MCP tools/list fails with "Date cannot be represented in JSON Schema" when a tool schema uses z.date() (Zod 4) #4939

What happens

The MCP server fails tools/list outright — clients load zero tools — whenever any tool's input schema contains a z.date() field. With trigger.dev@4.6.0:

trigger: npx trigger.dev@latest mcp - ! Connected · tools fetch failed — Date cannot be represented in JSON Schema

Reproduce directly against the CLI:

printf '%s\n' \
 '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"p","version":"1"}}}' \
 '{"jsonrpc":"2.0","method":"notifications/initialized"}' \
 '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}' \
 | npx trigger.dev@4.6.0 mcp
# -> {"jsonrpc":"2.0","id":2,"error":{"code":-32603,"message":"Date cannot be represented in JSON Schema"}}

Expected

tools/list succeeds and date fields serialize to a JSON Schema string (e.g. { "type": "string", "format": "date-time" }), matching how the Zod 3 path already handles z.date().

Root cause

In @trigger.dev/schema-to-json, convertZod4Schema() (packages/schema-to-json/src/index.ts) calls z4.toJSONSchema() without the unrepresentable option, so it defaults to "throw". Any z.date() throws Date cannot be represented in JSON Schema, which aborts the entire conversion and fails the whole tools/list response.

Version info

• Broken: trigger.dev@4.6.0 (also present on main).
• Works: 4.5.16, 4.5.0, 4.4.6.

Suggested fix

Pass unrepresentable: "any" to z4.toJSONSchema() so unrepresentable nodes emit {} and reach the existing override callback, and add a date case to override rewriting to { type: "string", format: "date-time" }. (Happy to open a PR.)