fix: bound partial number recovery to its token

src/_vendor/partial-json-parser/parser.ts

@@ -248,14 +248,15 @@ const _parseJSON = (jsonString: string, allow: number) => {
       markPartialJSON('Unterminated number literal');
     }
 
+    const number = jsonString.substring(start, index);
     try {
-      return JSON.parse(jsonString.substring(start, index));
+      return JSON.parse(number);
     } catch {
-      if (jsonString.substring(start, index) === '-' && Allow.NUM & allow) {
+      if (number === '-' && Allow.NUM & allow) {
         markPartialJSON("Not sure what '-' is");
       }
       try {
-        return JSON.parse(jsonString.substring(start, jsonString.lastIndexOf('e')));
+        return JSON.parse(number.substring(0, number.lastIndexOf('e')));
       } catch (e) {
         throwMalformedError(String(e));
       }

tests/_vendor/partial-json-parser/partial-json-parsing.test.ts

@@ -35,6 +35,29 @@ describe('partial parsing', () => {
     expect(partialParse('[1, 2e')).toEqual([1]);
   });
 
+  test.each<[string, number[]]>([
+    ['[1, 2e', [1]],
+    ['[1, 2e+', [1]],
+    ['[1, 2e-', [1]],
+    ['[1, 2e3]', [1, 2000]],
+    ['[1, 2E3]', [1, 2000]],
+    ['[1, 2e-2 ]', [1, 0.02]],
+    ['[1, 2e]', [1, 2]],
+    ['[1, 2e+, 3]', [1, 2, 3]],
+    ['[1, 2e-, 3]', [1, 2, 3]],
+    ['[1, 2e, 3e2]', [1, 2, 300]],
+  ])('preserves exponent recovery for %s', (input, expected) => {
+    expect(partialParse(input)).toEqual(expected);
+  });
+
+  test('bounds exponent recovery before a later string', () => {
+    expect(partialParse('[1, 2e, "else"]')).toEqual([1, 2, 'else']);
+  });
+
+  test('preserves partial arrays while recovering from malformed numeric tokens', () => {
+    expect(partialParse(`[${'[x,'.repeat(100)}]`)).toEqual(Array.from({ length: 100 }, () => []));
+  });
+
   test('should only throw errors parsing numbers', () =>
     assert(
       property(json({ depthSize: 'large', noUnicodeString: false }), (jsonString) => {

tests/lib/chat-completion-stream-partial-json-bounds.test.ts

@@ -207,6 +207,66 @@ function createStructuredStream(kind: 'content' | 'tool', fragments: Iterable<st
 
 afterEach(() => vi.restoreAllMocks());
 
+it.each(['content', 'tool'] as const)(
+  'keeps numeric recovery work linear for malformed serialized %s',
+  async (kind) => {
+    const content = `[${'[x,'.repeat(100)}"${'x'.repeat(1024 * 1024)}"]`;
+    const chunks = kind === 'content' ? contentFragments([content]) : argumentFragments([content]);
+    const client = createSerializedClient(chunks, vi.fn());
+    const { lastIndexOf } = String.prototype;
+    let searchedCharacters = 0;
+    const search = vi.spyOn(String.prototype, 'lastIndexOf').mockImplementation(function search(
+      this: string,
+      value: string,
+      position?: number,
+    ) {
+      if (value === 'e') {
+        searchedCharacters += this.length;
+      }
+      return lastIndexOf.call(this, value, position);
+    });
+    let failure: unknown;
+
+    try {
+      await client.chat.completions
+        .stream({
+          model: 'gpt-test',
+          messages: [{ role: 'user', content: 'Return structured output' }],
+          ...(kind === 'content' ? { response_format: structuredResponseFormat } : { tools: [strictTool] }),
+        })
+        .finalChatCompletion();
+    } catch (error) {
+      failure = error;
+    } finally {
+      search.mockRestore();
+    }
+
+    expect(failure).toBeInstanceOf(Error);
+    expect(failure).toMatchObject({ message: 'Error reading response: invalid structured output JSON.' });
+    expect(searchedCharacters).toBeLessThanOrEqual(content.length);
+  },
+);
+
+it.each(['content', 'tool'] as const)('preserves large valid serialized %s', async (kind) => {
+  const value = { value: 'x'.repeat(1024 * 1024) };
+  const content = JSON.stringify(value);
+  const chunks = kind === 'content' ? contentFragments([content]) : argumentFragments([content]);
+  const client = createSerializedClient(chunks, vi.fn());
+  const completion = await client.chat.completions
+    .stream({
+      model: 'gpt-test',
+      messages: [{ role: 'user', content: 'Return structured output' }],
+      ...(kind === 'content' ? { response_format: structuredResponseFormat } : { tools: [strictTool] }),
+    })
+    .finalChatCompletion();
+
+  expect(completion.choices[0]?.message).toMatchObject(
+    kind === 'content'
+      ? { parsed: value }
+      : { tool_calls: [{ type: 'function', function: { parsed_arguments: value } }] },
+  );
+});
+
 it.each(['strict', 'auto-parseable'] as const)(
   'captures receiver-bound %s argument accessors exactly once before all accounting and events',
   async (kind) => {