refactor(web): normalize Ask user message text extraction (#1371)

* refactor(web): normalize Ask user message text extraction

Introduce a shared `getUserMessageText` helper in the chat utils and use it
everywhere the user's typed text is read from an `SBChatMessage`. Previously
several call sites assumed the text lived at `parts[0]`, which silently drops
the user's text if any non-text part (e.g. a file attachment) is ever first.

The helper finds the first text part instead, making extraction robust to
non-text parts. This is behavior-preserving today (user messages currently
have a single leading text part) and is a prerequisite for chat file
attachments.

Co-authored-by: Cursor <cursoragent@cursor.com>

* docs: add changelog entry for #1371

Co-authored-by: Cursor <cursoragent@cursor.com>

---------

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: whoisthey

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - [EE] Improved Ask Sourcebot prompt caching by splitting static and dynamic prompt sections and advancing cache breakpoints after every agent step instead of only after each message. [#1366](https://github.com/sourcebot-dev/sourcebot/pull/1366)
+- Refactored Ask Sourcebot user message text extraction into a shared helper that robustly handles non-text message parts. [#1371](https://github.com/sourcebot-dev/sourcebot/pull/1371)
 
 ### Added
 - Added per-step token cost tracking and estimated tool call token usage to Ask Sourcebot chat history. [#1353](https://github.com/sourcebot-dev/sourcebot/pull/1353)

packages/web/src/app/(app)/chat/[id]/page.tsx

@@ -14,6 +14,7 @@ import { __unsafePrisma } from '@/prisma';
 import { ChatVisibility } from '@sourcebot/db';
 import { Metadata } from 'next';
 import { SBChatMessage } from '@/features/chat/types';
+import { getUserMessageText } from '@/features/chat/utils';
 import { env } from '@sourcebot/shared';
 import { hasEntitlement } from '@/lib/entitlements';
 import { ChatEntitlementMessage } from '@/features/chat/components/chatEntitlementMessage';
@@ -54,11 +55,11 @@ export const generateMetadata = async ({ params }: PageProps): Promise<Metadata>
 
     let description = 'A chat on Sourcebot';
     if (firstUserMessage) {
-        const textPart = firstUserMessage.parts.find(p => p.type === 'text');
-        if (textPart && textPart.type === 'text') {
-            description = textPart.text.length > 160
-                ? textPart.text.substring(0, 160).trim() + '...'
-                : textPart.text;
+        const text = getUserMessageText(firstUserMessage);
+        if (text) {
+            description = text.length > 160
+                ? text.substring(0, 160).trim() + '...'
+                : text;
         }
     }
 

packages/web/src/ee/features/chat/agent.ts

@@ -22,7 +22,7 @@ import { randomUUID } from "crypto";
 import _dedent from "dedent";
 import { ANSWER_TAG, FILE_REFERENCE_PREFIX } from "@/features/chat/constants";
 import { Source } from "@/features/chat/types";
-import { addLineNumbers, fileReferenceToString, getAnswerPartFromAssistantMessage, getTurnProgressState } from "@/features/chat/utils";
+import { addLineNumbers, fileReferenceToString, getAnswerPartFromAssistantMessage, getTurnProgressState, getUserMessageText } from "@/features/chat/utils";
 import { createTools } from "./tools";
 import { getConnectedMcpClients } from "@/ee/features/chat/mcp/mcpClientFactory";
 import { getMcpTools, McpToolsResult } from "@/ee/features/chat/mcp/mcpToolSets";
@@ -107,7 +107,7 @@ export const createMessageStream = async ({
             if (message.role === 'user') {
                 return {
                     role: 'user',
-                    content: message.parts[0].type === 'text' ? message.parts[0].text : '',
+                    content: getUserMessageText(message),
                 };
             }
 

packages/web/src/ee/features/chat/components/chatThread/chatThread.tsx

@@ -5,7 +5,7 @@ import { Button } from '@/components/ui/button';
 import { Separator } from '@/components/ui/separator';
 import { CustomSlateEditor } from '@/features/chat/customSlateEditor';
 import { AdditionalChatRequestParams, CustomEditor, LanguageModelInfo, SBChatMessage, SearchScope, Source } from '@/features/chat/types';
-import { createUIMessage, getAllMentionElements, getTurnProgressState, resetEditor, slateContentToString } from '@/features/chat/utils';
+import { createUIMessage, getAllMentionElements, getTurnProgressState, getUserMessageText, resetEditor, slateContentToString } from '@/features/chat/utils';
 import { useChat } from '@ai-sdk/react';
 import { CreateUIMessage, DefaultChatTransport, lastAssistantMessageIsCompleteWithApprovalResponses } from 'ai';
 import { ArrowDownIcon, CopyIcon } from 'lucide-react';
@@ -204,16 +204,16 @@ export const ChatThread = ({
             } satisfies AdditionalChatRequestParams,
         });
 
