[BUG] Error thrown for Object schemas

[oidebrett]

Issue

I am getting an error recently regarding using.safeExtend(), somewhere inside @mcpjam/inspector,

which breaks in Zod v4.

How to reproduce

1. Try to run: npx @mcpjam/inspector@latest
2. See error:

file:///Users/mattercoder/.npm/_npx/d1af9de5c448057a/node_modules/zod/v4/core/util.js:375
        throw new Error("Object schemas containing refinements cannot be extended. Use `.safeExtend()` instead.");
              ^

Error: Object schemas containing refinements cannot be extended. Use `.safeExtend()` instead.
    at Module.extend (file:///Users/mattercoder/.npm/_npx/d1af9de5c448057a/node_modules/zod/v4/core/util.js:375:15)
    at inst.extend (file:///Users/mattercoder/.npm/_npx/d1af9de5c448057a/node_modules/zod/v4/classic/schemas.js:536:21)
    at file:///Users/mattercoder/.npm/_npx/d1af9de5c448057a/node_modules/@mcpjam/inspector/dist/server/index.js:12026:45
    at ModuleJob.run (node:internal/modules/esm/module_job:413:25)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:654:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5)

Node.js v25.2.1
⚠️  Server did not become ready within 30s. Please visit http://127.0.0.1:6274 manually.

Expected Behavior

MCPJam inspector should open in browser but it doesnt

Screenshots

If applicable, add screenshots to help explain your problem.

Platform

% node --version                                                                              
v25.2.1
% npm --version                                                                               
11.6.2
% uname -a
Darwin MacBook 25.4.0 Darwin Kernel Version 25.4.0: Thu Mar 19 19:31:09 PDT 2026; root:xnu-12377.101.15~1/RELEASE_ARM64_T8132 arm64

Additional Context

Add any other context about the problem here.

[dosubot]

Hi @oidebrett! I'm Dosu and I’m helping the inspector team.

This is a real bug in the current codebase. The root cause is that workspaceServerSchema and hostedChatSchema are both wrapped with .superRefine() via the refineHostedTokens() helper [1], and then .extend() is called on them in multiple places. In Zod v4, calling .extend() on a schema that has refinements throws the error you're seeing.

Specifically, there are at least 9 .extend() calls on refined schemas across these files:

• auth.ts — 6 calls extending workspaceServerSchema for tools, resources, and prompts schemas [2]
• apps.ts — 2 calls extending workspaceServerSchema for MCP/ChatGPT widget schemas [3]
• xray-payload.ts — 1 call extending hostedChatSchema [4]

The fix would be to restructure the schemas so that refineHostedTokens() (which applies .superRefine()) is applied after .extend() calls rather than to the base schema that others extend from. For example, extract the plain unrefined base shape first, use .extend() on that, and then apply refineHostedTokens() to each final/leaf schema individually. Alternatively, z.intersection() / .and() could be used instead of .extend().

As a workaround, you can pin to an older version that still uses Zod v3 behavior:

npx @mcpjam/inspector@1.5.6

(though that version had other packaging issues — you may need to try a few recent versions to find one that works for your setup).

To reply, just mention @dosu.

---

^{How did I do? Good | Irrelevant | Incorrect | Verbose | Hallucination | Report 🐛 | Other}