Expose plugin authoring internals as public API

[elijahr]

Problem

Writing a custom bigfoot plugin requires importing from private modules:

from bigfoot._base_plugin import BasePlugin
from bigfoot._timeline import Interaction
from bigfoot._context import _GuardPassThrough, _get_verifier_or_raise
from bigfoot._registry import GUARD_ELIGIBLE_PREFIXES

Some related types are already public (StrictVerifier, UnmockedInteractionError, GuardedCallError are all importable from bigfoot directly), but the core plugin authoring types are not.

Requested public exports

Everything a plugin author needs should be importable from bigfoot (or bigfoot.plugins):

Type	Current path	Used for
BasePlugin	bigfoot._base_plugin	Subclassing to create plugins
Interaction	bigfoot._timeline	Type hint for matches(), format_interaction(), etc.
_GuardPassThrough	bigfoot._context	Catching guard passthrough in interceptors
_get_verifier_or_raise	bigfoot._context	Getting active verifier in interceptors
GUARD_ELIGIBLE_PREFIXES	bigfoot._registry	Registering custom source_id prefixes for guard mode
Timeline	bigfoot._timeline	Creating bare verifiers in test fixtures

Context

We built custom bigfoot plugins for claude-agent-sdk and openai-agents SDK. The plugins work great but rely on private imports that could break between releases.

A bigfoot.authoring or simply exporting from bigfoot would make plugin development a first-class use case.