fix: preserve tool_use blocks for all tool_results in kept messages during condensation

src/core/condense/__tests__/index.spec.ts

@@ -334,6 +334,254 @@ describe("getKeepMessagesWithToolBlocks", () => {
 		expect(result.toolUseBlocksToPreserve).toHaveLength(1)
 		expect(result.reasoningBlocksToPreserve).toHaveLength(0)
 	})
+
+	it("should preserve tool_use when tool_result is in 2nd kept message and tool_use is 2 messages before boundary", () => {
+		const toolUseBlock = {
+			type: "tool_use" as const,
+			id: "toolu_second_kept",
+			name: "read_file",
+			input: { path: "test.txt" },
+		}
+		const toolResultBlock = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_second_kept",
+			content: "file contents",
+		}
+
+		const messages: ApiMessage[] = [
+			{ role: "user", content: "Hello", ts: 1 },
+			{ role: "assistant", content: "Let me help", ts: 2 },
+			{
+				role: "assistant",
+				content: [{ type: "text" as const, text: "Reading file..." }, toolUseBlock],
+				ts: 3,
+			},
+			{ role: "user", content: "Some other message", ts: 4 },
+			{ role: "assistant", content: "First kept message", ts: 5 },
+			{
+				role: "user",
+				content: [toolResultBlock, { type: "text" as const, text: "Continue" }],
+				ts: 6,
+			},
+			{ role: "assistant", content: "Third kept message", ts: 7 },
+		]
+
+		const result = getKeepMessagesWithToolBlocks(messages, 3)
+
+		// keepMessages should be the last 3 messages (ts: 5, 6, 7)
+		expect(result.keepMessages).toHaveLength(3)
+		expect(result.keepMessages[0].ts).toBe(5)
+		expect(result.keepMessages[1].ts).toBe(6)
+		expect(result.keepMessages[2].ts).toBe(7)
+
+		// Should preserve the tool_use block from message at ts:3 (2 messages before boundary)
+		expect(result.toolUseBlocksToPreserve).toHaveLength(1)
+		expect(result.toolUseBlocksToPreserve[0]).toEqual(toolUseBlock)
+	})
+
+	it("should preserve tool_use when tool_result is in 3rd kept message and tool_use is at boundary edge", () => {
+		const toolUseBlock = {
+			type: "tool_use" as const,
+			id: "toolu_third_kept",
+			name: "search",
+			input: { query: "test" },
+		}
+		const toolResultBlock = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_third_kept",
+			content: "search results",
+		}
+
+		const messages: ApiMessage[] = [
+			{ role: "user", content: "Start", ts: 1 },
+			{
+				role: "assistant",
+				content: [{ type: "text" as const, text: "Searching..." }, toolUseBlock],
+				ts: 2,
+			},
+			{ role: "user", content: "First kept message", ts: 3 },
+			{ role: "assistant", content: "Second kept message", ts: 4 },
+			{
+				role: "user",
+				content: [toolResultBlock, { type: "text" as const, text: "Done" }],
+				ts: 5,
+			},
+		]
+
+		const result = getKeepMessagesWithToolBlocks(messages, 3)
+
+		// keepMessages should be the last 3 messages (ts: 3, 4, 5)
+		expect(result.keepMessages).toHaveLength(3)
+		expect(result.keepMessages[0].ts).toBe(3)
+		expect(result.keepMessages[1].ts).toBe(4)
+		expect(result.keepMessages[2].ts).toBe(5)
+
+		// Should preserve the tool_use block from message at ts:2 (at the search boundary edge)
+		expect(result.toolUseBlocksToPreserve).toHaveLength(1)
+		expect(result.toolUseBlocksToPreserve[0]).toEqual(toolUseBlock)
+	})
+
+	it("should preserve multiple tool_uses when tool_results are in different kept messages", () => {
+		const toolUseBlock1 = {
+			type: "tool_use" as const,
+			id: "toolu_multi_1",
+			name: "read_file",
+			input: { path: "file1.txt" },
+		}
+		const toolUseBlock2 = {
+			type: "tool_use" as const,
+			id: "toolu_multi_2",
+			name: "read_file",
+			input: { path: "file2.txt" },
+		}
+		const toolResultBlock1 = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_multi_1",
+			content: "contents 1",
+		}
+		const toolResultBlock2 = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_multi_2",
+			content: "contents 2",
+		}
+
+		const messages: ApiMessage[] = [
+			{ role: "user", content: "Start", ts: 1 },
+			{
+				role: "assistant",
+				content: [{ type: "text" as const, text: "Reading file 1..." }, toolUseBlock1],
+				ts: 2,
