Bash `sed -i` chained command silently emptied source file, wiping work

Model: Claude Opus 4.7 (model ID: claude-opus-4-7), 1M context, accessed via Claude Code.

Summary
A chained Bash command using sed -i '' (BSD/macOS variant) for a global rename inside a JavaScript source file resulted in the file being emptied (0 bytes) — losing several hours of in-progress work. The chained validation steps that followed (grep, node --check) reported success, masking the failure.

Approximate command shape

cd <dir> && sed -i '' 's/oldName/newName/g' <file.js> && grep -c "newName" <file.js> && grep -c "oldName" <file.js> && node --check <file.js> && echo "syntax ok"

The node --check passed because the empty file is technically valid JS, and the grep -c returns 0 (which is a non-zero exit code on no-match, short-circuiting the && chain after sed had already destroyed the file).

Outcome
~1700 lines of uncommitted source lost. Recovery was only possible because the user had not yet reloaded the unpacked Chrome extension that loaded the file — the source was still cached in Chrome DevTools' Sources panel under "Content scripts" and could be copy-pasted back into the empty file.

Suggested guardrails

1. Default-deny destructive in-place editors (sed -i, perl -i, gawk -i, etc.) in the harness, requiring explicit user opt-in. Configurable via permissions.deny, but should ship as default-deny — the model has the Edit tool available and shouldn't reach for shell file rewrites.
2. Train the model to never use shell-based in-place file rewrites; always use the Edit tool for source modifications.
3. Recommend frequent commits during long sessions (or surface a warning when uncommitted work crosses some threshold).

Workaround applied
User added the following to .claude/settings.local.json:

\\\json
"permissions": {
"deny": [
"Bash(sed -i:*)",
"Bash(perl -i:*)",
"Bash(gawk -i:*)"
]
}
\\\

Filed at user's request after this incident.