Fix Anthropic empty/garbled chat titles on 3rd message retitle

The retitle feature passed the full chat history (including assistant
messages) as user-messages to sync-prompt!. Anthropic's handler
detected assistant messages without thinking blocks and converted all
roles to user, producing a malformed conversation that yielded
empty or nonsensical titles.

Fix: pass chat history as past-messages (which bypasses the
fix-non-thinking-assistant-messages transform) and keep only the
current user message as user-messages.

🤖 Generated with [eca](https://eca.dev)

Co-Authored-By: eca-agent <git@eca.dev>

Author: ericdallo

CHANGELOG.md

@@ -5,6 +5,7 @@
 - Support `ask_user` tool allowing LLM to ask the user questions with optional selectable options. #338
 - Remove redundant system message when background jobs finish or are killed.
 - Remove timeout for `ask_user` tool so it waits indefinitely for user response.
+- Fix Anthropic chat titles being empty or garbled on 3rd message retitle by passing conversation history as past-messages.
 
 ## 0.126.0
 

src/eca/features/chat.clj

@@ -574,18 +574,17 @@
                                      retitle?))]
         (assert-compatible-apis-between-models! db chat-id provider model config)
         (when generate-title?
-          (let [title-messages (if retitle?
-                                 (into (get-in db [:chats chat-id :messages] [])
-                                       user-messages)
-                                 user-messages)]
+          (let [title-past-messages (when retitle?
+                                     (get-in db [:chats chat-id :messages] []))]
             (future* config
               (when-let [{:keys [output-text]} (llm-api/sync-prompt!
                                                 {:provider provider
                                                  :model model
                                                  :model-capabilities
                                                  (assoc model-capabilities :reason? false :tools false :web-search false)
                                                  :instructions (f.prompt/chat-title-prompt agent config)
-                                                 :user-messages title-messages
+                                                 :past-messages title-past-messages
+                                                 :user-messages user-messages
                                                  :config config
                                                  :provider-auth provider-auth
                                                  :subagent? true})]

test/eca/features/chat_test.clj

@@ -222,6 +222,23 @@
     (is (match? {:chat-id string? :status :prompting} resp))
     {:chat-id chat-id}))
 
+(deftest sanitize-title-test
+  (testing "strips markdown headers"
+    (is (= "My Title" (#'f.chat/sanitize-title "## My Title")))
+    (is (= "My Title" (#'f.chat/sanitize-title "### My Title"))))
+  (testing "takes first non-blank line"
+    (is (= "First Line" (#'f.chat/sanitize-title "\n\n  First Line\nSecond Line"))))
+  (testing "strips control characters"
+    (is (= "clean text" (#'f.chat/sanitize-title "clean\u0000 \u001ftext"))))
+  (testing "collapses whitespace"
+    (is (= "hello world" (#'f.chat/sanitize-title "hello   world"))))
+  (testing "truncates to 40 chars"
+    (is (= 40 (count (#'f.chat/sanitize-title (apply str (repeat 60 "a")))))))
+  (testing "returns empty string for blank input"
+    (is (= "" (#'f.chat/sanitize-title "  \n  \n  "))))
+  (testing "returns nil for nil input"
+    (is (nil? (#'f.chat/sanitize-title nil)))))
+
 (deftest title-generation-test
   (testing "generates title on first message and re-generates at third with full context"
     (h/reset-components!)
@@ -251,9 +268,11 @@
         (is (= 2 (count @sync-prompt-calls*))
             "Should call sync-prompt! again on third message")
         (is (= "Title 2" (get-in (h/db) [:chats chat-id :title])))
-        (let [retitle-messages (:user-messages (second @sync-prompt-calls*))]
-          (is (> (count retitle-messages) 1)
-              "Third message title should include full conversation history"))
+        (let [retitle-call (second @sync-prompt-calls*)]
+          (is (= 1 (count (:user-messages retitle-call)))
+              "Third message title should pass only current user message")
+          (is (seq (:past-messages retitle-call))
+              "Third message title should include chat history as past-messages"))
 
         ;; Message 4: should NOT re-generate title
         (h/reset-messenger!)