fix: strip thinking/redacted_thinking blocks from non-latest assistant messages for Anthropic
Fixes #39887 When compaction or session serialization modifies thinking/redacted_thinking content blocks in assistant messages, the Anthropic API rejects the next request because these blocks must remain byte-identical to the original response in the latest assistant message. Changes: 1. **dropThinkingBlocks**: Now strips both `type: "thinking"` and `type: "redacted_thinking"` blocks (previously only handled `thinking`). 2. **stripThinkingFromNonLatestAssistant** (new): Strips thinking and redacted_thinking blocks from all assistant messages EXCEPT the latest one. Anthropic allows omitting these blocks from non-latest messages but requires the latest message's blocks to be unmodified. This prevents compaction-corrupted blocks from reaching the API. 3. **sanitizeSessionHistory**: For Anthropic providers, applies stripThinkingFromNonLatestAssistant before other sanitization steps. This ensures that even if compaction modifies thinking blocks in older messages, they are cleanly removed before the API call. The fix is defensive: rather than trying to preserve exact byte representation through compaction (which crosses the pi-agent-core SDK boundary), we strip blocks that Anthropic doesn't require from older messages and preserve only the latest assistant's blocks which haven't been through compaction yet.
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taw0002
parent
d5b305b250
commit
738d6b6b52
@ -32,7 +32,7 @@ import {
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type UsageLike,
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} from "../usage.js";
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import { log } from "./logger.js";
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import { dropThinkingBlocks } from "./thinking.js";
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import { dropThinkingBlocks, stripThinkingFromNonLatestAssistant } from "./thinking.js";
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import { describeUnknownError } from "./utils.js";
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const GOOGLE_TURN_ORDERING_CUSTOM_TYPE = "google-turn-ordering-bootstrap";
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@ -549,9 +549,22 @@ export async function sanitizeSessionHistory(params: {
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...resolveImageSanitizationLimits(params.config),
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},
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);
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const droppedThinking = policy.dropThinkingBlocks
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? dropThinkingBlocks(sanitizedImages)
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// For Anthropic models, strip thinking/redacted_thinking blocks from all
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// non-latest assistant messages. Anthropic requires these blocks to be
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// byte-identical to the original response in the latest assistant message,
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// but allows omitting them from older messages. Compaction and session
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// serialization can corrupt these blocks, causing API rejections.
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const isAnthropicProvider =
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params.modelApi === "anthropic-messages" ||
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params.modelApi === "bedrock-converse-stream" ||
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(params.provider ?? "").toLowerCase() === "anthropic" ||
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(params.provider ?? "").toLowerCase() === "amazon-bedrock";
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const strippedNonLatestThinking = isAnthropicProvider
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? stripThinkingFromNonLatestAssistant(sanitizedImages)
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: sanitizedImages;
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const droppedThinking = policy.dropThinkingBlocks
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? dropThinkingBlocks(strippedNonLatestThinking)
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: strippedNonLatestThinking;
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const sanitizedToolCalls = sanitizeToolCallInputs(droppedThinking, {
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allowedToolNames: params.allowedToolNames,
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});
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@ -1,7 +1,11 @@
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import type { AgentMessage } from "@mariozechner/pi-agent-core";
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import { describe, expect, it } from "vitest";
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import { castAgentMessage } from "../test-helpers/agent-message-fixtures.js";
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import { dropThinkingBlocks, isAssistantMessageWithContent } from "./thinking.js";
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import {
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dropThinkingBlocks,
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isAssistantMessageWithContent,
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stripThinkingFromNonLatestAssistant,
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} from "./thinking.js";
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describe("isAssistantMessageWithContent", () => {
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it("accepts assistant messages with array content and rejects others", () => {
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@ -46,6 +50,40 @@ describe("dropThinkingBlocks", () => {
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expect(assistant.content).toEqual([{ type: "text", text: "final" }]);
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});
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it("drops redacted_thinking blocks", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "redacted_thinking", data: "opaque-base64-data" },
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{ type: "text", text: "visible" },
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],
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}),
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];
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const result = dropThinkingBlocks(messages);
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const assistant = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(result).not.toBe(messages);
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expect(assistant.content).toEqual([{ type: "text", text: "visible" }]);
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});
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it("drops both thinking and redacted_thinking blocks in the same message", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "internal" },
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{ type: "redacted_thinking", data: "opaque" },
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{ type: "text", text: "answer" },
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],
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}),
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];
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const result = dropThinkingBlocks(messages);
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const assistant = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(assistant.content).toEqual([{ type: "text", text: "answer" }]);
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});
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it("keeps assistant turn structure when all content blocks were thinking", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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@ -59,3 +97,145 @@ describe("dropThinkingBlocks", () => {
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expect(assistant.content).toEqual([{ type: "text", text: "" }]);
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});
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});
