fix: terminal tool crashes with 'embedded null byte' when command references a binary via absolute path

[lightnet19]

Summary

Fixes ValueError: embedded null byte crash in the terminal tool when a command references a binary by absolute path (e.g. the Hermes venv python). Fixes the whole bug class, including the sibling call path missed by #76762.

Root cause

cron/lifecycle_guard.py already skips binaries in _read_referenced_script (NUL byte in first chunk -> "nothing to scan", #76762). But tools/terminal_tool.py passes _read_script_in_env as read_remote_script=. When the local read reports "nothing to scan", the guard calls the fallback, which decoded ELF bytes with errors="replace". NUL (U+0000) is valid UTF-8, so it survives into the returned text. The guard then recurses into that NUL-laden text as if it were a shell script; tokenization produces NUL-bearing paths and os.open raises ValueError: embedded null byte, failing every terminal call that references a binary by absolute path.

Changes

• tools/terminal_tool.py: _read_script_in_env now mirrors _read_referenced_script — returns None when the file chunk contains a NUL byte (binary == nothing to scan); also guards the remote cat output for NUL.
• cron/lifecycle_guard.py: _read_referenced_script tolerates ValueError from os.open just as it already tolerates it from Path.resolve, so a NUL-bearing path token can never crash the guard.

Tests

Adds two regression tests:

• test_binary_read_via_remote_callback_does_not_crash_guard — reproduces the gateway path (a read_remote_script callback that decodes a binary with errors="replace")
• test_nul_bearing_script_path_does_not_crash_guard — defense-in-depth for NUL-bearing path tokens

Full suite: 84 passed. Runtime verified after gateway restart: venv/bin/python -c 'print(1)' previously crashed, now runs clean.

Closes #79148

[kshitijk4poor]

Closing as superseded by #80258, which fixes this whole bug class architecturally rather than per-callsite: path candidates are sanitized once at the ingestion boundary (NUL/empty/unexpandable tokens rejected before any OS call), text from any read_remote_script callback is sanitized at the recursion boundary (NUL = binary = nothing to scan; >1 MiB = fail closed), the remote fallback read is bounded at the source (head -c, so oversized binaries never cross the wire), and the public guard is total by construction — an unexpected walk failure logs and falls back to the direct-scan verdict instead of breaking every terminal command.

Your report and fix targeted a real member of this class — thank you. The per-callsite patches kept leaving sibling frames exposed (#76762 → #77703 → #77780 → #78256 each crashed one frame away from the previous fix), which is why we went with the boundary fix instead of merging the fragments individually. #80258 carries regression tests for the NUL-path, binary-callback, oversized-read, unset-HOME, and walk-crash cases plus an adversarial never-raises sweep.