fix(web): add SPA index fallback for embedded frontend routes

Serve existing static assets as-is, keep /api/* and missing asset paths returning 404, and add tests for SPA fallback behavior on refresh.

web/backend/embed.go

@@ -5,6 +5,8 @@ import (
 	"io/fs"
 	"log"
 	"net/http"
+	"path"
+	"strings"
 )
 
 //go:embed all:dist
@@ -24,6 +26,44 @@ func registerEmbedRoutes(mux *http.ServeMux) {
 		return
 	}
 
-	// Serve the static files at the root route
+	fileServer := http.FileServer(http.FS(subFS))
-	mux.Handle("/", http.FileServer(http.FS(subFS)))
+
+	// Serve static assets and fallback to index.html for SPA routes.
+	mux.Handle(
+		"/",
+		http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			if r.Method != http.MethodGet && r.Method != http.MethodHead {
+				http.NotFound(w, r)
+				return
+			}
+
+			// Keep unknown API paths as 404 instead of falling back to SPA entry.
+			if r.URL.Path == "/api" || strings.HasPrefix(r.URL.Path, "/api/") {
+				http.NotFound(w, r)
+				return
+			}
+
+			cleanPath := path.Clean(strings.TrimPrefix(r.URL.Path, "/"))
+			if cleanPath == "." {
+				cleanPath = ""
+			}
+
+			// Existing static files/directories should be served directly.
+			if cleanPath != "" {
+				if _, statErr := fs.Stat(subFS, cleanPath); statErr == nil {
+					fileServer.ServeHTTP(w, r)
+					return
+				}
+				// Missing asset-like paths should remain 404.
+				if strings.Contains(path.Base(cleanPath), ".") {
+					fileServer.ServeHTTP(w, r)
+					return
+				}
+			}
+
+			indexReq := r.Clone(r.Context())
+			indexReq.URL.Path = "/"
+			fileServer.ServeHTTP(w, indexReq)
+		}),
+	)
 }

web/backend/embed_test.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+func TestSPARouteFallsBackToIndex(t *testing.T) {
+	mux := http.NewServeMux()
+	registerEmbedRoutes(mux)
+
+	req := httptest.NewRequest(http.MethodGet, "/providers", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", rr.Code, http.StatusOK)
+	}
+	if !strings.Contains(rr.Body.String(), `<div id="root"></div>`) {
+		t.Fatalf("response does not look like index.html")
+	}
+}
+
+func TestUnknownAPIPathStays404(t *testing.T) {
+	mux := http.NewServeMux()
+	registerEmbedRoutes(mux)
+
+	req := httptest.NewRequest(http.MethodGet, "/api/not-found", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", rr.Code, http.StatusNotFound)
+	}
+}
+
+func TestMissingAssetStays404(t *testing.T) {
+	mux := http.NewServeMux()
+	registerEmbedRoutes(mux)
+
+	req := httptest.NewRequest(http.MethodGet, "/assets/not-found.js", nil)
+	rr := httptest.NewRecorder()
+	mux.ServeHTTP(rr, req)
+
+	if rr.Code != http.StatusNotFound {
+		t.Fatalf("status = %d, want %d", rr.Code, http.StatusNotFound)
+	}
+}