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describe("stripThinkingFromNonLatestAssistant", () => {
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it("returns original reference when no assistant messages have thinking blocks", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({ role: "user", content: "hi" }),
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castAgentMessage({ role: "assistant", content: [{ type: "text", text: "hello" }] }),
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];
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const result = stripThinkingFromNonLatestAssistant(messages);
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expect(result).toBe(messages);
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});
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it("returns original reference with zero or one assistant message", () => {
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const single: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "deep thought" },
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{ type: "text", text: "answer" },
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],
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}),
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];
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expect(stripThinkingFromNonLatestAssistant(single)).toBe(single);
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});
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it("preserves thinking blocks in the latest assistant message only", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "old thought" },
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{ type: "text", text: "old answer" },
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],
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}),
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castAgentMessage({ role: "user", content: "follow up" }),
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "new thought" },
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{ type: "redacted_thinking", data: "opaque" },
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{ type: "text", text: "new answer" },
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],
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}),
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];
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const result = stripThinkingFromNonLatestAssistant(messages);
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expect(result).not.toBe(messages);
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// First assistant: thinking stripped
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const first = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(first.content).toEqual([{ type: "text", text: "old answer" }]);
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// Latest assistant: thinking preserved exactly
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const latest = result[2] as Extract<AgentMessage, { role: "assistant" }>;
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expect(latest.content).toEqual([
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{ type: "thinking", thinking: "new thought" },
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{ type: "redacted_thinking", data: "opaque" },
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{ type: "text", text: "new answer" },
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]);
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});
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it("strips redacted_thinking blocks from non-latest assistant messages", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "redacted_thinking", data: "old-opaque" },
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{ type: "text", text: "first" },
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],
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}),
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castAgentMessage({ role: "user", content: "next" }),
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castAgentMessage({
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role: "assistant",
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content: [{ type: "text", text: "second" }],
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}),
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];
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const result = stripThinkingFromNonLatestAssistant(messages);
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const first = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(first.content).toEqual([{ type: "text", text: "first" }]);
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// Latest assistant untouched (no thinking blocks to worry about)
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const latest = result[2] as Extract<AgentMessage, { role: "assistant" }>;
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expect(latest.content).toEqual([{ type: "text", text: "second" }]);
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});
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it("replaces with empty text block when all blocks in non-latest are thinking", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "only thinking" },
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{ type: "redacted_thinking", data: "opaque" },
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],
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}),
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castAgentMessage({ role: "user", content: "next" }),
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castAgentMessage({
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role: "assistant",
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content: [{ type: "text", text: "latest" }],
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}),
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];
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const result = stripThinkingFromNonLatestAssistant(messages);
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const first = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(first.content).toEqual([{ type: "text", text: "" }]);
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});
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it("handles interleaved user and toolResult messages correctly", () => {
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const messages: AgentMessage[] = [
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "thought 1" },
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{ type: "text", text: "call tool" },
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],
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}),
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castAgentMessage({ role: "toolResult", content: "result" }),
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castAgentMessage({
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role: "assistant",
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content: [
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{ type: "thinking", thinking: "thought 2" },
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{ type: "text", text: "final" },
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],
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}),
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];
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const result = stripThinkingFromNonLatestAssistant(messages);
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// First assistant: thinking stripped
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const first = result[0] as Extract<AgentMessage, { role: "assistant" }>;
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expect(first.content).toEqual([{ type: "text", text: "call tool" }]);
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// toolResult: unchanged
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expect(result[1]).toBe(messages[1]);
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// Latest assistant: thinking preserved
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const latest = result[2] as Extract<AgentMessage, { role: "assistant" }>;
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expect(latest.content).toEqual([
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{ type: "thinking", thinking: "thought 2" },
