diff --git a/src/apps/chat/components/message/useSelHighlighterMemo.ts b/src/apps/chat/components/message/useSelHighlighterMemo.ts
index d1d7690a0..c4e830d9f 100644
--- a/src/apps/chat/components/message/useSelHighlighterMemo.ts
+++ b/src/apps/chat/components/message/useSelHighlighterMemo.ts
@@ -1,7 +1,7 @@
 import * as React from 'react';
 
 import type { DMessageId } from '~/common/stores/chat/chat.message';
-import { createTextContentFragment, DMessageFragment, DMessageFragmentId, isContentFragment, isTextPart } from '~/common/stores/chat/chat.fragments';
+import { createTextContentFragment, DMessageFragment, DMessageFragmentId, isTextContentFragment } from '~/common/stores/chat/chat.fragments';
 import { wrapWithMarkdownSyntax } from '~/modules/blocks/markdown/markdown.wrapper';
 
 import { BUBBLE_MIN_TEXT_LENGTH } from './ChatMessage';
@@ -41,7 +41,7 @@ export function useSelHighlighterMemo(
 
     // Create the highlighter function, if there's 1 and only 1 occurrence of the selection
     const highlightFunction = fragments.reduce((acc: false /* not found */ | ((tool: HighlightTool) => void) | true /* more than one */, fragment) => {
-      if (!acc && isContentFragment(fragment) && isTextPart(fragment.part)) {
+      if (!acc && isTextContentFragment(fragment)) {
         const fragmentText = fragment.part.text;
         let index = fragmentText.indexOf(selText);
 
diff --git a/src/apps/chat/editors/_handleExecute.ts b/src/apps/chat/editors/_handleExecute.ts
index 96738d105..a63aca7a6 100644
--- a/src/apps/chat/editors/_handleExecute.ts
+++ b/src/apps/chat/editors/_handleExecute.ts
@@ -4,7 +4,7 @@ import type { DConversationId } from '~/common/stores/chat/chat.conversation';
 import type { DMessage } from '~/common/stores/chat/chat.message';
 import { ConversationHandler } from '~/common/chat-overlay/ConversationHandler';
 import { ConversationsManager } from '~/common/chat-overlay/ConversationsManager';
-import { createTextContentFragment, isContentFragment, isTextPart } from '~/common/stores/chat/chat.fragments';
+import { createTextContentFragment, isTextContentFragment } from '~/common/stores/chat/chat.fragments';
 import { getConversationSystemPurposeId } from '~/common/stores/chat/store-chats';
 
 import type { ChatExecuteMode } from '../execute-mode/execute-mode.types';
@@ -80,7 +80,7 @@ export async function _handleExecute(chatExecuteMode: ChatExecuteMode, conversat
 
     case 'generate-image':
       // verify we were called with a single DMessageTextContent
-      if (!isContentFragment(firstFragment) || !isTextPart(firstFragment.part))
+      if (!isTextContentFragment(firstFragment))
         return false;
       const imagePrompt = firstFragment.part.text;
       cHandler.messageFragmentReplace(lastMessage.id, firstFragment.fId, createTextContentFragment(textToDrawCommand(imagePrompt)), true);
@@ -88,7 +88,7 @@ export async function _handleExecute(chatExecuteMode: ChatExecuteMode, conversat
 
     case 'react-content':
       // verify we were called with a single DMessageTextContent
-      if (!isContentFragment(firstFragment) || !isTextPart(firstFragment.part))
+      if (!isTextContentFragment(firstFragment))
         return false;
       const reactPrompt = firstFragment.part.text;
       cHandler.messageFragmentReplace(lastMessage.id, firstFragment.fId, createTextContentFragment(textToDrawCommand(reactPrompt)), true);
diff --git a/src/apps/chat/editors/_handleExecuteCommand.ts b/src/apps/chat/editors/_handleExecuteCommand.ts
index 604020234..6f54c7a29 100644
--- a/src/apps/chat/editors/_handleExecuteCommand.ts
+++ b/src/apps/chat/editors/_handleExecuteCommand.ts
@@ -1,7 +1,7 @@
 import type { DLLMId } from '~/common/stores/llms/llms.types';
 import type { DMessage, DMessageId } from '~/common/stores/chat/chat.message';
 import { ConversationHandler } from '~/common/chat-overlay/ConversationHandler';
-import { createTextContentFragment, DMessageFragment, isContentFragment, isTextPart } from '~/common/stores/chat/chat.fragments';
+import { createTextContentFragment, DMessageFragment, isTextContentFragment } from '~/common/stores/chat/chat.fragments';
 
 import { extractChatCommand, helpPrettyChatCommands } from '../commands/commands.registry';
 import { runBrowseGetPageUpdatingState } from './browse-load';
@@ -15,7 +15,7 @@ export const RET_NO_CMD = 'no-cmd';
 export async function _handleExecuteCommand(lastMessageId: DMessageId, lastMessageFirstFragment: DMessageFragment, lastMessage: Readonly<DMessage>, cHandler: ConversationHandler, chatLLMId: DLLMId) {
 
