[REFACTOR] Unify Model Interface Around Single Entry Point (model.stream)

[mkmeral]

Pull Request: Unify Model Interface Around Single Entry Point (model.stream)

Description

This PR refactors the model interface to use a unified, stream-first architecture that simplifies the model layer while maintaining external API compatibility.

Key Changes:

Interface Unification:

• Replace dual converse/stream pattern with unified stream method as single entry point
• Update stream method signature to accept (messages, tool_specs, system_prompt) directly
• Remove abstract format_request and format_chunk methods from base Model class
• Move request formatting and chunk processing inside individual stream implementations

Implementation Updates:

• Update all 7 model implementations: Anthropic, Bedrock, LiteLLM, LlamaAPI, Mistral, Ollama, OpenAI
• Add comprehensive debug logging to all stream methods (request formatting, invocation, completion)
• Eliminate converse method from Model base class
• Update event loop and streaming components to use unified interface

Testing & Quality:

• Add new logging test in test_bedrock.py to verify debug functionality
• Update all existing tests to use new interface
• Maintain backward compatibility of Agent

Benefits:

• Simplified Interface: Single method handles complete request lifecycle internally
• Better Observability: Consistent debug logging across all model implementations
• Easier Maintenance: Unified pattern makes adding new models more straightforward

Related Issues

Documentation PR

Type of Change

Breaking change

Note: While this is technically a breaking change to the model interface, it maintains full backward compatibility for external consumers (Agent class, event loops, etc.)

Testing

How have you tested the change?

• Unit Tests: All 46 existing Bedrock tests pass + new logging test added
• Model Coverage: Verified all 7 model implementations updated correctly
• Integration Tests: 20/24 integration tests pass (4 failures due to Meta model regional access restrictions, unrelated to code changes)
• Debug Logging: Verified comprehensive logging works across all models
• Interface Consistency: Confirmed unified stream method signature across all implementations
• I ran hatch run prepare

Test Results:

# Unit tests - all pass
hatch test tests/strands/models/test_bedrock.py  # 46 passed
hatch test tests/strands/models/               # All model tests pass

# Integration tests - 20 passed, 4 failed due to external access issues
hatch run test-integ  # Failures are Meta model regional restrictions, not code issues

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• [] I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed (No new external features)
• My changes generate no new warnings
• Any dependent changes have been merged and published (No dependencies)