diff --git a/.github/scripts/check-readme-sources.mjs b/.github/scripts/check-readme-sources.mjs
new file mode 100644
index 000000000..227bd06c1
--- /dev/null
+++ b/.github/scripts/check-readme-sources.mjs
@@ -0,0 +1,149 @@
+#!/usr/bin/env node
+// =============================================================================
+// README source gate
+//
+// Four artifacts publish a README to a registry — npm (`rocketride`), PyPI
+// (`rocketride`), PyPI (`rocketride-mcp`), and the VS Code Marketplace plus
+// OpenVSX. None of them stores its README in git: each package's
+// scripts/tasks.js copies one in from docs/ at build time, which is why those
+// directories have no README.md.
+//
+// That copy is silent when it goes wrong. If a README_SRC path is renamed on
+// one side only, the build copies nothing (or the wrong file) and every check
+// stays green while the registry page goes stale — and a registry README cannot
+// be corrected without publishing a new version, so the mistake is live until
+// the next release of that artifact.
+//
+// This gate makes the three failure modes loud:
+//
+//   1. a README_SRC pointing at a file that does not exist
+//   2. a README.md committed into a package directory, shadowing the generated
+//      one — whichever wins is then decided by build order, not intent
+//   3. a relative link or image in a source README
+//
+// (3) needs saying because it is invisible in review: each registry resolves
+// relative paths against ITSELF, not against GitHub. A README that renders
+// perfectly in the repo can render broken on npm, PyPI and the Marketplace
+// simultaneously, and the VS Code packer needs --baseContentUrl to have any
+// chance at all. Absolute URLs are the only form that works in all five places.
+//
+// Run: node .github/scripts/check-readme-sources.mjs
+// =============================================================================
+
+import { readFileSync, existsSync, readdirSync, statSync } from 'node:fs';
+import { join, relative, dirname, resolve, basename } from 'node:path';
+
+const ROOT = resolve(import.meta.dirname, '..', '..');
+const problems = [];
+
+/** Directories that may contain a package with a generated README. */
+function findTaskFiles(dir, found = []) {
+  for (const entry of readdirSync(dir, { withFileTypes: true })) {
+    if (entry.name === 'node_modules' || entry.name === '.git') continue;
+    const full = join(dir, entry.name);
+    if (entry.isDirectory()) findTaskFiles(full, found);
+    else if (entry.name === 'tasks.js') found.push(full);
+  }
+  return found;
+}
+
+// -- 1 + 2: every README_SRC resolves, and nothing shadows the generated file --
+const taskFiles = findTaskFiles(ROOT).filter((f) =>
+  readFileSync(f, 'utf8').includes('README_SRC')
+);
+
+if (taskFiles.length === 0) {
+  // Fail rather than pass vacuously. An empty match means the convention moved
+  // and this gate silently stopped checking anything — the exact class of
+  // failure it exists to prevent.
+  problems.push(
+    'no tasks.js references README_SRC at all — the copy convention has moved ' +
+      'and this gate is no longer checking anything. Update it or delete it.'
+  );
+}
+
+const sources = new Set();
+
+for (const taskFile of taskFiles) {
+  const src = readFileSync(taskFile, 'utf8');
+  const rel = relative(ROOT, taskFile);
+
+  // const README_SRC = path.join(DOCS_DIR, 'README-x.md')
+  const m = src.match(/README_SRC\s*=\s*path\.join\(\s*DOCS_DIR\s*,\s*['"]([^'"]+)['"]/);
+  if (!m) {
+    problems.push(
+      `${rel}: mentions README_SRC but not in the expected ` +
+        `path.join(DOCS_DIR, '...') form — this gate cannot verify it`
+    );
+    continue;
+  }
+
+  const docFile = join(ROOT, 'docs', m[1]);
+  if (!existsSync(docFile)) {
+    problems.push(`${rel}: README_SRC -> docs/${m[1]} does not exist`);
+  } else {
+    sources.add(docFile);
+  }
+
+  // scripts/tasks.js -> the package root two levels up
+  const pkgDir = dirname(dirname(taskFile));
+  for (const name of ['README.md', 'readme.md']) {
+    if (existsSync(join(pkgDir, name))) {
+      problems.push(
+        `${relative(ROOT, join(pkgDir, name))}: committed, but this package's ` +
+          `README is generated from docs/${m[1]} — delete the committed copy`
+      );
+    }
+  }
+}
+
+// -- 3: no relative links or images in any source README ----------------------
+// Anchors, mailto: and absolute URLs are fine everywhere. Anything else is a
+// path, and a path resolves differently on each registry.
