[AAASM-50] ✨ (adapters): Implement LangChain callback interception core

[Chisanan232]

Description

Implement AAASM-50 LangChain/LangGraph runtime interception architecture for the Python SDK with atomic commits.

This PR adds a LangChain callback handler with governance interception paths for tool and LLM events, runtime auto-injection from init_assembly, LangGraph StateGraph.compile() patching with pre/post invocation hooks, and focused tests/docs.

Type of Change

• ✨ New feature
• 🔧 Bug fix
• ♻️ Refactoring
• 🍀 Performance improvement
• 📚 Documentation update
• 🚀 Release

Breaking Changes

Does this PR introduce any breaking changes?

• No
• Yes (please describe below)

Related Issues

• Related JIRA ticket: AAASM-50
• Related GitHub issues: #XX

Testing

Describe the testing performed for this PR:

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed
• No tests required (explain why)

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex logic
• Documentation updated if needed
• All tests passing

[codecov]

Codecov Report

❌ Patch coverage is 91.69675% with 23 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...nt_assembly/adapters/langchain/callback_handler.py	82.53%	22 Missing ⚠️
...ent_assembly/adapters/langchain/langgraph_patch.py	99.16%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
91.7% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud