has knock-on effects worth their own PR.Test plan
npm run buildcleannpx tsx test-responsive-reflow.ts→ 12/12 passtest-fluid-widths,test-default-font,test-root-centering,test-ops-parser,test-guidelinesall still pass — no regression on PRs Phase 5: responsive hint API + renderer mapping (items #1+#2) #6-12