Request schemas should use additionalProperties: false

[bokelley]

Problem

Request schemas use additionalProperties: true (or omit it, defaulting to true). This causes json-schema-to-typescript to generate index signatures ({ [k: string]: unknown }) alongside named properties, producing TypeScript intersection types. When converted to Zod, these become ZodIntersection which loses .shape — breaking server.tool(name, schema.shape, handler).

We work around this with post-processing (postProcessRecordIntersections) but the root cause is in the schemas.

Proposal

Set additionalProperties: false on all request schemas. Agents send structured tool calls — there's no reason to accept arbitrary keys. Response schemas can remain open (agents may return platform-specific fields).

Discovered during createAdcpServer implementation (adcontextprotocol/adcp-client#541).

[bokelley]

Closing this — additionalProperties: false on request schemas breaks forward compatibility.

A v3.1 buyer sending a new optional field to a v3.0 seller would get a validation error instead of the field being silently ignored. That's the opposite of graceful degradation and makes minor version upgrades non-backward-compatible.

The root cause (open schemas producing ZodIntersection without .shape) is real but belongs in adcp-client's codegen layer, not the protocol schemas. The postProcessRecordIntersections workaround is the right fix at the right layer.