fix(server): handle ZodObject in RegisteredTool.update (#1960)

[MukundaKatta]

Fixes #1960.

RegisteredTool.update({ paramsSchema }) crashes with TypeError: Cannot read properties of null (reading '_zod') when paramsSchema is a ZodObject (e.g. z.object({...}).passthrough()) instead of a raw shape.

Why

The create path in _createRegisteredTool uses getZodSchemaObject(), which handles both raw shapes and ZodObject instances:

function getZodSchemaObject(schema) {
    if (!schema) return undefined;
    if (isZodRawShapeCompat(schema)) return objectFromShape(schema);
    return schema;
}

The update path was calling objectFromShape() directly. objectFromShape does Object.values(shape), which on a ZodObject iterates internal fields like _cached (which is null), and downstream isZ4Schema(null) accesses null._zod and throws.

Fix

• In RegisteredTool.update, route paramsSchema and outputSchema through getZodSchemaObject() (the same helper the create path uses) instead of objectFromShape() directly.
• Widen the update<InputArgs, OutputArgs> generic constraints from ZodRawShapeCompat to ZodRawShapeCompat | AnySchema, matching registerTool. This resolves the type-level inconsistency mentioned in the issue.

Net diff is ~3 lines of code; no new public API.

Test

Added should update tool with ZodObject paramsSchema in test/server/mcp.test.ts. It registers a tool with z.object({...}).passthrough(), updates it with a fresh ZodObject, and asserts tool.update(...) does not throw and the new schema is reflected in tools/list and the call result. The test runs under the existing zodTestMatrix, so it covers both Zod v3 and v4.

Reproduction (before this PR)

const schema = z.object({ id: z.string() }).passthrough();
const tool = server.registerTool('my_tool', { description: 'test', inputSchema: schema }, async () => ({ content: [{ type: 'text', text: 'ok' }] }));
tool.update({ paramsSchema: schema });
// TypeError: Cannot read properties of null (reading '_zod')

After the patch this is a no-op update with no crash.

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