fix: improve tool name resolution for gemini provider

Author: hannesrudolph

src/api/providers/gemini.ts

@@ -103,8 +103,22 @@ export class GeminiHandler extends BaseProvider implements SingleCompletionHandl
 			return true
 		})
 
+		// Build a map of tool IDs to names from previous messages
+		// This is needed because Anthropic's tool_result blocks only contain the ID,
+		// but Gemini requires the name in functionResponse
+		const toolIdToName = new Map<string, string>()
+		for (const message of messages) {
+			if (Array.isArray(message.content)) {
+				for (const block of message.content) {
+					if (block.type === "tool_use") {
+						toolIdToName.set(block.id, block.name)
+					}
+				}
+			}
+		}
+
 		const contents = geminiMessages
-			.map((message) => convertAnthropicMessageToGemini(message, { includeThoughtSignatures }))
+			.map((message) => convertAnthropicMessageToGemini(message, { includeThoughtSignatures, toolIdToName }))
 			.flat()
 
 		const tools: GenerateContentConfig["tools"] = []

src/api/transform/gemini-format.ts

@@ -15,9 +15,10 @@ function isThoughtSignatureContentBlock(block: ExtendedContentBlockParam): block
 
 export function convertAnthropicContentToGemini(
 	content: ExtendedAnthropicContent,
-	options?: { includeThoughtSignatures?: boolean },
+	options?: { includeThoughtSignatures?: boolean; toolIdToName?: Map<string, string> },
 ): Part[] {
 	const includeThoughtSignatures = options?.includeThoughtSignatures ?? true
+	const toolIdToName = options?.toolIdToName
 
 	// First pass: find thoughtSignature if it exists in the content blocks
 	let activeThoughtSignature: string | undefined
@@ -78,9 +79,15 @@ export function convertAnthropicContentToGemini(
 					return []
 				}
 
-				// Extract tool name from tool_use_id (e.g., "calculator-123" -> "calculator")
-				const lastHyphenIndex = block.tool_use_id.lastIndexOf("-")
-				const toolName = lastHyphenIndex >= 0 ? block.tool_use_id.slice(0, lastHyphenIndex) : block.tool_use_id
+				// 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)
+				if (!toolName) {
+					const lastHyphenIndex = block.tool_use_id.lastIndexOf("-")
+					toolName = lastHyphenIndex >= 0 ? block.tool_use_id.slice(0, lastHyphenIndex) : block.tool_use_id
+				}
 
 				if (typeof block.content === "string") {
 					return {
@@ -123,7 +130,7 @@ export function convertAnthropicContentToGemini(
 
 export function convertAnthropicMessageToGemini(
 	message: Anthropic.Messages.MessageParam,
-	options?: { includeThoughtSignatures?: boolean },
+	options?: { includeThoughtSignatures?: boolean; toolIdToName?: Map<string, string> },
 ): Content[] {
 	const parts = convertAnthropicContentToGemini(message.content, options)