isomorphisms · isomorphisms · Aug 22, 2026 · Aug 22, 2026 · Aug 22, 2026 · Aug 22, 2026
diff --git a/.github/workflows/prototype-prerender.yml b/.github/workflows/prototype-prerender.yml
@@ -0,0 +1,30 @@
+name: prototype prerender tests
+
+on:
+  push:
+    branches:
+      - prototype-stupid-prerenderers
+  pull_request:
+    paths:
+      - 'prototype/**'
+      - '.github/workflows/prototype-prerender.yml'
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run reference pre-renderer tests
+        run: python3 prototype/test_prerender.py
+      - name: Generate sample first paint
+        run: |
+          python3 prototype/prerender.py prototype/example.html \
+            --source https://example.test/ \
+            --out preview-out
+          ls -lh preview-out
+      - name: Retain sample preview
+        uses: actions/upload-artifact@v4
+        with:
+          name: stupid-prerender-sample
+          path: preview-out/
diff --git a/prototype/.gitignore b/prototype/.gitignore
@@ -0,0 +1,2 @@
+preview-out/
+*.pbm
diff --git a/prototype/NOTES.md b/prototype/NOTES.md
@@ -0,0 +1,12 @@
+# Notes
+
+This prototype is intentionally stupid.
+
+It exists to answer four questions before ib chooses its implementation language or real renderer:
+
+1. Can first paint be produced from browser-owned bytes without starting a full renderer?
+2. Can the first paint stay small enough to cache for many sleeping tabs?
+3. Can previews be deleted and regenerated without changing durable browsing state?
+4. Can the UI progressively ask for metadata, text, one visual screen, more visual screens, and finally a live renderer instead of loading everything at once?
+
+The answer should remain yes even if this Python prototype is thrown away completely.
diff --git a/prototype/README.md b/prototype/README.md
@@ -0,0 +1,32 @@
+# Deliberately stupid pre-renderers
+
+This directory is an executable design probe for the browser-core/renderer boundary. It is not a choice of implementation language and it is not intended to grow into the real renderer.
+
+`prerender.py` accepts already-fetched HTML and emits two disposable forms of first paint:
+
+- `preview.txt`: title, source URL/label, and visible-ish text, capped at 8 KiB by default.
+- `screen-01.pbm` through `screen-03.pbm`: at most three 180×320 one-bit rough visual previews. Each default PBM is about 7.2 KiB.
+
+The bitmap preview is deliberately not a screenshot of a fully rendered web page. It ignores CSS, JavaScript, images, fonts, layout, forms, media, and subresources. It rasterizes extracted text with a tiny built-in 5×7 font. Its purpose is to test whether ib can show something recognizable immediately while the real renderer is absent, sleeping, loading, crashed, or being replaced.
+
+## Try it
+
+```sh
+python3 prototype/prerender.py page.html \
+  --source https://example.org/ \
+  --out /tmp/ib-preview
+```
+
+The input may also be piped on stdin by using `-` as the input path.
+
+## Tests
+
+```sh
+python3 prototype/test_prerender.py
+```
+
+The tests check that scripts/styles are excluded, text output remains bounded, visual previews stay below 8 KiB per default screen, and visual output is capped at three screens.
+
+## Architectural rule being tested
+
+A pre-renderer consumes browser-owned fetched/snapshot material and produces a disposable preview. Neither `preview.txt` nor the PBM files are canonical browsing state. Deleting all of them must not delete a tab, a history entry, a snapshot, or user organization.
diff --git a/prototype/example.html b/prototype/example.html
@@ -0,0 +1,21 @@
+<!doctype html>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>IB pre-renderer example</title>
+  <style>body { color: red; }</style>
+</head>
+<body>
+  <h1>This appears before the real renderer</h1>
+  <p>The text preview is intentionally boring. It exists so a sleeping tab can show recognizable content without waking Chromium, Servo, WebView, or anything else.</p>
+  <p>The bitmap version is only a tiny monochrome approximation of this text. A real renderer may replace it whenever it becomes available.</p>
+  <script>throw new Error('a pre-renderer must not execute me');</script>
+  <h2>Second screen material</h2>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+  <p>This paragraph is repeated to make scrolling through a rough preview meaningful. The preview can contain one, two, or three phone-sized images and no more.</p>
+</body>
+</html>