feat: Add conversation context token counter

- Add contextTokens to ApiMetrics interface
- Calculate context size using last API request's tokens
- Display context token count in TaskHeader below total tokens
- Use exact token counts instead of character estimation

This helps users track the total size of their conversation context,
which is useful for managing context window limits.

src/shared/getApiMetrics.ts

@@ -6,6 +6,7 @@ interface ApiMetrics {
 	totalCacheWrites?: number
 	totalCacheReads?: number
 	totalCost: number
+	contextTokens: number // Total tokens in conversation (last message's tokensIn + tokensOut)
 }
 
 /**
@@ -32,8 +33,14 @@ export function getApiMetrics(messages: ClineMessage[]): ApiMetrics {
 		totalCacheWrites: undefined,
 		totalCacheReads: undefined,
 		totalCost: 0,
+		contextTokens: 0,
 	}
 
+	// Find the last api_req_started message to get the context size
+	const lastApiReq = [...messages]
+		.reverse()
+		.find((message) => message.type === "say" && message.say === "api_req_started" && message.text)
+
 	messages.forEach((message) => {
 		if (message.type === "say" && message.say === "api_req_started" && message.text) {
 			try {
@@ -55,6 +62,11 @@ export function getApiMetrics(messages: ClineMessage[]): ApiMetrics {
 				if (typeof cost === "number") {
 					result.totalCost += cost
 				}
+
+				// If this is the last api request, use its tokens for context size
+				if (message === lastApiReq) {
+					result.contextTokens = (tokensIn || 0) + (tokensOut || 0)
+				}
 			} catch (error) {
 				console.error("Error parsing JSON:", error)
 			}