diff --git a/apps/desktop-shell/scripts/check-config.mjs b/apps/desktop-shell/scripts/check-config.mjs
index b13428111..bbba1db18 100644
--- a/apps/desktop-shell/scripts/check-config.mjs
+++ b/apps/desktop-shell/scripts/check-config.mjs
@@ -2465,9 +2465,12 @@ if (
 for (const snippet of [
   'WINDOW_TITLE_MAX_LENGTH',
   'normalize_window_title',
+  'window_title_from_request',
   'required_string_payload(request, "title")',
   'window.set_title(&title)',
   '"title is required"',
+  'window_title_request_rejects_missing_or_invalid_payload',
+  'window_title_request_trims_and_truncates_shared_boundary',
 ]) {
   if (!desktopHostBridgeTitleSource.includes(snippet)) {
     throw new Error(`desktop shell title module is missing ${snippet}`);
diff --git a/apps/desktop-shell/src-tauri/src/host_bridge/title.rs b/apps/desktop-shell/src-tauri/src/host_bridge/title.rs
index 9e4bfdaae..43a6b0f45 100644
--- a/apps/desktop-shell/src-tauri/src/host_bridge/title.rs
+++ b/apps/desktop-shell/src-tauri/src/host_bridge/title.rs
@@ -15,16 +15,22 @@ fn normalize_window_title(raw_title: &str) -> Option<String> {
     Some(title.chars().take(WINDOW_TITLE_MAX_LENGTH).collect())
 }
 
+fn window_title_from_request(
+    request: &HostBridgeRequest,
+) -> Result<String, HostBridgeResponse> {
+    required_string_payload(request, "title")
+        .ok()
+        .and_then(normalize_window_title)
+        .ok_or_else(|| failed(request.id.clone(), "invalid_request", "title is required"))
+}
+
 pub(crate) fn set_desktop_host_bridge_window_title(
     app: &tauri::AppHandle,
     request: &HostBridgeRequest,
 ) -> HostBridgeResponse {
-    let title = match required_string_payload(request, "title")
-        .ok()
-        .and_then(normalize_window_title)
-    {
-        Some(title) => title,
-        None => return failed(request.id.clone(), "invalid_request", "title is required"),
+    let title = match window_title_from_request(request) {
+        Ok(title) => title,
+        Err(response) => return response,
     };
 
     match app.get_webview_window("main") {
@@ -39,6 +45,8 @@ pub(crate) fn set_desktop_host_bridge_window_title(
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::host_bridge::protocol::request;
+    use serde_json::json;
 
     #[test]
     fn window_title_normalization_requires_visible_text() {
@@ -58,4 +66,36 @@ mod tests {
             80
         );
     }
+
+    #[test]
+    fn window_title_request_rejects_missing_or_invalid_payload() {
+        for payload in [
+            None,
+            Some(json!({})),
+            Some(json!({ "title": 1 })),
+            Some(json!({ "title": "   " })),
+            Some(json!({ "title": "Genarrative\nDev" })),
+        ] {
+            let mut request = request("app.setTitle");
+            request.payload = payload;
+
+            let response = window_title_from_request(&request).expect_err("invalid title");
+            let error = response.error.expect("error");
+            assert_eq!(error.code, "invalid_request");
+            assert_eq!(error.message, "title is required");
+        }
+    }
+
+    #[test]
+    fn window_title_request_trims_and_truncates_shared_boundary() {
+        let mut request = request("app.setTitle");
+        request.payload = Some(json!({
+            "title": format!("  {}  ", "甲".repeat(120))
+        }));
+
+        let title = window_title_from_request(&request).expect("window title");
+
+        assert_eq!(title.chars().count(), WINDOW_TITLE_MAX_LENGTH);
+        assert!(title.chars().all(|character| character == '甲'));
+    }
 }