+const LINK = /(!?)\[[^\]]*\]\(([^)\s]+)(?:\s+"[^"]*")?\)/g;
+const ABSOLUTE = /^(https?:\/\/|mailto:|#)/;
+
+for (const docFile of [...sources].sort()) {
+  const text = readFileSync(docFile, 'utf8');
+  const rel = relative(ROOT, docFile);
+  const lines = text.split('\n');
+
+  lines.forEach((line, i) => {
+    for (const match of line.matchAll(LINK)) {
+      const [, bang, target] = match;
+      if (ABSOLUTE.test(target)) continue;
+      problems.push(
+        `${rel}:${i + 1}: ${bang ? 'image' : 'link'} target "${target}" is ` +
+          `relative — registries resolve it against themselves, not GitHub. ` +
+          `Use an absolute URL.`
+      );
+    }
+  });
+
+  // Bare <img src="..."> too — HTML is common in badge rows and PyPI sanitises
+  // it inconsistently, but a relative src is broken everywhere regardless.
+  for (const match of text.matchAll(/<img\s[^>]*src=["']([^"']+)["']/gi)) {
+    if (!ABSOLUTE.test(match[1])) {
+      problems.push(
+        `${rel}: <img src="${match[1]}"> is relative — use an absolute URL`
+      );
+    }
+  }
+}
+
+// -- report -------------------------------------------------------------------
+const checked = [...sources].map((f) => `docs/${basename(f)}`).sort();
+
+if (problems.length > 0) {
+  console.error(`README source gate FAILED (${problems.length} problem(s)):\n`);
+  for (const p of problems) console.error(`  - ${p}`);
+  console.error(
+    `\nChecked ${taskFiles.length} copy step(s) and ${checked.length} source file(s).`
+  );
+  process.exit(1);
+}
+
+console.log(
+  `README source gate OK — ${taskFiles.length} copy step(s), ` +
+    `${checked.length} source(s): ${checked.join(', ')}`
+);
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index edeed1460..0188fb634 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -215,6 +215,26 @@ jobs:
       - run: ruff check
       - run: ruff format --check
 
+  # ---------------------------------------------------------------------------
+  #  README sources — the four registry READMEs (npm, PyPI x2, VS Code
+  #  Marketplace + OpenVSX) are NOT stored in git: each package's
+  #  scripts/tasks.js copies one in from docs/ at build time. That copy is
+  #  silent when it breaks, and a registry README cannot be corrected without
+  #  publishing a new version — so a stale one is live until the next release
+  #  of that artifact. This makes the three ways it breaks loud instead.
+  # ---------------------------------------------------------------------------
+  readme-sources:
+    name: README sources
+    runs-on: ubuntu-latest
+    timeout-minutes: 5
+    steps:
+      - uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
+      - uses: actions/setup-node@49933ea5288caeca8642d1e84afbd3f7d6820020 # v4
+        with:
+          node-version: 22
+      # Dependency-free (node:fs + node:path only), so no install step.
+      - run: node .github/scripts/check-readme-sources.mjs
+
   # ---------------------------------------------------------------------------
   #  gitleaks — secret scan. Installs the binary directly because the upstream
   #  gitleaks-action v2 requires a paid GITLEAKS_LICENSE for org-owned repos;