fix: validate owner/repo split in create_issue.html before submission

Add client-side validation to ensure a repository is selected before
form submission. Split owner/repo on both change and submit events.
Show inline error messages via form-error div. Update CreateIssue
handler to return HTMX-friendly HTML error fragments on 400/500.

Closes leeworks-agents/gitea-mobile#30

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

internal/handlers/handlers.go

@@ -458,6 +458,12 @@ func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 	body := r.FormValue("body")
 
 	if owner == "" || repo == "" || title == "" {
+		if isHTMX(r) {
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusBadRequest)
+			fmt.Fprint(w, `<span class="empty">owner, repo, and title are required</span>`)
+			return
+		}
 		http.Error(w, "owner, repo, and title are required", http.StatusBadRequest)
 		return
 	}
@@ -465,6 +471,12 @@ func (h *Handler) CreateIssue(w http.ResponseWriter, r *http.Request) {
 	issue, err := h.Client.CreateIssue(r.Context(), token, owner, repo, title, body, nil)
 	if err != nil {
 		slog.Error("failed to create issue", "error", err)
+		if isHTMX(r) {
+			w.Header().Set("Content-Type", "text/html; charset=utf-8")
+			w.WriteHeader(http.StatusInternalServerError)
+			fmt.Fprint(w, `<span class="empty">Failed to create issue. Please try again.</span>`)
+			return
+		}
 		http.Error(w, "failed to create issue", http.StatusInternalServerError)
 		return
 	}

internal/templates/create_issue.html

@@ -1,7 +1,9 @@
 {{define "content"}}
 <h1>Create Issue</h1>
 
-<form hx-post="/issues" hx-swap="innerHTML" hx-target="#main-content">
+<div id="form-error" class="empty" style="display:none;"></div>
+
+<form id="create-issue-form" hx-post="/issues" hx-swap="innerHTML" hx-target="#main-content">
   <div class="form-group">
     <label for="repo-select">Repository</label>
     <select id="repo-select" name="owner_repo" required>
@@ -32,11 +34,43 @@
 </form>
 
 <script>
-  // Split owner/repo from select into hidden fields.
-  document.getElementById('repo-select').addEventListener('change', function() {
-    var parts = this.value.split('/');
-    document.getElementById('owner-input').value = parts[0] || '';
-    document.getElementById('repo-input').value = parts[1] || '';
+  (function() {
+    var repoSelect = document.getElementById('repo-select');
+    var ownerInput = document.getElementById('owner-input');
+    var repoInput = document.getElementById('repo-input');
+    var formError = document.getElementById('form-error');
+
+    function splitOwnerRepo() {
+      var val = repoSelect.value;
+      if (val) {
+        var parts = val.split('/');
+        ownerInput.value = parts[0] || '';
+        repoInput.value = parts[1] || '';
+      } else {
+        ownerInput.value = '';
+        repoInput.value = '';
+      }
+    }
+
+    repoSelect.addEventListener('change', splitOwnerRepo);
+
+    // Validate before HTMX submit.
+    document.getElementById('create-issue-form').addEventListener('htmx:configRequest', function(evt) {
+      splitOwnerRepo();
+      if (!ownerInput.value || !repoInput.value) {
+        evt.preventDefault();
+        formError.textContent = 'Please select a repository before submitting.';
+        formError.style.display = 'block';
+        return false;
+      }
+      formError.style.display = 'none';
     });
+
+    // Show server-side errors inline on HTMX error responses.
+    document.getElementById('create-issue-form').addEventListener('htmx:responseError', function(evt) {
+      formError.textContent = evt.detail.xhr.responseText || 'An error occurred. Please try again.';
+      formError.style.display = 'block';
+    });
+  })();
 </script>
 {{end}}