+			},
+			{ role: "user", content: "Some message", ts: 3 },
+			{
+				role: "assistant",
+				content: [{ type: "text" as const, text: "Reading file 2..." }, toolUseBlock2],
+				ts: 4,
+			},
+			{
+				role: "user",
+				content: [toolResultBlock1, { type: "text" as const, text: "First result" }],
+				ts: 5,
+			},
+			{
+				role: "user",
+				content: [toolResultBlock2, { type: "text" as const, text: "Second result" }],
+				ts: 6,
+			},
+			{ role: "assistant", content: "Got both files", ts: 7 },
+		]
+
+		const result = getKeepMessagesWithToolBlocks(messages, 3)
+
+		// keepMessages should be the last 3 messages (ts: 5, 6, 7)
+		expect(result.keepMessages).toHaveLength(3)
+
+		// Should preserve both tool_use blocks
+		expect(result.toolUseBlocksToPreserve).toHaveLength(2)
+		expect(result.toolUseBlocksToPreserve).toContainEqual(toolUseBlock1)
+		expect(result.toolUseBlocksToPreserve).toContainEqual(toolUseBlock2)
+	})
+
+	it("should not crash when tool_result references tool_use beyond search boundary", () => {
+		const toolResultBlock = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_beyond_boundary",
+			content: "result",
+		}
+
+		// Tool_use is at ts:1, but with N_MESSAGES_TO_KEEP=3, we only search back 3 messages
+		// from startIndex-1. StartIndex is 7 (messages.length=10, keepCount=3, startIndex=7).
+		// So we search from index 6 down to index 4 (7-1 down to 7-3).
+		// The tool_use at index 0 (ts:1) is beyond the search boundary.
+		const messages: ApiMessage[] = [
+			{
+				role: "assistant",
+				content: [
+					{ type: "text" as const, text: "Way back..." },
+					{
+						type: "tool_use" as const,
+						id: "toolu_beyond_boundary",
+						name: "old_tool",
+						input: {},
+					},
+				],
+				ts: 1,
+			},
+			{ role: "user", content: "Message 2", ts: 2 },
+			{ role: "assistant", content: "Message 3", ts: 3 },
+			{ role: "user", content: "Message 4", ts: 4 },
+			{ role: "assistant", content: "Message 5", ts: 5 },
+			{ role: "user", content: "Message 6", ts: 6 },
+			{ role: "assistant", content: "Message 7", ts: 7 },
+			{
+				role: "user",
+				content: [toolResultBlock],
+				ts: 8,
+			},
+			{ role: "assistant", content: "Message 9", ts: 9 },
+			{ role: "user", content: "Message 10", ts: 10 },
+		]
+
+		// Should not crash
+		const result = getKeepMessagesWithToolBlocks(messages, 3)
+
+		// keepMessages should be the last 3 messages
+		expect(result.keepMessages).toHaveLength(3)
+		expect(result.keepMessages[0].ts).toBe(8)
+		expect(result.keepMessages[1].ts).toBe(9)
+		expect(result.keepMessages[2].ts).toBe(10)
+
+		// Should not preserve the tool_use since it's beyond the search boundary
+		expect(result.toolUseBlocksToPreserve).toHaveLength(0)
+	})
+
+	it("should not duplicate tool_use blocks when same tool_result ID appears multiple times", () => {
+		const toolUseBlock = {
+			type: "tool_use" as const,
+			id: "toolu_duplicate",
+			name: "read_file",
+			input: { path: "test.txt" },
+		}
+		const toolResultBlock1 = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_duplicate",
+			content: "result 1",
+		}
+		const toolResultBlock2 = {
+			type: "tool_result" as const,
+			tool_use_id: "toolu_duplicate",
+			content: "result 2",
+		}
+
+		const messages: ApiMessage[] = [
+			{ role: "user", content: "Start", ts: 1 },
+			{
+				role: "assistant",
+				content: [{ type: "text" as const, text: "Using tool..." }, toolUseBlock],
+				ts: 2,
+			},
+			{
+				role: "user",
+				content: [toolResultBlock1],
+				ts: 3,
+			},
+			{ role: "assistant", content: "Processing", ts: 4 },
+			{
+				role: "user",
+				content: [toolResultBlock2], // Same tool_use_id as first result
+				ts: 5,
+			},
+		]
+
+		const result = getKeepMessagesWithToolBlocks(messages, 3)
+
+		// keepMessages should be the last 3 messages (ts: 3, 4, 5)
+		expect(result.keepMessages).toHaveLength(3)
+
+		// Should only preserve the tool_use block once, not twice
+		expect(result.toolUseBlocksToPreserve).toHaveLength(1)
+		expect(result.toolUseBlocksToPreserve[0]).toEqual(toolUseBlock)
+	})
 })
 
