The review's remaining code items:
- resolvePythonBin now skips RELATIVE PATH segments (a bare 'bin' or '.'): the
returned candidate must be absolute, because spawn() resolves a relative
pythonBin against the host CWD, outside the seam contract.
- A deterministic-ish regression pins the sealing-threshold corner: 64 MiB of
4 KiB (<= PIPE_BUF, atomic) newline-free writes plus 12289 more A's before
the first newline make the first frame exceed FRAME_PARSE_CAP_BYTES; the
newline-bearing chunk reaches the first-frame check (sealing is the ELSE
half of the newline branch), so the run reports worker-exit with the
protocol-frame-exceeded message.
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