chore: robustify the codebase

.claude/settings.local.json

@@ -0,0 +1,5 @@
+{
+  "permissions": {
+    "allow": ["Bash(wc:*)", "Bash(bats:*)"]
+  }
+}

.github/workflows/CI.yml

@@ -2,8 +2,9 @@
 name: CI
 on:
   pull_request:
-    branches:
-      - main
+    branches: [main]
+  push:
+    branches: [main]
   workflow_dispatch:
 
 concurrency:
@@ -16,18 +17,27 @@ defaults:
 
 jobs:
   test:
-    name: Run Tests
-    runs-on: ubuntu-latest
+    name: Run Tests (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
     steps:
       - uses: actions/checkout@v6
       - name: Setup BATS
         uses: bats-core/bats-action@3.0.1
+      - name: Install GNU parallel (macOS only)
+        if: matrix.os == 'macos-latest'
+        run: brew install parallel
       - name: Run BATS tests
         run: bats --jobs 4 --timing tests/*.bats
 
   run-ci:
-    name: Run CI
-    runs-on: ubuntu-latest
+    name: Run CI (${{ matrix.os }})
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
     steps:
       - uses: actions/checkout@v6
       - name: Install pre-commit

.github/workflows/dependabot-automerge.yml

@@ -2,7 +2,6 @@
 name: Dependabot auto-merge
 on:
   pull_request:
-    types: [opened, reopened, synchronize]
 
 # A ruleset that requires status checks to pass must be configured for the repository.
 

.github/workflows/pre-commit-autoupdate-automerge.yml

@@ -2,7 +2,6 @@
 name: pre-commit autoupdate auto-merge
 on:
   pull_request:
-    types: [opened, reopened, synchronize]
 
 # A ruleset that requires status checks to pass must be configured for the repository.
 

.specify/memory/constitution.md

@@ -0,0 +1,101 @@
+<!--
+Sync Impact Report:
+Version: 1.0.0 → 1.0.1
+Ratified: 2025-01-18
+Last Amended: 2026-01-18
+
+Principles Modified:
+- III. Test-First: Clarified scope - only scripts in project root require testing
+
+Sections Modified:
+- Quality Assurance / Testing Requirements: Clarified scope
+
+Templates Status:
+✅ plan-template.md - No changes needed (generic testing guidance)
+✅ spec-template.md - No changes needed (generic testing guidance)
+✅ tasks-template.md - No changes needed (tests are optional per spec)
+✅ Command files - No outdated references found
+
+Version Bump Rationale: PATCH - Clarification of testing scope (scripts in project root vs other scripts like dev scripts). No breaking changes, backward compatible.
+-->
+
+# bin Constitution
+
+## Core Principles
+
+### I. Script-First
+
+Every utility is a standalone, independently executable script. Scripts MUST be self-contained with no external runtime dependencies beyond standard Unix utilities. Each script MUST have a clear, single purpose. Scripts MUST be executable and callable directly from the command line.
+
+### II. CLI Interface
+
+All scripts MUST follow Unix conventions: text input/output via stdin/stdout/stderr, proper exit codes (0 for success, non-zero for failure), and comprehensive help messages via `--help` or `-h`. Scripts MUST support both interactive and non-interactive usage. Error messages MUST be clear and actionable, written to stderr.
+
+### III. Test-First (NON-NEGOTIABLE)
+
+Every script in the project root MUST have comprehensive test coverage using bats. Tests MUST be written before or alongside implementation. Tests MUST cover happy paths, error cases, edge cases, and help output. All tests MUST pass before merging. Test files MUST be located in `tests/` directory with naming convention `[script-name].bats`.
+
+**Scope**: This requirement applies to scripts located in the project root directory. Scripts in other locations (e.g., `.github/scripts/`, development tooling, or helper scripts) may be exempt from testing requirements at the project's discretion, but scripts in the project root that are part of the main utility suite MUST have tests.
+
+### IV. Simplicity
+
+Scripts MUST prioritize simplicity and maintainability. Follow YAGNI (You Aren't Gonna Need It) principles. Avoid unnecessary complexity, abstraction, or premature optimization. Scripts MUST be readable and understandable by developers familiar with bash. When complexity is unavoidable, it MUST be justified and documented.
+
+### V. Portability
+
+Scripts MUST work across Unix-like systems (Linux, macOS, BSD). Use POSIX-compliant constructs where possible. When bash-specific features are required, scripts MUST use `#!/usr/bin/env bash` shebang and document the minimum bash version. Avoid system-specific paths or assumptions. Test on multiple platforms when feasible.
+
+## Development Standards
+
+### Bash Best Practices
+
+- Scripts MUST use `set -euo pipefail` for strict error handling. Exceptions for `-u` may be justified when scripts need to check for unset variables using patterns like `${VAR:-default}` or explicit unset checks
+- Variables MUST be quoted to prevent word splitting and pathname expansion
+- Functions MUST be used for reusable logic
+- Scripts MUST include proper cleanup handlers (trap) for error recovery
+- Scripts MUST validate inputs and provide clear error messages
+
+### Code Quality
+
+- Scripts MUST pass shellcheck validation
+- Scripts MUST follow consistent formatting (use .editorconfig)
+- Scripts MUST include usage documentation in help output
+- Complex logic MUST be commented for clarity
+
+## Quality Assurance
+
+### Testing Requirements
+
+- All scripts in the project root MUST have corresponding test files in `tests/`
+- Scripts in other locations (e.g., `.github/scripts/`, dev tooling) may be exempt from testing at project discretion
+- Tests MUST use bats framework (minimum version 1.5.0)
+- Tests MUST be independent and idempotent
+- Tests MUST clean up after themselves
+- Integration tests MUST use isolated test environments
+
+### Continuous Integration
+
+- All tests MUST pass in CI before merging
+- Pre-commit hooks MUST validate script syntax and formatting
+- Code review MUST verify test coverage and constitution compliance
+
+## Governance
+
+This constitution supersedes all other development practices and guidelines. All pull requests and code reviews MUST verify compliance with these principles.
+
+**Amendment Process**: Amendments to this constitution require:
+
+1. Documentation of the proposed change and rationale
+2. Impact analysis on existing scripts and templates
+3. Update of dependent templates and documentation
+4. Version increment according to semantic versioning
+
+**Versioning Policy**:
+
+- MAJOR: Backward incompatible principle removals or redefinitions
+- MINOR: New principle added or materially expanded guidance
+- PATCH: Clarifications, wording improvements, typo fixes
+
+**Compliance Review**: All PRs MUST include a constitution check. Violations MUST be justified in the Complexity Tracking section of implementation plans, or the PR MUST be updated to comply.
+
+**Version**: 1.0.1 | **Ratified**: 2025-01-18 | **Last Amended**: 2026-01-18

