TypeError: e.custom is not a function in Deno environments (v1.23.0)

[tonxxd]

Version 1.23.0 of @modelcontextprotocol/sdk causes a runtime error when deployed to Deno environments (like Supabase Edge Functions) and loaded via esm.sh. The error manifests as:

TypeError: e.custom is not a function
 at https://esm.sh/@modelcontextprotocol/sdk@1.23.0/denonext/server.mjs:2:879

• SDK Version: @modelcontextprotocol/sdk@1.23.0
• Last Tested Working Version: 1.22.0

Full Error Message:

event loop error: TypeError: e.custom is not a function
 at https://esm.sh/@modelcontextprotocol/sdk@1.23.0/denonext/server.mjs:2:879

Metadata:

{
 "boot_time": null,
 "cpu_time_used": null,
 "deployment_id": "***-1128-40b3-beb9-407d0f792249_1",
 "event_type": "UncaughtException",
 "execution_id": "d87ff15d-c9bd-44b5-bd1e-0268e10cc797",
 "function_id": "daeab985-1128-40b3-beb9-407d0f792249",
 "level": "error",
 "memory_used": [],
 "project_ref": "****",
 "reason": null,
 "region": "eu-central-1",
 "served_by": "supabase-edge-runtime-1.69.25 (compatible with Deno v2.1.4)",
 "timestamp": "2025-11-27T13:39:44.249Z",
 "version": "1"
}

[tonxxd]

it seem the issue could be that 1.23.0 introduces new files that break Deno compatibility:

• server/zod-compat.js - Attempts to import zod/v3 and zod/v4-mini subpaths
• These subpath imports fail in Deno when loaded via esm.sh

New Files

• dist/esm/server/zod-compat.js
• dist/esm/server/zod-compat.d.ts
• dist/esm/server/zod-json-schema-compat.js
• dist/esm/server/zod-json-schema-compat.d.ts

[KKonstantinov]

Got this on the queue for merging. Closing this for now.