fix: split_chunks emits a duplicate trailing chunk for text over size-overlap (#1573)

tests/test_split_chunks_no_duplicate_tail.py

@@ -0,0 +1,33 @@
+"""Regression: split_chunks must not emit a duplicate trailing chunk.
+
+The loop advanced `i = j - overlap` even after `j` reached the end of the text,
+so any text longer than (size - overlap) got an extra final chunk duplicating
+the last `overlap` characters. That duplicate is indexed and keyword-scored
+twice, so retrieve_personal_keyword returns the same tail content twice.
+"""
+from src.personal_docs import split_chunks
+
+
+def test_no_duplicate_tail_chunk():
+    chunks = split_chunks("x" * 1100, size=1000, overlap=200)
+    assert [len(c) for c in chunks] == [1000, 300]
+
+
+def test_no_chunk_is_contained_in_another():
+    text = "".join(chr(33 + (k % 90)) for k in range(2000))
+    chunks = split_chunks(text, size=1000, overlap=200)
+    # The buggy version produced a final 200-char chunk fully inside the prior one.
+    for a in range(len(chunks)):
+        for b in range(len(chunks)):
+            if a != b:
+                assert chunks[a] not in chunks[b]
+
+
+def test_overlap_is_preserved_between_chunks():
+    chunks = split_chunks("x" * 1100, size=1000, overlap=200)
+    # Second chunk starts 200 chars before the first one ended (offset 800).
+    assert len(chunks) == 2 and chunks[1] == ("x" * 1100)[800:1100]
+
+
+def test_short_text_single_chunk():
+    assert split_chunks("hello world", size=1000, overlap=200) == ["hello world"]