Web UI: show Compaction divider in chat history (#11341)

src/gateway/session-utils.fs.test.ts

@@ -5,6 +5,7 @@ import { afterEach, beforeEach, describe, expect, test } from "vitest";
 import {
   readFirstUserMessageFromTranscript,
   readLastMessagePreviewFromTranscript,
+  readSessionMessages,
   readSessionPreviewItemsFromTranscript,
 } from "./session-utils.fs.js";
 
@@ -343,6 +344,53 @@ describe("readLastMessagePreviewFromTranscript", () => {
   });
 });
 
+describe("readSessionMessages", () => {
+  let tmpDir: string;
+  let storePath: string;
+
+  beforeEach(() => {
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), "openclaw-session-fs-test-"));
+    storePath = path.join(tmpDir, "sessions.json");
+  });
+
+  afterEach(() => {
+    fs.rmSync(tmpDir, { recursive: true, force: true });
+  });
+
+  test("includes synthetic compaction markers for compaction entries", () => {
+    const sessionId = "test-session-compaction";
+    const transcriptPath = path.join(tmpDir, `${sessionId}.jsonl`);
+    const lines = [
+      JSON.stringify({ type: "session", version: 1, id: sessionId }),
+      JSON.stringify({ message: { role: "user", content: "Hello" } }),
+      JSON.stringify({
+        type: "compaction",
+        id: "comp-1",
+        timestamp: "2026-02-07T00:00:00.000Z",
+        summary: "Compacted history",
+        firstKeptEntryId: "x",
+        tokensBefore: 123,
+      }),
+      JSON.stringify({ message: { role: "assistant", content: "World" } }),
+    ];
+    fs.writeFileSync(transcriptPath, lines.join("\n"), "utf-8");
+
+    const out = readSessionMessages(sessionId, storePath);
+    expect(out).toHaveLength(3);
+    const marker = out[1] as {
+      role: string;
+      content?: Array<{ text?: string }>;
+      __openclaw?: { kind?: string; id?: string };
+      timestamp?: number;
+    };
+    expect(marker.role).toBe("system");
+    expect(marker.content?.[0]?.text).toBe("Compaction");
+    expect(marker.__openclaw?.kind).toBe("compaction");
+    expect(marker.__openclaw?.id).toBe("comp-1");
+    expect(typeof marker.timestamp).toBe("number");
+  });
+});
+
 describe("readSessionPreviewItemsFromTranscript", () => {
   let tmpDir: string;
   let storePath: string;

src/gateway/session-utils.fs.ts

@@ -28,6 +28,23 @@ export function readSessionMessages(
       const parsed = JSON.parse(line);
       if (parsed?.message) {
         messages.push(parsed.message);
+        continue;
+      }
+
+      // Compaction entries are not "message" records, but they're useful context for debugging.
+      // Emit a lightweight synthetic message that the Web UI can render as a divider.
+      if (parsed?.type === "compaction") {
+        const ts = typeof parsed.timestamp === "string" ? Date.parse(parsed.timestamp) : Number.NaN;
+        const timestamp = Number.isFinite(ts) ? ts : Date.now();
+        messages.push({
+          role: "system",
+          content: [{ type: "text", text: "Compaction" }],
+          timestamp,
+          __openclaw: {
+            kind: "compaction",
+            id: typeof parsed.id === "string" ? parsed.id : undefined,
+          },
+        });
       }
     } catch {
       // ignore bad lines