chore: import upstream snapshot with attribution

tests/unit/compression/rtk-deduplicator.test.ts

@@ -0,0 +1,21 @@
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import { deduplicateRepeatedLines } from "../../../open-sse/services/compression/engines/rtk/deduplicator.ts";
+
+describe("RTK deduplicator", () => {
+  it("collapses consecutive repeated lines with counters", () => {
+    const result = deduplicateRepeatedLines(["same", "same", "same", "tail"].join("\n"), {
+      threshold: 3,
+    });
+
+    assert.equal(result.collapsed, 2);
+    assert.ok(result.text.includes("[line repeated 2x]"));
+    assert.ok(result.text.includes("[rtk:dropped 2 repeated lines]"));
+  });
+
+  it("honors configurable threshold", () => {
+    assert.equal(deduplicateRepeatedLines("a\na", { threshold: 3 }).collapsed, 0);
+    assert.equal(deduplicateRepeatedLines("a\na", { threshold: 2 }).collapsed, 1);
+  });
+});