002 phantom transition

// TEST: Auto-synthesized proc for phantom state transitions
//
// The core use case: state transitions where only the phantom type changes.
// The proc just passes through the pointer - zero runtime cost.

const std = @import("std");

const Resource = struct { value: i32 };

// Create resource - has a proc (does real work)
~pub event create { value: i32 }
| created *Resource[state_a!]

~proc create {
    const r = std.heap.page_allocator.create(Resource) catch unreachable;
    r.* = Resource{ .value = value };
    return .{ .created = r };
}

// Transition from state_a to state_b - NO PROC NEEDED
// Input and output have same shape (r: *Resource), just different phantom
// Compiler should synthesize: return .{ .transitioned = r };
~pub event transition { r: *Resource[!state_a] }
| transitioned *Resource[state_b!]

// Cleanup state_b - has a proc (does real work)
~pub event cleanup { r: *Resource[!state_b] }

~proc cleanup {
    std.debug.print("cleaned up resource with value {d}\n", .{r.value});
    std.heap.page_allocator.destroy(r);
}

// Test it
~create(value: 99)
| created c |> transition(r: c)
    | transitioned t |> cleanup(r: t)