diff --git a/mateclaw-server/src/main/java/vip/mate/agent/AgentGraphBuilder.java b/mateclaw-server/src/main/java/vip/mate/agent/AgentGraphBuilder.java
index a3a5701a..a6a3d058 100644
--- a/mateclaw-server/src/main/java/vip/mate/agent/AgentGraphBuilder.java
+++ b/mateclaw-server/src/main/java/vip/mate/agent/AgentGraphBuilder.java
@@ -926,9 +926,18 @@ public class AgentGraphBuilder {
             // capability from reasoningEffort == null.
             boolean supportsReasoningEffort = primaryModelConfig != null
                     && ModelFamily.detect(primaryModelConfig.getModelName()).supportsReasoningEffort();
+            // Honor the model's configured output cap. Passing 0 here made the
+            // node fall back to its 16384 default, so the user-configured
+            // maxTokens never took effect and strict local servers (vLLM's
+            // max_model_len pre-check) rejected the request outright.
+            int configuredMaxOutputTokens = (primaryModelConfig != null
+                    && primaryModelConfig.getMaxTokens() != null
+                    && primaryModelConfig.getMaxTokens() > 0)
+                    ? primaryModelConfig.getMaxTokens() : 0;
             ReasoningNode reasoningNode = new ReasoningNode(chatModel, toolSet, reasoningEffort,
                     supportsReasoningEffort,
-                    streamingHelper, conversationWindowManager, streamTracker, 0, wikiContextService,
+                    streamingHelper, conversationWindowManager, streamTracker,
+                    configuredMaxOutputTokens, wikiContextService,
                     skillCatalogRenderer, toolDisclosureService, progressLedgerService);
             reasoningNode.setPrefixBudgetPlan(prefixBudgetPlan);
             reasoningNode.setAutoDemotedTools(autoDemotedTools);
diff --git a/mateclaw-server/src/main/java/vip/mate/agent/graph/node/ReasoningNode.java b/mateclaw-server/src/main/java/vip/mate/agent/graph/node/ReasoningNode.java
index 4186f8a2..053b4223 100644
--- a/mateclaw-server/src/main/java/vip/mate/agent/graph/node/ReasoningNode.java
+++ b/mateclaw-server/src/main/java/vip/mate/agent/graph/node/ReasoningNode.java
@@ -376,6 +376,27 @@ public class ReasoningNode implements NodeAction {
         this.autoDemotedTools = autoDemotedTools == null ? Set.of() : autoDemotedTools;
     }
 
+    /** Floor for the window-aware output clamp — an answer needs at least this much room. */
+    private static final int MIN_CLAMPED_OUTPUT_TOKENS = 512;
+
+    /**
+     * Output cap actually sent to the provider. Strict local servers (vLLM)
+     * statically reject {@code max_tokens >= max_model_len}, so when the
+     * effective context window is known and smaller than the configured /
+     * default output cap, clamp to half the window (leaving the other half
+     * for the prompt). No-op when the window is unknown or already larger.
+     */
+    int effectiveMaxOutputTokens() {
+        int window = (prefixBudgetPlan != null) ? prefixBudgetPlan.effectiveMaxTokens() : 0;
+        if (window > 0 && maxOutputTokens >= window) {
+            int clamped = Math.max(MIN_CLAMPED_OUTPUT_TOKENS, window / 2);
+            log.info("[ReasoningNode] max_tokens {} ≥ 模型窗口 {},钳制为 {}(窗口一半)以避免服务端拒绝",
+                    maxOutputTokens, window, clamped);
+            return clamped;
+        }
+        return maxOutputTokens;
+    }
+
     public ReasoningNode(ChatModel chatModel, AgentToolSet toolSet, String reasoningEffort,
                          NodeStreamingChatHelper streamingHelper,
                          ConversationWindowManager conversationWindowManager,
@@ -1234,11 +1255,11 @@ public class ReasoningNode implements NodeAction {
                     default -> 16384;
                 };
                 builder.thinking(org.springframework.ai.anthropic.api.AnthropicApi.ThinkingType.ENABLED, budgetTokens);
-                builder.maxTokens(budgetTokens + maxOutputTokens);
+                builder.maxTokens(budgetTokens + effectiveMaxOutputTokens());
                 builder.temperature(1.0);
                 log.info("[ReasoningNode] Anthropic extended thinking enabled: model={}, budget={}", currentModel, budgetTokens);
             } else {
-                builder.maxTokens(maxOutputTokens);
+                builder.maxTokens(effectiveMaxOutputTokens());
                 if (thinkingOn && !isClaudeModel) {
                     log.debug("[ReasoningNode] Anthropic protocol model {} does not support thinking, skipping", currentModel);
                 }
@@ -1253,7 +1274,7 @@ public class ReasoningNode implements NodeAction {
         // DashScope rejects max_tokens above its 8192 ceiling with a 400 that
         // the failover layer misreads as "model not found"; clamp so a
         // DashScope-backed model never overflows the provider limit.
