feat: add mobile-friendly HTTP 404 and 500 error pages

Add ErrorNotFound and ErrorInternal handler methods that render styled
error pages using the error.html template, with proper status codes,
responsive layout, SVG icons, and HTMX fragment support. Replace the
plain-text http.NotFound call in Dashboard with the new styled handler.

Closes leeworks-agents/gitea-mobile#131

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

cmd/server/main.go

@@ -33,7 +33,7 @@ func main() {
 
 	// Apply middleware chain: logging -> auth.
 	var handler http.Handler = mux
-	handler = middleware.Auth(cfg.SessionSecret)(handler)
+	handler = middleware.Auth(cfg.SessionSecret, cfg.GiteaToken)(handler)
 	handler = middleware.Logging()(handler)
 
 	slog.Info("server starting", "addr", cfg.ListenAddr, "gitea_url", cfg.GiteaURL)

internal/gitea/client_test.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 )
@@ -893,6 +894,140 @@ func TestListAllPullRequests_StateFilter(t *testing.T) {
 	}
 }
 
+// --- Issue #127: Tests for ApplyLabel and SubmitReview ---
+
+func TestApplyLabel(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v1/repos/owner1/repo1/issues/42/labels" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		if r.Header.Get("Authorization") != "token test-token" {
+			t.Error("missing or wrong Authorization header")
+		}
+
+		var body map[string]interface{}
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Fatalf("failed to decode body: %v", err)
+		}
+		labels, ok := body["labels"].([]interface{})
+		if !ok {
+			t.Fatalf("expected labels array, got %T", body["labels"])
+		}
+		if len(labels) != 2 {
+			t.Errorf("expected 2 label IDs, got %d", len(labels))
+		}
+		// Verify the label IDs are correct (JSON numbers are float64).
+		if labels[0].(float64) != 10 || labels[1].(float64) != 20 {
+			t.Errorf("expected label IDs [10, 20], got %v", labels)
+		}
+
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode([]map[string]interface{}{
+			{"id": 10, "name": "bug"},
+			{"id": 20, "name": "enhancement"},
+		})
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	c.setCache("issues-org1", "should-be-invalidated")
+
+	err := c.ApplyLabel(context.Background(), "test-token", "owner1", "repo1", 42, []int64{10, 20})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Verify cache was invalidated.
+	_, ok := c.getFromCache("issues-org1")
+	if ok {
+		t.Error("expected cache to be invalidated after ApplyLabel")
+	}
+}
+
+func TestApplyLabel_Error(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNotFound)
+		fmt.Fprintln(w, `{"message":"issue not found"}`)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	err := c.ApplyLabel(context.Background(), "test-token", "owner1", "repo1", 999, []int64{10})
+	if err == nil {
+		t.Fatal("expected error for 404 response, got nil")
+	}
+	if !strings.Contains(err.Error(), "404") {
+		t.Errorf("error should contain status code 404, got: %v", err)
+	}
+}
+
+func TestSubmitReview(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v1/repos/owner1/repo1/pulls/7/reviews" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		if r.Header.Get("Authorization") != "token test-token" {
+			t.Error("missing or wrong Authorization header")
+		}
+
+		var body map[string]string
+		if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+			t.Fatalf("failed to decode body: %v", err)
+		}
+		if body["event"] != "APPROVED" {
+			t.Errorf("expected event=APPROVED, got %q", body["event"])
+		}
+		if body["body"] != "Looks good!" {
+			t.Errorf("expected body='Looks good!', got %q", body["body"])
+		}
+
+		w.WriteHeader(http.StatusOK)
+		json.NewEncoder(w).Encode(map[string]interface{}{
+			"id":    1,
+			"state": "APPROVED",
+			"body":  body["body"],
+		})
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	c.setCache("pulls-org1", "should-be-invalidated")
+
+	err := c.SubmitReview(context.Background(), "test-token", "owner1", "repo1", 7, "APPROVED", "Looks good!")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	// Verify cache was invalidated.
+	_, ok := c.getFromCache("pulls-org1")
+	if ok {
+		t.Error("expected cache to be invalidated after SubmitReview")
+	}
+}
+
+func TestSubmitReview_Error(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusUnprocessableEntity)
+		fmt.Fprintln(w, `{"message":"validation failed"}`)
+	}))
+	defer server.Close()
+
+	c := NewClient(server.URL)
+	err := c.SubmitReview(context.Background(), "test-token", "owner1", "repo1", 7, "INVALID", "")
+	if err == nil {
+		t.Fatal("expected error for 422 response, got nil")
+	}
+	if !strings.Contains(err.Error(), "422") {
+		t.Errorf("error should contain status code 422, got: %v", err)
+	}
+}
+
 func TestListAllPullRequests_Pagination(t *testing.T) {
 	now := time.Date(2026, 3, 28, 12, 0, 0, 0, time.UTC)
 

