fix(schemas): import from zod/v4 to match SDK's zod API

[ochafik]

Problem

After externalizing zod in #534, consumers on zod 3.25.x hit keyValidator._parse is not a function at runtime when parsing schemas that compose with SDK types.

Root cause

src/generated/schema.ts imports { z } from "zod" and then composes with schemas from @modelcontextprotocol/sdk/types.js:

import { z } from "zod";                              // ← v3 API when consumer has zod@3.x
import { ContentBlockSchema, ... } from "@modelcontextprotocol/sdk/types.js";  // ← v4 instances (SDK uses zod/v4)

// later: z.array(ContentBlockSchema), z.object({...params: CallToolResultSchema}), etc.

• In zod 3.25.x, import { z } from "zod" returns the v3 API
• In zod 4.x, the same import returns the v4 API
• The SDK always uses import * as z from 'zod/v4' → always v4 API

When a v3-created wrapper (z.array, z.object, z.record) parses a v4 schema instance, it tries to call the v3 internal ._parse() / ._parseSync() — which zod v4 removed. Result: TypeError: keyValidator._parse is not a function.

This was masked before #534 because zod was bundled — all schemas shared one inlined zod copy. Externalizing exposed the mismatch on zod-3.x consumers (e.g. anthropics/apps#27234).

Fix

Import from "zod/v4" in generated schemas. This subpath is exported by both zod 3.25+ and zod 4.x, so the existing peerDependencies.zod: "^3.25.0 || ^4.0.0" range is preserved.

Consumer zod	"zod" import	"zod/v4" import	SDK schemas	Compat
3.25.x	v3 API	v4 API	v4	✅ (after fix)
4.x	v4 API	v4 API	v4	✅

Testing

• ✅ npm test — 121 pass
• ✅ npx tsc --noEmit — typecheck clean (including schema.test.ts z.infer round-trip)
• ✅ Verified dist loads and parses in apps repo context with zod@3.25.76 (previously crashed)
• ✅ npm run build:all — all examples build (via pre-commit hook)

https://claude.ai/code/session_013xQUegrvVGct5xpqeSL5av

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commit: e746b73