-        int effectiveMaxTokens = maxOutputTokens;
+        int effectiveMaxTokens = effectiveMaxOutputTokens();
         if (chatModel instanceof com.alibaba.cloud.ai.dashscope.chat.DashScopeChatModel
                 && effectiveMaxTokens > DASHSCOPE_MAX_OUTPUT_TOKENS) {
             log.debug("[ReasoningNode] Clamping max_tokens {} -> {} for DashScope-backed model",
diff --git a/mateclaw-server/src/test/java/vip/mate/agent/graph/node/ReasoningNodeOutputClampTest.java b/mateclaw-server/src/test/java/vip/mate/agent/graph/node/ReasoningNodeOutputClampTest.java
new file mode 100644
index 00000000..fedd2ae7
--- /dev/null
+++ b/mateclaw-server/src/test/java/vip/mate/agent/graph/node/ReasoningNodeOutputClampTest.java
@@ -0,0 +1,56 @@
+package vip.mate.agent.graph.node;
+
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import vip.mate.agent.AgentToolSet;
+import vip.mate.agent.context.PrefixBudgetPlan;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+/**
+ * Window-aware output-cap clamp: strict local servers (vLLM) statically
+ * reject {@code max_tokens >= max_model_len}, so the cap sent to the
+ * provider must shrink when the known context window is smaller than the
+ * configured / default output cap.
+ */
+class ReasoningNodeOutputClampTest {
+
+    private static ReasoningNode nodeWithWindow(Integer windowTokens) {
+        @SuppressWarnings("deprecation")
+        ReasoningNode node = new ReasoningNode(null,
+                AgentToolSet.fromCallbacks(List.of(), List.of()), null);
+        if (windowTokens != null) {
+            node.setPrefixBudgetPlan(new PrefixBudgetPlan(
+                    true, windowTokens, PrefixBudgetPlan.Profile.COMPACT,
+                    0, 0, 0, 0, 0, 0, windowTokens / 4));
+        }
+        return node;
+    }
+
+    @Test
+    @DisplayName("default 16384 cap on an 8k window clamps to half the window")
+    void defaultCapClampsOnSmallWindow() {
+        // Deprecated ctor leaves maxOutputTokens at the 16384 default.
+        assertEquals(4096, nodeWithWindow(8192).effectiveMaxOutputTokens());
+    }
+
+    @Test
+    @DisplayName("large window leaves the cap untouched")
+    void largeWindowKeepsCap() {
+        assertEquals(16384, nodeWithWindow(128000).effectiveMaxOutputTokens());
+    }
+
+    @Test
+    @DisplayName("no budget plan (tests / legacy graphs) keeps previous behavior")
+    void noPlanKeepsCap() {
+        assertEquals(16384, nodeWithWindow(null).effectiveMaxOutputTokens());
+    }
+
+    @Test
+    @DisplayName("tiny window clamps no lower than the 512-token floor")
+    void tinyWindowRespectsFloor() {
+        assertEquals(512, nodeWithWindow(600).effectiveMaxOutputTokens());
+    }
+}