Refs #1308
Refs #2530

Adds regression coverage for McpServer tool outputSchema validation when the registered Zod schema is not a bare z.object(...).

This is test-only. It does not change production behavior or claim to close either referenced issue.

Motivation and Context

The original coverage handled Zod wrappers such as .optional() and unions of object schemas. Review feedback asked for actual non-object roots too, especially strings and arrays.

The tests now verify:

• z.object(...).optional() accepts matching structured output.
• z.union([z.object(...), z.object(...)]) accepts matching structured output.
• Invalid structured output is still rejected against wrapper/non-object schemas, so validation is not skipped.
• On the default/in-memory legacy path, z.string() and z.array(z.string()) output schemas are projected into the legacy { result: ... } wrapper and the returned structuredContent is wrapped the same way.
• On a real modern createMcpHandler HTTP connection negotiated through server/discover, z.string() and z.array(z.string()) keep their natural output schemas and return bare structuredContent values.

How Has This Been Tested?

corepack pnpm --filter @modelcontextprotocol/test-integration test -- test/server/mcp.test.ts
corepack pnpm --filter @modelcontextprotocol/test-integration test -- test/server/createMcpHandler.test.ts
corepack pnpm --filter @modelcontextprotocol/test-integration exec eslint test/server/mcp.test.ts test/server/createMcpHandler.test.ts
corepack pnpm exec prettier --config .prettierrc.json --check test/integration/test/server/mcp.test.ts test/integration/test/server/createMcpHandler.test.ts
git diff --check

Breaking Changes

None.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

No changeset is included because this is test-only.

The default/in-memory McpServer.server.connect() integration path negotiates a 2025-era connection, where non-object outputs are intentionally wrapped for compatibility. The added createMcpHandler coverage exercises the 2026-era path and shows that modern clients receive the natural string/array schema and structuredContent values.