fix(ai): add types to untyped enums in Moonshot tool schemas - #50961

Problem

Moonshot's Chat Completions API rejects any tool schema node that has an enum but no type:

Invalid request: tools.function.parameters is not a valid moonshot flavored json schema,
details: <At path 'properties.requestBody.properties.kind': type is not defined>

The whole request fails, not just the tool. OpenAPI-derived MCP tools often omit the type. For example, Vercel's MCP create_flag tool has kind: {"description": "The kind of flag", "enum": ["boolean", "string", "number", "json"]}, so enabling that server breaks every Kimi request on the Moonshot chat route, which is the default route for moonshotai. Found while surveying provider schema limits for #50297.

Verified live against kimi-k3 and kimi-k2.6:

• The rule applies wherever the node appears: properties, anyOf branches, items, additionalProperties, and $defs.
• const without a type, {}, $ref, and typed anyOf branches are accepted.
• type may be one type, or a pair with "null" (["string", "null"]). Other type arrays such as ["string", "number"] are rejected.

Change

packages/ai/src/protocols/utils/tool-schema.ts: the moonshot projection adds a type derived from the enum values to any node that has an enum and no type:

• one JSON type → that type (all numbers become "number")
• one type plus null → [type, "null"]
• mixed non-null types → left unchanged, since Moonshot has no valid type for them

The added type matches every enum value, so the schema still accepts the same values.

Verification

• test/tool-schema-projection.test.ts: untyped enums under properties, anyOf, items, additionalProperties, and $defs; numeric, boolean, and nullable enums; typed and mixed enums left unchanged. Fails without the change.
• Live through the V2 client (Moonshot.chat("kimi-k3")), each of the 21 Vercel MCP request bodies that contain an untyped enum as a tool: 11/21 rejected before, 21/21 accepted after.
• Live tool use on kimi-k3 and kimi-k2.6 (3 trials each): the models called the projected tools, and every call validated against the original schema. create_flag for an on/off flag picked kind: "boolean" in 6/6. A synthetic tool with untyped integer, nullable, anyOf, items, additionalProperties, and boolean enums produced exactly the expected arguments in 12/12, including 3 (not "3"), null (not "null"), and false (not "false").
• bun test in packages/ai: 1497 pass. bun run check: 35/35.