fix(title): deduplicate title-setting logic, handle empty input

Extract shared set_title_if_missing() helper into db module to eliminate
duplicated title-setting code between thread_ops.rs and bridge/router.rs.
Skip empty/whitespace-only input to prevent permanently blocking
title-setting on image-only or attachment-only messages.

Addresses PR #2348 review feedback (duplicated code, empty input blocking).

[skip-regression-check]

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: zmanian

src/agent/thread_ops.rs

@@ -1078,19 +1078,7 @@ impl Agent {
             }
         }
 
-        // Set a conversation title from the first user message so the
-        // thread list shows a descriptive name in the sidebar.
-        if let Ok(None) = store
-            .get_conversation_metadata(thread_id)
-            .await
-            .map(|m| m.and_then(|v| v.get("title").and_then(|t| t.as_str()).map(String::from)))
-        {
-            let title_text: String = user_input.chars().take(100).collect();
-            let title_val = serde_json::json!(title_text);
-            let _ = store
-                .update_conversation_metadata_field(thread_id, "title", &title_val)
-                .await;
-        }
+        crate::db::set_title_if_missing(store.as_ref(), thread_id, user_input).await;
     }
 
     /// Persist the assistant response to the DB after the agentic loop completes.

src/bridge/router.rs

@@ -2969,20 +2969,7 @@ async fn handle_with_engine_inner(
         };
         if let Some(cid) = v1_conv_id {
             let _ = db.add_conversation_message(cid, "user", content).await;
-            // Set a conversation title from the first user message so the
-            // thread list shows a descriptive name even if the subquery-based
-            // title derivation has timing issues.
-            if let Ok(None) = db
-                .get_conversation_metadata(cid)
-                .await
-                .map(|m| m.and_then(|v| v.get("title").and_then(|t| t.as_str()).map(String::from)))
-            {
-                let title_text: String = content.chars().take(100).collect();
-                let title_val = serde_json::json!(title_text);
-                let _ = db
-                    .update_conversation_metadata_field(cid, "title", &title_val)
-                    .await;
-            }
+            crate::db::set_title_if_missing(db.as_ref(), cid, content).await;
         }
     }
 

src/channels/web/handlers/chat.rs

@@ -174,7 +174,7 @@ pub async fn chat_threads_handler(
             let title = t
                 .turns
                 .first()
-                .map(|turn| turn.user_input.chars().take(100).collect::<String>())
+                .map(|turn| turn.user_input.trim().chars().take(100).collect::<String>())
                 .filter(|s| !s.is_empty());
             ThreadInfo {
                 id: t.id,

src/channels/web/server.rs

@@ -1261,7 +1261,7 @@ pub(crate) async fn chat_threads_handler(
             let title = t
                 .turns
                 .first()
-                .map(|turn| turn.user_input.chars().take(100).collect::<String>())
+                .map(|turn| turn.user_input.trim().chars().take(100).collect::<String>())
                 .filter(|s| !s.is_empty());
             ThreadInfo {
                 id: t.id,

src/db/mod.rs

@@ -494,6 +494,39 @@ pub trait ConversationStore: Send + Sync {
     ) -> Result<Option<String>, DatabaseError>;
 }
 
+/// Set a conversation title from user input if one hasn't been set yet.
+///
+/// Skips empty/whitespace-only input so that image-only or attachment-only
+/// messages don't permanently block title-setting with an empty string.
+/// Truncates to the first 100 characters for sidebar display.
+pub async fn set_title_if_missing(
+    store: &(dyn ConversationStore + Send + Sync),
+    conversation_id: Uuid,
+    user_input: &str,
+) {
+    let trimmed = user_input.trim();
+    if trimmed.is_empty() {
+        return;
+    }
+
+    let has_title = match store.get_conversation_metadata(conversation_id).await {
+        Ok(Some(meta)) => meta
+            .get("title")
+            .and_then(|t| t.as_str())
+            .is_some_and(|s| !s.is_empty()),
+        Ok(None) => false,
+        Err(_) => return,
+    };
+
+    if !has_title {
+        let title_text: String = trimmed.chars().take(100).collect();
+        let title_val = serde_json::json!(title_text);
+        let _ = store
+            .update_conversation_metadata_field(conversation_id, "title", &title_val)
+            .await;
+    }
+}
+
 #[async_trait]
 pub trait JobStore: Send + Sync {
     async fn save_job(&self, ctx: &JobContext) -> Result<(), DatabaseError>;