[🐞] v2: zod$ crashes when the router resolves zod 4 — z.Schema was removed (`instanceof` TypeError, every action 500s)

[blakeley]

Which component is affected?

Qwik Router

Describe the bug

The zod$ validator in @qwik.dev/router 2.0.0-beta.38 checks if (obj instanceof z.Schema) (lib/index.qwik.mjs, zodQrl.validate). z.Schema — a zod 3 alias of ZodType — no longer exists in zod 4. When the router's import ... from "zod" resolves to zod 4 (which happens in real-world hoisted layouts where the app itself depends on zod 4 and the package manager nests no private zod 3 copy for the router), every zod$-validated action throws server-side:

TypeError: Right-hand side of 'instanceof' is not an object
at zodQrl.validate (lib/index.qwik.mjs:1259)

and returns 500. Note the schema and the check use the SAME zod module (the router's re-exported z), so this isn't a mixed-versions problem — z.Schema is simply undefined in zod 4.

Reproduction

https://github.com/blakeley/zod4-zodschema-crash

Steps to reproduce

1. bun install; if your package manager nested a private zod 3 under node_modules/@qwik.dev/router, remove just that copy to mirror hoisted-workspace layouts (README explains; in a real bun workspace no nested copy was produced)
2. bun run dev
3. POST the action: curl -s -o /dev/null -w '%{http_code}' -X POST "localhost:5173/?qaction=" -H 'Origin: http://localhost:5173' --data 'msg=hi' → 500, server logs the TypeError
4. Sanity: node -e "const z=require('zod'); console.log('Schema' in z, 'ZodType' in z)" → false true

System Info

@qwik.dev/core 2.0.0-beta.38, @qwik.dev/router 2.0.0-beta.38, zod 4.4.3, vite 6, bun 1.2.17, macOS (darwin arm64), Node 22.

Additional Information

One-line fix verified empirically — obj instanceof z.ZodType works in zod 3 AND zod 4 (patched install turns the same POST into a 200). Related: PR #8887 touches the zod export for tree-shaking but keeps z.Schema.