Add events and relationships API (Phase 1: flesh out the graph)

Events (create/list-per-person/soft-delete) and relationships (create/list-per-person/soft-delete) through the layered stack: editor-gated writes, privacy-engine reads, audit on every change. Events carry exactly one subject (person XOR partnership); relationships are typed qualified edges (parent_child gets a biological/adoptive/step/foster/donor/guardian qualifier). Adds a single-person GET. 18 tests pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/services/person_service.py

@@ -14,7 +14,7 @@ from app.models.tree import Tree
 from app.models.user import User
 from app.services import privacy
 from app.services.audit import record_audit
-from app.services.exceptions import Forbidden
+from app.services.exceptions import Forbidden, NotFound
 from app.services.privacy import Visibility
 
 
@@ -86,6 +86,32 @@ async def create_person(
     return person
 
 
+async def get_person(
+    session: AsyncSession, *, viewer_id: uuid.UUID, tree: Tree, person_id: uuid.UUID
+) -> Person:
+    if not await privacy.can_view_tree(session, user_id=viewer_id, tree=tree):
+        raise Forbidden("not permitted to view this tree")
+    person = (
+        await session.execute(
+            select(Person).where(
+                Person.id == person_id,
+                Person.tree_id == tree.id,
+                Person.deleted_at.is_(None),
+            )
+        )
+    ).scalar_one_or_none()
+    if person is None:
+        raise NotFound("person not found")
+    # Run the single person through the privacy engine (redaction lands Phase 2).
+    if (
+        await privacy.person_visibility(session, user_id=viewer_id, tree=tree, person=person)
+        == Visibility.hidden
+    ):
+        raise NotFound("person not found")
+    await _attach_primary_name(session, person)
+    return person
+
+
 async def list_persons(
     session: AsyncSession, *, viewer_id: uuid.UUID, tree: Tree
 ) -> list[Person]: