docs(downgrader): note Hey API drops a bare object anyOf branch beside readOnly

packages/downgrader/README.md

@@ -287,7 +287,7 @@ Accepts the default OAS dialect, which adds `discriminator`, `xml`, `externalDoc
 - CreateAPI 0.2, a Swift generator that reads 3.0 only, by default stops with `Enum "…" has no values` on a string `enum` with no string in it, as the `"null"` branch is. So a nullable `$ref`, enum or union, such as Zod's `z.enum(["a", "b"]).nullable()`, and a property of `type: "null"` alone, such as Zod's `z.null()`, fail the whole run, or with `--allow-errors` drop the schema or property that holds them.
 - clientele 2.3 leaves out `enum` everywhere but in a component of its own, so it reads the `"null"` branch as a nullable string. A nullable `$ref`, to an enum or an object, and a nullable union of types other than strings then also take any string, and a property of `type: "null"` alone, such as Zod's `z.null()`, becomes an optional string. It reads 3.1 too, which keeps `{ type: "null" }`.
 - guardrail 1.0.0-M1, which types every inline 3.1 schema as untyped JSON, so reads 3.0 in practice, makes each inline string `enum` in a `oneOf`, the `"null"` branch among them, an empty case class in its circe models. That class takes any value and writes it back as `{}`, so a nullable `$ref` or union, such as Zod's `z.union([z.string(), z.number()]).nullable()`, takes any value and writes null back as `{}`. A nullable enum, such as Zod's `z.enum(["a", "b"]).nullable()`, does that for each of its own values too.
-- Hey API's Zod and Valibot plugins read the `"null"` branch as any value, so a union with null, such as a nullable `$ref`, accepts every value. Hey API also types an array as its item when the item holds an `enum` beside an `anyOf`, as a `type` list with an `enum` becomes, such as Valibot's `picklist` of strings and numbers, so those plugins then reject the array. Its transformers plugin skips a union with the `"null"` branch, such as a nullable `$ref`, so the dates inside it stay strings, although its types say `Date`. Its Zod and Valibot plugins pin each branch of a `discriminator` to its tag when the tag is a one-value `enum`, as a `const` becomes, so they reject a value that leaves out a tag that has a `default`, such as Pydantic's `Literal["a"] = "a"` in a tagged union. Hey API reads 3.1 too, which keeps the `"null"` type, the `type` list, and the `const` tag, which it leaves as the branch says.
+- Hey API's Zod and Valibot plugins read the `"null"` branch as any value, so a union with null, such as a nullable `$ref`, accepts every value. Hey API also types an array as its item when the item holds an `enum` beside an `anyOf`, as a `type` list with an `enum` becomes, such as Valibot's `picklist` of strings and numbers, so those plugins then reject the array. Hey API also drops a `{ type: "object" }` branch with nothing else in it from an `anyOf`, as a `type` list with `"object"` becomes, in a schema that holds a `readOnly` or `writeOnly` property, so its types and those plugins then reject an object there, such as Celigo's `encrypted` fields. Its transformers plugin skips a union with the `"null"` branch, such as a nullable `$ref`, so the dates inside it stay strings, although its types say `Date`. Its Zod and Valibot plugins pin each branch of a `discriminator` to its tag when the tag is a one-value `enum`, as a `const` becomes, so they reject a value that leaves out a tag that has a `default`, such as Pydantic's `Literal["a"] = "a"` in a tagged union. Hey API reads 3.1 too, which keeps the `"null"` type, the `type` list, and the `const` tag, which it leaves as the branch says.
 - dtsgenerator 3.19, and the `typegen` of openapi-client-axios, which builds on it, put every value of an `enum` beside an `anyOf` into each branch, the shape a `type` list with an `enum` becomes, such as Valibot's `picklist` of strings and numbers. They type `picklist(["a", 1])` as `("a" | "1") | (a | 1)`, whose bare `a` does not compile and leaves the property open to any value. Both read 3.1 too, which keeps the `type` list.
 - openapi-generator-plus 2.33's TypeScript clients read the `"null"` branch as an enum of the string `"null"`, so a nullable `$ref`, enum or union of scalars, which becomes a `oneOf` with that branch, takes that string in place of null in its type, as for Zod's `z.enum(["a", "b"]).nullable()`. Its parser also rejects `openapi: 3.0.4`, so set `3.0.3`. It reads 3.1 too, which keeps null, but stops on a `const` without a `type`, as Valibot and ArkType write a literal.
 - openapi-to-rust 0.23, like openapi-generator-plus, reads the `"null"` branch as an enum of the string `"null"`, since it takes `enum: [null]` as null only without a `type`. So a nullable `$ref`, enum or union, such as Zod's `z.enum(["a", "b"]).nullable()`, becomes an `Option` of an untagged union with that enum as one more member, which also takes the string `"null"`, in place of an `Option` of the type itself. It reads 3.1 too, which keeps `{ type: "null" }`.