Fix prompt cache invalidation warning after clearing chat

Also add missing line break after "Prompt stopped" message.

Closes #530

Author: ericdallo

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+- Fix prompt cache invalidation warning after clearing the chat and changing model. #530
+- Fix missing line break after "Prompt stopped" message when followed by another system message.
+
 ## 0.147.0
 
 - Granular shell/git approve & remember by command + subcommand (e.g. `git checkout`) instead of whole tool; details carry breakdown, approval keys and remembered state. #153

src/eca/features/chat.clj

@@ -1885,7 +1885,7 @@
                       :parent-chat-id (db/parent-chat-id @db* chat-id)}]
         (when-not silent?
           (lifecycle/send-content! chat-ctx :system {:type :text
-                                                     :text "\nPrompt stopped"}))
+                                                     :text "\nPrompt stopped\n"}))
 
         ;; Handle each active tool call
         (doseq [[tool-call-id _] (tc/get-active-tool-calls @db* chat-id)]
@@ -1925,8 +1925,12 @@
     (swap! db* update-in [:chats chat-id]
            (fn [chat]
              (cond-> chat
+               ;; A cleared chat is a fresh conversation: drop the prompt cache
+               ;; so the next prompt rebuilds the system prompt silently instead
+               ;; of warning about an invalidated cache that no longer exists. #530
                messages (-> (assoc :messages [])
-                            (dissoc :tool-calls :last-api :usage :task)))))
+                            (dissoc :tool-calls :last-api :usage :task
+                                    :prompt-cache :last-editor-state)))))
     (messenger/chat-cleared messenger {:chat-id chat-id :messages messages})
     (db/update-workspaces-cache! @db* metrics)))
 

test/eca/features/chat_test.clj

@@ -1198,7 +1198,7 @@
                     {:role :assistant :content {:type :toolCalled :id "call-3" :name "ro_tool_3" :arguments {}
                                                 :outputs [{:type :text :text "RO tool call 3 result"}]}}
                     {:role :system :content {:type :progress :state :running :text "Generating"}}
-                    {:role :system :content {:type :text :text "\nPrompt stopped"}}
+                    {:role :system :content {:type :text :text "\nPrompt stopped\n"}}
                     {:role :system :content {:type :progress :state :finished}}
                     {:role :assistant :content {:type :toolCallRejected :id "call-2" :name "ro_tool_2" :arguments {} :reason :user}}
                     {:role :assistant :content {:type :toolCallRejected :id "call-1" :name "ro_tool_1" :arguments {} :reason :user}}]}
@@ -1656,6 +1656,23 @@
           (is (= 2 @build-calls*) "Next message rebuilds the system prompt")
           (is (empty? (system-prompt-notices)) "Explicit sync rebuild does not notify"))))))
 
+(deftest clear-chat-resets-prompt-cache-test
+  (testing "Clearing a chat drops the prompt cache so a model switch does not warn (#530)"
+    (h/reset-components!)
+    (let [mocks {:all-tools-mock (constantly [])
+                 :api-mock (fn [{:keys [on-message-received]}]
+                             (on-message-received {:type :finish}))}
+          {:keys [chat-id]} (prompt! {:message "Hi" :model "openai/gpt-5.2"} mocks)]
+      (is (some? (get-in (h/db) [:chats chat-id :prompt-cache])))
+      (f.chat/clear-chat {:chat-id chat-id :messages true} (h/db*) (h/messenger) (h/metrics))
+      (is (nil? (get-in (h/db) [:chats chat-id :prompt-cache]))
+          "Clearing messages drops the prompt cache")
+      (swap! (h/db*) update :models #(merge % {"anthropic/claude-opus-4" {:tools true}}))
+      (h/reset-messenger!)
+      (prompt! {:message "Fresh" :chat-id chat-id :model "anthropic/claude-opus-4"} mocks)
+      (is (empty? (system-prompt-notices))
+          "No prompt cache invalidation notice on an empty chat"))))
+
 (deftest prompt-cache-key-includes-agent-test
   (testing "sync-or-async-prompt! receives prompt-cache-key scoped by active agent"
     (h/reset-components!)