AGENTS.md: clean-room codecs are spec-only — no reading reference decoder source even when permissively licensed (libvpx is BSD, not GPL)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

AGENTS.md

@@ -49,8 +49,12 @@ reproduce an image (for example, point lists traced from someone else's icon).
 - Never read, disassemble or copy anything inside Adobe application bundles; file names and listings only.
   Observe behaviour by using the app; never capture its Home screen, recent projects, account info or
   file browsers.
-- Never copy GPL/LGPL/AGPL code (FFmpeg, x264, x265, libvpx, MLT, Kdenlive, Shotcut, Olive, LAME…).
-  Implement codecs and formats from public specifications.
+- Never copy GPL/LGPL/AGPL code (FFmpeg, x264, x265, MLT, Kdenlive, Shotcut, Olive, LAME…).
+- Implement codecs and formats from public specifications (ITU-T/ISO/IEC standards, IETF RFCs, the VP9
+  and AV1 bitstream specs, SMPTE documents, published container specs). Do not read the source of
+  reference or third-party decoders/encoders while implementing a format, even permissively licensed
+  ones (libvpx, libopus, libaom, dav1d, openh264…); spec text and conformance vectors only. Record the
+  spec edition used in the crate README.
 - ffmpeg/ffprobe may be used only as external test oracles and fixture generators. They are never
   linked, bundled or shipped.
 - Dependencies must use permissive licences: MIT/Apache-2.0/BSD/ISC/Zlib/Unicode/CC0/BSL-1.0, or