   // commands must have a first Content DMessageTextPart
-  if (!isContentFragment(lastMessageFirstFragment) || !isTextPart(lastMessageFirstFragment.part))
+  if (!isTextContentFragment(lastMessageFirstFragment))
     return RET_NO_CMD;
 
   // check if we have a command
diff --git a/src/apps/chat/editors/persona/PersonaChatMessageSpeak.ts b/src/apps/chat/editors/persona/PersonaChatMessageSpeak.ts
index 3e1acf5e6..a016af1da 100644
--- a/src/apps/chat/editors/persona/PersonaChatMessageSpeak.ts
+++ b/src/apps/chat/editors/persona/PersonaChatMessageSpeak.ts
@@ -1,6 +1,6 @@
 import { speakText } from '~/modules/elevenlabs/elevenlabs.client';
 
-import { isContentFragment, isTextPart } from '~/common/stores/chat/chat.fragments';
+import { isTextContentFragment } from '~/common/stores/chat/chat.fragments';
 
 import type { AixChatGenerateContent_DMessage } from '~/modules/aix/client/aix.client';
 
@@ -20,7 +20,7 @@ export class PersonaChatMessageSpeak implements PersonaProcessorInterface {
     if (this.autoSpeakType === 'off' || this.spokenLine) return;
 
     // Require a Content.Text first fragment
-    if (!accumulatedMessage.fragments?.length || !isContentFragment(accumulatedMessage.fragments[0]) || !isTextPart(accumulatedMessage.fragments[0].part))
+    if (!accumulatedMessage.fragments?.length || !isTextContentFragment(accumulatedMessage.fragments[0]))
       return;
     const text = accumulatedMessage.fragments[0].part.text;
 
diff --git a/src/common/stores/chat/chat.fragments.ts b/src/common/stores/chat/chat.fragments.ts
index 3576aef62..46f895214 100644
--- a/src/common/stores/chat/chat.fragments.ts
+++ b/src/common/stores/chat/chat.fragments.ts
@@ -176,6 +176,10 @@ export function isContentFragment(fragment: DMessageFragment) {
   return fragment.ft === 'content';
 }
 
+export function isTextContentFragment(fragment: DMessageFragment): fragment is DMessageContentFragment & { part: DMessageTextPart } {
+  return fragment.ft === 'content' && fragment.part.pt === 'text';
+}
+
 export function isAttachmentFragment(fragment: DMessageFragment) {
   return fragment.ft === 'attachment';
 }
@@ -205,7 +209,7 @@ export function isErrorPart(part: DMessageContentFragment['part']) {
   return part.pt === 'error';
 }
 
-export function isToolResponseFunctionCallPart(part: DMessageContentFragment['part']) {
+export function isToolResponseFunctionCallPart(part: DMessageContentFragment['part']): part is DMessageToolResponsePart & { response: { type: 'function_call' } } {
   return part.pt === 'tool_response' && part.response.type === 'function_call';
 }
 
@@ -443,14 +447,14 @@ function _duplicate_DataReference(ref: DMessageDataRef): DMessageDataRef {
 
 export function editTextPartsInline(fragments: DMessageFragment[], editText: (text: string, idx: number) => string): void {
   fragments.forEach((fragment, idx) => {
-    if (isContentFragment(fragment) && isTextPart(fragment.part))
+    if (isTextContentFragment(fragment))
       fragment.part.text = editText(fragment.part.text, idx);
   });
 }
 
 export function prependTextPartsInline(fragments: DMessageFragment[], textPrefix: string): void {
   for (const fragment of fragments) {
-    if (!isContentFragment(fragment) || !isTextPart(fragment.part))
+    if (!isTextContentFragment(fragment))
       continue;
     fragment.part.text = textPrefix + ' ' + fragment.part.text;
     return;
diff --git a/src/common/stores/chat/chat.message.ts b/src/common/stores/chat/chat.message.ts
index cbce6ac9b..bb867c8bf 100644
--- a/src/common/stores/chat/chat.message.ts
+++ b/src/common/stores/chat/chat.message.ts
@@ -237,31 +237,34 @@ export function messageFragmentsReduceText(fragments: DMessageFragment[], fragme
 
