fix(memory): remove Zod-based outputSchema to fix serialization failures

[ianliuy]

What's broken?

The memory server's tool definitions pass Zod schema objects directly to outputSchema, which violates the MCP spec requiring plain JSON Schema objects. This causes _zod serialization errors when the tools/list endpoint serializes schemas to JSON-RPC responses.

Who is affected?

Projects using the npm @modelcontextprotocol/sdk directly (rather than Claude Desktop's bundled SDK) encounter serialization failures when calling tools/list or invoking tools with outputSchema defined.

Root cause

outputSchema fields use Zod raw shapes like:

outputSchema: {
  entities: z.array(EntitySchema),
  relations: z.array(RelationSchema)
}

The MCP spec requires these to be plain JSON Schema objects.

Why not just replace with plain JSON Schema?

I investigated replacing Zod schemas with hand-written JSON Schema objects (the approach suggested in the issue). However, the current SDK (v1.26.0–1.29.0) cannot accept plain JSON Schema for outputSchema:

1. tools/list silently drops it — normalizeObjectSchema() returns undefined for non-Zod objects, so outputSchema never appears in the response
2. Tool calls crash — validateToolOutput() calls safeParseAsync(undefined, ...) which throws Cannot read properties of undefined (reading '_zod')

This is a TypeScript SDK limitation, not a spec issue. Until the SDK adds native JSON Schema passthrough for outputSchema, the safest fix is to remove it entirely.

Fix

Remove outputSchema and structuredContent from all 9 tool registrations. Tools continue to return data via the content array (JSON text), preserving full functionality. The only change is that tools/list no longer advertises output schemas for these tools.

Testing

• npm run build passes (TypeScript compilation clean)
• Verified at runtime that tools still return correct JSON data via content
• Verified that removing outputSchema skips output validation (no crashes)

Fixes #3622