fix: handle nested code fences in extract_code_block

The non-greedy regex in FIRST_CODE_BLOCK_PATTERN stopped at the first
``` occurrence, even inside triple-quoted strings or nested code fence
blocks. This truncated the extracted code and lost test functions when
LLMs embedded function definitions using ```python:filepath syntax.

Switch to greedy matching and require the closing ``` to be alone on
its line so intermediate backticks are skipped.

django/aiservice/aiservice/common/markdown_utils.py

@@ -13,8 +13,10 @@ from aiservice.common.llm_output_utils import truncate_pathological_output
 # Matches both ```python and ```python:filepath blocks, captures content only
 MARKDOWN_CODE_BLOCK_PATTERN = re.compile(r"```python(?::[^\n]*)?\n(.*?)```", re.DOTALL)
 
-# Matches first ```python block (no filepath), captures content
-FIRST_CODE_BLOCK_PATTERN = re.compile(r"^```python\s*\n(.*?)\n```", re.MULTILINE | re.DOTALL)
+# Matches first ```python block (no filepath), captures content.
+# Uses greedy (.*) to handle LLM outputs with nested code fences (e.g. ```python:filepath
+# blocks inside the main block). Requires closing ``` to be alone on its line.
+FIRST_CODE_BLOCK_PATTERN = re.compile(r"^```python\s*\n(.*)\n```[ \t]*$", re.MULTILINE | re.DOTALL)
 
 # Fallback for incomplete code blocks (missing closing ```)
 FIRST_CODE_BLOCK_FALLBACK_PATTERN = re.compile(r"^```python\s*\n(.*)", re.MULTILINE | re.DOTALL)

django/aiservice/tests/aiservice/test_markdown_utils.py

@@ -181,6 +181,20 @@ x ="""
     assert result == expected
 
 
+def test_extract_code_block_nested_code_fence_in_triple_quote() -> None:
+    # LLM embeds function definition in a triple-quoted string containing ```
+    text = '```python\nimport pytest\n_source = """```python:file.py\ndef foo(): pass\n```"""\ndef test_foo():\n    assert True\n```'
+    result = extract_code_block(text)
+    assert result == 'import pytest\n_source = """```python:file.py\ndef foo(): pass\n```"""\ndef test_foo():\n    assert True'
+
+
+def test_extract_code_block_nested_code_fence_block() -> None:
+    # LLM nests a ```python:filepath block inside the main block
+    text = '```python\nimport pytest\n```python:src/mod.py\ndef foo(): pass\n```\ndef test_foo():\n    assert True\n```'
+    result = extract_code_block(text)
+    assert result == 'import pytest\n```python:src/mod.py\ndef foo(): pass\n```\ndef test_foo():\n    assert True'
+
+
 def test_extract_all_code_single_block() -> None:
     text = "```python\ncode1\n```"
     result = extract_all_code_from_markdown(text)