diff --git a/README_ERROR_VISIBILITY_PATCH.md b/README_ERROR_VISIBILITY_PATCH.md
new file mode 100644
index 0000000..642a698
--- /dev/null
+++ b/README_ERROR_VISIBILITY_PATCH.md
@@ -0,0 +1,10 @@
+# RetrieX error visibility patch
+
+This patch makes Shopware Store API authentication/configuration failures visible in the chat stream and improves client-side display of SSE/job errors.
+
+Changed files:
+- src/Shopware/StoreApiClient.php
+- src/Shopware/StoreApiException.php
+- src/Agent/AgentRunner.php
+- src/Controller/AskSseController.php
+- public/assets/js/base.js
diff --git a/public/assets/js/base.js b/public/assets/js/base.js
index cba6c90..f54eac9 100644
--- a/public/assets/js/base.js
+++ b/public/assets/js/base.js
@@ -69,8 +69,28 @@ document.addEventListener('DOMContentLoaded', () => {
         ) !== null;
     }
 
+    function isWhitespaceTextNode(node) {
+        return node.nodeType === Node.TEXT_NODE && (node.textContent || '').trim() === '';
+    }
+
+    function isBreakNode(node) {
+        return node.nodeType === Node.ELEMENT_NODE && node.tagName === 'BR';
+    }
+
+    function trimEdgeBreaks(element) {
+        while (element.firstChild && (isWhitespaceTextNode(element.firstChild) || isBreakNode(element.firstChild))) {
+            element.firstChild.remove();
+        }
+
+        while (element.lastChild && (isWhitespaceTextNode(element.lastChild) || isBreakNode(element.lastChild))) {
+            element.lastChild.remove();
+        }
+    }
+
     function cleanupEmptyBlocks(container) {
         container.querySelectorAll('p, div, li, blockquote').forEach((el) => {
+            trimEdgeBreaks(el);
+
             const html = el.innerHTML
                 .replace(/<br\s*\/?>/gi, '')
                 .replace(/&nbsp;/gi, '')
@@ -87,6 +107,8 @@ document.addEventListener('DOMContentLoaded', () => {
                 el.remove();
             }
         });
+
+        trimEdgeBreaks(container);
     }
 
     function removeThinkSpansOnly(container) {
@@ -165,6 +187,7 @@ document.addEventListener('DOMContentLoaded', () => {
         const thinkSpans = Array.from(container.querySelectorAll('.think'));
 
         if (thinkSpans.length === 0) {
+            cleanupEmptyBlocks(container);
             return;
         }
 
@@ -350,7 +373,8 @@ document.addEventListener('DOMContentLoaded', () => {
                 firstChunk = false;
             }
 
-            raw += `\n\n<em>${safeMessage}</em>`;
+            const formattedMessage = `<em>${safeMessage}</em>`;
+            raw += raw.trim() === '' ? formattedMessage : `\n\n${formattedMessage}`;
             finalizeStream(bubble, raw);
         };
 
@@ -486,7 +510,8 @@ document.addEventListener('DOMContentLoaded', () => {
                 const userMessage = 'Die Verbindung zum Antwort-Stream wurde unterbrochen. Bitte sende die Anfrage erneut, falls die Antwort unvollständig ist.';
 
                 if (raw.trim() !== '') {
-                    raw += `\n\n<em>${userMessage}</em>`;
+                    const formattedMessage = `<em>${userMessage}</em>`;
+                    raw += raw.trim() === '' ? formattedMessage : `\n\n${formattedMessage}`;
                     renderBubbleContent(bubble, raw);
                 } else {
                     bubble.innerHTML = `<em>${userMessage}</em>`;
diff --git a/src/Agent/AgentRunner.php b/src/Agent/AgentRunner.php
index 06bc43e..c685459 100644
--- a/src/Agent/AgentRunner.php
+++ b/src/Agent/AgentRunner.php
@@ -156,7 +156,7 @@ final readonly class AgentRunner
 
                     yield $this->systemMsg(
                         $this->buildShopUnavailableMessage($primaryShopSearchFailureReason),
-                        'info'
+                        'err'
                     );
 
                     $repairPayload = [
@@ -811,12 +811,21 @@ final readonly class AgentRunner
 
     private function buildUserErrorMessage(Throwable $e): string
     {
+        $message = trim($e->getMessage());
+
+        if ($message === '') {
+            $message = $e::class;
+        }
+
+        $safeMessage = htmlspecialchars($message, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
+
         if (!$this->debug) {
-            return $this->agentRunnerConfig->getGenericInternalErrorMessage();
+            return $this->agentRunnerConfig->getGenericInternalErrorMessage()
+                . '<br><small>Technischer Fehler: ' . $safeMessage . '</small>';
         }
 
         return $this->agentRunnerConfig->getDebugInternalErrorPrefix()
-            . htmlspecialchars($e->getMessage(), ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
+            . $safeMessage;
     }
 