   return fragments
     .map(fragment => {
-      if (isContentFragment(fragment)) {
-        switch (fragment.part.pt) {
-          case 'text':
-            return fragment.part.text;
-          case 'error':
-            return fragment.part.error;
-          case 'image_ref':
-            return '';
-          case 'tool_invocation':
-          case 'tool_response':
-            // Ignore tools for the text reduction
-            return '';
-        }
-      } else if (isAttachmentFragment(fragment)) {
-        switch (fragment.part.pt) {
-          case 'doc':
-            return fragment.part.data.text;
-          case 'image_ref':
-            return '';
-        }
-      } else if (isVoidFragment(fragment)) {
-        // all void fragments are ignored by definition when doing a text reduction
-        return '';
+      switch (true) {
+        case isContentFragment(fragment):
+          switch (fragment.part.pt) {
+            case 'text':
+              return fragment.part.text;
+            case 'error':
+              return fragment.part.error;
+            case 'image_ref':
+              return '';
+            case 'tool_invocation':
+            case 'tool_response':
+              // Ignore tools for the text reduction
+              return '';
+          }
+          break;
+        case isAttachmentFragment(fragment):
+          switch (fragment.part.pt) {
+            case 'doc':
+              return fragment.part.data.text;
+            case 'image_ref':
+              return '';
+          }
+          break;
+        case isVoidFragment(fragment):
+          // all void fragments are ignored by definition when doing a text reduction
+          return '';
       }
-      console.warn(`DEV: messageFragmentsReduceText: unexpected '${fragment.ft}' fragment with '${(fragment as any)?.part?.pt}' part`);
+      console.warn(`[DEV] messageFragmentsReduceText: unexpected '${fragment.ft}' fragment with '${(fragment as any)?.part?.pt}' part`);
       return '';
     })
     .filter(text => !!text)
diff --git a/src/common/stores/chat/chats.converters.ts b/src/common/stores/chat/chats.converters.ts
index 9100933c3..3981f6c82 100644
--- a/src/common/stores/chat/chats.converters.ts
+++ b/src/common/stores/chat/chats.converters.ts
@@ -8,7 +8,7 @@ import type { DModelsService } from '~/common/stores/llms/modelsservice.types';
 
 import { createDConversation, DConversation, type DConversationId } from './chat.conversation';
 import { createDMessageTextContent, DMessage, MESSAGE_FLAG_NOTIFY_COMPLETE, messageSetUserFlag } from './chat.message';
-import { createErrorContentFragment, isAttachmentFragment, isContentFragment, isContentOrAttachmentFragment, isDocPart, isPlaceholderPart, isTextPart, isVoidFragment } from './chat.fragments';
+import { createErrorContentFragment, isAttachmentFragment, isContentFragment, isContentOrAttachmentFragment, isDocPart, isPlaceholderPart, isTextContentFragment, isTextPart, isVoidFragment } from './chat.fragments';
 
 
 // configuration
@@ -63,7 +63,8 @@ export namespace V4ToHeadConverters {
       // [Emergency] validate part types, can mess up in development
       if (EMERGENCY_CLEANUP_PARTS) {
         // If a text part has 'object' in place of 'string' for pText: remove the part altogether
-        if (isContentFragment(fragment) && isTextPart(fragment.part)) {
+        if (isTextContentFragment(fragment)) {
+          // noinspection SuspiciousTypeOfGuard
           if (typeof fragment.part.text !== 'string') {
             // Remove this fragment
             m.fragments.splice(i, 1);
diff --git a/src/modules/aix/client/aix.client.chatGenerateRequest.ts b/src/modules/aix/client/aix.client.chatGenerateRequest.ts
index d66edf7fa..cd92598b3 100644
--- a/src/modules/aix/client/aix.client.chatGenerateRequest.ts
+++ b/src/modules/aix/client/aix.client.chatGenerateRequest.ts
@@ -1,7 +1,7 @@
 import { getImageAsset } from '~/modules/dblobs/dblobs.images';
 
 import { DMessage, DMessageRole, DMetaReferenceItem, MESSAGE_FLAG_AIX_SKIP, MESSAGE_FLAG_VND_ANT_CACHE_AUTO, MESSAGE_FLAG_VND_ANT_CACHE_USER, messageHasUserFlag } from '~/common/stores/chat/chat.message';
-import { DMessageFragment, DMessageImageRefPart, isContentFragment, isContentOrAttachmentFragment, isTextPart, isToolResponseFunctionCallPart } from '~/common/stores/chat/chat.fragments';
+import { DMessageFragment, DMessageImageRefPart, isContentOrAttachmentFragment, isTextContentFragment, isToolResponseFunctionCallPart } from '~/common/stores/chat/chat.fragments';
 import { Is } from '~/common/util/pwaUtils';
 import { LLMImageResizeMode, resizeBase64ImageIfNeeded } from '~/common/util/imageUtils';
 
@@ -85,7 +85,7 @@ export async function aixCGR_FromDMessagesOrThrow(
         };
       }
       for (const systemFragment of m.fragments) {
-        if (isContentFragment(systemFragment) && isTextPart(systemFragment.part)) {
+        if (isTextContentFragment(systemFragment)) {
           acc.systemMessage.parts.push(systemFragment.part);
         } else {
           console.warn('aixCGR_FromDMessages: unexpected system fragment', systemFragment);