Run list loops under bash, not zsh

[EdbertChan]

Summary

List loops run under bash, because zsh does not split an unquoted variable into words.

Under zsh, a loop over a list kept in one variable runs just once, with the whole list as a single item, and still exits 0.

So the loop looks done, even though it only ever saw one item.

Review Claim

The learned working-style rules require running list loops under bash and counting failed lookups as unchecked.

Review Lane

behavior

Review Unit

corpus-lesson

Safety Invariant

Adds one rule; the test runs both shells so the rule fails loudly if the shell behavior changes.

Slice Rationale

One rule and its test.

Non-goals

• No hook enforces this yet.

Test Plan

Test Plan

• python3 -m unittest tests.test_zsh_loop_rule: rule checks fail before, pass after; the premise checks print zsh 1 and bash 3 for the same loop

• Every step in .github/workflows/ci.yml ran locally on the full stack with rc=0: run_all_tests.sh, check_no_tracked_local_artifacts, check_hook_test_coverage, check_no_silent_hook_except, check_rules_are_wired, check_skills_three_harnesses, check_ecosystem_boundaries, check_skill_file_refs, check_skill_test_coverage, check_skill_test_debt_no_growth, check_skill_trigger_mechanism, check_dora_baseline, check_no_dated_provenance, check_no_new_comments, ruff check . --select E9,F, shellcheck install.sh

• zsh keeps an unquoted variable whole; bash splits it:

  $ zsh -c 'v="a b"; for w in $v; do echo "[$w]"; done'
  [a b]
  $ bash -c 'v="a b"; for w in $v; do echo "[$w]"; done'
  [a]
  [b]
  

Revert Plan

Revert Plan

• Safe to revert? Yes
• Revert command: git revert <sha>
• Post-revert steps: rerun ./install.sh so installed copies match
• Data migration? No

🤖 Generated with Claude Code

[EdbertChan]

This pull request is part of a Mergify stack:

#	Pull Request	Link
1	Run list loops under bash, not zsh	#736	👈
2	Read a script's whole body before asking to run it	#737
3	Reconcile declared intent, code, and result when finishing a merge	#738
4	Keep approved fix-later items in every status update	#739
5	Search saved memory both ways before a deep dive	#740

[EdbertChan]

Revision history

#	Type	Changes	Reason	Date
1	initial	1b75246		2026-09-17 04:23 UTC
2	rebase	1b75246 → b400645 (rebase only)		2026-09-17 04:23 UTC
3	rebase	b400645 → 81cc51b (rebase only)		2026-09-17 04:37 UTC
4	rebase	81cc51b → aba9455 (rebase only)		2026-09-17 04:55 UTC

[mergify]

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

[EdbertChan]

@Mergifyio queue

[mergify]

Merge Queue Status

• ✅ Entered queue — 2026-09-17 05:03 UTC · Rule: admin-bypass · triggered by @EdbertChan with the @mergifyio queue command
• ✅ Checks passed · on draft merge queue: checking #736 on main (ddbacf1) #758
• ✅ Merged — 2026-09-17 05:10 UTC · at 81da61ceb58552f50e495d2e1999954fd40bc710 · squash

This pull request spent 6 minutes 57 seconds in the queue, including 6 minutes 27 seconds running CI.

Required conditions to merge

• check-success = lint
• check-success = test
• check-success = validate