The normalizer currently collapses anyOf/oneOf to the first branch, so discriminated union schemas lose all variant-specific properties:

// before — choices and scale are gone
{type: object, properties: {kind: {enum: ['open']}, text: ...}, required: [kind, text]}

// after
{type: object, properties: {kind: {enum: ['open', 'choice', 'rating']}, text: ..., choices: ..., scale: ...}, required: [kind]}

All plain-object branches are unioned into one schema. For a shared discriminator property with enum values in each branch, the enums are merged. The required intersection keeps only fields required in every opinionated branch.

Three correctness fixes are also included: required was incorrectly promoted when only one of multiple branches declared it; the array_merge fallback now uses mergeSchema to avoid shallow-overwriting already-merged properties when both anyOf and oneOf appear on the same node; and is_array guards prevent a TypeError from non-array enum values in malformed MCP tool schemas.