refactor(evidence): migrate acquisition and preprocessing (#30)

harness/tht/evidence/acquisition.py

@@ -0,0 +1,18 @@
+"""Evidence acquisition operations over the credential-free source contract."""
+
+from collections.abc import Iterable
+
+from tht.evidence.contracts import AcquiredDocument, EvidenceSource, SourceObject
+
+
+def discover(source: EvidenceSource) -> Iterable[SourceObject]:
+    """Discover source objects without changing source-defined laziness or ordering."""
+    return source.discover()
+
+
+def acquire(source: EvidenceSource, item: SourceObject) -> AcquiredDocument:
+    """Acquire one discovered object, preserving the source's classified failures."""
+    return source.acquire(item)
+
+
+__all__ = ["acquire", "discover"]