[moetemp]

What changed?

This PR adds @nexus.helper, which lets a helper of the support package implement a resource method.

/// @nexus.function signature="record-predicate"
type read-predicate = placeholder;

/// @nexus.helper python="take_stream"
take: func(timeout: duration, until: option<read-predicate>) -> stream-read;

• The method binds no operation. Its generated body calls the helper with the resource and the method's parameters.
• A parameter can be a function of the caller. Its alias uses @nexus.function, and the function stays in the process. A signature function is no longer an operation.
• A record that only helper methods reach never goes on the wire. So it is a plain model, and it can hold proto-backed records.
• targets limits a helper method to one target. Only Python takes a helper, and the other languages leave the method out.
• The stream sample gets take and filter on both Stream classes.

Why?

The Stream API needs methods that are not one wire operation. A take reads many pages in one call and stops at a predicate of the caller. The SDK's support package does that work, and nexgen couldn't generate a method for it.

How did you test it?

cargo validate passes. The stream tests check that each Stream has the methods, that each passes its arguments to its helper, and that a typed use type-checks. A fixture checks the error for @nexus.helper together with @nexus.operation.

Link to a test plan if any -

• Unit Tests
• Staging
• End to End Tests