diff --git a/agentscope-harness/src/main/java/io/agentscope/harness/agent/tool/SessionSearchTool.java b/agentscope-harness/src/main/java/io/agentscope/harness/agent/tool/SessionSearchTool.java
index a06e1460da..1cf3ce23d7 100644
--- a/agentscope-harness/src/main/java/io/agentscope/harness/agent/tool/SessionSearchTool.java
+++ b/agentscope-harness/src/main/java/io/agentscope/harness/agent/tool/SessionSearchTool.java
@@ -34,6 +34,13 @@
 
 /** Read-only session discovery and full conversation views from the authoritative native log. */
 public class SessionSearchTool {
+    /**
+     * Hard ceiling for model-supplied result limits. The tool is excluded from
+     * {@code ToolResultEvictionConfig} on the "bounded results" rationale, so nothing
+     * downstream trims an oversized result — the clamp has to happen here (#3270).
+     */
+    private static final int MAX_RESULTS_CEILING = 100;
+
     private final SessionLogStore store;
 
     public SessionSearchTool(WorkspaceManager workspace) {
@@ -76,7 +83,7 @@ public ToolResultBlock sessionSearch(
                     String agentId,
             @ToolParam(
                             name = "maxResults",
-                            description = "Maximum number of results (default: 10)",
+                            description = "Maximum number of results (default: 10, capped at 100)",
                             required = false)
                     Integer maxResults,
             @ToolParam(
@@ -157,7 +164,7 @@ public ToolResultBlock sessionHistory(
             @ToolParam(name = "sessionId", description = "Session ID") String sessionId,
             @ToolParam(
                             name = "lastN",
-                            description = "Number of recent messages (default: 20)",
+                            description = "Number of recent messages (default: 20, capped at 100)",
                             required = false)
                     Integer lastN) {
         if (agentId == null || agentId.isBlank() || sessionId == null || sessionId.isBlank()) {
@@ -207,6 +214,6 @@ private static RuntimeContext context(RuntimeContext context) {
     }
 
     private static int positiveLimit(Integer value, int fallback) {
-        return value == null || value <= 0 ? fallback : value;
+        return value == null || value <= 0 ? fallback : Math.min(value, MAX_RESULTS_CEILING);
     }
 }
diff --git a/agentscope-harness/src/test/java/io/agentscope/harness/agent/tool/SessionSearchToolCeilingTest.java b/agentscope-harness/src/test/java/io/agentscope/harness/agent/tool/SessionSearchToolCeilingTest.java
new file mode 100644
index 0000000000..1483c4a1ce
--- /dev/null
+++ b/agentscope-harness/src/test/java/io/agentscope/harness/agent/tool/SessionSearchToolCeilingTest.java
@@ -0,0 +1,128 @@
+/*
+ * Copyright 2024-2026 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.agentscope.harness.agent.tool;
+
+import static io.agentscope.harness.agent.tool.ToolResultAssertions.assertText;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import io.agentscope.core.agent.RuntimeContext;
+import io.agentscope.core.message.Msg;
+import io.agentscope.core.message.MsgRole;
+import io.agentscope.core.message.TextBlock;
+import io.agentscope.core.message.ToolResultState;
+import io.agentscope.core.session.SessionEvent;
+import io.agentscope.core.session.SessionKey;
+import io.agentscope.core.util.JsonUtils;
+import io.agentscope.harness.agent.filesystem.local.LocalFilesystem;
+import io.agentscope.harness.agent.session.WorkspaceSessionLogStore;
+import java.nio.file.Path;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Map;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+/**
+ * Regression tests for the model-supplied result-limit clamp (#3270): {@code session_search}
+ * and {@code session_history} are excluded from {@code ToolResultEvictionConfig} on the
+ * "bounded results" rationale, so an unbounded model-supplied limit bypasses every downstream
+ * trim.
+ */
+class SessionSearchToolCeilingTest {
+
+    @TempDir Path directory;
+    private final SessionKey key = new SessionKey("u", "agent-a", "session-1");
+    private final RuntimeContext rc = RuntimeContext.builder().userId("u").build();
+
+    private SessionSearchTool seedMessages(int count) {
+        var store = new WorkspaceSessionLogStore(new LocalFilesystem(directory));
+        var log = store.open(key, rc);
+        var writer = log.acquire("owner", Duration.ofMinutes(2));
+        var events = new ArrayList<SessionEvent>();
+        for (int i = 1; i <= count; i++) {
+            var message =
+                    Msg.builder()
+                            .id("m" + i)
+                            .role(MsgRole.USER)
+                            .content(TextBlock.builder().text("needle item " + i).build())
+                            .build();
+            events.add(
+                    new SessionEvent(
+                            1,
+                            "m" + i,
+                            i,
+                            i,
+                            "message/user",
+                            "run",
+                            "turn",
+                            true,
+                            JsonUtils.getJsonCodec().toJson(Map.of("message", message))));
+        }
+        log.commit(writer, "messages", 0, events);
+        log.release(writer);
+        return new SessionSearchTool(new WorkspaceSessionLogStore(new LocalFilesystem(directory)));
+    }
+
+    private static int countMatches(String json) {
+        return (json.length() - json.replace("needle item", "").length()) / "needle item".length();
+    }
+
+    @Test
+    void sessionSearchClampsModelSuppliedMaxResults() {
+        var tool = seedMessages(150);
+        var out =
+                assertText(
+                        tool.sessionSearch(rc, "needle", "agent-a", 100000),
+                        ToolResultState.SUCCESS);
+        assertEquals(100, countMatches(out));
+    }
+
+    @Test
+    void sessionHistoryClampsModelSuppliedLastN() {
+        var tool = seedMessages(150);
+        var out =
+                assertText(
+                        tool.sessionHistory(rc, "agent-a", "session-1", 100000),
+                        ToolResultState.SUCCESS);
+        assertEquals(100, countMatches(out));
+    }
+
+    @Test
+    void sessionHistoryBoundaryLastN99And101() {
+        var tool = seedMessages(150);
+        assertEquals(
+                99,
+                countMatches(
+                        assertText(
+                                tool.sessionHistory(rc, "agent-a", "session-1", 99),
+                                ToolResultState.SUCCESS)));
+        assertEquals(
+                100,
+                countMatches(
+                        assertText(
+                                tool.sessionHistory(rc, "agent-a", "session-1", 101),
+                                ToolResultState.SUCCESS)));
+    }
+
+    @Test
+    void defaultLimitStillApplies() {
+        var tool = seedMessages(15);
+        var out =
+                assertText(
+                        tool.sessionSearch(rc, "needle", "agent-a", null), ToolResultState.SUCCESS);
+        assertEquals(10, countMatches(out));
+    }
+}