refactor: migrate DirectiveDrafter integrations to 0.2.0dev1

[rlippmann]

Summary

• bump context-compiler-directive-drafter to 0.2.0dev1
• update the LiteLLM proxy DirectiveDrafter integration to consume DirectiveDrafter.draft_directive(...)
• switch the LiteLLM fallback callback to the new str | None contract and use DirectiveDrafter's shared converter prompt
• update the OpenWebUI DirectiveDrafter integration to use DirectiveDrafter's shared converter prompt
• update the LiteLLM prompt-construction example to use the new DirectiveDrafter prompt API
• update focused tests to match the new consumer boundaries and prompt API usage

Why

DirectiveDrafter 0.2.0dev1 changes the public integration surface in two important ways:

• fallback callbacks now return str | None
• prompt consumers should use DirectiveDrafter's shared converter prompt API instead of the removed template-rendering helpers

This PR keeps the existing LiteLLM and OpenWebUI flows intact while aligning them with the new DirectiveDrafter contract.

Example metadata

• Enforcement point: host-side prompt construction / policy injection in reference integrations and examples
• Domain: general assistant policy constraints
• Technology/runtime: Python, LiteLLM Proxy, Open WebUI
• Example type: reference integration / example compatibility migration
• Does this use directive drafter? should normally be no: yes
• Does this derive state from model output? must be no for primary examples: authoritative state mutation still happens only through Context Compiler

Checklist

• Repository scaffolding / governance change
• One primary enforcement point
• Explicit authoritative state
• No model-derived state mutation
• Adversarial stub or equivalent test
• Observable runtime behavior change
• Domain vocabulary is natural
• Framework is secondary to the enforcement point
• Docs updated
• Tests/smoke checks added where practical

Notes

Focused validation passed for the updated areas:

• LiteLLM proxy integration:
  • uv run --no-sync ruff check python/reference_integrations/litellm_proxy/context_compiler_precall_hook_with_directive_drafter.py python/tests/test_litellm_proxy_with_directive_drafter.py
  • uv run --no-sync mypy python/reference_integrations/litellm_proxy/context_compiler_precall_hook_with_directive_drafter.py python/tests/test_litellm_proxy_with_directive_drafter.py
  • uv run --no-sync pytest python/tests/test_litellm_proxy_with_directive_drafter.py python/tests/test_litellm_proxy_hooks.py python/tests/test_litellm_proxy_runtime.py
• OpenWebUI DirectiveDrafter integration:
  • uv run --no-sync pytest python/tests/test_openwebui_pipe_with_directive_drafter.py
  • uv run --no-sync mypy python/reference_integrations/openwebui_pipe/open_webui_pipe_with_directive_drafter.py
  • uv run --no-sync ruff check python/reference_integrations/openwebui_pipe/open_webui_pipe_with_directive_drafter.py
• LiteLLM prompt-construction example:
  • uv run --no-sync pytest python/tests/test_litellm_with_directive_drafter.py
  • uv run --no-sync mypy python/examples/prompt_construction/litellm/with_directive_drafter.py python/tests/test_litellm_with_directive_drafter.py
  • uv run --no-sync ruff check python/examples/prompt_construction/litellm/with_directive_drafter.py python/tests/test_litellm_with_directive_drafter.py

At the time of the LiteLLM-only migration, repo-wide ./scripts/validate_python.sh was blocked by removed render_prompt imports in the OpenWebUI integration and the LiteLLM example. Those compatibility issues are now included in this branch.