diff --git a/config/retriex/chat-messages.yaml b/config/retriex/chat-messages.yaml
index 1871e89..5aa91b8 100644
--- a/config/retriex/chat-messages.yaml
+++ b/config/retriex/chat-messages.yaml
@@ -92,6 +92,7 @@ parameters:
         shop_query_optimization_heartbeat: Shop-Suchanfrage wird optimiert…
         generic_internal_error: ❌ Bei der Verarbeitung der Anfrage ist ein interner Fehler aufgetreten.
         debug_internal_error_prefix: '❌ Interner Fehler: '
+        technical_error_detail_template: '<br><small>Technischer Fehler: {message}</small>'
       final_answer_guard:
         truncation_message: |2-
 
@@ -231,6 +232,7 @@ parameters:
           shop_meta_result_count: 'Shoptreffer: {count}'
           history_notice_without_detail: 'Systemhinweis: {title}.'
           history_notice_with_detail: 'Systemhinweis: {title}. Ursache: {detail}'
+          history_response_system_notice: 'Systemhinweis: {message}'
         follow_up_actions:
           commerce:
           - label: Im Shop suchen
diff --git a/patch_history/RETRIEX_PATCH_66_CHAT_MESSAGE_RESIDUAL_CLEANUP_README.md b/patch_history/RETRIEX_PATCH_66_CHAT_MESSAGE_RESIDUAL_CLEANUP_README.md
new file mode 100644
index 0000000..3073bef
--- /dev/null
+++ b/patch_history/RETRIEX_PATCH_66_CHAT_MESSAGE_RESIDUAL_CLEANUP_README.md
@@ -0,0 +1,56 @@
+# RetrieX Patch 66 - Chat Message Residual Cleanup
+
+## Ziel
+
+p66 schliesst die Chat-Messages-Migration nach p63, p64 und p65 ab, indem zwei verbliebene user-lesbare Resttexte aus `AgentRunner.php` nach `config/retriex/chat-messages.yaml` verschoben werden.
+
+## Geaenderte Dateien
+
+- `config/retriex/chat-messages.yaml`
+  - neuer Key `agent.messages.technical_error_detail_template`
+  - neuer Key `agent.production_ui.templates.history_response_system_notice`
+- `src/Config/ChatMessagesConfig.php`
+  - Validation der neuen Chat-Message-Keys
+- `src/Config/AgentRunnerConfig.php`
+  - neue Getter fuer die beiden Rest-Templates
+  - neue chat-only Zugriffsmethode fuer neue Keys ohne Legacy-Agent-Fallback
+- `src/Agent/AgentRunner.php`
+  - History-Fallback-Systemhinweis rendert ueber YAML-Template
+  - technischer Fehlerdetail-Hinweis rendert ueber YAML-Template
+
+## Bewusst nicht geaendert
+
+- keine Aenderung an Retrieval
+- keine Aenderung an Scoring oder Ranking
+- keine Aenderung an Intent- oder Shop-Matching
+- keine Aenderung an `AgentRunner.php`-Ablauflogik ausser der Message-Template-Herkunft
+- keine neuen chat-sichtbaren Legacy-Keys in `agent.yaml`
+
+## Ergebnis
+
+Nach p66 liegen die bekannten user-lesbaren Chat-/SSE-/Frontend-/Agent-Messages zentral in `config/retriex/chat-messages.yaml`.
+
+## Lokale Checks
+
+Gruen:
+
+```bash
+php -l src/Config/ChatMessagesConfig.php
+php -l src/Config/AgentRunnerConfig.php
+php -l src/Agent/AgentRunner.php
+python3 -c "import yaml; yaml.safe_load(open('config/retriex/chat-messages.yaml'))"
+php /tmp/p66_smoke.php
+php /tmp/p66_agent_config_smoke.php
+```
+
+Nicht lokal ausfuehrbar im ZIP ohne `vendor/`:
+
+```bash
+php bin/console mto:agent:config:validate
+```
+
+Fehler:
+
+```text
+Dependencies are missing. Try running "composer install".
+```
diff --git a/src/Agent/AgentRunner.php b/src/Agent/AgentRunner.php
index 82c5d09..d605002 100644
--- a/src/Agent/AgentRunner.php
+++ b/src/Agent/AgentRunner.php
@@ -4516,7 +4516,10 @@ final readonly class AgentRunner
                 $noLlmMessage = $this->agentRunnerConfig->getProductionUiText('no_llm_history_default');
             }
 
