chore: import upstream snapshot with attribution

tests/unit/compression-header-echo-6422.test.ts

@@ -0,0 +1,89 @@
+/**
+ * #6422 — X-OmniRoute-Compression response header echo.
+ *
+ * Docs promise that when a request supplies `x-omniroute-compression`, the response
+ * echoes `X-OmniRoute-Compression: <mode>; source=<source>`. Internal early-returns
+ * (idempotency-cache short-circuit, some combo/fusion assembly paths) omit that
+ * header, so the outermost route layer echoes a best-effort value from the request.
+ * These tests lock the helper's contract so a future refactor cannot silently drop
+ * the echo again.
+ */
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import {
+  readCompressionRequestHeader,
+  withCompressionHeaderEcho,
+} from "../../src/shared/utils/compressionHeaderEcho";
+
+function makeRequest(headerValue: string | null): {
+  headers: { get(name: string): string | null };
+} {
+  return {
+    headers: {
+      get(name: string) {
+        if (name.toLowerCase() === "x-omniroute-compression") return headerValue;
+        return null;
+      },
+    },
+  };
+}
+
+describe("compressionHeaderEcho (#6422)", () => {
+  it("reads the request header (case-insensitive, trimmed)", () => {
+    assert.equal(readCompressionRequestHeader(makeRequest("engine:rtk")), "engine:rtk");
+    assert.equal(readCompressionRequestHeader(makeRequest("  off  ")), "  off  ");
+    assert.equal(readCompressionRequestHeader(makeRequest(null)), null);
+    assert.equal(readCompressionRequestHeader(makeRequest("")), null);
+    assert.equal(readCompressionRequestHeader(makeRequest("   ")), null);
+  });
+
+  it("echoes the request header value onto the response when missing", () => {
+    const inner = new Response("body", { status: 200 });
+    const wrapped = withCompressionHeaderEcho(inner, "engine:rtk");
+    assert.equal(wrapped.headers.get("X-OmniRoute-Compression"), "engine:rtk; source=request-header");
+    assert.equal(wrapped.status, 200);
+  });
+
+  it("normalizes off / default / engine:* to lowercase", () => {
+    assert.equal(
+      withCompressionHeaderEcho(new Response(""), "OFF").headers.get("X-OmniRoute-Compression"),
+      "off; source=request-header"
+    );
+    assert.equal(
+      withCompressionHeaderEcho(new Response(""), "Default").headers.get("X-OmniRoute-Compression"),
+      "default; source=request-header"
+    );
+    assert.equal(
+      withCompressionHeaderEcho(new Response(""), "Engine:Rtk").headers.get(
+        "X-OmniRoute-Compression"
+      ),
+      "engine:rtk; source=request-header"
+    );
+  });
+
+  it("preserves operator casing on named-combo values", () => {
+    const wrapped = withCompressionHeaderEcho(new Response(""), "  MyCombo  ");
+    assert.equal(wrapped.headers.get("X-OmniRoute-Compression"), "MyCombo; source=request-header");
+  });
+
+  it("never overwrites an existing X-OmniRoute-Compression header set by the inner pipeline", () => {
+    const inner = new Response("", {
+      headers: {
+        "X-OmniRoute-Compression": "stacked; source=routing; tokens=100->42; rules: rtk-nl x2",
+      },
+    });
+    const wrapped = withCompressionHeaderEcho(inner, "engine:rtk");
+    assert.equal(
+      wrapped.headers.get("X-OmniRoute-Compression"),
+      "stacked; source=routing; tokens=100->42; rules: rtk-nl x2"
+    );
+  });
+
+  it("is a no-op when the request did not supply the header", () => {
+    const inner = new Response("", { headers: { "X-Other": "keep" } });
+    const wrapped = withCompressionHeaderEcho(inner, null);
+    assert.equal(wrapped, inner);
+    assert.equal(wrapped.headers.get("X-OmniRoute-Compression"), null);
+    assert.equal(wrapped.headers.get("X-Other"), "keep");
+  });
+});