1 files changed, 63 insertions, 6 deletions

diff --git a/packages/cli/src/ui/hooks/useToolScheduler.ts b/packages/cli/src/ui/hooks/useToolScheduler.ts
index 7d8cfbe4..e6e80785 100644
--- a/packages/cli/src/ui/hooks/useToolScheduler.ts
+++ b/packages/cli/src/ui/hooks/useToolScheduler.ts
@@ -13,7 +13,7 @@ import {
   ToolCallConfirmationDetails,
   ToolResult,
 } from '@gemini-code/server';
-import { Part } from '@google/genai';
+import { Part, PartUnion, PartListUnion } from '@google/genai';
 import { useCallback, useEffect, useState } from 'react';
 import {
   HistoryItemToolGroup,
@@ -88,6 +88,60 @@ export type CompletedToolCall =
   | CancelledToolCall
   | ErroredToolCall;
 
+/**
+ * Formats a PartListUnion response from a tool into JSON suitable for a Gemini
+ * FunctionResponse and additional Parts to include after that response.
+ *
+ * This is required because FunctionReponse appears to only support JSON
+ * and not arbitrary parts. Including parts like inlineData or fileData
+ * directly in a FunctionResponse confuses the model resulting in a failure
+ * to interpret the multimodal content and context window exceeded errors.
+ */
+
+export function formatLlmContentForFunctionResponse(
+  llmContent: PartListUnion,
+): {
+  functionResponseJson: Record<string, string>;
+  additionalParts: PartUnion[];
+} {
+  const additionalParts: PartUnion[] = [];
+  let functionResponseJson: Record<string, string>;
+
+  if (Array.isArray(llmContent) && llmContent.length === 1) {
+    // Ensure that length 1 arrays are treated as a single Part.
+    llmContent = llmContent[0];
+  }
+
+  if (typeof llmContent === 'string') {
+    functionResponseJson = { output: llmContent };
+  } else if (Array.isArray(llmContent)) {
+    functionResponseJson = { status: 'Tool execution succeeded.' };
+    additionalParts.push(...llmContent);
+  } else {
+    if (
+      llmContent.inlineData !== undefined ||
+      llmContent.fileData !== undefined
+    ) {
+      // For Parts like inlineData or fileData, use the returnDisplay as the textual output for the functionResponse.
+      // The actual Part will be added to additionalParts.
+      functionResponseJson = {
+        status: `Binary content of type ${llmContent.inlineData?.mimeType || llmContent.fileData?.mimeType || 'unknown'} was processed.`,
+      };
+      additionalParts.push(llmContent);
+    } else if (llmContent.text !== undefined) {
+      functionResponseJson = { output: llmContent.text };
+    } else {
+      functionResponseJson = { status: 'Tool execution succeeded.' };
+      additionalParts.push(llmContent);
+    }
+  }
+
+  return {
+    functionResponseJson,
+    additionalParts,
+  };
+}
+
 export function useToolScheduler(
   onComplete: (tools: CompletedToolCall[]) => void,
   config: Config,
@@ -201,7 +255,7 @@ export function useToolScheduler(
                 status: 'cancelled',
                 response: {
                   callId: c.request.callId,
-                  responsePart: {
+                  responseParts: {
                     functionResponse: {
                       id: c.request.callId,
                       name: c.request.name,
@@ -276,21 +330,24 @@ export function useToolScheduler(
             .execute(t.request.args, signal, onOutputChunk)
             .then((result: ToolResult) => {
               if (signal.aborted) {
+                // TODO(jacobr): avoid stringifying the LLM content.
                 setToolCalls(
                   setStatus(callId, 'cancelled', String(result.llmContent)),
                 );
                 return;
               }
+              const { functionResponseJson, additionalParts } =
+                formatLlmContentForFunctionResponse(result.llmContent);
               const functionResponse: Part = {
                 functionResponse: {
                   name: t.request.name,
                   id: callId,
-                  response: { output: result.llmContent },
+                  response: functionResponseJson,
                 },
               };
               const response: ToolCallResponseInfo = {
                 callId,
-                responsePart: functionResponse,
+                responseParts: [functionResponse, ...additionalParts],
                 resultDisplay: result.returnDisplay,
                 error: undefined,
               };
@@ -401,7 +458,7 @@ function setStatus(
             status: 'cancelled',
             response: {
               callId: t.request.callId,
-              responsePart: {
+              responseParts: {
                 functionResponse: {
                   id: t.request.callId,
                   name: t.request.name,
@@ -446,7 +503,7 @@ const toolErrorResponse = (
 ): ToolCallResponseInfo => ({
   callId: request.callId,
   error,
-  responsePart: {
+  responseParts: {
     functionResponse: {
       id: request.callId,
       name: request.name,