Pin zig version to 0.16 LTS

build.zig

@@ -1,6 +1,24 @@
 const std = @import("std");
+const builtin = @import("builtin");
+
+/// danos is developed against Zig 0.16.x. Pre-1.0 Zig makes breaking API changes
+/// between minor releases, and the .zon's `minimum_zig_version` only enforces a
+/// floor — so reject anything off the 0.16 line to keep the build reproducible.
+fn ensureZigVersion() void {
+    const v = builtin.zig_version;
+    if (v.major != 0 or v.minor != 16) {
+        std.debug.print(
+            "danos requires Zig 0.16.x, but this is {d}.{d}.{d}. " ++
+                "Zig makes breaking changes between minor releases pre-1.0.\n",
+            .{ v.major, v.minor, v.patch },
+        );
+        std.process.exit(1);
+    }
+}
 
 pub fn build(b: *std.Build) void {
+    ensureZigVersion();
+
     const target = b.standardTargetOptions(.{});
     const optimize = b.standardOptimizeOption(.{});