CONTRIBUTING.md

@@ -0,0 +1,170 @@
+<!-- omit in toc -->
+
+# Regarding contributions
+
+All types of contributions are encouraged and valued. See the [Table of Contents](#table-of-contents) for different ways to help and details about how this project handles them. Please make sure to read the relevant section before making your contribution. It will make it a lot easier for us maintainers and smooth out the experience for all involved. We look forward to your contributions!
+
+The project has defined a [code of conduct](https://github.com/michen00/.github/blob/main/CODE_OF_CONDUCT.md), providing a welcoming and friendly environment. Please adhere to it in all interactions.
+
+> And if you like the project, but just don't have time to contribute, that's fine. There are other easy ways to support the project and show your appreciation, which we would also be very happy about:
+>
+> - Star the project
+> - Post about it on LinkedIn or other social media
+> - Refer this project in your project's README
+> - Mention the project at local meetups and tell your friends/colleagues
+
+<!-- omit in toc -->
+
+## Table of Contents
+
+- [I have a question](#i-have-a-question)
+- [I want to contribute](#i-want-to-contribute)
+  - [Reporting bugs](#reporting-bugs)
+    - [Before submitting a bug report](#before-submitting-a-bug-report)
+    - [How do I submit a good bug report?](#how-do-i-submit-a-good-bug-report)
+  - [Suggesting enhancements](#suggesting-enhancements)
+    - [Before Submitting an Enhancement](#before-submitting-an-enhancement)
+    - [How do I submit a good enhancement suggestion?](#how-do-i-submit-a-good-enhancement-suggestion)
+  - [Your first code contribution](#your-first-code-contribution)
+
+## I have a question
+
+Before you ask a question, it is best to search for existing [issues][issues] and [discussions][discussions] that might help you. In case you have found a suitable issue and still need clarification, you can write your question in this issue. It is also advisable to search the internet for answers first.
+
+If you then still feel the need to ask a question and need clarification, we recommend the following:
+
+- Create a [discussion][discussions_new].
+- Provide as much context as you can about what you're running into.
+- Provide project and platform versions, depending on what seems relevant.
+
+We will then take care of the discussion as soon as possible.
+
+## I want to contribute
+
+### Reporting bugs
+
+#### Before submitting a bug report
+
+A good bug report shouldn't leave others needing to chase you up for more information. Therefore, we ask you to investigate carefully, collect information and describe the issue in detail in your report. Please complete the following steps in advance to help us fix any potential bug as fast as possible:
+
+- Make sure that you are using the latest version.
+- Determine if your bug is really a bug and not an error on your side e.g. using incompatible environment components/versions.
+- To see if other users have experienced (and potentially already solved) the same issue you are having, check if there is not already a bug report existing for your bug or error in the [bug tracker][issues_bugs].
+- Also make sure to search the internet to see if users outside of the GitHub community have discussed the issue.
+- Collect information about the bug:
+  - Stack trace
+  - OS and version (Windows, Linux, macOS, x86, ARM)
+  - Version of the interpreter, compiler, SDK, runtime environment, package manager, depending on what seems relevant
+  - Possibly your input and the output
+  - Can you reliably reproduce the issue? And can you also reproduce it with older versions?
+  - Screenshots or animated GIFs showing the problem
+
+#### How do I submit a good bug report?
+
+We use GitHub issues to track bugs and errors. If you run into an issue with the project:
+
+- Open an [issue][issues_new].
+- Explain the behavior you would expect and the actual behavior.
+- Please provide as much context as possible and describe the _reproduction steps_ that someone else can follow to recreate the issue on their own.
+- Provide the information you collected in the previous section.
+
+Once it's filed:
+
+- The project team will label the issue accordingly.
