Vocabulary Chain Transformation

You are given a vocabulary transformation puzzle where you need to convert a source word into a destination word by following these rules:

1. You must build a transformation chain that starts with the source word and ends with the destination word.
2. In each step of the chain, you can only change exactly one character of the current word to form the next word.
3. Every intermediate word in the chain (except the source word) must exist in the provided dictionary of valid words.
4. The source word itself does not need to be present in the dictionary.

A transformation chain is a sequence: sourceWord → word₁ → word₂ → ... → wordₖ where:

• Each consecutive pair of words differs by exactly one character position.
• All intermediate words (word₁ through wordₖ₋₁) and the destination word (wordₖ) are present in the dictionary.
• wordₖ equals the destination word.

Your task is to determine the length of the shortest transformation chain (counting all words in the chain including both the source and destination words). If no valid transformation chain exists, return 0.

Key Observations:

• The source word is always counted as part of the chain length, even if it's not in the dictionary.
• Each step must change exactly one letter—no insertions, deletions, or multiple character changes are allowed.
• If the destination word is not in the dictionary, transformation is impossible.
• All words, including the source word, destination word, and dictionary words, have the same length.