Fix budget projection truncation accounting

sdk/packages/core/src/extensions/context/budget-projection/project.test.ts

@@ -291,4 +291,28 @@ describe("buildBudgetProjection", () => {
 			]),
 		);
 	});
+
+	it("clears thinking blocks after the message text budget is exhausted", () => {
+		const result = buildBudgetProjection({
+			messages: [
+				{ role: "user", content: "latest typed prompt" },
+				{
+					role: "assistant",
+					content: [
+						{ type: "text", text: "a".repeat(1_000) },
+						{ type: "thinking", thinking: "b".repeat(1_000) },
+					],
+				},
+			],
+			targetTokens: 190,
+			policyIntent: "agentic_summary",
+			estimateMessageTokens: estimateChars,
+		});
+
+		const assistant = result.messages.find(
+			(message) => message.role === "assistant",
+		);
+		expect(JSON.stringify(assistant)).not.toContain("b".repeat(100));
+	});
+
 });

sdk/packages/core/src/extensions/context/budget-projection/project.ts

@@ -260,6 +260,21 @@ function truncateToolResultContent(
 	});
 }
 
+function toolResultTextLength(content: ToolResultContent["content"]): number {
+	if (typeof content === "string") {
+		return content.length;
+	}
+	return content.reduce((total, block) => {
+		if (block.type === "text") {
+			return total + block.text.length;
+		}
+		if (block.type === "file") {
+			return total + block.content.length;
+		}
+		return total;
+	}, 0);
+}
+
 function truncateMessageText(
 	message: MessageWithMetadata,
 	maxChars: number,
@@ -269,17 +284,20 @@ function truncateMessageText(
 	}
 	let remaining = maxChars;
 	return {
-			...message,
-			content: message.content.map((block) => {
-				if (remaining <= 0) {
-					if (block.type === "text") {
-						return { ...block, text: "" };
-					}
-					if (block.type === "file") {
-						return { ...block, content: "" };
-					}
-					return block;
+		...message,
+		content: message.content.map((block) => {
+			if (remaining <= 0) {
+				if (block.type === "text") {
+					return { ...block, text: "" };
 				}
+				if (block.type === "file") {
+					return { ...block, content: "" };
+				}
+				if (block.type === "thinking") {
+					return { ...block, thinking: "" };
+				}
+				return block;
+			}
 			if (block.type === "text") {
 				const text = truncateText(block.text, remaining);
 				remaining -= text.length;
@@ -297,7 +315,7 @@ function truncateMessageText(
 			}
 			if (block.type === "tool_result") {
 				const content = truncateToolResultContent(block.content, remaining);
-				remaining -= safeJsonSize(content);
+				remaining -= toolResultTextLength(content);
 				return { ...block, content };
 			}
 			return block;