Fix sliding window taking into account message order

src/utils/context-management.ts

@@ -7,7 +7,7 @@ export function slidingWindowContextManagement(
 	messages: Anthropic.Messages.MessageParam[],
 	tools: Anthropic.Messages.Tool[]
 ): Anthropic.Messages.MessageParam[] {
-	const adjustedContextWindow = contextWindow - 10000 // Buffer to account for tokenizer differences
+	const adjustedContextWindow = contextWindow - 10_000 // Buffer to account for tokenizer differences
 	const systemPromptTokens = countTokens(systemPrompt)
 	const toolsTokens = countTokens(JSON.stringify(tools))
 	let availableTokens = adjustedContextWindow - systemPromptTokens - toolsTokens
@@ -19,17 +19,50 @@ export function slidingWindowContextManagement(
 
 	// If over limit, remove messages starting from the third message onwards (task and claude's step-by-step thought process are important to keep in context)
 	const newMessages = [...messages]
-	while (totalMessageTokens > availableTokens && newMessages.length > 2) {
-		const removedMessage = newMessages.splice(2, 1)[0]
-		const removedTokens = countMessageTokens(removedMessage)
-		totalMessageTokens -= removedTokens
+	let index = 2
+	while (totalMessageTokens > availableTokens && index < newMessages.length) {
+		const messageToEmpty = newMessages[index]
+		const originalTokens = countMessageTokens(messageToEmpty)
+		// Empty the content of the message (messages must be in a specific order so we can't just remove)
+		if (typeof messageToEmpty.content === "string") {
+			messageToEmpty.content = ""
+		} else if (Array.isArray(messageToEmpty.content)) {
+			messageToEmpty.content = messageToEmpty.content.map((item) => {
+				if (typeof item === "string") {
+					return {
+						type: "text",
+						text: "(truncated due to context window)",
+					} as Anthropic.Messages.TextBlockParam
+				} else if (item.type === "text") {
+					return {
+						type: "text",
+						text: "(truncated due to context window)",
+					} as Anthropic.Messages.TextBlockParam
+				} else if (item.type === "image") {
+					return { ...item, source: { type: "base64", data: "" } } as Anthropic.Messages.ImageBlockParam
+				} else if (item.type === "tool_use") {
+					return { ...item, input: {} } as Anthropic.Messages.ToolUseBlockParam
+				} else if (item.type === "tool_result") {
+					return {
+						...item,
+						content: Array.isArray(item.content)
+							? item.content.map((contentItem) =>
+									contentItem.type === "text"
+										? { ...contentItem, text: "(truncated due to context window)" }
+										: contentItem.type === "image"
+										? { ...contentItem, source: { type: "base64", data: "" } }
+										: contentItem
+							  )
+							: "",
+					} as Anthropic.Messages.ToolResultBlockParam
+				}
+				return item
+			})
+		}
+		const newTokens = countMessageTokens(messageToEmpty)
+		totalMessageTokens -= originalTokens - newTokens
+		index++
 	}
-
-	if (totalMessageTokens > availableTokens) {
-		// Over the limit due to the first two messages
-		throw new Error("Task exceeds available context window")
-	}
-
 	return newMessages
 }