diff --git a/src/cron/isolated-agent/session.test.ts b/src/cron/isolated-agent/session.test.ts
index e9089dafb..9826ca441 100644
--- a/src/cron/isolated-agent/session.test.ts
+++ b/src/cron/isolated-agent/session.test.ts
@@ -4,9 +4,14 @@ import type { OpenClawConfig } from "../../config/config.js";
 vi.mock("../../config/sessions.js", () => ({
   loadSessionStore: vi.fn(),
   resolveStorePath: vi.fn().mockReturnValue("/tmp/test-store.json"),
+  evaluateSessionFreshness: vi.fn().mockReturnValue({ fresh: true }),
+  resolveSessionResetPolicy: vi.fn().mockReturnValue({ mode: "idle", idleMinutes: 60 }),
 }));
 
-import { loadSessionStore } from "../../config/sessions.js";
+import {
+  loadSessionStore,
+  evaluateSessionFreshness,
+} from "../../config/sessions.js";
 import { resolveCronSession } from "./session.js";
 
 describe("resolveCronSession", () => {
@@ -21,6 +26,7 @@ describe("resolveCronSession", () => {
         model: "k2p5",
       },
     });
+    vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: true });
 
     const result = resolveCronSession({
       cfg: {} as OpenClawConfig,
@@ -44,6 +50,7 @@ describe("resolveCronSession", () => {
         model: "claude-opus-4-5",
       },
     });
+    vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: true });
 
     const result = resolveCronSession({
       cfg: {} as OpenClawConfig,
@@ -69,5 +76,98 @@ describe("resolveCronSession", () => {
     expect(result.sessionEntry.modelOverride).toBeUndefined();
     expect(result.sessionEntry.providerOverride).toBeUndefined();
     expect(result.sessionEntry.model).toBeUndefined();
+    expect(result.isNewSession).toBe(true);
+  });
+
+  // New tests for session reuse behavior (#18027)
+  describe("session reuse for webhooks/cron", () => {
+    it("reuses existing sessionId when session is fresh", () => {
+      vi.mocked(loadSessionStore).mockReturnValue({
+        "webhook:stable-key": {
+          sessionId: "existing-session-id-123",
+          updatedAt: Date.now() - 1000,
+          systemSent: true,
+        },
+      });
+      vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: true });
+
+      const result = resolveCronSession({
+        cfg: {} as OpenClawConfig,
+        sessionKey: "webhook:stable-key",
+        agentId: "main",
+        nowMs: Date.now(),
+      });
+
+      expect(result.sessionEntry.sessionId).toBe("existing-session-id-123");
+      expect(result.isNewSession).toBe(false);
+      expect(result.systemSent).toBe(true);
+    });
+
+    it("creates new sessionId when session is stale", () => {
+      vi.mocked(loadSessionStore).mockReturnValue({
+        "webhook:stable-key": {
+          sessionId: "old-session-id",
+          updatedAt: Date.now() - 86400000, // 1 day ago
+          systemSent: true,
+        },
+      });
+      vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: false });
+
+      const result = resolveCronSession({
+        cfg: {} as OpenClawConfig,
+        sessionKey: "webhook:stable-key",
+        agentId: "main",
+        nowMs: Date.now(),
+      });
+
+      expect(result.sessionEntry.sessionId).not.toBe("old-session-id");
+      expect(result.isNewSession).toBe(true);
+      expect(result.systemSent).toBe(false);
+    });
+
+    it("creates new sessionId when forceNew is true", () => {
+      vi.mocked(loadSessionStore).mockReturnValue({
+        "webhook:stable-key": {
+          sessionId: "existing-session-id-456",
+          updatedAt: Date.now() - 1000,
+          systemSent: true,
+        },
+      });
+      vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: true });
+
+      const result = resolveCronSession({
+        cfg: {} as OpenClawConfig,
+        sessionKey: "webhook:stable-key",
+        agentId: "main",
+        nowMs: Date.now(),
+        forceNew: true,
+      });
+
+      expect(result.sessionEntry.sessionId).not.toBe("existing-session-id-456");
+      expect(result.isNewSession).toBe(true);
+      expect(result.systemSent).toBe(false);
+    });
+
+    it("creates new sessionId when entry exists but has no sessionId", () => {
+      vi.mocked(loadSessionStore).mockReturnValue({
+        "webhook:stable-key": {
+          updatedAt: Date.now() - 1000,
+          modelOverride: "some-model",
+        } as any,
+      });
+      vi.mocked(evaluateSessionFreshness).mockReturnValue({ fresh: true });
+
+      const result = resolveCronSession({
+        cfg: {} as OpenClawConfig,
+        sessionKey: "webhook:stable-key",
+        agentId: "main",
+        nowMs: Date.now(),
+      });
+
+      expect(result.sessionEntry.sessionId).toBeDefined();
+      expect(result.isNewSession).toBe(true);
+      // Should still preserve other fields from entry
+      expect(result.sessionEntry.modelOverride).toBe("some-model");
+    });
   });
 });
diff --git a/src/cron/isolated-agent/session.ts b/src/cron/isolated-agent/session.ts
index cd66a442f..1e1442eb4 100644
--- a/src/cron/isolated-agent/session.ts
+++ b/src/cron/isolated-agent/session.ts
@@ -1,12 +1,19 @@
 import crypto from "node:crypto";
 import type { OpenClawConfig } from "../../config/config.js";
-import { loadSessionStore, resolveStorePath, type SessionEntry } from "../../config/sessions.js";
+import {
+  evaluateSessionFreshness,
+  loadSessionStore,
+  resolveSessionResetPolicy,
+  resolveStorePath,
+  type SessionEntry,
+} from "../../config/sessions.js";
 
