Diff Format Explained: Search-Replace Blocks in AI Code Editing

filename.py
```
<<<<<<< SEARCH
def calculate_total(items):
    total = 0
    for item in items:
        total += item.price
    return total
=======
def calculate_total(items):
    total = 0
    tax_rate = 0.08
    for item in items:
        total += item.price
    return total * (1 + tax_rate)
>>>>>>> REPLACE
```

# Original function the AI expects to find:
<<<<<<< SEARCH
def process_data(data):
    result = []
    for item in data:
        result.append(transform(item))
    return result
=======
def process_data(data):
    result = []
    for item in data:
        processed = transform(item)
        result.append(processed)
    return result
>>>>>>> REPLACE

# But actual code in file (after formatting/evolution):
def process_data(data):
    result = []
    # Process each item
    for item in data:
        result.append(transform(item))
    return result

# FAILURE: Search pattern doesn't match due to added comment
# AI cannot find exact string, edit fails

# OLD: Diff format (prone to failure)
filename.py
```
<<<<<<< SEARCH
def authenticate_user(username, password):
    if check_credentials(username, password):
        return True
    return False
=======
def authenticate_user(username, password):
    if check_credentials(username, password):
        set_last_login(username)
        return True
    return False
>>>>>>> REPLACE
```

# NEW: Semantic instruction (98% reliable)
curl -X POST https://api.morphllm.com/v1/chat/completions \
  -d '{
    "model": "morph-v3-large",
    "messages": [{
      "role": "user",
      "content": "<instruction>Add a call to set_last_login(username) after successful authentication but before returning True</instruction>\n<code>...full file content...</code>"
    }]
  }'