Two live failures on the same guard (cron/lifecycle_guard.py), both of
which blocked legitimate diagnostics from inside the gateway:
1. Crash class: the referenced-script walk read compiled binaries as if
they were shell scripts. Reading/inspecting a referenced file is now
best-effort by construction: executable magic numbers (ELF, PE,
Mach-O fat/thin) short-circuit before any full read via a 4KB sniff,
NUL-bearing heads are skipped as non-scripts, and unreadable paths of
every kind (NUL bytes in the token, ENAMETOOLONG, missing files)
degrade to "nothing to scan" instead of raising. A second fail-safe
layer wraps the pure-string fallback so the boundary function stays
total even if the tokenizer itself fails.
2. False-positive class: the lifecycle regex matched its command shapes
inside DATA arguments — SQL string literals passed to sqlite3/psql
and grep/rg/journalctl patterns hunting for the lifecycle string in
logs. Added a fail-closed second-pass exemption: on a raw regex hit,
re-scan with data-sink executables' arguments masked; only a match
that survives (i.e. sits in command position) blocks. Masking is
skipped for pipes into shells/xargs, command/process substitution,
sqlite3 dot-commands and psql backslash escapes, so it can only ever
allow, never miss.
Behavioral tests: exact live false-positive shapes as negatives, the
smuggling shapes as positives, the kill-primitive positive catalog
unchanged, and an adversarial never-raises suite (NUL bytes, non-UTF-8,
/dev/*, directories, missing files, magic-prefix binaries).
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