oss(py): make anthropic middleware examples work e2e

[mdrxy]

4/5 of the listed examples did not run successfully. Hydrated examples to work e2e when copy / pasting

[github-actions]

❌ Import check failed

This PR contains imports from langchain_core that should be imported from langchain instead.

Detailed issues

Analyzing diff for import issues...
 Found 3 import issues:

File: src/oss/python/integrations/middleware/anthropic.mdx
Line: 81
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage
Suggested: from langchain.messages import HumanMessage
--------------------------------------------------------------------------------
File: src/oss/python/integrations/middleware/anthropic.mdx
Line: 506
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage
Suggested: from langchain.messages import HumanMessage
--------------------------------------------------------------------------------
File: src/oss/python/integrations/middleware/anthropic.mdx
Line: 567
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage
Suggested: from langchain.messages import HumanMessage
--------------------------------------------------------------------------------

 Found 3 import issues that need to be fixed.

Why this is a problem

The langchain package re-exports many modules and classes from langchain_core. When possible, imports should use langchain instead of langchain_core for:

• Better user experience (single import source)
• Consistency across documentation
• Reduced cognitive load for users

How to fix

Replace the imports as suggested above. For example:

• ❌ from langchain_core.messages import HumanMessage
• ✅ from langchain.messages import HumanMessage

🤖 Automated check

This check is based on the latest analysis of langchain re-exports from langchain_core.

[github-actions]

Mintlify preview ID generated: preview-mdrxyf-1765341759-4660171

[github-actions]

Mintlify preview ID generated: preview-mdrxyf-1765343241-c0ef69d