docs: add HippoDid persistent character memory integration

[snowmanjy]

Summary

Adds documentation for the langchain-hippodid integration — persistent, structured character memory for LangChain agents.

This is a docs-only PR. No code changes to langchain-core or langchain-community. The langchain-hippodid package is already published on PyPI (v0.1.0).

What is HippoDid?

HippoDid provides character-scoped cloud memory for AI agents. Each user/customer gets their own character with categorized, searchable memory that persists across sessions and frameworks.

• Package: pip install langchain-hippodid (PyPI)
• Core SDK: pip install hippodid (PyPI)
• Source: github.com/SameThoughts/langchain-hippodid

Classes provided

• HippoDidChatMessageHistory — extends BaseChatMessageHistory, stores messages in HippoDid cloud
• HippoDidMemory — convenience wrapper with get_history() factory for RunnableWithMessageHistory

Changes

1. src/oss/integrations/providers/hippodid.mdx — Provider overview page with installation, capabilities, and links
2. src/oss/python/integrations/chat_message_histories/hippodid.mdx — Component page with usage examples:
   • Basic chat message history (add/retrieve/clear)
   • Semantic search and context assembly
   • Multi-user pattern (external_id)
   • RunnableWithMessageHistory (LCEL) integration
   • Memory modes comparison table
3. packages.yml — Added langchain-hippodid to package registry
4. src/oss/python/integrations/providers/all_providers.mdx — Added HippoDid card in alphabetical order

AI disclosure

This PR was authored with assistance from Claude Code (AI agent).

[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/chat_message_histories/hippodid.mdx
Line: 84
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import AIMessage, HumanMessage
Suggested: from langchain.messages import AIMessage, HumanMessage
--------------------------------------------------------------------------------
File: src/oss/python/integrations/chat_message_histories/hippodid.mdx
Line: 130
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/chat_message_histories/hippodid.mdx
Line: 207
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage, SystemMessage
Suggested: from langchain.messages import HumanMessage, SystemMessage
--------------------------------------------------------------------------------

 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.

[snowmanjy]

Adding the standard PR checklist that was missing from the original description:

Checklist

• I have read the contributing guidelines, including the language policy
• I have tested my changes locally using docs dev
• All code examples have been tested and work correctly
• I have used root relative paths for internal links
• I have updated navigation in src/docs.json if needed

Notes:

• Code examples validated against langchain-hippodid==0.1.0 and hippodid==0.2.0 (both on PyPI). All HippoDidChatMessageHistory and HippoDidMemory methods tested with langchain==1.2.15 and langchain-core==1.2.26.
• docs dev not run locally — relying on CI preview for visual validation.
• src/docs.json was not modified in this PR. Happy to add the navigation entry if reviewers confirm the new integration page (src/oss/python/integrations/chat_message_histories/hippodid.mdx) needs to be registered there for sidebar discoverability — please advise.

[snowmanjy]

Mason Daugherty (@mdrxy) Can you please take a look? Thanks!