diff --git a/src/auto-reply/reply/session-fork.runtime.test.ts b/src/auto-reply/reply/session-fork.runtime.test.ts
index 6bf4e75cd44..a1254dda20b 100644
--- a/src/auto-reply/reply/session-fork.runtime.test.ts
+++ b/src/auto-reply/reply/session-fork.runtime.test.ts
@@ -3,7 +3,10 @@ import os from "node:os";
 import path from "node:path";
 import { afterEach, describe, expect, it } from "vitest";
 import type { SessionEntry } from "../../config/sessions/types.js";
-import { resolveParentForkTokenCountRuntime } from "./session-fork.runtime.js";
+import {
+  forkSessionFromParentRuntime,
+  resolveParentForkTokenCountRuntime,
+} from "./session-fork.runtime.js";
 
 const roots: string[] = [];
 
@@ -71,3 +74,136 @@ describe("resolveParentForkTokenCountRuntime", () => {
     expect(tokens).toBeGreaterThan(100_000);
   });
 });
+
+describe("forkSessionFromParentRuntime", () => {
+  it("forks the active branch without synchronously opening the session manager", async () => {
+    const root = await makeRoot("openclaw-parent-fork-");
+    const sessionsDir = path.join(root, "sessions");
+    await fs.mkdir(sessionsDir);
+    const parentSessionFile = path.join(sessionsDir, "parent.jsonl");
+    const cwd = path.join(root, "workspace");
+    await fs.mkdir(cwd);
+    const parentSessionId = "parent-session";
+    const lines = [
+      {
+        type: "session",
+        version: 3,
+        id: parentSessionId,
+        timestamp: "2026-05-01T00:00:00.000Z",
+        cwd,
+      },
+      {
+        type: "message",
+        id: "user-1",
+        parentId: null,
+        timestamp: "2026-05-01T00:00:01.000Z",
+        message: { role: "user", content: "hello" },
+      },
+      {
+        type: "message",
+        id: "assistant-1",
+        parentId: "user-1",
+        timestamp: "2026-05-01T00:00:02.000Z",
+        message: {
+          role: "assistant",
+          content: [{ type: "text", text: "hi" }],
+          api: "openai-responses",
+          provider: "openai",
+          model: "gpt-5.4",
+          stopReason: "stop",
+          timestamp: 2,
+        },
+      },
+      {
+        type: "label",
+        id: "label-1",
+        parentId: "assistant-1",
+        timestamp: "2026-05-01T00:00:03.000Z",
+        targetId: "user-1",
+        label: "start",
+      },
+    ];
+    await fs.writeFile(
+      parentSessionFile,
+      `${lines.map((entry) => JSON.stringify(entry)).join("\n")}\n`,
+      "utf-8",
+    );
+
+    const fork = await forkSessionFromParentRuntime({
+      parentEntry: {
+        sessionId: parentSessionId,
+        sessionFile: parentSessionFile,
+        updatedAt: Date.now(),
+      },
+      agentId: "main",
+      sessionsDir,
+    });
+
+    expect(fork).not.toBeNull();
+    expect(fork?.sessionFile).toContain(sessionsDir);
+    expect(fork?.sessionId).not.toBe(parentSessionId);
+    const raw = await fs.readFile(fork?.sessionFile ?? "", "utf-8");
+    const forkedEntries = raw
+      .trim()
+      .split(/\r?\n/u)
+      .map((line) => JSON.parse(line) as Record<string, unknown>);
+    const resolvedParentSessionFile = await fs.realpath(parentSessionFile);
+    expect(forkedEntries[0]).toMatchObject({
+      type: "session",
+      id: fork?.sessionId,
+      cwd,
+      parentSession: resolvedParentSessionFile,
+    });
+    expect(forkedEntries.map((entry) => entry.type)).toEqual([
+      "session",
+      "message",
+      "message",
+      "label",
+    ]);
+    expect(forkedEntries.at(-1)).toMatchObject({
+      type: "label",
+      targetId: "user-1",
+      label: "start",
+    });
+  });
+
+  it("creates a header-only child when the parent has no entries", async () => {
+    const root = await makeRoot("openclaw-parent-fork-empty-");
+    const sessionsDir = path.join(root, "sessions");
+    await fs.mkdir(sessionsDir);
