[MAINT] Github Actions Reunification - `coding-standard`

[damienwebdev]

Action: coding-standard

Status: 🔴 Significantly diverged
Files: coding-standard/action.yml

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Summary of differences

Area	Graycore (source of truth)	Mage-OS (fork)
php_version / composer_version inputs	Not present — PHP setup is done by the calling workflow	Present — action handles its own PHP setup
composer_auth input	Present	Absent
Checkout step	Absent — caller must checkout	Present — action checks out project at path: project
Standard install dir	inputs.path (caller's working dir)	Separate standard/ directory
Already-installed check	Checks if coding standard is already installed and skips install	Always installs fresh
Changed-files detection	Absent	Present — on PRs, only checks changed files
mage-os vendor support	Yes — handles both vendor/magento and vendor/mage-os	No — hardcodes vendor/magento
php-compatibility-fork	Required alongside coding standard	Not required
Action refs	graycoreio/github-actions-magento2/...@main	mage-os/github-actions/...@main
Branding	Present (icon: code, color: green)	Absent
path default	.	app/code

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Dependents (mage-os/github-actions consumers)

No external repos depend on coding-standard directly (per dependents.md).
Note: coding-standard-baseline (a separate mage-os-only action) has external dependents — do not confuse the two.

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Changes needed in mage-os fork

This is a substantive architectural difference. The mage-os fork reimplemented the action to embed its own PHP setup and checkout, while graycore keeps the action lean and delegates PHP setup to callers.

1. Adopt graycore's architecture — remove embedded checkout/PHP-setup steps; let calling workflows handle PHP version and composer version
2. Add composer_auth input
3. Port the already-installed check (steps.check-installed) to skip install when coding standard is already present
4. Port mage-os vendor support — handle both vendor/magento/magento-coding-standard and vendor/mage-os/magento-coding-standard
5. Port php-compatibility-fork requirement to composer require
6. Port improved phpcs flags handling — bash array approach with conditional appending
7. Port branding block
8. Update path default from app/code to .
9. Remove changed-files detection step (not present in graycore) — or keep as mage-os addition after discussion

Internal workflow impact

After this action is updated, _internal-coding-standard.yaml also needs:

• supported-version kind changed from all to currently-supported
• actions/checkout bumped from v4 to v6

[damienwebdev]

Closed by #342