## Summary
Document why the `window.__name` polyfill in `frameCapture.ts` is necessary, expand the inline comment with the full per-runtime matrix, and add a regression test that surfaces transpiler behavior on the next failure.
Outcome of the Chunk 12 investigation: **keep the polyfill**.
## Why
`Chunk 12` of `plans/hdr-followups.md`. The polyfill had a vague comment and no test, so it was unclear whether it was still needed or could be deleted.
## Empirical findings
Probe in `/tmp/hf-name-probe`:
| Runtime / build | Injects `__name(fn, "name")` wrappers in `Function.prototype.toString()`? |
|-----------------|---------------------------------------------------------------------------|
| `bun` (TS loader) | No — verified for top-level and nested named functions / arrow expressions. |
| `tsx` (esbuild loader, `keepNames=true`) | **Yes** for nested named functions / arrows; observed crash mode in dev/test. |
| `tsc` (`noEmit` and emit) | No — does not inject the helper. |
| `tsup` for `@hyperframes/cli` (`noExternal: ["@hyperframes/engine"]`) | Polyfill *definition* is bundled, but `__name(...)` *call sites* are absent in `packages/cli/dist/cli.js` (grepped). |
**Root cause.** `@hyperframes/engine`'s `package.json` exports raw TypeScript (`main`/`exports` → `./src/index.ts`), so every consumer's transpiler decides whether to inject `__name`. Anything that runs through `tsx` (producer parity-harness, ad-hoc dev scripts, `bun run --filter @hyperframes/engine test` via Vitest's loader) will serialize wrapped function bodies into `page.evaluate(...)` and crash with `ReferenceError: __name is not defined`.
**Decision.** Keep the no-op `window.__name` shim. Cost is one `evaluateOnNewDocument` call. The alternative (rewriting every `page.evaluate(fn)` site to `page.addScriptTag({ content: "..." })`, like `packages/cli/src/commands/contrast-audit.browser.js` already does) is far more invasive and easy to regress.
## What changed
- Expanded the inline comment in `packages/engine/src/services/frameCapture.ts` to explain the per-runtime matrix above and point to the script-tag alternative.
- New `packages/engine/src/services/frameCapture-namePolyfill.test.ts` — a pure unit test (matches the rest of the engine package's no-browser-launch convention) that:
1. Asserts the polyfill is wired up via `evaluateOnNewDocument` and runs before the first awaited `browser.version()` call.
2. Probes the active Vitest transpiler for `__name(...)` injection so the next maintainer can see at a glance whether the upstream behavior has shifted.
## Test plan
- [x] `bun run --filter @hyperframes/engine test` → 408/408 pass (3 new tests in this file).
- [x] `bunx tsc --noEmit -p packages/engine` clean.
- [x] `bunx oxlint` and `bunx oxfmt --check` clean on edited files.
## Stack
Chunk 12 of `plans/hdr-followups.md`. Independent of all other chunks; closes out the investigation item.