+        const userMessageText = getUserMessageText(message);
         if (
             messages.length === 0 &&
-            message.parts.length > 0 &&
-            message.parts[0].type === 'text'
+            userMessageText.length > 0
         ) {
             generateAndUpdateChatNameFromMessage(
                 {
                     chatId,
                     languageModelId: selectedLanguageModel.model,
-                    message: message.parts[0].text,
+                    message: userMessageText,
                 },
             ).then((response) => {
                 if (isServiceError(response)) {

packages/web/src/ee/features/chat/components/chatThread/chatThreadListItem.tsx

@@ -8,7 +8,7 @@ import { CSSProperties, forwardRef, memo, useCallback, useEffect, useMemo, useRe
 import scrollIntoView from 'scroll-into-view-if-needed';
 import { Reference, referenceSchema, SBChatMessage, Source } from "@/features/chat/types";
 import { useExtractReferences } from '../../useExtractReferences';
-import { getAnswerPartFromAssistantMessage, getLastStepParts, groupMessageIntoSteps, isSBChatToolPart, repairReferences, tryResolveFileReference } from '@/features/chat/utils';
+import { getAnswerPartFromAssistantMessage, getLastStepParts, getUserMessageText, groupMessageIntoSteps, isSBChatToolPart, repairReferences, tryResolveFileReference } from '@/features/chat/utils';
 import { AnswerCard } from './answerCard';
 import { DetailsCard } from './detailsCard';
 import { ApprovalRequestedToolPart, ToolApprovalBanner } from './toolApprovalBanner';
@@ -49,7 +49,7 @@ const ChatThreadListItemComponent = forwardRef<HTMLDivElement, ChatThreadListIte
     const userHasManuallyExpanded = useRef(false);
 
     const userQuestion = useMemo(() => {
-        return userMessage.parts.length > 0 && userMessage.parts[0].type === 'text' ? userMessage.parts[0].text : '';
+        return getUserMessageText(userMessage);
     }, [userMessage]);
 
     // Take the assistant message and repair any references that are not properly formatted.

packages/web/src/features/chat/utils.test.ts

@@ -1,5 +1,5 @@
 import { expect, test, describe, vi } from 'vitest'
-import { createUIMessage, fileReferenceToString, getAnswerPartFromAssistantMessage, getLastStepParts, getTurnProgressState, groupMessageIntoSteps, repairReferences } from './utils'
+import { createUIMessage, fileReferenceToString, getAnswerPartFromAssistantMessage, getLastStepParts, getTurnProgressState, getUserMessageText, groupMessageIntoSteps, repairReferences } from './utils'
 import { FILE_REFERENCE_REGEX, ANSWER_TAG } from './constants';
 import { SBChatMessage, SBChatMessagePart } from './types';
 
@@ -537,6 +537,75 @@ test('getAnswerPartFromAssistantMessage returns undefined when turn is in progre
     expect(result).toBeUndefined();
 });
 
+describe('getUserMessageText', () => {
+    test('returns the text when the text part is first', () => {
+        const message: SBChatMessage = {
+            role: 'user',
+            parts: [
+                {
+                    type: 'text',
+                    text: 'Hello, world!',
+                },
+            ],
+        } as SBChatMessage;
+
+        expect(getUserMessageText(message)).toBe('Hello, world!');
+    });
+
+    test('returns the text when a non-text part precedes the text part', () => {
+        const message: SBChatMessage = {
+            role: 'user',
+            parts: [
+                {
+                    type: 'data-source',
+                    data: {
+                        type: 'file',
+                        path: 'auth.ts',
+                        repo: 'github.com/sourcebot-dev/sourcebot',
+                        name: 'auth.ts',
+                        revision: 'main',
+                    },
+                },
+                {
+                    type: 'text',
+                    text: 'Explain this file',
+                },
+            ],
+        } as SBChatMessage;
+
+        expect(getUserMessageText(message)).toBe('Explain this file');
+    });
+
+    test('returns an empty string when there is no text part', () => {
+        const message: SBChatMessage = {
+            role: 'user',
+            parts: [
+                {
+                    type: 'data-source',
+                    data: {
+                        type: 'file',
+                        path: 'auth.ts',
+                        repo: 'github.com/sourcebot-dev/sourcebot',
+                        name: 'auth.ts',
+                        revision: 'main',
+                    },
+                },
+            ],
+        } as SBChatMessage;
+
+        expect(getUserMessageText(message)).toBe('');
+    });
+
+    test('returns an empty string when there are no parts', () => {
+        const message: SBChatMessage = {
+            role: 'user',
+            parts: [],
+        } as unknown as SBChatMessage;
+
+        expect(getUserMessageText(message)).toBe('');
+    });
+});
+
 test('repairReferences fixes missing colon after @file', () => {
     const input = 'See the function in @file{github.com/sourcebot-dev/sourcebot::auth.ts} for details.';
     const expected = 'See the function in @file:{github.com/sourcebot-dev/sourcebot::auth.ts} for details.';

packages/web/src/features/chat/utils.ts

@@ -397,6 +397,14 @@ export const repairReferences = (text: string): string => {
         .replace(/`(@file:\{[^`]+)`\}/g, '$1}');
 };
 
+// Extracts the user's text from a message by finding the first text part.
+// User messages may contain non-text parts (e.g., file attachments), so we
+// cannot assume the text is always at index 0. Accepts anything carrying
+// `parts` so it works for both persisted and freshly created messages.
+export const getUserMessageText = (message: Pick<SBChatMessage, 'parts'>): string => {
+    return message.parts.find((part) => part.type === 'text')?.text ?? '';
+}
+
 // Attempts to find the part of the assistant's message
 // that contains the answer.
 export const getAnswerPartFromAssistantMessage = (message: SBChatMessage, isTurnInProgress: boolean): TextUIPart | undefined => {