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fix(llm): auto-shape multimodal mediaPath messages in chat template #1089

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Merged
msluszniak merged 1 commit into from
Apr 22, 2026
+23 −14
Merged

fix(llm): auto-shape multimodal mediaPath messages in chat template #1089

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37 changes: 23 additions & 14 deletions packages/react-native-executorch/src/controllers/LLMController.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -354,18 +354,6 @@ export class LLMController {
const updatedHistory = [...this._messageHistory, newMessage];
this.messageHistoryCallback(updatedHistory);

const historyForTemplate = updatedHistory.map((m) =>
m.mediaPath
? {
...m,
content: [
{ type: 'image' },
{ type: 'text', text: m.content },
] as any,
}
: m
);

const visualTokenCount = this.nativeModule.getVisualTokenCount();
const countTokensCallback = (messages: Message[]) => {
const rendered = this.applyChatTemplate(
Expand All @@ -383,7 +371,7 @@ export class LLMController {
const messageHistoryWithPrompt =
this.chatConfig.contextStrategy.buildContext(
this.chatConfig.systemPrompt,
historyForTemplate,
updatedHistory,
maxContextLength,
countTokensCallback
);
Expand Down Expand Up @@ -448,7 +436,7 @@ export class LLMController {
);

const result = template.render({
messages,
messages: messagesForChatTemplate(messages),
tools,
...templateFlags,
...specialTokens,
Expand All @@ -468,3 +456,24 @@ export class LLMController {
function normalizeImagePath(path: string): string {
return path.startsWith('file://') ? path : `file://${path}`;
}

/**
* Multimodal chat templates expect message content for image-bearing turns
* to be an array of content parts with an `image` part as a placeholder.
* Callers of `LLMController.generate` and `LLMController.sendMessage` pass
* messages with a plain string `content` plus an optional `mediaPath`; this
* helper rewrites them into the structured form that the template engine
* understands.
* @param messages - Messages to prepare for the chat template engine.
* @returns Messages with image-bearing turns rewritten to structured content.
*/
function messagesForChatTemplate(messages: Message[]): any[] {
return messages.map((m) =>
m.mediaPath && typeof m.content === 'string'
? {
...m,
content: [{ type: 'image' }, { type: 'text', text: m.content }],
}
: m
);
}
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