test(compaction): cover staged pruning

src/agents/compaction.test.ts

@@ -30,6 +30,20 @@ describe("splitMessagesByTokenShare", () => {
     expect(parts[1]?.length).toBeGreaterThan(0);
     expect(parts.flat().length).toBe(messages.length);
   });
+
+  it("preserves message order across parts", () => {
+    const messages: AgentMessage[] = [
+      makeMessage(1, 4000),
+      makeMessage(2, 4000),
+      makeMessage(3, 4000),
+      makeMessage(4, 4000),
+      makeMessage(5, 4000),
+      makeMessage(6, 4000),
+    ];
+
+    const parts = splitMessagesByTokenShare(messages, 3);
+    expect(parts.flat().map((msg) => msg.timestamp)).toEqual(messages.map((msg) => msg.timestamp));
+  });
 });
 
 describe("pruneHistoryForContextShare", () => {
@@ -53,6 +67,29 @@ describe("pruneHistoryForContextShare", () => {
     expect(pruned.messages.length).toBeGreaterThan(0);
   });
 
+  it("keeps the newest messages when pruning", () => {
+    const messages: AgentMessage[] = [
+      makeMessage(1, 4000),
+      makeMessage(2, 4000),
+      makeMessage(3, 4000),
+      makeMessage(4, 4000),
+      makeMessage(5, 4000),
+      makeMessage(6, 4000),
+    ];
+    const totalTokens = estimateMessagesTokens(messages);
+    const maxContextTokens = Math.max(1, Math.floor(totalTokens * 0.5)); // budget = 25%
+    const pruned = pruneHistoryForContextShare({
+      messages,
+      maxContextTokens,
+      maxHistoryShare: 0.5,
+      parts: 2,
+    });
+
+    const keptIds = pruned.messages.map((msg) => msg.timestamp);
+    const expectedSuffix = messages.slice(-keptIds.length).map((msg) => msg.timestamp);
+    expect(keptIds).toEqual(expectedSuffix);
+  });
+
   it("keeps history when already within budget", () => {
     const messages: AgentMessage[] = [makeMessage(1, 1000)];
     const maxContextTokens = 2000;