fix: prevent list_index variable shadowing in fix_incorrect_toc

[luojiyin1987]

Bug Description

The fix_incorrect_toc function in pageindex/page_index.py:760-827 has a variable shadowing bug that causes results to be written back to wrong index positions.

Problem

The list_index variable (storing the original TOC index to fix) is overwritten by the page loop iterator:

async def process_and_check_item(incorrect_item):
    list_index = incorrect_item['list_index']  # ← Original TOC index
    
    # ...
    
    for page_index in range(prev_correct, next_correct+1):
        list_index = page_index - start_index  # ← Overwrites list_index!
        # ...
    
    return {
        'list_index': list_index,  # ← Uses overwritten value!
        # ...
    }

When the result is written back to toc_with_page_number[list_idx], it updates the wrong position.

Example

If incorrect_item['list_index'] = 5 and the page loop iterates [10, 20]:

• Original list_index = 5 (correct)
• After loop, list_index = 19 (wrong)
• Update goes to index 19 instead of 5

Fix

Rename the loop variable to page_list_idx to avoid shadowing:

for page_index in range(prev_correct, next_correct+1):
    page_list_idx = page_index - start_index
    if page_list_idx >= 0 and page_list_idx < len(page_list):
        page_text = f"..."

[BukeLy]

Refer to #67

[BukeLy]

Thanks for catching this! The list_index variable shadowing is a real bug — good find.

However, the associated PR #67 includes a lot of unrelated changes (docstring, defensive checks, logging)that aren't needed. We'll fix the shadowing issue separately with a minimal change.