diff --git a/src/config/config.memory-search-defaults.test.ts b/src/config/config.memory-search-defaults.test.ts
new file mode 100644
index 00000000000..f18b8734f1c
--- /dev/null
+++ b/src/config/config.memory-search-defaults.test.ts
@@ -0,0 +1,52 @@
+import { describe, expect, it } from "vitest";
+import { loadConfig } from "./config.js";
+import { withTempHomeConfig } from "./test-helpers.js";
+
+describe("config memory search defaults", () => {
+  it("enables session memory indexing, temporal decay, and MMR by default", async () => {
+    await withTempHomeConfig({}, async () => {
+      const cfg = loadConfig();
+      const ms = cfg.agents?.defaults?.memorySearch;
+
+      // Session memory indexing should be on
+      expect((ms?.experimental as Record<string, unknown>)?.sessionMemory).toBe(true);
+      expect(ms?.sources).toContain("sessions");
+      expect(ms?.sources).toContain("memory");
+
+      // Hybrid search with temporal decay
+      const hybrid = ms?.query?.hybrid;
+      expect(hybrid?.enabled).toBe(true);
+      expect(hybrid?.temporalDecay?.enabled).toBe(true);
+      expect(hybrid?.temporalDecay?.halfLifeDays).toBe(30);
+
+      // MMR re-ranking
+      expect(hybrid?.mmr?.enabled).toBe(true);
+      expect(hybrid?.mmr?.lambda).toBe(0.7);
+    });
+  });
+
+  it("does not overwrite explicit memorySearch config", async () => {
+    await withTempHomeConfig(
+      {
+        agents: {
+          defaults: {
+            memorySearch: {
+              sources: ["memory"],
+            },
+          },
+        },
+      },
+      async () => {
+        const cfg = loadConfig();
+        const ms = cfg.agents?.defaults?.memorySearch;
+
+        // User explicitly set sources — respect it, don't inject sessions
+        expect(ms?.sources).toEqual(["memory"]);
+        expect(ms?.sources).not.toContain("sessions");
+
+        // No defaults injected since user provided explicit config
+        expect((ms?.experimental as Record<string, unknown>)?.sessionMemory).toBeUndefined();
+      },
+    );
+  });
+});
diff --git a/src/config/defaults.ts b/src/config/defaults.ts
index 2febc3869ee..ec511a3992f 100644
--- a/src/config/defaults.ts
+++ b/src/config/defaults.ts
@@ -531,6 +531,68 @@ export function applyCompactionDefaults(cfg: OpenClawConfig): OpenClawConfig {
   };
 }
 
+/**
+ * Applies smart memory search defaults for new installations.
+ *
+ * Enables three features that work together to solve the multi-session
+ * continuity problem (e.g. webchat and Telegram feeling like "two twins
+ * who don't share memory") without requiring any agent-level instructions:
+ *
+ * 1. **Session memory indexing** – every conversation across all channels is
+ *    automatically indexed so `memory_search` can find context from any session.
+ *
+ * 2. **Temporal decay** – recent memories rank higher automatically; a note
+ *    from yesterday beats one from 6 months ago on the same topic.
+ *
+ * 3. **MMR re-ranking** – avoids returning near-duplicate memory snippets;
+ *    the agent gets diverse, complementary results instead of repetition.
+ *
+ * All three are off by default today. This function enables them for users
+ * who haven't explicitly configured `memorySearch`, so new installations
+ * get the best out-of-the-box experience. Existing explicit config is
+ * never overwritten (opt-out by setting any memorySearch field).
+ */
+export function applyMemorySearchDefaults(cfg: OpenClawConfig): OpenClawConfig {
+  const defaults = cfg.agents?.defaults;
+  if (!defaults) {
+    return cfg;
+  }
+
+  // Don't touch anything if the user has explicitly configured memorySearch
+  if (defaults.memorySearch !== undefined) {
+    return cfg;
+  }
+
+  return {
+    ...cfg,
+    agents: {
+      ...cfg.agents,
+      defaults: {
+        ...defaults,
+        memorySearch: {
+          experimental: { sessionMemory: true },
+          sources: ["memory", "sessions"],
+          query: {
+            hybrid: {
+              enabled: true,
+              vectorWeight: 0.7,
+              textWeight: 0.3,
+              temporalDecay: {
+                enabled: true,
+                halfLifeDays: 30,
+              },
+              mmr: {
+                enabled: true,
+                lambda: 0.7,
+              },
+            },
+          },
+        },
+      },
+    },
+  };
+}
+
 export function resetSessionDefaultsWarningForTests() {
   defaultWarnState = { warned: false };
 }
diff --git a/src/config/io.ts b/src/config/io.ts
index fba17f253aa..76ade2159a8 100644
--- a/src/config/io.ts
+++ b/src/config/io.ts
@@ -20,6 +20,7 @@ import { maintainConfigBackups } from "./backup-rotation.js";
 import {
   applyCompactionDefaults,
   applyContextPruningDefaults,
+  applyMemorySearchDefaults,
   applyAgentDefaults,
   applyLoggingDefaults,
   applyMessageDefaults,
@@ -800,8 +801,12 @@ export function createConfigIO(overrides: ConfigIoDeps = {}) {
         applyModelDefaults(
           applyCompactionDefaults(
             applyContextPruningDefaults(
-              applyAgentDefaults(
-                applySessionDefaults(applyLoggingDefaults(applyMessageDefaults(validated.config))),
+              applyMemorySearchDefaults(
+                applyAgentDefaults(
+                  applySessionDefaults(
+                    applyLoggingDefaults(applyMessageDefaults(validated.config)),
+                  ),
+                ),
               ),
             ),
           ),
@@ -892,7 +897,9 @@ export function createConfigIO(overrides: ConfigIoDeps = {}) {
           applyModelDefaults(
             applyCompactionDefaults(
               applyContextPruningDefaults(
-                applyAgentDefaults(applySessionDefaults(applyMessageDefaults({}))),
+                applyMemorySearchDefaults(
+                  applyAgentDefaults(applySessionDefaults(applyMessageDefaults({}))),
+                ),
               ),
             ),
           ),