internal/handlers/handlers.go

@@ -181,11 +181,58 @@ func renderPage(w http.ResponseWriter, r *http.Request, title, activeTab string,
 	}
 }
 
+// errorData holds the template data for error pages.
+type errorData struct {
+	Code    int
+	Title   string
+	Message string
+}
+
+// ErrorNotFound renders a mobile-friendly 404 error page.
+func (h *Handler) ErrorNotFound(w http.ResponseWriter, r *http.Request) {
+	data := errorData{
+		Code:    http.StatusNotFound,
+		Title:   "Page Not Found",
+		Message: "The page you are looking for does not exist or has been moved.",
+	}
+	h.renderError(w, r, data)
+}
+
+// ErrorInternal renders a mobile-friendly 500 error page.
+func (h *Handler) ErrorInternal(w http.ResponseWriter, r *http.Request) {
+	data := errorData{
+		Code:    http.StatusInternalServerError,
+		Title:   "Internal Server Error",
+		Message: "Something went wrong on our end. Please try again later.",
+	}
+	h.renderError(w, r, data)
+}
+
+// renderError renders the error template with the given data and status code.
+func (h *Handler) renderError(w http.ResponseWriter, r *http.Request, data errorData) {
+	tmpl, err := template.ParseFiles("internal/templates/error.html")
+	if err != nil {
+		slog.Error("failed to parse error template", "error", err)
+		http.Error(w, fmt.Sprintf("%d %s", data.Code, data.Title), data.Code)
+		return
+	}
+
+	var buf strings.Builder
+	if err := tmpl.ExecuteTemplate(&buf, "content", data); err != nil {
+		slog.Error("failed to execute error template", "error", err)
+		http.Error(w, fmt.Sprintf("%d %s", data.Code, data.Title), data.Code)
+		return
+	}
+
+	w.WriteHeader(data.Code)
+	renderPage(w, r, data.Title, "", buf.String())
+}
+
 // Dashboard handles GET / — the triage queue.
 func (h *Handler) Dashboard(w http.ResponseWriter, r *http.Request) {
 	// Only handle exact root path.
 	if r.URL.Path != "/" {
-		http.NotFound(w, r)
+		h.ErrorNotFound(w, r)
 		return
 	}
 

