Summary

src/features/__init__.py eagerly imported FeatureEngineering (from base.py) and the regime feature classes (from regime_features.py) at package import time. base.py imports the data layer (from ..data import get_default_provider, CacheManager, MarketDataRequest), so that one broken import took down the entire package: importing the self-contained modules — greeks, pnl, position_models, position_state, position_vector — failed even though none of them depend on base or data.

Closes #10.

Dependency map

Under the eager __init__, the five clean modules were unreachable because of the two that aren't.

Fix

Switch __init__ to PEP 562 lazy attribute loading (__getattr__). The public API is unchanged — from src.features import FeatureEngineering still works, importing base on first access — but importing the package or any clean submodule no longer triggers base's dependency chain.

Verification (with the data layer still absent, i.e. before #1)

import src.features                  -> OK; base NOT eagerly loaded
import src.features.greeks           -> OK (previously failed)
import src.features.position_models  -> OK
from src.features import FeatureEngineering -> still needs #1 (lazy, by design)
src.features.UnknownName             -> AttributeError

Adds tests/features/test_lazy_init.py (3 tests) pinning the laziness.

Relationship to #1

Complementary, not overlapping. #1 (PR #19) fixes the missing data layer at the root; this PR contains the blast radius so a broken module in src.features can't sink unrelated ones. They touch different files and merge independently.

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