fix(schema): respect "required" for properties inside oneOf/anyOf

[schani]

Bug

required had no effect on properties reached through JSON Schema oneOf/anyOf. A property required in the branch where it's declared would come out optional in generated code, while the exact same property/required shape outside of oneOf/anyOf correctly stayed required.

Repro (from the issue, --src-lang schema --lang typescript):

{
  "properties": {
    "anyof": {
      "anyOf": [
        { "type": "object", "properties": { "name": {"type": ["string","null"]} }, "required": ["name"], "additionalProperties": false },
        { "type": "object", "properties": { "size": {"type": "string"} }, "required": [], "additionalProperties": false }
      ]
    }
  }
}

Before:

export interface Anyof {
    name?: null | string;   // wrong: required in its branch, still comes out optional
    size?: string;
}

After:

export interface Anyof {
    name: null | string;    // correct
    size?: string;
}

Root cause

quicktype's default pipeline flattens a union of several object (ClassType) branches — which is how oneOf/anyOf alternatives are represented internally — into a single merged interface (FlattenUnions.ts → UnifyClasses.ts). The property-merging logic (getCliqueProperties in UnifyClasses.ts) unconditionally marked a property optional whenever it was absent from any one of the merged branches, without considering that the branch it's missing from might be a closed schema (additionalProperties: false) that simply doesn't declare it — so the presence/absence heuristic (correct for merging differently-shaped plain JSON samples) silently dropped the required information declared for JSON Schema oneOf/anyOf alternatives.

Fix

• Added a schemaSetOperationTypeAttributeKind type attribute (packages/quicktype-core/src/attributes/Schema.ts) that JSONSchemaInput.ts stamps on the union type it builds for oneOf/anyOf (convertOneOrAnyOf).
• FlattenUnions.ts checks for that attribute on the unions it's about to merge and, when present, tells UnifyUnionBuilder/getCliqueProperties (UnifyClasses.ts) to preserve a property's required-ness instead of forcing it optional purely because a closed sibling branch (additionalProperties: false) doesn't declare it. Properties still become optional when the branch that lacks them is "open" (could carry the property as untyped additional data) or when the property is itself optional within the branch(es) that do declare it.
• Plain multi-sample JSON inference (no JSON Schema involved) is untouched — presence-based optionality there is still correct and desired, since it's not gated by the new attribute.

Test coverage

Added test/inputs/schema/required-in-any-of.schema (a two-branch anyOf, one branch requiring name, the other requiring nothing and being closed) plus .1.json (valid) and .2.fail.strict-optional.json (an object missing name, expected to fail under the strict-optional feature — TypeScript's schema fixture already declares that feature). This is picked up automatically by the existing schema-typescript fixture.

Verification

• New fixture (required-in-any-of.schema) fails on unfixed code, passes after the fix.
• QUICKTEST=true FIXTURE=schema-typescript script/test — all 71 cases pass.
• npx vitest run test/unit — 170 tests pass.
• npm run build passes.
• Manually confirmed the exact repro from the issue now generates name: null | string; instead of name?: null | string;.
• Manually confirmed plain (non-schema) multi-sample JSON inference still generates optional properties for fields missing in some samples (unaffected).
• CI will additionally validate the other language schema fixtures.

Fixes #1104

🤖 Generated with Claude Code

[github-actions]

Generated-output differences

154 files differ — 77 modified, 53 new, 24 deleted
14504 changed lines — +8094 / −6410

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