+    const parentSessionFile = path.join(sessionsDir, "parent.jsonl");
+    const parentSessionId = "parent-empty";
+    await fs.writeFile(
+      parentSessionFile,
+      `${JSON.stringify({
+        type: "session",
+        version: 3,
+        id: parentSessionId,
+        timestamp: "2026-05-01T00:00:00.000Z",
+        cwd: root,
+      })}\n`,
+      "utf-8",
+    );
+
+    const fork = await forkSessionFromParentRuntime({
+      parentEntry: {
+        sessionId: parentSessionId,
+        sessionFile: parentSessionFile,
+        updatedAt: Date.now(),
+      },
+      agentId: "main",
+      sessionsDir,
+    });
+
+    expect(fork).not.toBeNull();
+    const raw = await fs.readFile(fork?.sessionFile ?? "", "utf-8");
+    const lines = raw.trim().split(/\r?\n/u);
+    expect(lines).toHaveLength(1);
+    const resolvedParentSessionFile = await fs.realpath(parentSessionFile);
+    expect(JSON.parse(lines[0] ?? "{}")).toMatchObject({
+      type: "session",
+      id: fork?.sessionId,
+      parentSession: resolvedParentSessionFile,
+    });
+  });
+});
diff --git a/src/auto-reply/reply/session-fork.runtime.ts b/src/auto-reply/reply/session-fork.runtime.ts
index 732c4fede9c..ef278cee4f0 100644
--- a/src/auto-reply/reply/session-fork.runtime.ts
+++ b/src/auto-reply/reply/session-fork.runtime.ts
@@ -1,13 +1,32 @@
 import crypto from "node:crypto";
-import fs from "node:fs";
+import fs from "node:fs/promises";
 import path from "node:path";
 import type { AgentMessage } from "@mariozechner/pi-agent-core";
-import { CURRENT_SESSION_VERSION, SessionManager } from "@mariozechner/pi-coding-agent";
+import {
+  CURRENT_SESSION_VERSION,
+  migrateSessionEntries,
+  parseSessionEntries,
+  type FileEntry,
+  type SessionEntry as PiSessionEntry,
+  type SessionHeader,
+} from "@mariozechner/pi-coding-agent";
+import { v7 as uuidv7 } from "uuid";
 import { estimateMessagesTokens } from "../../agents/compaction.js";
 import { resolveSessionFilePath } from "../../config/sessions/paths.js";
-import { resolveFreshSessionTotalTokens, type SessionEntry } from "../../config/sessions/types.js";
+import {
+  resolveFreshSessionTotalTokens,
+  type SessionEntry as StoreSessionEntry,
+} from "../../config/sessions/types.js";
 import { readSessionMessagesAsync } from "../../gateway/session-utils.fs.js";
 
+type ForkSourceTranscript = {
+  cwd: string;
+  sessionDir: string;
+  leafId: string | null;
+  branchEntries: PiSessionEntry[];
+  labelsToWrite: Array<{ targetId: string; label: string; timestamp: string }>;
+};
+
 function resolvePositiveTokenCount(value: number | undefined): number | undefined {
   return typeof value === "number" && Number.isFinite(value) && value > 0
     ? Math.floor(value)
@@ -15,7 +34,7 @@ function resolvePositiveTokenCount(value: number | undefined): number | undefine
 }
 
 export async function resolveParentForkTokenCountRuntime(params: {
-  parentEntry: SessionEntry;
+  parentEntry: StoreSessionEntry;
   storePath: string;
 }): Promise<number | undefined> {
   const freshPersistedTokens = resolveFreshSessionTotalTokens(params.parentEntry);
@@ -45,47 +64,216 @@ export async function resolveParentForkTokenCountRuntime(params: {
   return resolvePositiveTokenCount(params.parentEntry.totalTokens);
 }
 
-export function forkSessionFromParentRuntime(params: {
-  parentEntry: SessionEntry;
+function isSessionEntry(entry: FileEntry): entry is PiSessionEntry {
+  return (
+    entry.type !== "session" &&
+    typeof (entry as { id?: unknown }).id === "string" &&
+    (typeof (entry as { timestamp?: unknown }).timestamp === "string" ||
+      typeof (entry as { timestamp?: unknown }).timestamp === "number")
+  );
+}
+
+function buildEntryIndex(entries: PiSessionEntry[]): Map<string, PiSessionEntry> {
+  return new Map(entries.map((entry) => [entry.id, entry]));
