`$autocomplete` filter operator not supported on custom channel data fields

[mikhail-fedosenko]

Problem
The $autocomplete query operator cannot be used on custom channel data fields (via CustomChannelData) without a type assertion workaround. The API itself supports it, but the TypeScript types reject it.

// TS Error ❌
const filters: ChannelFilters = {
  $or: [
    { my_custom_name: { $autocomplete: "search term" } },
  ],
};

Simplified my life by asking AI to analyze the root cause and suggest a solution, so this is what it has come with:

Why
ChannelFilters maps custom fields through ContainsOperator → QueryFilter. The QueryFilter type only includes $eq, $exists, $gt, $gte, $in, $lt, $lte — no $autocomplete.
The operator is only available on a few hardcoded built-in fields (name, member.user.name). Because the relevant types are type aliases, users can't fix this via declaration merging.

Suggested Fix
Add $autocomplete to QueryFilter for string types:

export type QueryFilter<ObjectType = string> =
  NonNullable<ObjectType> extends string | number | boolean
    ? {
        $autocomplete?: NonNullable<ObjectType> extends string ? string : never; // add this
        $eq?: PrimitiveFilter<ObjectType>;
        $exists?: boolean;
        // ...rest unchanged
      }
    : { /* ...unchanged */ };

This is additive and non-breaking — it would make $autocomplete available on all string custom fields via ContainsOperator.

Workaround

// @ts-expect-error stream-chat's QueryFilter doesn't include $autocomplete for custom channel data fields
const filters: ChannelFilters = { $or: [...] };