The ISO build now writes the minted throwaway root plaintext to a 0600
sibling file (<iso>.rootpw.txt: password + ISO name + build date) — the
single record of truth. Never stdout/logs/manifest; the manifest carries
only a pointer line. OUT_ISO naming hoisted above the mint (the sibling
is named after the ISO); the mint itself and ROOT_PLAIN's lifetime are
unchanged beyond the one file write. FELHOM_ISO_KEEP_WORK=1 debug escape
added for the harness. New test/rootpw-emission.sh: dry-run emission,
0600, plaintext<->answer-hash cross-check (openssl -6 -salt), no
plaintext on stdout, manifest-heredoc guard. Red-proof run: plaintext
injected into the manifest heredoc -> harness FAILs -> restored.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UuFPHmHNrCJj1VhY6QdDMU