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{ type: "text", text: "final" },
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]);
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});
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});
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@ -3,6 +3,17 @@ import type { AgentMessage } from "@mariozechner/pi-agent-core";
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type AssistantContentBlock = Extract<AgentMessage, { role: "assistant" }>["content"][number];
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type AssistantMessage = Extract<AgentMessage, { role: "assistant" }>;
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/** Block types that Anthropic considers immutable once returned. */
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const THINKING_BLOCK_TYPES: ReadonlySet<string> = new Set(["thinking", "redacted_thinking"]);
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function isThinkingBlock(block: unknown): boolean {
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if (!block || typeof block !== "object") {
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return false;
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}
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const type = (block as { type?: unknown }).type;
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return typeof type === "string" && THINKING_BLOCK_TYPES.has(type);
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}
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export function isAssistantMessageWithContent(message: AgentMessage): message is AssistantMessage {
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return (
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!!message &&
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@ -13,7 +24,8 @@ export function isAssistantMessageWithContent(message: AgentMessage): message is
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}
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/**
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* Strip all `type: "thinking"` content blocks from assistant messages.
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* Strip all `type: "thinking"` and `type: "redacted_thinking"` content blocks
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* from assistant messages.
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*
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* If an assistant message becomes empty after stripping, it is replaced with
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* a synthetic `{ type: "text", text: "" }` block to preserve turn structure
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@ -33,7 +45,7 @@ export function dropThinkingBlocks(messages: AgentMessage[]): AgentMessage[] {
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const nextContent: AssistantContentBlock[] = [];
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let changed = false;
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for (const block of msg.content) {
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if (block && typeof block === "object" && (block as { type?: unknown }).type === "thinking") {
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if (isThinkingBlock(block)) {
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touched = true;
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changed = true;
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continue;
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@ -51,3 +63,67 @@ export function dropThinkingBlocks(messages: AgentMessage[]): AgentMessage[] {
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}
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return touched ? out : messages;
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}
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/**
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* Strip `thinking` and `redacted_thinking` blocks from all assistant messages
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* **except** the latest (last) assistant message in the array.
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*
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* Anthropic requires that thinking/redacted_thinking blocks in the latest
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* assistant message remain byte-identical to the original API response.
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* Blocks in non-latest assistant messages may be omitted entirely.
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*
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* This prevents compaction or session serialization from corrupting thinking
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* blocks that are later rejected by the Anthropic API.
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*
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* Returns the original array reference when nothing was changed.
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*/
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export function stripThinkingFromNonLatestAssistant(messages: AgentMessage[]): AgentMessage[] {
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// Find the index of the last assistant message with array content.
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let lastAssistantIndex = -1;
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for (let i = messages.length - 1; i >= 0; i--) {
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if (isAssistantMessageWithContent(messages[i])) {
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lastAssistantIndex = i;
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break;
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}
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}
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// Nothing to do if there is zero or one assistant message.
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if (lastAssistantIndex <= 0) {
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return messages;
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}
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let touched = false;
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const out: AgentMessage[] = [];
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for (let i = 0; i < messages.length; i++) {
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const msg = messages[i];
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// Skip non-assistant or the latest assistant — keep them as-is.
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if (i === lastAssistantIndex || !isAssistantMessageWithContent(msg)) {
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out.push(msg);
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continue;
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}
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const nextContent: AssistantContentBlock[] = [];
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let changed = false;
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for (const block of msg.content) {
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if (isThinkingBlock(block)) {
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touched = true;
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changed = true;
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continue;
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}
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nextContent.push(block);
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}
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if (!changed) {
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out.push(msg);
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continue;
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}
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const content =
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nextContent.length > 0 ? nextContent : [{ type: "text", text: "" } as AssistantContentBlock];
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out.push({ ...msg, content });
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}
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return touched ? out : messages;
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}
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