Thanks @michalbiarda — this is a really important fix. The root cause analysis is spot-on: linkExtenders() was only ever called from SchemaRegistry::registerEntities() (CLI-only), so during HTTP requests the extender map was always empty and EntityHydrator silently skipped companion attachment.

The two-part fix is exactly right:

1. Make EntityMetadataFactory a singleton so the populated extender cache is shared by every Repository / EntityHydrator that the container resolves.
2. boot callback discovers all entities and links extenders at startup — runs once per request boot, before any repository touches an entity.

I particularly like that linkExtendersFrom() throws loudly via EntityException::extenderParentClassNotFound() when an extender references a missing parent class, rather than letting it silently no-op. That matches the framework's loud-errors philosophy.

Maintainer changes

Small style polish to match conventions in the rest of the file:

• Added @throws EntityException|MissingPrimaryKeyException|ReflectionException to linkExtendersFrom() (since the method calls new ReflectionClass(), linkExtenders(), and constructs EntityException).
• Promoted ReflectionException to a use import.
• Switched count($tableAttrs) === 0 to $tableAttrs === [].
• Added blank lines between logical blocks for readability — matched the existing style of parse() / linkExtenders() in the same file.
• Ran phpcbf on the new tests — three multi-line-call style fixes.

Rebased onto current develop, force-pushed to your branch. Full suite green (5145 passing). Merging via merge commit.

Follow-up consideration

Running EntityDiscovery::discoverInVendor/Modules/App() on every request boot does mean a filesystem scan + reflection per request. For projects with many entities this could add measurable boot overhead. Not blocking this fix — correctness over perf — but worth tracking as a future optimization (cached entity-classes list invalidated on file changes, similar to how Laravel does package discovery). I'll let you decide whether that's worth an issue right now.