Keep the license code when the server rejects it

[shazzad]

Closes #19

Summary

invalid_license is returned by the server for any unmatched code + product_id pair — a site pointed at the wrong product, a license row removed by mistake, a product recreated — not only for a genuinely revoked license. Enforcement is server-side regardless (UpdatesController blanks the package URL, DownloadController 404s), so deleting the customer's only copy of the key achieved nothing while turning a recoverable state into a support round-trip.

• Tracker::sync_license_data() and Admin::handle_sync() now call the new Integration::mark_license_invalid(), which sets status: invalid on the stored data and preserves everything else — notably renewal_url, so the panel can still offer a renewal link.
• Admin::handle_save() no longer touches the stored license when a submitted key is rejected. The submitted key is only written in the success branch (src/Admin.php:203), so the old failure path deleted the working key and stored nothing — one typo, or one server blip, and the site was left with no license at all.
• The admin panel explains an unrecognised key instead of falling through to "Upgrade package file missing, unable to upgrade", which is what an invalid license used to render.
• The deliberate empty-field deactivation (src/Admin.php:171) is unchanged — that is a user asking to remove their license.

Outage handling was already correct and is untouched: a 502 decodes to wprepo_api_fail, a timeout to http_request_failed, a deactivated repo plugin to rest_no_route, and the sales-channel providers return wprepo_api_error on upstream failure. None reach this branch.

Test plan

• invalid_license marks data invalid and keeps the code (TrackerSyncLicenseTest)
• A transient API failure touches neither the code nor the data
• A valid response still stores the returned license data
• mark_license_invalid() preserves renewal_url/buyer_email, works with no stored data, and never calls delete_option
• Full suite: 68 tests, 123 assertions, green
• Verified the new tests fail against the old source (3 errors + 1 failure) and pass with the change
• phpcs unchanged except one added short-array-syntax hit matching the file's existing style

Not included

Deferred per discussion: gating automatic clearing behind N consecutive failures. With deletion removed entirely there is nothing left to debounce.

🤖 Generated with Claude Code