- Extract check_duplicate_in_previous_message() helper to reduce nesting
from 6+ levels to 2 levels in stream_completion_with_tools
- Create do_thin_context() and do_thin_context_all() helpers to centralize
context thinning with event tracking
- Use provider_config::parse_provider_ref() in additional call sites
- All 295 tests pass
This continues the refactoring to eliminate code-path aliasing and
reduce cyclomatic complexity in the Agent implementation.
e2445a5d22