PixelFailure wrote a 128x128 payload, exactly the 64 KiB a default Linux
pipe holds. Once the consumer read the 54-byte header, the whole payload
fit in the pipe, so the write could finish before the reader closed and
the expected EPIPE never came. agc_frame_dump_io failed in 147 of 300 runs
on Linux. A 512x512 payload exceeds the default pipe capacity on Linux and
macOS, so the write always reaches the closed reader.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Use checked host stdio for BMP output and stop requesting dumps after the first write failure. Keep pixel validation, allocation and non-I/O failures on the existing fatal path.
Co-Authored-By: Codex <noreply@openai.com>
