Improve collection/global hook type safety

[V1RE]

Problem

Currently, collection hooks use T extends TypeWithID = any:

export type BeforeChangeHook<T extends TypeWithID = any> = (args: {
  collection: SanitizedCollectionConfig;
  data: Partial<T>;
  operation: CreateOrUpdateOperation;
  originalDoc?: T; // Always optional, even on 'update'
  // ...
}) => any;

Issues:

1. Default any - no type safety unless you manually provide a type
2. No slug-based inference - can't use 'posts' to get Post type automatically
3. originalDoc not narrowed - it's undefined on create, but TypeScript doesn't know that
4. No exported args types - can't easily type standalone hook functions

Proposal

Improve existing hooks with slug-based generics and export args types, similar to how BeforeOperationHook already works:

// BeforeOperationHook already uses CollectionSlug - extend this pattern
export type BeforeOperationHook<TSlug extends CollectionSlug = CollectionSlug> = ...

1. Add slug-based overloads

// Keep existing for backwards compat
export type BeforeChangeHook<T extends TypeWithID = any> = (args: BeforeChangeHookArgs<T>) => any;

// Add exported args type with slug-based variant
export type BeforeChangeHookArgs<T extends TypeWithID = any> = {
  collection: SanitizedCollectionConfig;
  context: RequestContext;
  data: Partial<T>;
  operation: CreateOrUpdateOperation;
  originalDoc?: T;
  req: PayloadRequest;
};

// Slug-based utility (uses DataFromCollectionSlug)
export type BeforeChangeHookArgsFromSlug<TSlug extends CollectionSlug> = BeforeChangeHookArgs<
  DataFromCollectionSlug<TSlug>
>;

2. Add discriminated union for operation

export type AfterChangeHookArgs<T extends TypeWithID = any> = {
  collection: SanitizedCollectionConfig;
  context: RequestContext;
  doc: T;
  req: PayloadRequest;
} & (
  | { operation: 'create'; previousDoc: Record<string, never> } // Empty on create
  | { operation: 'update'; previousDoc: T }
);

This lets TypeScript narrow previousDoc based on operation:

const hook: AfterChangeHook<Post> = (args) => {
  if (args.operation === 'update') {
    args.previousDoc.title; // ✅ Typed as Post
  }
};

3. Apply to globals too

Same pattern for GlobalBeforeChangeHook, GlobalAfterReadHook, etc.

Benefits

• Backwards compatible - existing hooks continue to work
• Opt-in type safety - use BeforeChangeHookArgsFromSlug<'posts'> for full inference
• IDE autocomplete - proper suggestions for doc, data, previousDoc
• Discriminated unions - operation narrows related fields

Files to Modify

• packages/payload/src/collections/config/types.ts - collection hooks
• packages/payload/src/globals/config/types.ts - global hooks

I'm Willing to Implement

I've already built and tested these types in a project. Happy to submit a PR if this approach looks good.