fix(hooks): remove unchecked perl dependency in simplify-ignore.sh

[HoneyTyagii]

Summary

hooks/simplify-ignore.sh used perl -pe 'chomp if eof' to preserve a file's trailing-newline status, but perl was never dependency-checked (unlike jq and shasum/sha1sum, which are validated up front) and it isn't listed in the script's Dependencies header.

The bug

In the PostToolUse (Edit/Write) branch, the trailing-newline block runs at top level under set -euo pipefail:

perl -pe 'chomp if eof' "$EXPANDED" > "${EXPANDED}.nnl" && \
  cat "${EXPANDED}.nnl" > "$EXPANDED" && rm -f "${EXPANDED}.nnl"

On a host without perl (minimal CI images, or Alpine/busybox containers, which are common places for Claude Code hooks to run), this command fails. Because it's the last command in the then clause and set -e is active, the script aborts before the expanded content is written back to disk.

The result is not a cosmetic newline glitch. The file is left in its BLOCK_<hash> placeholder state and the backup is never refreshed, so the model's edits are effectively stranded, which is a data-integrity failure.

The same perl call is also used in filter_file, where it silently mishandles trailing-newline preservation on perl-less hosts.

The fix

Replace both perl invocations with a POSIX-safe equivalent that removes the hidden dependency entirely:

printf '%s' "$(cat "$EXPANDED")" > "${EXPANDED}.nnl"

Command substitution $(...) strips all trailing newlines, matching the behavior of perl -pe 'chomp if eof'. This aligns with the script's established pattern of validating (or not depending on) every external tool.

Testing

• bash -n hooks/simplify-ignore.sh passes
• hooks/simplify-ignore-test.sh: the trailing-newline preservation test (Test 5) passes, and results are unchanged from before this patch

[Copilot]

Pull request overview

This PR removes an unchecked perl dependency from hooks/simplify-ignore.sh by replacing the trailing-newline-preservation logic with a POSIX-oriented alternative, improving reliability on minimal CI/container images where Perl isn’t installed.

Changes:

• Replaced perl -pe 'chomp if eof' usage in filter_file() with a shell-based approach.
• Replaced the same Perl usage in the PostToolUse (Edit/Write) expansion path.
• Expanded inline comments explaining the trailing-newline handling and motivation (avoid hard Perl dependency).

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[addyosmani]

Good catch, and exactly the portability bug that only shows up on the one machine without perl installed. Swapping to the tools the hook already dependency-checks (jq, shasum) keeps it honest about what it actually needs, instead of silently relying on perl being around. I verified it merges clean and the suite stays green. Straightforward yes from me, thanks for tightening it.