https://asciinema.org/a/dJ8iLKpje6fsJygM8r1qw5e6M

example.c

#include "zp.h"
#include <string.h>
#include <unistd.h>

int main(int argc, char **argv) {
    zp_node root_node = zp_init();

    const char *task_name = "making orange juice";
    zp_node sub_node = zp_start(root_node, task_name, strlen(task_name), 5);
    for (int i = 0; i < 5; i += 1) {
        zp_complete_one(sub_node);
        sleep(1);
    }
    zp_end(sub_node);
    zp_end(root_node);
}

zp.h

#include <stdint.h>
#include <stddef.h>

typedef uint8_t zp_node;

zp_node zp_init(void);
zp_node zp_start(zp_node parent, const char *name_ptr, size_t name_len, size_t estimated_total);
zp_node zp_end(zp_node node);
zp_node zp_complete_one(zp_node node);

zp.zig

const std = @import("std");

export fn zp_init() std.Progress.Node.OptionalIndex {
    return std.Progress.start(.{}).index;
}

export fn zp_start(
    parent: std.Progress.Node.OptionalIndex,
    name_ptr: [*]const u8,
    name_len: usize,
    estimated_total_items: usize,
) std.Progress.Node.OptionalIndex {
    const node: std.Progress.Node = .{ .index = parent };
    return node.start(name_ptr[0..name_len], estimated_total_items).index;
}

export fn zp_end(node_index: std.Progress.Node.OptionalIndex) void {
    const node: std.Progress.Node = .{ .index = node_index };
    node.end();
}

export fn zp_complete_one(node_index: std.Progress.Node.OptionalIndex) void {
    const node: std.Progress.Node = .{ .index = node_index };
    node.completeOne();
}

pub const _start = void;