diff --git a/CHANGELOG.md b/CHANGELOG.md
index 40b22bf18e3..0bd0b75bbf5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -43,6 +43,7 @@ Docs: https://docs.openclaw.ai
 - WebChat/exec approvals: use native approval UI guidance in agent system prompts instead of telling agents to paste manual `/approve` commands in webchat sessions. Thanks @vincentkoc.
 - Plugins/install: forward `--dangerously-force-unsafe-install` through archive and npm-spec plugin installs so the documented override reaches the security scanner on those install paths. (#58879) Thanks @ryanlee-gemini.
 - Chat/error replies: stop leaking raw provider/runtime failures into external chat channels, return a friendly retry message instead, and add a specific `/new` hint for Bedrock toolResult/toolUse session mismatches. (#58831) Thanks @ImLukeF.
+- Memory/session indexing: keep full reindexes from skipping session transcripts when sync is triggered by `session-start` or `watch`, so restart-driven reindexes preserve session memory (#39732) thanks @upupc
 
 ## 2026.3.31
 
diff --git a/extensions/memory-core/src/memory/manager-sync-ops.ts b/extensions/memory-core/src/memory/manager-sync-ops.ts
index 11d10561818..c10c5dc0c3d 100644
--- a/extensions/memory-core/src/memory/manager-sync-ops.ts
+++ b/extensions/memory-core/src/memory/manager-sync-ops.ts
@@ -680,13 +680,13 @@ export abstract class MemoryManagerSyncOps {
     if (params?.force) {
       return true;
     }
+    if (needsFullReindex) {
+      return true;
+    }
     const reason = params?.reason;
     if (reason === "session-start" || reason === "watch") {
       return false;
     }
-    if (needsFullReindex) {
-      return true;
-    }
     return this.sessionsDirty && this.sessionsDirtyFiles.size > 0;
   }
 
diff --git a/extensions/memory-core/src/memory/manager.session-reindex.test.ts b/extensions/memory-core/src/memory/manager.session-reindex.test.ts
new file mode 100644
index 00000000000..91875148636
--- /dev/null
+++ b/extensions/memory-core/src/memory/manager.session-reindex.test.ts
@@ -0,0 +1,78 @@
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import type { OpenClawConfig } from "openclaw/plugin-sdk/memory-core-host-engine-foundation";
+import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it } from "vitest";
+import type { MemoryIndexManager } from "./index.js";
+import { getRequiredMemoryIndexManager } from "./test-manager-helpers.js";
+
+describe("memory manager session reindex gating", () => {
+  let fixtureRoot = "";
+  let caseId = 0;
+  let workspaceDir: string;
+  let indexPath: string;
+  let manager: MemoryIndexManager | null = null;
+
+  beforeAll(async () => {
+    fixtureRoot = await fs.mkdtemp(path.join(os.tmpdir(), "openclaw-mem-session-reindex-"));
+  });
+
+  beforeEach(async () => {
+    workspaceDir = path.join(fixtureRoot, `case-${caseId++}`);
+    await fs.mkdir(path.join(workspaceDir, "memory"), { recursive: true });
+    await fs.writeFile(path.join(workspaceDir, "MEMORY.md"), "Hello memory.");
+    indexPath = path.join(workspaceDir, "index.sqlite");
+  });
+
+  afterEach(async () => {
+    if (manager) {
+      await manager.close();
+      manager = null;
+    }
+  });
+
+  afterAll(async () => {
+    if (!fixtureRoot) {
+      return;
+    }
+    await fs.rm(fixtureRoot, { recursive: true, force: true });
+  });
+
+  it("keeps session syncing enabled for full reindexes triggered from session-start/watch", async () => {
+    const cfg = {
+      agents: {
+        defaults: {
+          workspace: workspaceDir,
+          memorySearch: {
+            provider: "openai",
+            model: "mock-embed",
+            store: { path: indexPath, vector: { enabled: false } },
+            cache: { enabled: false },
+            query: { minScore: 0, hybrid: { enabled: false } },
+            chunking: { tokens: 4000, overlap: 0 },
+            experimental: { sessionMemory: true },
+            sources: ["memory", "sessions"],
+            sync: { watch: false, onSessionStart: false, onSearch: false },
+          },
+        },
+        list: [{ id: "main", default: true }],
+      },
+    } as OpenClawConfig;
+
+    manager = await getRequiredMemoryIndexManager({ cfg, agentId: "main" });
+
+    const shouldSyncSessions = (
+      manager as unknown as {
+        shouldSyncSessions: (
+          params?: { reason?: string; force?: boolean },
+          needsFullReindex?: boolean,
+        ) => boolean;
+      }
+    ).shouldSyncSessions.bind(manager);
+
+    expect(shouldSyncSessions({ reason: "session-start" }, true)).toBe(true);
+    expect(shouldSyncSessions({ reason: "watch" }, true)).toBe(true);
+    expect(shouldSyncSessions({ reason: "session-start" }, false)).toBe(false);
+    expect(shouldSyncSessions({ reason: "watch" }, false)).toBe(false);
+  });
+});