internal/handlers/handlers_test.go

@@ -183,6 +183,87 @@ func TestAddComment_EmptyBody(t *testing.T) {
 	}
 }
 
+func TestErrorNotFound(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/nonexistent", nil)
+	w := httptest.NewRecorder()
+
+	h.ErrorNotFound(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	if body == "" {
+		t.Error("expected non-empty response body")
+	}
+	if !contains(body, "404") {
+		t.Error("expected body to contain '404'")
+	}
+	if !contains(body, "Page Not Found") {
+		t.Error("expected body to contain 'Page Not Found'")
+	}
+}
+
+func TestErrorInternal(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/error", nil)
+	w := httptest.NewRecorder()
+
+	h.ErrorInternal(w, req)
+
+	if w.Code != http.StatusInternalServerError {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusInternalServerError)
+	}
+	body := w.Body.String()
+	if body == "" {
+		t.Error("expected non-empty response body")
+	}
+	if !contains(body, "500") {
+		t.Error("expected body to contain '500'")
+	}
+	if !contains(body, "Internal Server Error") {
+		t.Error("expected body to contain 'Internal Server Error'")
+	}
+}
+
+func TestDashboard_NonRootPath_Returns404(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/unknown/path", nil)
+	w := httptest.NewRecorder()
+
+	h.Dashboard(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	if !contains(body, "404") {
+		t.Error("expected body to contain '404' for non-root path")
+	}
+}
+
+func TestErrorNotFound_HTMX(t *testing.T) {
+	h := newTestHandler()
+	req := httptest.NewRequest(http.MethodGet, "/nonexistent", nil)
+	req.Header.Set("HX-Request", "true")
+	w := httptest.NewRecorder()
+
+	h.ErrorNotFound(w, req)
+
+	if w.Code != http.StatusNotFound {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusNotFound)
+	}
+	body := w.Body.String()
+	// HTMX response should not contain DOCTYPE.
+	if contains(body, "<!DOCTYPE") {
+		t.Error("HTMX response should not contain DOCTYPE")
+	}
+	if !contains(body, "Page Not Found") {
+		t.Error("expected body to contain 'Page Not Found'")
+	}
+}
+
 func contains(s, substr string) bool {
 	return len(s) >= len(substr) && searchString(s, substr)
 }

internal/middleware/auth.go

@@ -23,9 +23,12 @@ func TokenFromContext(ctx context.Context) string {
 }
 
 // Auth returns middleware that checks for a valid token cookie.
+// If no cookie token is found and fallbackToken is non-empty, the fallback
+// token is used instead (useful for single-user or service-account deployments
+// where GITEA_TOKEN is set in the environment).
 // Unauthenticated requests are redirected to the settings page.
 // The /health, /settings, and /static/ paths are exempt from auth.
-func Auth(sessionSecret string) func(http.Handler) http.Handler {
+func Auth(sessionSecret, fallbackToken string) func(http.Handler) http.Handler {
 	return func(next http.Handler) http.Handler {
 		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 			// Skip auth for exempt paths.
@@ -37,6 +40,13 @@ func Auth(sessionSecret string) func(http.Handler) http.Handler {
 
 			token, err := auth.GetToken(r, sessionSecret)
 			if err != nil || token == "" {
+				// Fall back to environment token if available.
+				if fallbackToken != "" {
+					slog.Debug("using fallback token from environment", "path", path)
+					ctx := context.WithValue(r.Context(), TokenContextKey, fallbackToken)
+					next.ServeHTTP(w, r.WithContext(ctx))
+					return
+				}
 				slog.Debug("unauthenticated request, redirecting to settings", "path", path, "error", err)
 				http.Redirect(w, r, "/settings", http.StatusSeeOther)
 				return

internal/middleware/auth_test.go

@@ -11,7 +11,7 @@ import (
 const testSecret = "test-secret-that-is-at-least-32-chars-long"
 
 func TestAuth_HealthBypass(t *testing.T) {
-	handler := Auth(testSecret)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	handler := Auth(testSecret, "")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	}))
 
@@ -25,7 +25,7 @@ func TestAuth_HealthBypass(t *testing.T) {
 }
 
 func TestAuth_SettingsBypass(t *testing.T) {
-	handler := Auth(testSecret)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	handler := Auth(testSecret, "")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	}))
 
@@ -39,7 +39,7 @@ func TestAuth_SettingsBypass(t *testing.T) {
 }
 
 func TestAuth_RedirectWithoutToken(t *testing.T) {
-	handler := Auth(testSecret)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	handler := Auth(testSecret, "")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 	}))
 