+}
+
+function readBranch(params: {
+  byId: Map<string, PiSessionEntry>;
+  leafId: string | null;
+}): PiSessionEntry[] {
+  const branchEntries: PiSessionEntry[] = [];
+  let current = params.leafId ? params.byId.get(params.leafId) : undefined;
+  while (current) {
+    branchEntries.unshift(current);
+    current = current.parentId ? params.byId.get(current.parentId) : undefined;
+  }
+  return branchEntries;
+}
+
+function generateEntryId(existingIds: Set<string>): string {
+  for (let attempt = 0; attempt < 100; attempt += 1) {
+    const id = crypto.randomUUID().slice(0, 8);
+    if (!existingIds.has(id)) {
+      existingIds.add(id);
+      return id;
+    }
+  }
+  const id = crypto.randomUUID();
+  existingIds.add(id);
+  return id;
+}
+
+function collectBranchLabels(params: {
+  allEntries: PiSessionEntry[];
+  pathEntryIds: Set<string>;
+}): Array<{ targetId: string; label: string; timestamp: string }> {
+  const labelsToWrite: Array<{ targetId: string; label: string; timestamp: string }> = [];
+  for (const entry of params.allEntries) {
+    if (
+      entry.type === "label" &&
+      entry.label &&
+      params.pathEntryIds.has(entry.targetId) &&
+      typeof entry.timestamp === "string"
+    ) {
+      labelsToWrite.push({
+        targetId: entry.targetId,
+        label: entry.label,
+        timestamp: entry.timestamp,
+      });
+    }
+  }
+  return labelsToWrite;
+}
+
+async function readForkSourceTranscript(
+  parentSessionFile: string,
+): Promise<ForkSourceTranscript | null> {
+  const raw = await fs.readFile(parentSessionFile, "utf-8");
+  const fileEntries = parseSessionEntries(raw);
+  migrateSessionEntries(fileEntries);
+  const header =
+    fileEntries.find((entry): entry is SessionHeader => entry.type === "session") ?? null;
+  const entries = fileEntries.filter(isSessionEntry);
+  const byId = buildEntryIndex(entries);
+  const leafId = entries.at(-1)?.id ?? null;
+  const branchEntries = readBranch({ byId, leafId });
+  const pathEntryIds = new Set(
+    branchEntries.filter((entry) => entry.type !== "label").map((entry) => entry.id),
+  );
+  return {
+    cwd: header?.cwd ?? process.cwd(),
+    sessionDir: path.dirname(parentSessionFile),
+    leafId,
+    branchEntries,
+    labelsToWrite: collectBranchLabels({ allEntries: entries, pathEntryIds }),
+  };
+}
+
+function buildBranchLabelEntries(params: {
+  labelsToWrite: Array<{ targetId: string; label: string; timestamp: string }>;
+  pathEntryIds: Set<string>;
+  lastEntryId: string | null;
+}): PiSessionEntry[] {
+  let parentId = params.lastEntryId;
+  const labelEntries: PiSessionEntry[] = [];
+  for (const { targetId, label, timestamp } of params.labelsToWrite) {
+    const labelEntry = {
+      type: "label",
+      id: generateEntryId(params.pathEntryIds),
+      parentId,
+      timestamp,
+      targetId,
+      label,
+    } satisfies PiSessionEntry;
+    params.pathEntryIds.add(labelEntry.id);
+    labelEntries.push(labelEntry);
+    parentId = labelEntry.id;
+  }
+  return labelEntries;
+}
+
+async function writeForkHeaderOnly(params: {
+  parentSessionFile: string;
+  sessionDir: string;
+  cwd: string;
+}): Promise<{ sessionId: string; sessionFile: string }> {
+  const sessionId = uuidv7();
+  const timestamp = new Date().toISOString();
+  const fileTimestamp = timestamp.replace(/[:.]/g, "-");
+  const sessionFile = path.join(params.sessionDir, `${fileTimestamp}_${sessionId}.jsonl`);
+  const header = {
+    type: "session",
+    version: CURRENT_SESSION_VERSION,
+    id: sessionId,
+    timestamp,
+    cwd: params.cwd,
+    parentSession: params.parentSessionFile,
+  } satisfies SessionHeader;
+  await fs.mkdir(path.dirname(sessionFile), { recursive: true });
+  await fs.writeFile(sessionFile, `${JSON.stringify(header)}\n`, {
