fix: remove broken tool name extraction fallback in Gemini format converter

- Remove fragile string manipulation fallback that fails with Anthropic tool IDs
- Throw clear error when toolIdToName map is missing required entries
- Update all tests to provide toolIdToName map (reflects real usage)
- Add tests to verify error throwing behavior

The fallback attempted to extract tool names from IDs using lastIndexOf('-'),
which completely fails with Anthropic's native tool IDs like 'toolu_01RxWc...'.
Instead, now fails fast with diagnostic error showing missing ID and available IDs.

Author: daniel-lxs

src/api/transform/__tests__/gemini-format.spec.ts

@@ -141,6 +141,9 @@ describe("convertAnthropicMessageToGemini", () => {
 	})
 
 	it("should convert a message with tool result as string", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("calculator-123", "calculator")
+
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",
 			content: [
@@ -153,7 +156,7 @@ describe("convertAnthropicMessageToGemini", () => {
 			],
 		}
 
-		const result = convertAnthropicMessageToGemini(anthropicMessage)
+		const result = convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })
 
 		expect(result).toEqual([
 			{
@@ -193,6 +196,9 @@ describe("convertAnthropicMessageToGemini", () => {
 	})
 
 	it("should convert a message with tool result as array with text only", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("search-123", "search")
+
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",
 			content: [
@@ -207,7 +213,7 @@ describe("convertAnthropicMessageToGemini", () => {
 			],
 		}
 
-		const result = convertAnthropicMessageToGemini(anthropicMessage)
+		const result = convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })
 
 		expect(result).toEqual([
 			{
@@ -228,6 +234,9 @@ describe("convertAnthropicMessageToGemini", () => {
 	})
 
 	it("should convert a message with tool result as array with text and images", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("search-123", "search")
+
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",
 			content: [
@@ -257,7 +266,7 @@ describe("convertAnthropicMessageToGemini", () => {
 			],
 		}
 
-		const result = convertAnthropicMessageToGemini(anthropicMessage)
+		const result = convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })
 
 		expect(result).toEqual([
 			{
@@ -290,6 +299,9 @@ describe("convertAnthropicMessageToGemini", () => {
 	})
 
 	it("should convert a message with tool result containing only images", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("imagesearch-123", "imagesearch")
+
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",
 			content: [
@@ -310,7 +322,7 @@ describe("convertAnthropicMessageToGemini", () => {
 			],
 		}
 
-		const result = convertAnthropicMessageToGemini(anthropicMessage)
+		const result = convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })
 
 		expect(result).toEqual([
 			{
@@ -336,7 +348,10 @@ describe("convertAnthropicMessageToGemini", () => {
 		])
 	})
 
-	it("should handle tool names with hyphens", () => {
+	it("should handle tool names with hyphens using toolIdToName map", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("search-files-123", "search-files")
+
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",
 			content: [
@@ -348,7 +363,7 @@ describe("convertAnthropicMessageToGemini", () => {
 			],
 		}
 
-		const result = convertAnthropicMessageToGemini(anthropicMessage)
+		const result = convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })
 
 		expect(result).toEqual([
 			{
@@ -368,6 +383,43 @@ describe("convertAnthropicMessageToGemini", () => {
 		])
 	})
 
+	it("should throw error when toolIdToName map is not provided", () => {
+		const anthropicMessage: Anthropic.Messages.MessageParam = {
+			role: "user",
+			content: [
+				{
+					type: "tool_result",
+					tool_use_id: "calculator-123",
+					content: "result is 5",
+				},
+			],
+		}
+
+		expect(() => convertAnthropicMessageToGemini(anthropicMessage)).toThrow(
+			'Unable to find tool name for tool_use_id "calculator-123"',
+		)
+	})
+
+	it("should throw error when tool_use_id is not in the map", () => {
+		const toolIdToName = new Map<string, string>()
+		toolIdToName.set("other-tool-456", "other-tool")
+
+		const anthropicMessage: Anthropic.Messages.MessageParam = {
+			role: "user",
+			content: [
+				{
+					type: "tool_result",
+					tool_use_id: "calculator-123",
+					content: "result is 5",
+				},
+			],
+		}
+
+		expect(() => convertAnthropicMessageToGemini(anthropicMessage, { toolIdToName })).toThrow(
+			'Unable to find tool name for tool_use_id "calculator-123"',
+		)
+	})
+
 	it("should throw an error for unsupported content block type", () => {
 		const anthropicMessage: Anthropic.Messages.MessageParam = {
 			role: "user",

src/api/transform/gemini-format.ts

@@ -79,14 +79,16 @@ export function convertAnthropicContentToGemini(
 					return []
 				}
 
-				// Extract tool name from tool_use_id
-				// 1. Try to look up the name from the provided map (reliable source)
-				// 2. Fallback: Extract from ID if it follows "name-counter" format (heuristic)
-				// 3. Fallback: Use ID as name (likely to fail validation but better than crashing)
-				let toolName = toolIdToName?.get(block.tool_use_id)
+				// Get tool name from the map (built from tool_use blocks in message history).
+				// The map must contain the tool name - if it doesn't, this indicates a bug
+				// where the conversation history is incomplete or tool_use blocks are missing.
+				const toolName = toolIdToName?.get(block.tool_use_id)
 				if (!toolName) {
-					const lastHyphenIndex = block.tool_use_id.lastIndexOf("-")
-					toolName = lastHyphenIndex >= 0 ? block.tool_use_id.slice(0, lastHyphenIndex) : block.tool_use_id
+					throw new Error(
+						`Unable to find tool name for tool_use_id "${block.tool_use_id}". ` +
+							`This indicates the conversation history is missing the corresponding tool_use block. ` +
+							`Available tool IDs: ${Array.from(toolIdToName?.keys() ?? []).join(", ") || "none"}`,
+					)
 				}
 
 				if (typeof block.content === "string") {