+- A team member will try to reproduce the issue with your provided steps. If there are no reproduction steps or no obvious way to reproduce the issue, the team will ask you for those steps. Bugs without steps will not be addressed until they can be reproduced.
+- If the team is able to reproduce the issue, it will be prioritized according to severity.
+
+### Suggesting enhancements
+
+This section guides you through submitting an enhancement suggestion, **including completely new features and minor improvements to existing functionality**. Following these guidelines will help maintainers and the community understand your suggestion and find related suggestions.
+
+#### Before Submitting an Enhancement
+
+- Make sure that you are using the latest version.
+- Read the documentation carefully and find out if the functionality is already covered, maybe by an individual configuration.
+- Perform a [search][issues] to see if the enhancement has already been suggested. If it has, add a comment to the existing issue instead of opening a new one.
+- Find out whether your idea fits with the scope and aims of the project. Keep in mind that we want features that will be useful to the majority of our users and not just a small subset.
+
+#### How do I submit a good enhancement suggestion?
+
+Enhancement suggestions are tracked as [GitHub issues][issues].
+
+- Use a **clear and descriptive title** for the issue to identify the suggestion.
+- Provide a **step-by-step description of the suggested enhancement** in as many details as possible.
+- **Describe the current behavior** and **explain which behavior you expected to see instead** and why. At this point you can also tell which alternatives do not work for you.
+- You may want to **include screenshots and animated GIFs** which help you demonstrate the steps or point out the part which the suggestion is related to.
+- **Explain why this enhancement would be useful** to most users. You may also want to point out other projects that solved it better and could serve as inspiration.
+
+### Your first code contribution
+
+#### Getting started
+
+Start by [forking the repository](https://docs.github.com/en/github/getting-started-with-github/fork-a-repo), i.e. copying the repository to your account to grant you write access. Continue with cloning the forked repository to your local machine.
+
+From the project root, run `make develop` to set up the project for development.
+
+#### Development workflow
+
+Make your changes to the code, then verify everything works:
+
+```sh
+make check
+```
+
+##### Running tests
+
+To run all tests:
+
+```sh
+make test
+```
+
+To run tests for a specific script:
+
+```sh
+make test SCRIPTS=ach
+```
+
+To run tests for multiple scripts:
+
+```sh
+make test SCRIPTS=ach,chdirx,gcfixup
+```
+
+The test runner validates that both the script file and its test file exist. If you specify an invalid script name, you'll see an error message listing available scripts.
+
+You can combine script selection with other test options:
+
+```sh
+# Run specific tests sequentially (useful for debugging)
+make test SCRIPTS=ach,touchx PARALLEL=false
+
+# Run all tests sequentially
+make test PARALLEL=false
+```
+
+Note: When running a single script, tests always run sequentially. When running multiple scripts with `PARALLEL=true`, the job count is automatically optimized based on the number of scripts.
+
+#### Committing your changes
+
+Commit the changes using the [conventional commits](https://www.conventionalcommits.org) message style:
+
+```sh
+git commit -am 'feat: add new feature'
+```
+
+Common commit types: `feat`, `fix`, `docs`, `style`, `refactor`, `test`, `chore`
+
+Continue with pushing the local commits to GitHub:
+
+```sh
+git push origin <branch name>
+```
+
+And finally, when you are satisfied with your changes, open a new PR.
+
+[issues]: https://github.com/michen00/invisible-squiggles/issues
+[issues_new]: https://github.com/michen00/invisible-squiggles/issues/new
+[issues_bugs]: https://github.com/michen00/invisible-squiggles/issues?q=label%3Abug
+[discussions]: https://github.com/michen00/invisible-squiggles/discussions
+[discussions_new]: https://github.com/michen00/invisible-squiggles/discussions/new/choose