[Bug]: Proxied MCP server tools fail to load when inputSchema declares a draft 2020-12 $schema #1477

Problem

getMCPServerTools() (src/mcp/proxy.ts) compiles each proxied tool's inputSchema with the shared AJV instance, which only has the draft-07 meta-schema. When a tool's inputSchema declares "$schema": "https://json-schema.org/draft/2020-12/schema", compilation throws and none of the Actor's tools load, not just that one tool.

Zod 4 toJSONSchema() adds this $schema, so TypeScript MCP servers that use Zod 4 run into this. MCP 2025-11-25 makes 2020-12 the default dialect for tool schemas.

Regular Actor tools are not affected because buildActorInputSchema() already removes $schema.

Evidence

Hosted server log, 2026-10-04:

ERROR {"actorFullName":"lexxer/transcriptpack-youtube-transcripts","actorId":"g4kWYLgKjbOSH30qB","error":{"message":"no schema with key or ref \"https://json-schema.org/draft/2020-12/schema\"","name":"Error","stack":"Error: no schema with key or ref ...\n    at Ajv.validate ...\n    at Ajv.validateSchema ..."},"msg":"Failed to load tools from MCP server"}

To reproduce, call getMCPServerTools() with a mock client whose listTools() returns one tool with that $schema. It throws the same error.

Affected

Any Actor MCP server whose tool schemas declare a draft other than 07. This happens in both stdio and hosted mode. Adding such an Actor as a tool loads none of its tools.

Expected

The Actor's tools load and their input is validated.

Found in production logs. Drafted and reproduced with Claude Code.