Extension direct fallback decodes binary media into an unused text copy #53

Impact: when a proxied response passes Chrome's 64 MiB message limit (any MP4 over ~48 MB, whose base64 alone is too large), compat.js falls back to directHttpRequest. That function always sets responseText: new TextDecoder().decode(buffer), even for responseType: 'arraybuffer'. For a 52 MB video that is a ~52-million-character string held next to the buffer, which nothing reads. The proxy path already omits responseText for binary replies (#13), so the two paths also disagree.

Evidence: live run 2026-10-05, v1.6.7 in Brave 154. A 51,986,124-byte MP4 (1080p variant of x.com/TuckerCarlson/status/1666203439146172419) came back through the fallback with responseText set; a 31 MB file through the proxy came back without it.

Next action: set responseText only for text responses, matching the proxy path; add a regression assert in test/extension.test.mjs.