fix #84: security headers dropped because they were set post-flush; set pre-handler

internal/web/web.go

@@ -304,13 +304,15 @@ func (u *UI) Handlers() *Handlers { return &Handlers{UI: u} }
 // pentest. Runs after the handler so the Content-Type is already set.
 func SecurityHeaders(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		next.ServeHTTP(w, r)
+		// Set before the handler runs: once a handler writes (template render
+		// flushes), header mutations are silently dropped. Setting the headers
+		// unconditionally is safe: CSP/nosniff/referrer on JSON or /raw bodies
+		// is harmless and arguably desirable.
 		h := w.Header()
-		if strings.HasPrefix(h.Get("Content-Type"), "text/html") {
-			h.Set("Content-Security-Policy",
-				"default-src 'self'; script-src 'self' 'unsafe-inline'; frame-ancestors 'none'")
-			h.Set("Referrer-Policy", "no-referrer")
-			h.Set("X-Content-Type-Options", "nosniff")
-		}
+		h.Set("Content-Security-Policy",
+			"default-src 'self'; script-src 'self' 'unsafe-inline'; frame-ancestors 'none'")
+		h.Set("Referrer-Policy", "no-referrer")
+		h.Set("X-Content-Type-Options", "nosniff")
+		next.ServeHTTP(w, r)
 	})
 }