fix(web): fix inflated MCP DAU by threading user identity through tool telemetry

captureEvent() relies on tryGetPostHogDistinctId() which reads cookies,
session, or API key headers. In the MCP server and ask agent contexts,
none of these are available, so every tool_used event got a random
distinct_id — inflating DAU counts (e.g., 8 tool calls = 8 "users").

Fix: add optional distinctId to ToolContext and captureEvent(). Thread
user.id from the auth context through:
- MCP route → createMcpServer(userId) → ToolContext.distinctId
- chat route / askCodebase → createMessageStream(distinctId) →
  createAgentStream → createTools

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: msukkari

packages/web/src/app/api/(server)/chat/route.ts

@@ -112,6 +112,7 @@ export const POST = apiHandler(async (req: NextRequest) => {
                 modelName: languageModelConfig.displayName ?? languageModelConfig.model,
                 modelProviderOptions: providerOptions,
                 modelTemperature: temperature,
+                distinctId: user?.id,
                 onFinish: async ({ messages }) => {
                     await updateChatMessages({ chatId: id, messages, prisma });
                 },

packages/web/src/app/api/(server)/mcp/route.ts

@@ -79,7 +79,7 @@ export const POST = apiHandler(async (request: NextRequest) => {
                 },
             });
 
-            const mcpServer = await createMcpServer();
+            const mcpServer = await createMcpServer({ userId: user?.id });
             await mcpServer.connect(transport);
 
             return transport.handleRequest(request);

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

@@ -43,6 +43,8 @@ interface CreateMessageStreamResponseProps {
     modelProviderOptions?: Record<string, Record<string, JSONValue>>;
     modelTemperature?: number;
     metadata?: Partial<SBChatMessageMetadata>;
+    /** PostHog distinct ID for telemetry attribution on tool_used events. */
+    distinctId?: string;
 }
 
 export const createMessageStream = async ({
@@ -56,6 +58,7 @@ export const createMessageStream = async ({
     modelTemperature,
     onFinish,
     onError,
+    distinctId,
 }: CreateMessageStreamResponseProps) => {
     const latestMessage = messages[messages.length - 1];
     const sources = latestMessage.parts
@@ -101,6 +104,7 @@ export const createMessageStream = async ({
                 inputMessages: messageHistory,
                 inputSources: sources,
                 selectedRepos,
+                distinctId,
                 onWriteSource: (source) => {
                     writer.write({
                         type: 'data-source',
@@ -154,6 +158,7 @@ interface AgentOptions {
     onWriteSource: (source: Source) => void;
     traceId: string;
     chatId: string;
+    distinctId?: string;
 }
 
 const createAgentStream = async ({
@@ -166,6 +171,7 @@ const createAgentStream = async ({
     onWriteSource,
     traceId,
     chatId,
+    distinctId,
 }: AgentOptions) => {
     // For every file source, resolve the source code so that we can include it in the system prompt.
     const fileSources = inputSources.filter((source) => source.type === 'file');
@@ -202,7 +208,7 @@ const createAgentStream = async ({
         providerOptions,
         messages: inputMessages,
         system: systemPrompt,
-        tools: createTools({ source: 'sourcebot-ask-agent', selectedRepos }),
+        tools: createTools({ source: 'sourcebot-ask-agent', selectedRepos, distinctId }),
         temperature: temperature ?? env.SOURCEBOT_CHAT_MODEL_TEMPERATURE,
         stopWhen: [
             stepCountIsGTE(env.SOURCEBOT_CHAT_MAX_STEP_COUNT),

packages/web/src/features/mcp/askCodebase.ts

@@ -159,6 +159,7 @@ export const askCodebase = (params: AskCodebaseParams): Promise<AskCodebaseResul
                 modelName,
                 modelProviderOptions: providerOptions,
                 modelTemperature: temperature,
+                distinctId: user?.id,
                 onFinish: async ({ messages }) => {
                     finalMessages = messages;
                 },

packages/web/src/features/mcp/server.ts

@@ -26,7 +26,7 @@ import {
 const dedent = _dedent.withOptions({ alignValues: true });
 const logger = createLogger('mcp-server');
 