 export function resolveCronSession(params: {
   cfg: OpenClawConfig;
   sessionKey: string;
   nowMs: number;
   agentId: string;
+  forceNew?: boolean;
 }) {
   const sessionCfg = params.cfg.session;
   const storePath = resolveStorePath(sessionCfg?.store, {
@@ -14,12 +21,50 @@ export function resolveCronSession(params: {
   });
   const store = loadSessionStore(storePath);
   const entry = store[params.sessionKey];
-  const sessionId = crypto.randomUUID();
-  const systemSent = false;
+
+  // Check if we can reuse an existing session
+  let sessionId: string;
+  let isNewSession: boolean;
+  let systemSent: boolean;
+
+  if (!params.forceNew && entry?.sessionId) {
+    // Evaluate freshness using the configured reset policy
+    // Cron/webhook sessions use "direct" reset type (1:1 conversation style)
+    const resetPolicy = resolveSessionResetPolicy({
+      sessionCfg,
+      resetType: "direct",
+    });
+    const freshness = evaluateSessionFreshness({
+      updatedAt: entry.updatedAt,
+      now: params.nowMs,
+      policy: resetPolicy,
+    });
+
+    if (freshness.fresh) {
+      // Reuse existing session
+      sessionId = entry.sessionId;
+      isNewSession = false;
+      systemSent = entry.systemSent ?? false;
+    } else {
+      // Session expired, create new
+      sessionId = crypto.randomUUID();
+      isNewSession = true;
+      systemSent = false;
+    }
+  } else {
+    // No existing session or forced new
+    sessionId = crypto.randomUUID();
+    isNewSession = true;
+    systemSent = false;
+  }
+
   const sessionEntry: SessionEntry = {
+    // Spread existing entry to preserve conversation context when reusing
+    ...(isNewSession ? undefined : entry),
     sessionId,
     updatedAt: params.nowMs,
     systemSent,
+    // Preserve user preferences from existing entry
     thinkingLevel: entry?.thinkingLevel,
     verboseLevel: entry?.verboseLevel,
     model: entry?.model,
@@ -34,5 +79,5 @@ export function resolveCronSession(params: {
     displayName: entry?.displayName,
     skillsSnapshot: entry?.skillsSnapshot,
   };
-  return { storePath, store, sessionEntry, systemSent, isNewSession: true };
+  return { storePath, store, sessionEntry, systemSent, isNewSession };
 }