diff --git a/zigux/tests/phase1_bench_checker_selftest_contract.zig b/zigux/tests/phase1_bench_checker_selftest_contract.zig
new file mode 100644
index 00000000000000..7cb16bfd0a4fa5
--- /dev/null
+++ b/zigux/tests/phase1_bench_checker_selftest_contract.zig
@@ -0,0 +1,52 @@
+const std = @import("std");
+const testing = std.testing;
+
+fn readCheckerSource() ![]u8 {
+    return try std.Io.Dir.cwd().readFileAlloc(
+        testing.io,
+        "scripts/zigux/check-phase1-bench.py",
+        testing.allocator,
+        .limited(1024 * 1024),
+    );
+}
+
+fn expectContains(checker_source: []const u8, needle: []const u8) !void {
+    try testing.expect(std.mem.indexOf(u8, checker_source, needle) != null);
+}
+
+test "phase1 bench checker keeps self-test cli and success packet" {
+    const checker_source = try readCheckerSource();
+    defer testing.allocator.free(checker_source);
+
+    try expectContains(checker_source, "--self-test");
+    try expectContains(checker_source, "Run checker self-test cases without invoking Zig.");
+    try expectContains(checker_source, "if args.self_test:");
+    try expectContains(checker_source, "run_self_test()");
+    try expectContains(checker_source, "PHASE1_BENCH_CHECK_SELF_TEST=pass");
+    try expectContains(checker_source, "PHASE1_BENCH_CHECK_SELF_TEST_CASE_COUNT=");
+}
+
+test "phase1 bench checker self-test covers local root and source drift" {
+    const checker_source = try readCheckerSource();
+    defer testing.allocator.free(checker_source);
+
+    try expectContains(checker_source, "validate_bench_source");
+    try expectContains(checker_source, "missing_bitmap_source_markers");
+    try expectContains(checker_source, "missing_find_bit_source_markers");
+    try expectContains(checker_source, "missing_string_source_markers");
+    try expectContains(checker_source, "missing_rbtree_source_markers");
+    try expectContains(checker_source, "PHASE1_BENCH_RBTREE_CACHED_CHECKSUM");
+}
+
+test "phase1 bench checker preserves fail-closed expectation diagnostics" {
+    const checker_source = try readCheckerSource();
+    defer testing.allocator.free(checker_source);
+
+    try expectContains(checker_source, "EXPECTATIONS_JSON_ERROR={exc.msg}");
+    try expectContains(checker_source, "EXPECTATIONS_JSON_LINE={exc.lineno}");
+    try expectContains(checker_source, "EXPECTATIONS_JSON_COLUMN={exc.colno}");
+    try expectContains(checker_source, "expectations_duplicate_keys");
+    try expectContains(checker_source, "expectations_duplicate_checksums");
+    try expectContains(checker_source, "expectations_missing_exact_checksums");
+    try expectContains(checker_source, "missing_exact_checksums");
+}