     private function badge(string $label): string
diff --git a/src/Controller/AskSseController.php b/src/Controller/AskSseController.php
index 6bee4a0..fc7be8c 100644
--- a/src/Controller/AskSseController.php
+++ b/src/Controller/AskSseController.php
@@ -55,9 +55,9 @@ final readonly class AskSseController
                 'includeFullContext' => $includeFullContext,
                 'createdAt' => time(),
             ]);
-        } catch (\Throwable) {
+        } catch (\Throwable $e) {
             return new JsonResponse(
-                ['error' => 'Stream job could not be created.'],
+                ['error' => 'Stream job could not be created: ' . $this->formatThrowableForClient($e)],
                 Response::HTTP_INTERNAL_SERVER_ERROR
             );
         }
@@ -139,6 +139,7 @@ final readonly class AskSseController
         ?Response $cookieResponse
     ): void {
         $this->prepareStreamRuntime();
+        $this->registerStreamShutdownErrorHandler();
 
         if ($cookieResponse !== null) {
             foreach ($cookieResponse->headers->getCookies() as $cookie) {
@@ -167,13 +168,51 @@ final readonly class AskSseController
         } catch (\Throwable $e) {
             $this->sendEvent(
                 'error',
-                '❌ Stream abgebrochen: ' . $e->getMessage()
+                '❌ Stream abgebrochen: ' . $this->formatThrowableForClient($e)
             );
         }
 
         $this->sendEvent('done', '[DONE]');
     }
 
+    private function registerStreamShutdownErrorHandler(): void
+    {
+        register_shutdown_function(function (): void {
+            $error = error_get_last();
+
+            if ($error === null) {
+                return;
+            }
+
+            $fatalTypes = [E_ERROR, E_PARSE, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR];
+
+            if (!in_array((int) ($error['type'] ?? 0), $fatalTypes, true)) {
+                return;
+            }
+
+            $message = sprintf(
+                '❌ Fataler Serverfehler: %s in %s:%s',
+                (string) ($error['message'] ?? 'unknown error'),
+                (string) ($error['file'] ?? 'unknown file'),
+                (string) ($error['line'] ?? '?')
+            );
+
+            $this->sendEvent('error', $message);
+            $this->sendEvent('done', '[DONE]');
+        });
+    }
+
+    private function formatThrowableForClient(\Throwable $e): string
+    {
+        $message = trim($e->getMessage());
+
+        if ($message === '') {
+            $message = $e::class;
+        }
+
+        return preg_replace('/\s+/u', ' ', $message) ?? $message;
+    }
+
     private function prepareStreamRuntime(): void
     {
         @set_time_limit(0);
diff --git a/src/Shopware/StoreApiClient.php b/src/Shopware/StoreApiClient.php
index 754f321..730de82 100644
--- a/src/Shopware/StoreApiClient.php
+++ b/src/Shopware/StoreApiClient.php
@@ -83,19 +83,32 @@ final readonly class StoreApiClient
     {
         $preview = mb_substr(trim($content), 0, 1000);
         $utf8Failure = $this->containsUtf8FailureSignal($preview);
-        $serverFailure = $statusCode >= 500;
+        $normalizedPreview = mb_strtolower($preview, 'UTF-8');
+        $accessKeyFailure = $statusCode === 401
+            || $statusCode === 403
+            || str_contains($preview, 'FRAMEWORK__API_INVALID_ACCESS_KEY')
+            || str_contains($normalizedPreview, 'access key is invalid');
+        $serverFailure = $statusCode >= 500 || $accessKeyFailure;
+
+        $hint = '';
+
+        if ($accessKeyFailure) {
+            $hint = ' Hint: The configured Shopware Sales Channel access key is invalid or does not match the Store API endpoint.';
+        } elseif ($utf8Failure) {
+            $hint = ' Hint: The request body was valid JSON; this Shopware error usually means Shopware failed while encoding response/product data as UTF-8.';
+        }
 
         return new StoreApiException(
             sprintf(
                 'Shopware Store API request failed with status %d. Response: %s%s',
                 $statusCode,
                 $preview,
-                $utf8Failure ? ' Hint: The request body was valid JSON; this Shopware error usually means Shopware failed while encoding response/product data as UTF-8.' : ''
+                $hint
             ),
             $statusCode,
             $serverFailure,
             $utf8Failure,
-            $serverFailure || $utf8Failure
+            $serverFailure || $utf8Failure || $accessKeyFailure
         );
     }
 
diff --git a/src/Shopware/StoreApiException.php b/src/Shopware/StoreApiException.php
index 9e278ab..1a3cdfe 100644
--- a/src/Shopware/StoreApiException.php
+++ b/src/Shopware/StoreApiException.php
@@ -42,6 +42,10 @@ final class StoreApiException extends RuntimeException
 
     public function isSystemFailure(): bool
     {
-        return $this->serverFailure || $this->utf8Failure;
+        if ($this->serverFailure || $this->utf8Failure) {
+            return true;
+        }
+
+        return $this->statusCode === 401 || $this->statusCode === 403;
     }
 }