refactor(web): remove wa_ask_message_sent, set source header on chat transport

Instead of a separate client-side event, the web client now sets the
X-Sourcebot-Client-Source header on DefaultChatTransport. This makes
ask_message_sent fire with source='sourcebot-web-client' for web UI
calls, enabling web-only filtering directly on the server-side event.

Updated Ask Usage and Any Feature Usage PostHog actions to filter
ask_message_sent by source=sourcebot-web-client.

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

Author: msukkari

CHANGELOG.md

@@ -10,7 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - Added `thinkingLevel` and `thinkingBudget` configuration options for Google Generative AI and Google Vertex providers. [#1110](https://github.com/sourcebot-dev/sourcebot/pull/1110)
 - Added unified `tool_used` PostHog event tracking for all tool calls across the ask agent and MCP server. [#1111](https://github.com/sourcebot-dev/sourcebot/pull/1111)
-- Added client-side `wa_ask_thread_created` and `wa_ask_message_sent` PostHog events for web-only ask usage tracking. [#1111](https://github.com/sourcebot-dev/sourcebot/pull/1111)
+- Web app now sets `X-Sourcebot-Client-Source: sourcebot-web-client` header on chat API requests, enabling web-only ask usage filtering in dashboards. [#1111](https://github.com/sourcebot-dev/sourcebot/pull/1111)
 
 ### Changed
 - Deprecated `GOOGLE_VERTEX_THINKING_BUDGET_TOKENS` environment variable in favor of per-model `thinkingBudget` config. [#1110](https://github.com/sourcebot-dev/sourcebot/pull/1110)

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

@@ -102,6 +102,9 @@ export const ChatThread = ({
         messages: initialMessages,
         transport: new DefaultChatTransport({
             api: '/api/chat',
+            headers: {
+                'X-Sourcebot-Client-Source': 'sourcebot-web-client',
+            },
         }),
         onData: (dataPart) => {
             // Keeps sources added by the assistant in sync.
@@ -126,12 +129,6 @@ export const ChatThread = ({
             .map((part) => part.data);
         setSources((prev) => [...prev, ...sources]);
 
-        captureEvent('wa_ask_message_sent', {
-            chatId,
-            messageCount: messages.length + 1,
-            selectedReposCount: selectedSearchScopes.length,
-        });
-
         _sendMessage(message, {
             body: {
                 selectedSearchScopes,

packages/web/src/lib/posthogEvents.ts

@@ -159,11 +159,6 @@ export type PosthogEventMap = {
         chatId: string,
         messageId: string,
     },
-    wa_ask_message_sent: {
-        chatId: string,
-        messageCount: number,
-        selectedReposCount: number,
-    },
     ask_thread_created: {
         chatId: string,
         isAnonymous: boolean,