-            $parts[] = 'Systemhinweis: ' . $noLlmMessage;
+            $parts[] = $this->renderAgentTemplate(
+                $this->agentRunnerConfig->getHistoryResponseSystemNoticeTemplate(),
+                ['message' => $noLlmMessage]
+            );
         }
 
         return trim(implode("\n\n", $parts));
@@ -5015,7 +5018,10 @@ final readonly class AgentRunner
 
         if (!$this->debug) {
             return $this->agentRunnerConfig->getGenericInternalErrorMessage()
-                . '<br><small>Technischer Fehler: ' . $safeMessage . '</small>';
+                . $this->renderAgentTemplate(
+                    $this->agentRunnerConfig->getTechnicalErrorDetailTemplate(),
+                    ['message' => $safeMessage]
+                );
         }
 
         return $this->agentRunnerConfig->getDebugInternalErrorPrefix()
diff --git a/src/Config/AgentRunnerConfig.php b/src/Config/AgentRunnerConfig.php
index b6bc405..f722cf7 100644
--- a/src/Config/AgentRunnerConfig.php
+++ b/src/Config/AgentRunnerConfig.php
@@ -386,6 +386,15 @@ final class AgentRunnerConfig
         return $this->getRequiredString($legacyKey);
     }
 
+    private function getChatOnlyRequiredString(string $chatKey): string
+    {
+        if ($this->chatMessages === null) {
+            throw new \InvalidArgumentException(sprintf('RetrieX chat messages config key "%s" is required.', $chatKey));
+        }
+
+        return $this->chatMessages->getString($chatKey);
+    }
+
     private function getChatStringAllowEmpty(string $chatKey, string $legacyKey): string
     {
         if ($this->chatMessages !== null) {
@@ -1045,6 +1054,16 @@ final class AgentRunnerConfig
         return $this->getChatRequiredString('agent.messages.debug_internal_error_prefix', 'messages.debug_internal_error_prefix');
     }
 
+    public function getTechnicalErrorDetailTemplate(): string
+    {
+        return $this->getChatOnlyRequiredString('agent.messages.technical_error_detail_template');
+    }
+
+    public function getHistoryResponseSystemNoticeTemplate(): string
+    {
+        return $this->getChatOnlyRequiredString('agent.production_ui.templates.history_response_system_notice');
+    }
+
     public function getExternalUrlSourceLabel(): string
     {
         return $this->getChatRequiredString('agent.source_labels.external_url', 'source_labels.external_url');
diff --git a/src/Config/ChatMessagesConfig.php b/src/Config/ChatMessagesConfig.php
index cb45520..98543d6 100644
--- a/src/Config/ChatMessagesConfig.php
+++ b/src/Config/ChatMessagesConfig.php
@@ -298,6 +298,7 @@ final class ChatMessagesConfig
             'agent.messages.shop_query_optimization_heartbeat',
             'agent.messages.generic_internal_error',
             'agent.messages.debug_internal_error_prefix',
+            'agent.messages.technical_error_detail_template',
             'agent.final_answer_guard.truncation_message',
             'agent.no_llm_fallback.messages.shop_only',
             'agent.no_llm_fallback.messages.shop_with_knowledge',
@@ -419,6 +420,7 @@ final class ChatMessagesConfig
             'agent.production_ui.templates.shop_meta_result_count',
             'agent.production_ui.templates.history_notice_without_detail',
             'agent.production_ui.templates.history_notice_with_detail',
+            'agent.production_ui.templates.history_response_system_notice',
             'agent.source_labels.external_url',
             'agent.source_labels.rag_knowledge',
             'agent.source_labels.conversation_history',