@@ -57,7 +57,7 @@ func TestAuth_RedirectWithoutToken(t *testing.T) {
 
 func TestAuth_PassWithToken(t *testing.T) {
 	called := false
-	handler := Auth(testSecret)(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	handler := Auth(testSecret, "")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		called = true
 		token := TokenFromContext(r.Context())
 		if token != "my-token" {
@@ -83,3 +83,72 @@ func TestAuth_PassWithToken(t *testing.T) {
 		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
 	}
 }
+
+func TestAuth_FallbackToken_UsedWhenNoCookie(t *testing.T) {
+	called := false
+	handler := Auth(testSecret, "env-fallback-token")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		called = true
+		token := TokenFromContext(r.Context())
+		if token != "env-fallback-token" {
+			t.Errorf("token = %q, want %q", token, "env-fallback-token")
+		}
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if !called {
+		t.Error("next handler was not called with fallback token")
+	}
+	if w.Code != http.StatusOK {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+	}
+}
+
+func TestAuth_FallbackToken_CookieTakesPrecedence(t *testing.T) {
+	called := false
+	handler := Auth(testSecret, "env-fallback-token")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		called = true
+		token := TokenFromContext(r.Context())
+		if token != "cookie-token" {
+			t.Errorf("token = %q, want %q (cookie should take precedence over fallback)", token, "cookie-token")
+		}
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	// Set a cookie token.
+	cookieW := httptest.NewRecorder()
+	auth.SetTokenCookie(cookieW, "cookie-token", testSecret, false)
+	cookie := cookieW.Result().Cookies()[0]
+
+	req := httptest.NewRequest(http.MethodGet, "/", nil)
+	req.AddCookie(cookie)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if !called {
+		t.Error("next handler was not called")
+	}
+	if w.Code != http.StatusOK {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusOK)
+	}
+}
+
+func TestAuth_NoFallbackToken_RedirectsWithoutCookie(t *testing.T) {
+	handler := Auth(testSecret, "")(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+
+	req := httptest.NewRequest(http.MethodGet, "/issues", nil)
+	w := httptest.NewRecorder()
+	handler.ServeHTTP(w, req)
+
+	if w.Code != http.StatusSeeOther {
+		t.Errorf("status = %d, want %d", w.Code, http.StatusSeeOther)
+	}
+	if loc := w.Header().Get("Location"); loc != "/settings" {
+		t.Errorf("Location = %q, want %q", loc, "/settings")
+	}
+}

internal/templates/error.html

@@ -0,0 +1,23 @@
+{{define "content"}}
+<div class="error-page">
+  <div class="error-icon">
+    {{if eq .Code 404}}
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" width="64" height="64">
+      <circle cx="11" cy="11" r="8"/>
+      <line x1="21" y1="21" x2="16.65" y2="16.65"/>
+      <line x1="8" y1="11" x2="14" y2="11"/>
+    </svg>
+    {{else}}
+    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.5" width="64" height="64">
+      <path d="M10.29 3.86L1.82 18a2 2 0 001.71 3h16.94a2 2 0 001.71-3L13.71 3.86a2 2 0 00-3.42 0z"/>
+      <line x1="12" y1="9" x2="12" y2="13"/>
+      <line x1="12" y1="17" x2="12.01" y2="17"/>
+    </svg>
+    {{end}}
+  </div>
+  <h1 class="error-code">{{.Code}}</h1>
+  <p class="error-title">{{.Title}}</p>
+  <p class="error-message">{{.Message}}</p>
+  <a href="/" class="error-home-link">Go to Dashboard</a>
+</div>
+{{end}}

static/style.css

@@ -545,3 +545,56 @@ a:active {
     --text-link: #0969da;
   }
 }
+
+/* Error page */
+.error-page {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  justify-content: center;
+  min-height: 60vh;
+  text-align: center;
+  padding: var(--spacing-lg);
+}
+
+.error-icon {
+  color: var(--text-secondary);
+  margin-bottom: var(--spacing-lg);
+}
+
+.error-code {
+  font-size: 4rem;
+  font-weight: 700;
+  color: var(--text-primary);
+  line-height: 1;
+  margin-bottom: var(--spacing-sm);
+}
+
+.error-title {
+  font-size: var(--font-xl);
+  color: var(--text-primary);
+  margin-bottom: var(--spacing-sm);
+}
+
+.error-message {
+  font-size: var(--font-base);
+  color: var(--text-secondary);
+  margin-bottom: var(--spacing-lg);
+  max-width: 300px;
+}
+
+.error-home-link {
+  display: inline-block;
+  padding: var(--spacing-sm) var(--spacing-lg);
+  background: var(--accent-blue);
+  color: #fff;
+  border-radius: var(--radius);
+  text-decoration: none;
+  font-size: var(--font-base);
+  font-weight: 500;
+  transition: opacity 0.15s;
+}
+
+.error-home-link:active {
+  opacity: 0.8;
+}