[Feat] Reuse Isolated User + Default Username

[RichardAnderson]

This pull request introduces significant improvements to the handling of isolated users and PHP version management for sites, focusing on safety, concurrency, and user experience. The main changes include the addition of distributed locking to prevent race conditions when manipulating isolated users, improved validation and error handling, and new endpoints and utilities for managing and suggesting isolated usernames. It also improves the existing reserved user name list to prevent the use of system or privileged accounts as site users, as well as allow isolated users to be shared across sites.

Isolated User Selection

Isolated User Default

Change Isolated User / Create New

Concurrency and Safety Improvements:

• Added distributed locking (isolatedUserLock) when creating, deleting, or modifying isolated users and their PHP FPM pools to prevent race conditions and ensure that only one operation can proceed per user at a time. This affects site deletion, PHP version updates, and user isolation logic. User-friendly validation errors are now returned if a lock cannot be acquired.
• Refactored site deletion and PHP version change logic to use the new locking mechanism and to avoid deleting shared users or FPM pools if they are still in use by sibling sites.

Validation and Reserved User Names:

• Introduced a reserved_user_names configuration to block the use of system/service accounts as site users, and updated validation logic to enforce this restriction. The reserved list is now shared with the frontend for consistent validation.

API and Utility Additions:

• Added a new backend action and API endpoint to list all isolated users and their site counts per server, supporting better UI/UX for user selection and management.
• Introduced utility methods on the Site model to check if a user or PHP FPM pool is shared with sibling sites, supporting safer resource cleanup.

Frontend Enhancements:

• Added isolated user name suggestion logic in the site creation form, using the reserved names and existing users to suggest safe, unique, and valid usernames.

Codebase Cleanup:

• Removed the now-obsolete changePHPVersion method from the Site model, centralizing PHP version switching logic in the action class for better separation of concerns.

These changes collectively enhance the reliability, safety, and usability of isolated user management and PHP version switching in the application.

[Copilot]

Pull request overview

Allows multiple sites on the same server to share an isolated Linux user (and FPM pool) safely. Adds distributed locking around isolated-user mutations, a reserved-username blocklist, an API + UI for picking/creating isolated users on site creation, and refactors PHP-version switching out of the Site model into the action layer.

Changes:

• Concurrency: introduces Server::isolatedUserLock() and wraps create / delete / PHP-version-switch flows in it; refuses to delete users/pools still used by sibling sites.
• Validation/UX: adds reserved_user_names config (shared with frontend), drops the per-server unique-user constraint, adds GetIsolatedUsers action + sites.isolated-users endpoint, and a new IsolatedUserSelect combobox with auto-suggested usernames.
• Idempotency: create-isolated-user.blade.php short-circuits if the user already exists and tightens home-dir permissions.

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tests/Feature/SitesTest.php	Adds tests for reuse, isolated-users endpoint, shared-user delete, and PHP version switch behavior.
resources/views/ssh/os/create-isolated-user.blade.php	Skips creation if user exists; uses mkdir -p and tighter chmods.
resources/js/types/index.d.ts	Exposes reserved_user_names on the shared configs.site type.
resources/js/pages/sites/components/isolated-user-select.tsx	New combobox listing existing isolated users with site counts and a "create new" affordance.
resources/js/pages/sites/components/create-site.tsx	Wires the new select, suggests usernames using existing+reserved, invalidates query on submit.
config/core.php	Adds the reserved_user_names blocklist.
app/SiteTypes/AbstractSiteType.php	Locks isolation; skips user/FPM-pool creation when already shared with siblings.
app/Models/Site.php	Removes changePHPVersion; adds userSharedWithSiblings/fpmPoolSharedWithSiblings helpers.
app/Models/Server.php	Adds isolatedUserLock() cache lock helper.
app/Http/Middleware/HandleInertiaRequests.php	Shares reserved usernames with the frontend.
app/Http/Controllers/SiteController.php	Adds sites.isolated-users endpoint.
app/Actions/SSL/GetMatchingSslCertificates.php	Loosens PHPDoc array shape from non-falsy-string to string.
app/Actions/Site/UpdatePHPVersion.php	Centralizes PHP version switching with locking and shared-pool checks.
app/Actions/Site/GetIsolatedUsers.php	New action returning isolated users with per-server site counts.
app/Actions/Site/DeleteSite.php	Refactored to lock and skip teardown of user/pool still used by siblings.
app/Actions/Site/CreateSite.php	Replaces unique-user rule with reserved-name + SSH-user blocklist.