-export async function createMcpServer(): Promise<McpServer> {
+export async function createMcpServer(options?: { userId?: string }): Promise<McpServer> {
     const server = new McpServer({
         name: 'sourcebot-mcp-server',
         version: SOURCEBOT_VERSION,
@@ -37,6 +37,7 @@ export async function createMcpServer(): Promise<McpServer> {
 
     const toolContext: ToolContext = {
         source: 'sourcebot-mcp-server',
+        distinctId: options?.userId,
     }
 
     registerMcpTool(server, grepDefinition, toolContext);
@@ -63,7 +64,7 @@ export async function createMcpServer(): Promise<McpServer> {
                 toolName: 'list_language_models',
                 source: 'sourcebot-mcp-server',
                 success: true,
-            }).catch((error) => {
+            }, { distinctId: options?.userId }).catch((error) => {
                 logger.warn('Failed to capture tool_used event:', error);
             });
             return { content: [{ type: "text", text: JSON.stringify(models) }] };
@@ -114,7 +115,7 @@ export async function createMcpServer(): Promise<McpServer> {
                         toolName: 'ask_codebase',
                         source: 'sourcebot-mcp-server',
                         success: false,
-                    }).catch((error) => {
+                    }, { distinctId: options?.userId }).catch((error) => {
                         logger.warn('Failed to capture tool_used event:', error);
                     });
                     return {
@@ -126,7 +127,7 @@ export async function createMcpServer(): Promise<McpServer> {
                     toolName: 'ask_codebase',
                     source: 'sourcebot-mcp-server',
                     success: true,
-                }).catch((error) => {
+                }, { distinctId: options?.userId }).catch((error) => {
                     logger.warn('Failed to capture tool_used event:', error);
                 });
 

packages/web/src/features/tools/adapters.ts

@@ -25,7 +25,7 @@ export function toVercelAITool<TName extends string, TShape extends z.ZodRawShap
                     toolName: def.name,
                     source: context.source ?? 'unknown',
                     success,
-                }).catch((error) => {
+                }, { distinctId: context.distinctId }).catch((error) => {
                     logger.warn(`Failed to capture tool_used event for ${def.name}:`, error);
                 });
             }
@@ -63,7 +63,7 @@ export function registerMcpTool<TName extends string, TShape extends z.ZodRawSha
                     toolName: def.name,
                     source: context.source ?? 'unknown',
                     success: true,
-                }).catch((error) => {
+                }, { distinctId: context.distinctId }).catch((error) => {
                     logger.warn(`Failed to capture tool_used event for ${def.name}:`, error);
                 });
                 return { content: [{ type: "text" as const, text: result.output }] };
@@ -72,7 +72,7 @@ export function registerMcpTool<TName extends string, TShape extends z.ZodRawSha
                     toolName: def.name,
                     source: context.source ?? 'unknown',
                     success: false,
-                }).catch((error) => {
+                }, { distinctId: context.distinctId }).catch((error) => {
                     logger.warn(`Failed to capture tool_used event for ${def.name}:`, error);
                 });
                 const message = error instanceof Error ? error.message : String(error);

packages/web/src/features/tools/types.ts

@@ -17,6 +17,8 @@ export type Source = z.infer<typeof sourceSchema>;
 export interface ToolContext {
     source?: string;
     selectedRepos?: string[];
+    /** PostHog distinct ID for telemetry attribution. When set, tool_used events will be attributed to this user. */
+    distinctId?: string;
 }
 
 export interface ToolDefinition<

packages/web/src/lib/posthog.ts

@@ -87,12 +87,12 @@ export const createPostHogClient = async () => {
     return posthog;
 }
 
-export async function captureEvent<E extends PosthogEvent>(event: E, properties: PosthogEventMap[E]) {
+export async function captureEvent<E extends PosthogEvent>(event: E, properties: PosthogEventMap[E], options?: { distinctId?: string }) {
     if (env.SOURCEBOT_TELEMETRY_DISABLED === 'true') {
         return;
     }
 
-    const distinctId = await tryGetPostHogDistinctId();
+    const distinctId = options?.distinctId ?? await tryGetPostHogDistinctId();
     const posthog = await createPostHogClient();
 
     const headersList = await headers();