test(compression): verify unchanged-history prefix reuse

changelog.d/maintenance/18304-live-zone-history-regression-coverage.md

@@ -0,0 +1 @@
+- **test(compression):** cover unchanged live-zone histories for both Chat Completions `messages` and Responses `input`: frozen-prefix reuse, current request controls, no needless compressor call, and fail-open to full compression when `instructions` change. Regression coverage for existing behavior, with no production change ([#18304](https://github.com/cheaper-inference/OmniRoute/pull/18304)) — thanks @aldoeliacim

tests/unit/compression/live-zone.test.ts

@@ -257,4 +257,56 @@ describe("cache-aligned live-zone compression", () => {
     assert.equal((calls[1].messages as unknown[]).length, 2);
     assert.equal(getLiveZoneCacheStats().entries, 0);
   });
+
+  for (const field of ["messages", "input"] as const) {
+    it(`preserves an unchanged ${field} history and current request controls`, async () => {
+      const calls: Array<Record<string, unknown>> = [];
+      const compress = toolCompressor(calls);
+      const first = {
+        model: "synthetic-model",
+        stream: false,
+        max_output_tokens: 1024,
+        reasoning: { effort: "medium" },
+        instructions: "stable instructions",
+        [field]: [
+          { role: "user", content: "user turn" },
+          { role: "tool", content: "tool output" },
+        ],
+      };
+      const firstResult = await applyLiveZoneCompression(first, options, compress);
+      const repeated = { ...first, stream: true, max_output_tokens: 2048 };
+      const unchangedResult = await applyLiveZoneCompression(repeated, options, compress);
+
+      assert.equal(calls.length, 1, "unchanged history must not rerun the compressor");
+      assert.deepEqual(unchangedResult.body, {
+        ...repeated,
+        [field]: firstResult.body[field],
+      });
+      assert.deepEqual(unchangedResult.stats?.liveZone, {
+        cacheHit: true,
+        frozenItems: first[field].length,
+        liveItems: 0,
+      });
+    });
+
+    it(`recompresses an unchanged ${field} history when instructions change`, async () => {
+      const calls: Array<Record<string, unknown>> = [];
+      const compress = toolCompressor(calls);
+      const first = {
+        instructions: "stable instructions",
+        [field]: [
+          { role: "user", content: "user turn" },
+          { role: "tool", content: "tool output" },
+        ],
+      };
+      await applyLiveZoneCompression(first, options, compress);
+      const edited = { ...first, instructions: "edited instructions" };
+      const editedResult = await applyLiveZoneCompression(edited, options, compress);
+
+      assert.equal(calls.length, 2, "changed instructions must not reuse the frozen prefix");
+      assert.equal(calls[1].instructions, "edited instructions");
+      assert.deepEqual(calls[1][field], first[field]);
+      assert.equal(editedResult.body.instructions, "edited instructions");
+    });
+  }
 });