diff --git a/mateclaw-server/src/main/java/vip/mate/channel/feishu/FeishuChannelAdapter.java b/mateclaw-server/src/main/java/vip/mate/channel/feishu/FeishuChannelAdapter.java
index 9fbe6786..718d50ff 100644
--- a/mateclaw-server/src/main/java/vip/mate/channel/feishu/FeishuChannelAdapter.java
+++ b/mateclaw-server/src/main/java/vip/mate/channel/feishu/FeishuChannelAdapter.java
@@ -1412,8 +1412,13 @@ public class FeishuChannelAdapter extends AbstractChannelAdapter implements Stre
      * {@code senderId} is the full open id. Mirror that exactly:
      * {@code groups → feishu:{shortSuffix}}, {@code DMs → feishu:{senderOpenId}}.
      */
-    private String buildConversationId(String shortSuffix, String senderOpenId, boolean isGroup) {
-        String identifier = isGroup ? shortSuffix : senderOpenId;
+    static String buildConversationId(String shortSuffix, String senderOpenId, boolean isGroup) {
+        // The routed ChannelMessage carries chatId = (isGroup ? shortSuffix : null);
+        // the router then falls back to senderId when that chatId is null. Mirror both
+        // steps so the storage id matches the runtime id in every case (including the
+        // degenerate group-with-no-suffix path).
+        String routedChatId = isGroup ? shortSuffix : null;
+        String identifier = routedChatId != null ? routedChatId : senderOpenId;
         return identifier != null ? CHANNEL_TYPE + ":" + identifier : null;
     }
 
diff --git a/mateclaw-server/src/test/java/vip/mate/channel/feishu/FeishuConversationIdAlignmentTest.java b/mateclaw-server/src/test/java/vip/mate/channel/feishu/FeishuConversationIdAlignmentTest.java
new file mode 100644
index 00000000..ec7812b0
--- /dev/null
+++ b/mateclaw-server/src/test/java/vip/mate/channel/feishu/FeishuConversationIdAlignmentTest.java
@@ -0,0 +1,74 @@
+package vip.mate.channel.feishu;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Locks the invariant that {@link FeishuChannelAdapter#buildConversationId} produces
+ * exactly the id {@code ChannelMessageRouter} derives for the same chat.
+ *
+ * <p>The recent-file cache saves inbound attachments under
+ * {@code data/chat-uploads/{conversationId}/}; the prompt only exposes a file's
+ * name (not its path) to the model, so {@code ReadFileTool}/{@code DocumentExtractTool}
+ * resolve it through {@code ChatUploadResolver} under the runtime conversationId.
+ * If the storage id and the runtime id diverge, those tools cannot find the file
+ * and document reads silently fail — which is precisely the regression these tests
+ * guard against.
+ *
+ * <p>The router derives its id from the routed {@code ChannelMessage}, whose
+ * {@code chatId} is {@code (isGroup ? shortSuffix : null)} and whose {@code senderId}
+ * is the full open id, via {@code feishu:{chatId != null ? chatId : senderId}}.
+ */
+class FeishuConversationIdAlignmentTest {
+
+    private static final String CHANNEL = FeishuChannelAdapter.CHANNEL_TYPE; // "feishu"
+    private static final String SHORT_SUFFIX = "cli2_abcd1234";
+    private static final String SENDER = "ou_user0123456789";
+
+    /** Mirror of ChannelMessageRouter#buildConversationId against the routed message. */
+    private static String routerConversationId(String shortSuffix, String senderId, boolean isGroup) {
+        String routedChatId = isGroup ? shortSuffix : null;
+        String identifier = routedChatId != null ? routedChatId : senderId;
+        return identifier != null ? CHANNEL + ":" + identifier : null;
+    }
+
+    @Test
+    void group_usesShortSuffix() {
+        assertEquals(CHANNEL + ":" + SHORT_SUFFIX,
+                FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, SENDER, true));
+    }
+
+    @Test
+    void dm_usesSenderOpenIdAndIgnoresShortSuffix() {
+        assertEquals(CHANNEL + ":" + SENDER,
+                FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, SENDER, false));
+    }
+
+    @Test
+    void group_nullShortSuffix_fallsBackToSender() {
+        // Degenerate group path: routed chatId is null, so the router (and this helper)
+        // fall back to the sender open id — never null when a sender is present.
+        assertEquals(CHANNEL + ":" + SENDER,
+                FeishuChannelAdapter.buildConversationId(null, SENDER, true));
+    }
+
+    @Test
+    void dm_nullSender_returnsNull() {
+        assertNull(FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, null, false));
+    }
+
+    @Test
+    void matchesRouterFormula_acrossCases() {
+        // Group and DM, with and without a short suffix — the storage id must equal
+        // the id the router computes for the routed ChannelMessage in every case.
+        assertEquals(routerConversationId(SHORT_SUFFIX, SENDER, true),
+                FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, SENDER, true));
+        assertEquals(routerConversationId(SHORT_SUFFIX, SENDER, false),
+                FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, SENDER, false));
+        assertEquals(routerConversationId(null, SENDER, true),
+                FeishuChannelAdapter.buildConversationId(null, SENDER, true));
+        assertEquals(routerConversationId(SHORT_SUFFIX, null, false),
+                FeishuChannelAdapter.buildConversationId(SHORT_SUFFIX, null, false));
+    }
+}