fix(compression): keep lite from truncating the latest tool results

changelog.d/fixes/15037-lite-current-turn.md

@@ -0,0 +1 @@
+- **fix(compression):** Lite no longer truncates the results of the latest tool calls, so OpenAI-format agents (Cursor IDE, Kilo/OpenCode) stop re-reading a file whose content was cut to 2000 characters every time ([#15037](https://github.com/diegosouzapw/OmniRoute/pull/15037)).

open-sse/services/compression/lite.ts

@@ -154,8 +154,14 @@ export function compressToolResults(
 } {
   if (!body.messages) return { body, applied: false };
   const MAX_TOOL_LENGTH = resolveLiteMaxToolLength(options.maxToolLength);
+  // Results of the latest tool calls (after the last assistant message) are
+  // what the model asked for this turn. Cutting them makes it re-read the same
+  // file forever, since every re-read is cut again.
+  const lastAssistant = body.messages.findLastIndex((msg) => msg.role === "assistant");
+  const currentTurnStart = lastAssistant === -1 ? body.messages.length : lastAssistant + 1;
   let applied = false;
-  const messages = body.messages.map((msg) => {
+  const messages = body.messages.map((msg, index) => {
+    if (index >= currentTurnStart) return msg;
     if (msg.role !== "tool" || typeof msg.content !== "string") return msg;
     if (msg.content.length <= MAX_TOOL_LENGTH) return msg;
     applied = true;

tests/unit/compression/lite-current-turn.test.ts

@@ -0,0 +1,87 @@
+/**
+ * Lite must not truncate the results of the latest tool calls (the tool
+ * messages after the last assistant message). The model asked for that content
+ * this turn; cutting it to 2000 chars left it re-reading the same file forever,
+ * because every re-read was cut (or deduped against the cut copy) again.
+ * Run: node --import tsx/esm --test tests/unit/compression/lite-current-turn.test.ts
+ */
+
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import { compressToolResults } from "../../../open-sse/services/compression/lite.ts";
+import { applyCompression } from "../../../open-sse/services/compression/strategySelector.ts";
+
+const FILE = Array.from({ length: 400 }, (_, i) => `${i + 1}: def metric_${i}(x): return x`).join(
+  "\n"
+);
+
+type Msg = { role: string; content: string | null; [key: string]: unknown };
+
+function readCall(id: string): Msg {
+  return {
+    role: "assistant",
+    content: null,
+    tool_calls: [
+      { id, type: "function", function: { name: "read", arguments: '{"filePath":"/s.py"}' } },
+    ],
+  };
+}
+
+describe("lite tool-result truncation and the current turn", () => {
+  it("keeps the newest tool result whole", () => {
+    const { body } = compressToolResults({
+      messages: [
+        { role: "user", content: "read it" },
+        readCall("c1"),
+        { role: "tool", tool_call_id: "c1", content: FILE },
+      ],
+    });
+    assert.equal(body.messages![2].content, FILE);
+  });
+
+  it("still truncates tool results from earlier turns", () => {
+    const { body, applied } = compressToolResults({
+      messages: [
+        { role: "user", content: "read it" },
+        readCall("c1"),
+        { role: "tool", tool_call_id: "c1", content: FILE },
+        readCall("c2"),
+        { role: "tool", tool_call_id: "c2", content: FILE },
+      ],
+    });
+    assert.equal(applied, true);
+    assert.match(String(body.messages![2].content), /\.\.\.\[truncated\]$/);
+    assert.equal(body.messages![4].content, FILE);
+  });
+
+  it("keeps a re-read whole through the default session-dedup + lite pipeline", () => {
+    const result = applyCompression(
+      {
+        messages: [
+          { role: "user", content: "read it" },
+          readCall("c1"),
+          { role: "tool", tool_call_id: "c1", content: FILE },
+          readCall("c2"),
+          { role: "tool", tool_call_id: "c2", content: FILE },
+        ],
+      },
+      "stacked",
+      {
+        config: {
+          enabled: true,
+          defaultMode: "off",
+          autoTriggerTokens: 0,
+          cacheMinutes: 5,
+          preserveSystemPrompt: true,
+          comboOverrides: {},
+          engines: {},
+          activeComboId: null,
+          stackedPipeline: [{ engine: "session-dedup" }, { engine: "lite" }],
+        },
+      }
+    );
+    const messages = result.body.messages as Msg[];
+    assert.equal(messages[4].content, FILE);
+  });
+});