Improve error handling when MCP promtps fail on server side

Author: ericdallo

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 - Consider Anthropic internal server error as a retriable error.
 - Improve MCP error logging to show error code, message, and data instead of null.
+- Improve error handling when MCP promtps fail on server side.
 
 ## 0.115.1
 

src/eca/features/chat.clj

@@ -669,12 +669,23 @@
   (let [{:keys [arguments]} (first (filter #(= prompt (:name %)) (f.mcp/all-prompts @db*)))
         args-vals (zipmap (map :name arguments) args)
         {:keys [messages error-message]} (f.prompt/get-prompt! prompt args-vals @db*)]
-    (if error-message
-      (lifecycle/send-content! chat-ctx
-                               :system
-                               {:type :text
-                                :text error-message})
-      (prompt-messages! messages :mcp-prompt chat-ctx))))
+    (cond
+      error-message
+      (do (lifecycle/send-content! chat-ctx
+                                   :system
+                                   {:type :text
+                                    :text error-message})
+          (lifecycle/finish-chat-prompt! :idle chat-ctx))
+
+      (seq messages)
+      (prompt-messages! messages :mcp-prompt chat-ctx)
+
+      :else
+      (do (lifecycle/send-content! chat-ctx
+                                   :system
+                                   {:type :text
+                                    :text (format "No response from prompt '%s'." prompt)})
+          (lifecycle/finish-chat-prompt! :idle chat-ctx)))))
 
 (defn ^:private handle-command! [{:keys [command args]} chat-ctx]
   (try

src/eca/features/tools/mcp.clj

@@ -653,19 +653,25 @@
         (:mcp-clients db)))
 
 (defn get-prompt! [name arguments db]
-  (when-let [mcp-client (->> (vals (:mcp-clients db))
-                             (keep (fn [{:keys [client prompts]}]
-                                     (when (some #(= name (:name %)) prompts)
-                                       client)))
-                             first)]
-    (when-let [prompt (->> {:on-error (fn [_id jsonrpc-error]
-                                        (logger/warn logger-tag "Error getting prompt:" (format-jsonrpc-error jsonrpc-error)))}
-                           (pmc/get-prompt mcp-client name arguments))]
-      {:description (:description prompt)
-       :messages (mapv (fn [each-message]
-                         {:role (string/lower-case (:role each-message))
-                          :content [(->content (:content each-message))]})
-                       (:messages prompt))})))
+  (if-let [mcp-client (->> (vals (:mcp-clients db))
+                           (keep (fn [{:keys [client prompts]}]
+                                   (when (some #(= name (:name %)) prompts)
+                                     client)))
+                           first)]
+    (let [error* (atom nil)
+          prompt (->> {:on-error (fn [_id jsonrpc-error]
+                                   (logger/warn logger-tag "Error getting prompt:" (format-jsonrpc-error jsonrpc-error))
+                                   (reset! error* (format-jsonrpc-error jsonrpc-error)))}
+                      (pmc/get-prompt mcp-client name arguments))]
+      (if-let [error @error*]
+        {:error-message (str "MCP error getting prompt: " error)}
+        (when prompt
+          {:description (:description prompt)
+           :messages (mapv (fn [each-message]
+                             {:role (string/lower-case (:role each-message))
+                              :content [(->content (:content each-message))]})
+                           (:messages prompt))})))
+    {:error-message (format "Prompt '%s' not found in any connected MCP server" name)}))
 
 (defn get-resource! [uri db]
   (when-let [mcp-client (->> (vals (:mcp-clients db))

test/eca/features/chat_test.clj

@@ -4,6 +4,7 @@
    [clojure.string :as string]
    [clojure.test :refer [deftest is testing]]
    [eca.features.chat :as f.chat]
+   [eca.features.chat.lifecycle :as lifecycle]
    [eca.features.prompt :as f.prompt]
    [eca.features.tools :as f.tools]
    [eca.features.tools.mcp :as f.mcp]
@@ -588,7 +589,40 @@
              {"foo" 42 "bar" "yo"}))
         (is (match?
              @invoked?
-             [[{:role :user :content "test"}] :mcp-prompt test-chat-ctx]))))))
+             [[{:role :user :content "test"}] :mcp-prompt test-chat-ctx])))))
+
+  (testing "shows error message and finishes chat when get-prompt! returns error-message"
+    (let [test-chat-ctx {:db* (atom {})}
+          sent-content (atom nil)
+          finished-status (atom nil)]
+      (with-redefs [f.mcp/all-prompts (fn [_]
+                                        [{:name "failing-prompt" :arguments [{:name "arg1"}]}])
+                    f.prompt/get-prompt! (fn [_ _ _]
+                                           {:error-message "MCP error getting prompt: code=-32603 message=Invalid required argument: arg1"})
+                    lifecycle/send-content! (fn [_ctx _role content]
+                                              (reset! sent-content content))
+                    lifecycle/finish-chat-prompt! (fn [status _ctx]
+                                                    (reset! finished-status status))]
+        (#'f.chat/send-mcp-prompt! {:prompt "failing-prompt" :args ["val1"]} test-chat-ctx)
+        (is (= :text (:type @sent-content)))
+        (is (string/includes? (:text @sent-content) "MCP error getting prompt"))
+        (is (= :idle @finished-status)))))
+
+  (testing "shows error message and finishes chat when get-prompt! returns nil"
+    (let [test-chat-ctx {:db* (atom {})}
+          sent-content (atom nil)
+          finished-status (atom nil)]
+      (with-redefs [f.mcp/all-prompts (fn [_]
+                                        [{:name "nil-prompt" :arguments []}])
+                    f.prompt/get-prompt! (fn [_ _ _] nil)
+                    lifecycle/send-content! (fn [_ctx _role content]
+                                              (reset! sent-content content))
+                    lifecycle/finish-chat-prompt! (fn [status _ctx]
+                                                    (reset! finished-status status))]
+        (#'f.chat/send-mcp-prompt! {:prompt "nil-prompt" :args []} test-chat-ctx)
+        (is (= :text (:type @sent-content)))
+        (is (string/includes? (:text @sent-content) "No response from prompt"))
+        (is (= :idle @finished-status))))))
 
 (deftest message->decision-test
   (testing "plain prompt message"

test/eca/oauth_test.clj

@@ -4,7 +4,6 @@
    [clojure.test :refer [deftest is testing]]
    [eca.oauth :as oauth]
    [hato.client :as http]
-   [matcher-combinators.test :refer [match?]]
    [ring.util.codec :as ring.util]))
 
 (deftest generate-pkce-test
@@ -33,7 +32,7 @@
                                   {:status 404}
                                   (make-auth-response
                                    "Bearer realm=\"test\", resource_metadata=\"https://example.com/prm\"")))
-                    http/get (fn [url opts]
+                    http/get (fn [url _opts]
                                (swap! get-urls conj url)
                                (cond
                                  (= url "https://example.com/prm")