test(server): retain compacted rewind diagnostic

Reproduces stale compaction references through the current transcript-store path. Native resume of the synthetic source, fork, and repaired control succeeds, so this is not evidence of the reported context overflow.

Co-authored-by: kesiyuan <kesiyuan@bytedance.com>

packages/server/src/server/agent/providers/claude/rewind-compaction.local.e2e.test.ts

@@ -0,0 +1,86 @@
+import { mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import path from "node:path";
+import { expect, test } from "vitest";
+import { realClaudeRewindSdk, revertClaudeConversation } from "./rewind.js";
+
+interface TranscriptEntry {
+  uuid: string;
+  sessionId: string;
+  subtype?: string;
+  forkedFrom?: { messageUuid: string };
+  compactMetadata?: {
+    preservedSegment: {
+      headUuid: string;
+      anchorUuid: string;
+      tailUuid: string;
+    };
+    preservedMessages: {
+      anchorUuid: string;
+      uuids: string[];
+      allUuids: string[];
+    };
+  };
+}
+
+function parseEntries(text: string): TranscriptEntry[] {
+  return text
+    .trim()
+    .split("\n")
+    .map((line) => JSON.parse(line) as TranscriptEntry);
+}
+
+// Fixture from PR #3938, commit 374b08f9d56d9dabc62f8e4e01acc73d1c619548.
+// This proves stale metadata, not the reported model context overflow.
+test("keeps compaction references attached to forked messages", async () => {
+  const root = await mkdtemp(path.join(process.cwd(), ".compacted-rewind-"));
+  try {
+    const fixture = await readFile(
+      new URL(
+        "./test-fixtures/issue-3837-compacted-session.jsonl",
+        import.meta.url
+      ),
+      "utf8"
+    );
+    const entries = parseEntries(fixture);
+    const sourceSessionId = entries[0]!.sessionId;
+    const transcriptPath = path.join(root, `${sourceSessionId}.jsonl`);
+    await writeFile(transcriptPath, fixture);
+    let forkId = sourceSessionId;
+    await revertClaudeConversation({
+      sdk: realClaudeRewindSdk,
+      sessionId: sourceSessionId,
+      transcriptPath,
+      messageId: entries.at(-1)!.uuid,
+      setSessionId: (id) => {
+        forkId = id;
+      },
+    });
+    const fork = parseEntries(
+      await readFile(path.join(root, `${forkId}.jsonl`), "utf8")
+    );
+    const ids = new Map(
+      fork.map((entry) => [entry.forkedFrom?.messageUuid, entry.uuid])
+    );
+    const remap = (id: string) => ids.get(id) ?? id;
+    const source = entries.find(
+      (entry) => entry.subtype === "compact_boundary"
+    )!.compactMetadata!;
+    const actual = fork.find((entry) => entry.subtype === "compact_boundary")!
+      .compactMetadata!;
+    expect(actual).toEqual({
+      ...source,
+      preservedSegment: {
+        headUuid: remap(source.preservedSegment.headUuid),
+        anchorUuid: remap(source.preservedSegment.anchorUuid),
+        tailUuid: remap(source.preservedSegment.tailUuid),
+      },
+      preservedMessages: {
+        anchorUuid: remap(source.preservedMessages.anchorUuid),
+        uuids: source.preservedMessages.uuids.map(remap),
+        allUuids: source.preservedMessages.allUuids.map(remap),
+      },
+    });
+  } finally {
+    await rm(root, { recursive: true, force: true });
+  }
+});

packages/server/src/server/agent/providers/claude/test-fixtures/issue-3837-compacted-session.jsonl

@@ -0,0 +1,6 @@
+{"type":"user","uuid":"10000000-0000-4000-8000-000000000002","parentUuid":null,"isSidechain":false,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z","message":{"role":"user","content":"Before compaction"}}
+{"type":"assistant","uuid":"10000000-0000-4000-8000-000000000003","parentUuid":"10000000-0000-4000-8000-000000000002","isSidechain":false,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z","message":{"role":"assistant","content":[{"type":"text","text":"Done"}]}}
+{"type":"system","subtype":"stop_hook_summary","uuid":"10000000-0000-4000-8000-000000000004","parentUuid":"10000000-0000-4000-8000-000000000003","isSidechain":false,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z"}
+{"type":"system","subtype":"compact_boundary","uuid":"10000000-0000-4000-8000-000000000005","parentUuid":null,"logicalParentUuid":"10000000-0000-4000-8000-000000000004","isSidechain":false,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z","compactMetadata":{"trigger":"auto","preTokens":900000,"preservedSegment":{"headUuid":"10000000-0000-4000-8000-000000000003","anchorUuid":"10000000-0000-4000-8000-000000000006","tailUuid":"10000000-0000-4000-8000-000000000004"},"preservedMessages":{"anchorUuid":"10000000-0000-4000-8000-000000000006","uuids":["10000000-0000-4000-8000-000000000003","10000000-0000-4000-8000-000000000004"],"allUuids":["10000000-0000-4000-8000-000000000003","10000000-0000-4000-8000-000000000008","10000000-0000-4000-8000-000000000004"]},"postTokens":10000}}
+{"type":"user","uuid":"10000000-0000-4000-8000-000000000006","parentUuid":"10000000-0000-4000-8000-000000000005","isSidechain":false,"isCompactSummary":true,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z","message":{"role":"user","content":"Compacted summary"}}
+{"type":"user","uuid":"10000000-0000-4000-8000-000000000007","parentUuid":"10000000-0000-4000-8000-000000000006","isSidechain":false,"sessionId":"10000000-0000-4000-8000-000000000001","timestamp":"2026-08-27T08:00:00.000Z","message":{"role":"user","content":"Continue after compaction"}}