`injectInterceptor` used `String.prototype.replace(target, replacement)`
to inject the runtime `<script>` before `</head>`. The replacement
string is a substitution template — `$&` expands to the matched
substring, and the minified runtime IIFE contains legitimate `$&`
sequences (e.g. `if(te&&$&!y.hasAttribute(...))`), so every `$&` in
the body was silently rewritten to `</head>`, producing
`Unexpected token '<'` SyntaxErrors and breaking every timeline in
the bundle.
Switch to the function-replacer form so the runtime body is passed
through verbatim. Add a regression test that diffs the bundled
runtime body against `getHyperframeRuntimeScript()` and asserts only
one `</head>` survives in the document — the test exercises the
`<head>`-present injection path (the only branch that uses the
substitution template; the no-`<head>` fallback uses slice+concat
and was unaffected).
Only the bundler is affected — `producer/fileServer.ts` already uses
the function form via `injectScriptsIntoHtml` in
`htmlDocument.ts`, so render output was correct. Snapshot, preview,
studio, layout, and validate all consume `bundleToSingleHtml` and
were broken before this fix.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
