From 229aba7c3e33a95c9c654826504ffc4f163f8003 Mon Sep 17 00:00:00 2001
From: Pascal <admin@serveurperso.com>
Date: Fri, 16 Jan 2026 19:49:48 +0100
Subject: [PATCH] fix: strip reasoning content and UI proprietary tags from
 prompts

TODO: add toggle and ensure backend API compliance for reasoning format
---
 .../server/webui/src/lib/constants/agentic.ts |  4 +++
 .../webui/src/lib/services/chat.service.ts    | 34 ++++++++++++++++++-
 2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/tools/server/webui/src/lib/constants/agentic.ts b/tools/server/webui/src/lib/constants/agentic.ts
index 5b57294eb4..a877c600fe 100644
--- a/tools/server/webui/src/lib/constants/agentic.ts
+++ b/tools/server/webui/src/lib/constants/agentic.ts
@@ -36,6 +36,10 @@ export const AGENTIC_REGEX = {
 	EARLY_MATCH: /<<<AGENTIC_TOOL_CALL_START>>>([\s\S]*)$/,
 	// Matches partial marker at end of content
 	PARTIAL_MARKER: /<<<[A-Za-z_]*$/,
+	// Matches reasoning content blocks (including tags)
+	REASONING_BLOCK: /<<<reasoning_content_start>>>[\s\S]*?<<<reasoning_content_end>>>/g,
+	// Matches an opening reasoning tag and any remaining content (unterminated)
+	REASONING_OPEN: /<<<reasoning_content_start>>>[\s\S]*$/,
 	// Matches tool name inside content
 	TOOL_NAME_EXTRACT: /<<<TOOL_NAME:([^>]+)>>>/
 } as const;
diff --git a/tools/server/webui/src/lib/services/chat.service.ts b/tools/server/webui/src/lib/services/chat.service.ts
index 861363e5e1..5bf8cd9a0e 100644
--- a/tools/server/webui/src/lib/services/chat.service.ts
+++ b/tools/server/webui/src/lib/services/chat.service.ts
@@ -1,5 +1,7 @@
 import { getJsonHeaders } from '$lib/utils';
+import { AGENTIC_REGEX } from '$lib/constants/agentic';
 import { AttachmentType } from '$lib/enums';
+import type { ApiChatMessageContentPart } from '$lib/types/api';
 
 /**
  * ChatService - Low-level API communication layer for Chat Completions
@@ -34,6 +36,34 @@ import { AttachmentType } from '$lib/enums';
  * - Request lifecycle management (abort via AbortSignal)
  */
 export class ChatService {
+	private static stripReasoningContent(
+		content: ApiChatMessageData['content'] | null | undefined
+	): ApiChatMessageData['content'] | null | undefined {
+		if (!content) {
+			return content;
+		}
+
+		if (typeof content === 'string') {
+			return content
+				.replace(AGENTIC_REGEX.REASONING_BLOCK, '')
+				.replace(AGENTIC_REGEX.REASONING_OPEN, '');
+		}
+
+		if (!Array.isArray(content)) {
+			return content;
+		}
+
+		return content.map((part: ApiChatMessageContentPart) => {
+			if (part.type !== 'text' || !part.text) return part;
+			return {
+				...part,
+				text: part.text
+					.replace(AGENTIC_REGEX.REASONING_BLOCK, '')
+					.replace(AGENTIC_REGEX.REASONING_OPEN, '')
+			};
+		});
+	}
+
 	/**
 	 *
 	 *
@@ -122,7 +152,9 @@ export class ChatService {
 		const requestBody: ApiChatCompletionRequest = {
 			messages: normalizedMessages.map((msg: ApiChatMessageData) => ({
 				role: msg.role,
-				content: msg.content,
+				// Strip reasoning tags/content from the prompt to avoid polluting KV cache.
+				// TODO: investigate backend expectations for reasoning tags and add a toggle if needed.
+				content: ChatService.stripReasoningContent(msg.content),
 				tool_calls: msg.tool_calls,
 				tool_call_id: msg.tool_call_id
 			})),