+    encoding: "utf-8",
+    mode: 0o600,
+    flag: "wx",
+  });
+  return { sessionId, sessionFile };
+}
+
+async function writeBranchedSession(params: {
+  parentSessionFile: string;
+  source: ForkSourceTranscript;
+}): Promise<{ sessionId: string; sessionFile: string }> {
+  const sessionId = uuidv7();
+  const timestamp = new Date().toISOString();
+  const fileTimestamp = timestamp.replace(/[:.]/g, "-");
+  const sessionFile = path.join(params.source.sessionDir, `${fileTimestamp}_${sessionId}.jsonl`);
+  const pathWithoutLabels = params.source.branchEntries.filter((entry) => entry.type !== "label");
+  const pathEntryIds = new Set(pathWithoutLabels.map((entry) => entry.id));
+  const labelEntries = buildBranchLabelEntries({
+    labelsToWrite: params.source.labelsToWrite,
+    pathEntryIds,
+    lastEntryId: pathWithoutLabels.at(-1)?.id ?? null,
+  });
+  const header = {
+    type: "session",
+    version: CURRENT_SESSION_VERSION,
+    id: sessionId,
+    timestamp,
+    cwd: params.source.cwd,
+    parentSession: params.parentSessionFile,
+  } satisfies SessionHeader;
+  const entries = [header, ...pathWithoutLabels, ...labelEntries];
+  const hasAssistant = entries.some(
+    (entry) => entry.type === "message" && entry.message.role === "assistant",
+  );
+  if (hasAssistant) {
+    await fs.mkdir(path.dirname(sessionFile), { recursive: true });
+    await fs.writeFile(
+      sessionFile,
+      `${entries.map((entry) => JSON.stringify(entry)).join("\n")}\n`,
+      {
+        encoding: "utf-8",
+        mode: 0o600,
+        flag: "wx",
+      },
+    );
+  }
+  return { sessionId, sessionFile };
+}
+
+async function fileExists(filePath: string): Promise<boolean> {
+  try {
+    const stat = await fs.stat(filePath);
+    return stat.isFile();
+  } catch {
+    return false;
+  }
+}
+
+export async function forkSessionFromParentRuntime(params: {
+  parentEntry: StoreSessionEntry;
   agentId: string;
   sessionsDir: string;
-}): { sessionId: string; sessionFile: string } | null {
+}): Promise<{ sessionId: string; sessionFile: string } | null> {
   const parentSessionFile = resolveSessionFilePath(
     params.parentEntry.sessionId,
     params.parentEntry,
     { agentId: params.agentId, sessionsDir: params.sessionsDir },
   );
-  if (!parentSessionFile || !fs.existsSync(parentSessionFile)) {
+  if (!parentSessionFile || !(await fileExists(parentSessionFile))) {
     return null;
   }
   try {
-    const manager = SessionManager.open(parentSessionFile);
-    const leafId = manager.getLeafId();
-    if (leafId) {
-      const sessionFile = manager.createBranchedSession(leafId) ?? manager.getSessionFile();
-      const sessionId = manager.getSessionId();
-      if (sessionFile && sessionId) {
-        return { sessionId, sessionFile };
-      }
+    const source = await readForkSourceTranscript(parentSessionFile);
+    if (!source) {
+      return null;
     }
-    const sessionId = crypto.randomUUID();
-    const timestamp = new Date().toISOString();
-    const fileTimestamp = timestamp.replace(/[:.]/g, "-");
-    const sessionFile = path.join(manager.getSessionDir(), `${fileTimestamp}_${sessionId}.jsonl`);
-    const header = {
-      type: "session",
-      version: CURRENT_SESSION_VERSION,
-      id: sessionId,
-      timestamp,
-      cwd: manager.getCwd(),
-      parentSession: parentSessionFile,
-    };
-    fs.writeFileSync(sessionFile, `${JSON.stringify(header)}\n`, {
-      encoding: "utf-8",
-      mode: 0o600,
-      flag: "wx",
-    });
-    return { sessionId, sessionFile };
+    return source.leafId
+      ? await writeBranchedSession({ parentSessionFile, source })
+      : await writeForkHeaderOnly({
+          parentSessionFile,
+          sessionDir: source.sessionDir,
+          cwd: source.cwd,
+        });
   } catch {
     return null;
   }