Follow-up: tools with a non-object `inputSchema` are not callable over MCP (argument wrapping needed)

[V3RON]

Split out of #26.

Problem

MCP tools/call arguments are always a JSON object (CallToolRequest.params.arguments is Record<string, unknown> in the SDK), and Tool.inputSchema.type must be the literal "object". Cordierite lets an app register inputSchema: z.string() or z.array(...); the app then validates the incoming args against that schema (packages/react-native/src/client/tool-invocation.ts:143).

After #26 the MCP server falls back to an empty object schema for such tools so tools/list keeps working, but an agent's {} arguments still fail the app's validation, so the tool is effectively uncallable from MCP. The CLI (invoke --input '"text"') and cordierite/client are unaffected because they pass the raw value through the daemon.

Options

1. Wrap in the MCP layer only: emit inputSchema: { type: "object", properties: { value: <real schema> }, required: ["value"] } and unwrap arguments.value in server.ts before calling the daemon. Keeps the wire and CLI unchanged. Needs a marker so the unwrap only applies to tools that were wrapped.
2. Restrict at registration: dev-time error in registerTool when the exported input schema is not object-rooted, pointing users at z.object({ value: ... }). Simplest, but a breaking dev-time change.

Recommend option 2 unless there is a known consumer relying on non-object inputs, since option 1 hides a shape difference the CLI user will still see.

Acceptance

• Either wrapped calls work end to end over MCP with a test, or registerTool rejects non-object input schemas in dev with a test, and the README documents the rule.