 describe("getMessagesSinceLastSummary", () => {

src/core/condense/index.ts

@@ -7,6 +7,7 @@ import { t } from "../../i18n"
 import { ApiHandler } from "../../api"
 import { ApiMessage } from "../task-persistence/apiMessages"
 import { maybeRemoveImageBlocks } from "../../api/transform/image-cleaning"
+import { findLast } from "../../shared/array"
 
 /**
  * Checks if a message contains tool_result blocks.
@@ -30,6 +31,28 @@ function getToolUseBlocks(message: ApiMessage): Anthropic.Messages.ToolUseBlock[
 	return message.content.filter((block) => block.type === "tool_use") as Anthropic.Messages.ToolUseBlock[]
 }
 
+/**
+ * Gets the tool_result blocks from a message.
+ */
+function getToolResultBlocks(message: ApiMessage): Anthropic.ToolResultBlockParam[] {
+	if (message.role !== "user" || typeof message.content === "string") {
+		return []
+	}
+	return message.content.filter((block): block is Anthropic.ToolResultBlockParam => block.type === "tool_result")
+}
+
+/**
+ * Finds a tool_use block by ID in a message.
+ */
+function findToolUseBlockById(message: ApiMessage, toolUseId: string): Anthropic.Messages.ToolUseBlock | undefined {
+	if (message.role !== "assistant" || typeof message.content === "string") {
+		return undefined
+	}
+	return message.content.find(
+		(block): block is Anthropic.Messages.ToolUseBlock => block.type === "tool_use" && block.id === toolUseId,
+	)
+}
+
 /**
  * Gets reasoning blocks from a message's content array.
  * Task stores reasoning as {type: "reasoning", text: "..."} blocks,
@@ -57,11 +80,11 @@ export type KeepMessagesResult = {
 
 /**
  * Extracts tool_use blocks that need to be preserved to match tool_result blocks in keepMessages.
- * When the first kept message is a user message with tool_result blocks,
- * we need to find the corresponding tool_use blocks from the preceding assistant message.
+ * Checks ALL kept messages for tool_result blocks and searches backwards through the condensed
+ * region (bounded by N_MESSAGES_TO_KEEP) to find the matching tool_use blocks by ID.
  * These tool_use blocks will be appended to the summary message to maintain proper pairing.
  *
- * Also extracts reasoning blocks from the preceding assistant message, which are required
+ * Also extracts reasoning blocks from messages containing preserved tool_uses, which are required
  * by DeepSeek and Z.ai for interleaved thinking mode. Without these, the API returns a 400 error
  * "Missing reasoning_content field in the assistant message".
  * See: https://api-docs.deepseek.com/guides/thinking_mode#tool-calls
@@ -78,28 +101,53 @@ export function getKeepMessagesWithToolBlocks(messages: ApiMessage[], keepCount:
 	const startIndex = messages.length - keepCount
 	const keepMessages = messages.slice(startIndex)
 
-	// Check if the first kept message is a user message with tool_result blocks
-	if (keepMessages.length > 0 && hasToolResultBlocks(keepMessages[0])) {
-		// Look for the preceding assistant message with tool_use blocks
-		const precedingIndex = startIndex - 1
-		if (precedingIndex >= 0) {
-			const precedingMessage = messages[precedingIndex]
-			const toolUseBlocks = getToolUseBlocks(precedingMessage)
-			if (toolUseBlocks.length > 0) {
-				// Also extract reasoning blocks for DeepSeek/Z.ai interleaved thinking
-				// Task stores reasoning as {type: "reasoning", text: "..."} content blocks
-				const reasoningBlocks = getReasoningBlocks(precedingMessage)
-				// Return the tool_use blocks and reasoning blocks to be merged into the summary message
-				return {
-					keepMessages,
-					toolUseBlocksToPreserve: toolUseBlocks,
-					reasoningBlocksToPreserve: reasoningBlocks,
-				}
+	const toolUseBlocksToPreserve: Anthropic.Messages.ToolUseBlock[] = []
+	const reasoningBlocksToPreserve: Anthropic.Messages.ContentBlockParam[] = []
+	const preservedToolUseIds = new Set<string>()
+
+	// Check ALL kept messages for tool_result blocks
+	for (const keepMsg of keepMessages) {
+		if (!hasToolResultBlocks(keepMsg)) {
+			continue
+		}
+
+		const toolResults = getToolResultBlocks(keepMsg)
+
+		for (const toolResult of toolResults) {
+			const toolUseId = toolResult.tool_use_id
+
+			// Skip if we've already found this tool_use
+			if (preservedToolUseIds.has(toolUseId)) {
+				continue
+			}
+
+			// Search backwards through the condensed region (bounded)
+			const searchStart = startIndex - 1
+			const searchEnd = Math.max(0, startIndex - N_MESSAGES_TO_KEEP)
+			const messagesToSearch = messages.slice(searchEnd, searchStart + 1)
+
+			// Find the message containing this tool_use
+			const messageWithToolUse = findLast(messagesToSearch, (msg) => {
+				return findToolUseBlockById(msg, toolUseId) !== undefined
+			})
+
+			if (messageWithToolUse) {
+				const toolUse = findToolUseBlockById(messageWithToolUse, toolUseId)!
+				toolUseBlocksToPreserve.push(toolUse)
+				preservedToolUseIds.add(toolUseId)
+
+				// Also preserve reasoning blocks from that message
+				const reasoning = getReasoningBlocks(messageWithToolUse)
+				reasoningBlocksToPreserve.push(...reasoning)
 			}
 		}
 	}
 
-	return { keepMessages, toolUseBlocksToPreserve: [], reasoningBlocksToPreserve: [] }
+	return {
+		keepMessages,
+		toolUseBlocksToPreserve,
+		reasoningBlocksToPreserve,
+	}
 }
 
 export const N_MESSAGES_TO_KEEP = 3