fix: preserve bounded inline images during tool artifact sizing

src/utils/toolContent.test.ts

@@ -16,6 +16,33 @@ import {
 type ToolContent = BaseMessage['content'];
 
 describe('toolContent', () => {
+  it('counts bounded inline images without exhausting structured character work', () => {
+    const content: ToolContent = [
+      {
+        type: 'image_url',
+        image_url: {
+          url: `data:image/png;base64,${Buffer.alloc(2_477_915).toString('base64')}`,
+        },
+      },
+    ];
+    expect(getToolContentCharLength(content)).toBe(
+      JSON.stringify(content).length
+    );
+    expect(compactToolContent(content, 4_000_000).changed).toBe(false);
+    expect(compactToolContent(content, 400_000).changed).toBe(true);
+  });
+
+  it('retains character traversal protection for escaped and oversized strings', () => {
+    for (const url of [
+      `data:image/png;"base64,${'A'.repeat(1_100_000)}`,
+      `data:image/png;base64,${'A'.repeat(5_000_004)}`,
+      'A'.repeat(1_100_000),
+    ]) {
+      const content: ToolContent = [{ type: 'image_url', image_url: { url } }];
+      expect(compactToolContent(content, 8_000_000).changed).toBe(true);
+    }
+  });
+
   it('normalizes a small opaque array to provider-neutral text', () => {
     const content = [{ type: 'json', rows: [{ id: 1 }] }] as ToolContent;
 

src/utils/toolContent.ts

@@ -109,6 +109,16 @@ function jsonStringLength(
   limit: number,
   work: StructuredWorkState
 ): number {
+  /** Bounded inline images contain no JSON escapes; count their characters directly. */
+  if (
+    value.length <= HARD_MAX_TOTAL_TOOL_OUTPUT_SIZE &&
+    value.startsWith('data:image/') &&
+    /^data:image\/[a-z0-9.+-]+;base64,[a-z0-9+/]+={0,2}$/i.test(value)
+  ) {
+    return value.length + 2 > limit
+      ? conservativeStructuredLength(limit)
+      : value.length + 2;
+  }
   let length = 2;
   for (let i = 0; i < value.length; i++) {
     if (!consumeStructuredCharacterWork(work)) {