From b461b8e7660da5d1a5ebcf95c028d676152f82f2 Mon Sep 17 00:00:00 2001
From: roboomp <omp@can.ac>
Date: Fri, 24 Jul 2026 10:43:58 +0000
Subject: [PATCH] fix(agent): counted Anthropic server-tool blocks in token
 estimate

estimateTokens now charges for serialized anthropicServerTool blocks so context maintenance sees the server-tool payload replayed on the wire; excluded from the compaction floor like other encrypted reasoning.
---
 packages/agent/src/compaction/compaction.ts |  8 ++++++
 packages/agent/test/message-cache.test.ts   | 28 +++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/packages/agent/src/compaction/compaction.ts b/packages/agent/src/compaction/compaction.ts
index 7f0bf7980..b31015947 100644
--- a/packages/agent/src/compaction/compaction.ts
+++ b/packages/agent/src/compaction/compaction.ts
@@ -427,6 +427,14 @@ function computeMessageTokens(message: AgentMessage, options?: { excludeEncrypte
 					// Encrypted reasoning blob the provider still bills for on replay;
 					// excluded from the compaction floor for the same reason as above.
 					if (!options?.excludeEncryptedReasoning) fragments.push(block.data);
+				} else if (block.type === "anthropicServerTool") {
+					// Native Anthropic server-tool call/result replayed verbatim on the
+					// wire (server_tool_use input, web_search_tool_result
+					// encrypted_content). Opaque provider-replay state the provider still
+					// bills for on same-provider replay; excluded from the compaction
+					// floor like other encrypted reasoning because its local byte size
+					// diverges from provider billing.
+					if (!options?.excludeEncryptedReasoning) fragments.push(stringifyJson(block.block) ?? "null");
 				}
 			}
 			break;
diff --git a/packages/agent/test/message-cache.test.ts b/packages/agent/test/message-cache.test.ts
index ac3db9997..bb2a1398c 100644
--- a/packages/agent/test/message-cache.test.ts
+++ b/packages/agent/test/message-cache.test.ts
@@ -110,6 +110,34 @@ describe("estimate cache option split", () => {
 		expect(estimateTokens(msg as AgentMessage)).toBe(withBlob);
 		expect(estimateTokens(msg as AgentMessage, { excludeEncryptedReasoning: true })).toBe(floored);
 	});
+
+	test("counts native server-tool blocks by default and drops them from the compaction floor", () => {
+		const encrypted = "cipher".repeat(4000);
+		const msg: AssistantMessage = {
+			...settledAssistant("with search"),
+			content: [
+				{ type: "text", text: "answer" },
+				{
+					type: "anthropicServerTool",
+					block: {
+						type: "web_search_tool_result",
+						tool_use_id: "srvtoolu_1",
+						content: [{ type: "web_search_result", encrypted_content: encrypted }],
+					},
+				},
+			],
+		};
+		const textOnly = estimateTokens({
+			...settledAssistant("x"),
+			content: [{ type: "text", text: "answer" }],
+		} as AgentMessage);
+		const withServerTool = estimateTokens(msg as AgentMessage);
+		const floored = estimateTokens(msg as AgentMessage, { excludeEncryptedReasoning: true });
+		// Default estimate charges for the serialized server-tool payload…
+		expect(withServerTool).toBeGreaterThan(floored + 500);
+		// …while the compaction floor ignores the opaque encrypted blob entirely.
+		expect(floored).toBe(textOnly);
+	});
 });
 
 describe("estimate cache invalidation seams", () => {