Use namespace prefix on all vendor dependecies

[superdav42]

Problem

WP-Stateless ships psr/simple-cache v3.0.0 in its vendor/ directory, which defines CacheInterface with native PHP 8 type declarations:

// psr/simple-cache v3 — shipped by wp-stateless
public function get(string $key, mixed $default = null): mixed;

Any other plugin that implements Psr\SimpleCache\CacheInterface against v1 (no native types) will fatal when both plugins are active, because the Jetpack autoloader loads the highest available version globally:

PHP Fatal error: Declaration of WordPress_Simple_Cache::get($key, $default = null)
must be compatible with Psr\SimpleCache\CacheInterface::get(string $key, mixed $default = null): mixed

This was observed in production with WP Ultimo's SSO cache class, but any plugin implementing PSR-16 v1 will hit the same conflict.

Root cause

psr/simple-cache is a transitive dependency (brianhenryie/strauss → json-mapper/json-mapper → psr/simple-cache). All upstream packages accept ^1.0 || ^2.0 || ^3.0, so Composer resolves to v3. The vendored Psr\SimpleCache\CacheInterface class is then loaded into the global namespace, where it conflicts with any other plugin's v1-compatible implementation.

This is not specific to psr/simple-cache — the same class of conflict can occur with any shared PSR interface or common library (e.g., psr/log, psr/container, monolog/monolog, guzzlehttp/guzzle) where wp-stateless ships a different major version than another active plugin.

Suggested fix

Use PHP-Scoper or expand the existing Strauss configuration to prefix all vendor namespaces under a plugin-specific prefix (e.g., wpCloud\StatelessMedia\). This is the standard approach for WordPress plugins that ship Composer dependencies — it isolates vendor classes entirely and eliminates cross-plugin autoloader conflicts.

wp-stateless already has Strauss configured in composer.json, but currently only prefixes deliciousbrains/wp-background-processing. Expanding it to cover all packages in vendor/ (particularly PSR interfaces, Symfony components, Monolog, and Guzzle) would prevent this entire class of conflict.

Workaround

Pinning "psr/simple-cache": "^1.0" in composer.json resolves the immediate conflict by forcing v1 (no native types), which is compatible with both wp-stateless's own dependencies and other plugins' v1-style implementations. However, this is a band-aid — the underlying namespace collision risk remains for every other shared library.

Environment

• WordPress: 6.8
• PHP: 8.2
• WP-Stateless: latest develop branch
• Conflicting plugin: WP Ultimo (any plugin implementing PSR-16 v1 will trigger it)