optional shape error

// Test 918d: Optional Branches - Shape Validation Error (NEGATIVE TEST)
//
// This test demonstrates:
// 1. Optional branches are STILL subject to shape checking
// 2. Handler that uses wrong payload shape on optional branch
// 3. Should FAIL compilation with shape mismatch error
// 4. Proves that "optional" means "can be omitted", NOT "can be misused"

const std = @import("std");

// Event with required + optional branches
~event process { value: u32 }
| success { result: u32 }        // REQUIRED
| ?warning { msg: []const u8 }   // OPTIONAL - has 'msg' field

~proc process {
    if (value > 100) {
        return .{ .warning = .{ .msg = "Value too large" } };
    }
    const doubled = value * 2;
    return .{ .success = .{ .result = doubled } };
}

// Handler with WRONG payload binding on optional branch
// warning branch has 'msg: []const u8' but handler tries to access 'result: u32'
// This should ERROR even though warning is optional!
~process(value: 150)
| success { result } |> std.debug.print("Success: {}\n", .{result})
| warning { result } |> std.debug.print("Warning: {}\n", .{result})
//           ^^^^^^ ERROR: warning branch has 'msg', not 'result'!