Make the pre-push check run on the shell macOS ships

[EdbertChan]

Summary

Before a push, catstack runs a safety check on the files you changed. On a Mac it crashed, because the built-in shell lacks a feature it used.

So every push from a Mac stopped at the check, even a harmless one.

This change reads the list of changed files with a loop that every shell supports.

The check blocks the same pushes as before. It only stopped crashing.

Review Claim

The push safety check runs on the shell a Mac ships with, and blocks exactly the same pushes as before.

Review Lane

behavior

Review Unit

engine-runtime

Safety Invariant

The check still blocks the same pushes, and only the way it reads file lists changes.

Slice Rationale

One small portability fix, kept apart from the rule and hook changes that were blocked by it.

Non-goals

• No change to which pushes the check allows or blocks.
• No change to the installer or to any other script.

Measured

Why it crashed, from the default Mac shell and the file at the base commit:

$ /bin/bash --version | head -1
GNU bash, version 3.2.57(1)-release (arm64-apple-darwin26)
$ /bin/bash -c 'mapfile -d "" files </dev/null'
/bin/bash: mapfile: command not found
$ git show origin/main:scripts/git-hooks/pre-push | grep -n mapfile
160:  mapfile -d '' files <"$names"
176:        mapfile -d '' old_files <"$old_names"
185:            mapfile -d '' delta_files <"$delta_names"

Command: python3 -m unittest tests.test_pre_push_hook on a Mac with the default shell

• base: Ran 27 tests in 15.623s -- FAILED (failures=19)
• head: Ran 27 tests in 18.762s -- OK

Test Plan

Test Plan

• python3 -m unittest tests.test_pre_push_hook (head: Ran 27 tests, OK; base: failures=19)
• python3 engine/skills/make-pr/scripts/preflight.py --base origin/main --commit-only (ok preflight passed)
• python3 scripts/ci/check_hook_test_coverage.py --base origin/main --head HEAD (OK, 4 hook(s) checked)

Revert Plan

Revert Plan

• Safe to revert? Yes
• Revert command: git revert 680674c3
• Post-revert steps: Pushes from a Mac stop at the check again until the installed copy is replaced
• Data migration? No

🤖 Generated with Claude Code

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(requestId: ace5f03c-7516-4c7b-b87d-03c5e9c01793)

[mergify]

Queued — the merge queue status continues in this comment ↓.

[EdbertChan]

@Mergifyio queue

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-10-13 10:13 UTC · Rule: admin-bypass · triggered by a @mergifyio queue command
• 🟠 Checks running · on draft merge queue: checking #1378 + #1381 + #1387 + #1388 together on main (ff82cf8) #1395
• 🚫 Left the queue — 2026-10-13 10:15 UTC · at 680674c3077b77f784d7bd90a4bdfcb96694bbf1

This pull request spent 1 minute 25 seconds in the queue, with no time running CI.

Reason

Pull request #1388 has been merged manually at 12ae673

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[mergify]

queue

☑️ The pull request has been merged manually

Details

The pull request has been merged manually at 12ae673