Add sources and citations API (Phase 1: sources-first spine)

Source CRUD (reusable, tree-scoped) and Citation create/list/soft-delete linking one source to exactly one fact (person/event/name/relationship). Editor-gated writes, privacy-filtered reads, audit throughout; tenant + existence validation on source and target. list_citations returns all tree citations so the UI can render 'sourced' indicators in one round-trip. 22 tests pass.

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

backend/tests/test_sources.py

@@ -0,0 +1,96 @@
+"""Sources and citations (the provenance spine)."""
+
+import uuid
+
+from tests.conftest import auth, register
+
+
+async def _setup(client, email):
+    h = auth(await register(client, email))
+    tree_id = (await client.post("/api/v1/trees", json={"name": "S"}, headers=h)).json()["id"]
+    person = (
+        await client.post(
+            f"/api/v1/trees/{tree_id}/persons", json={"given": "Cy"}, headers=h
+        )
+    ).json()["id"]
+    event = (
+        await client.post(
+            f"/api/v1/trees/{tree_id}/events",
+            json={"event_type": "birth", "person_id": person},
+            headers=h,
+        )
+    ).json()["id"]
+    return h, tree_id, person, event
+
+
+async def test_source_and_citation_flow(client):
+    h, tree_id, person, event = await _setup(client, "src1@example.com")
+
+    src = await client.post(
+        f"/api/v1/trees/{tree_id}/sources",
+        json={"title": "1880 Census", "repository": "NARA"},
+        headers=h,
+    )
+    assert src.status_code == 201, src.text
+    source_id = src.json()["id"]
+
+    assert len((await client.get(f"/api/v1/trees/{tree_id}/sources", headers=h)).json()) == 1
+
+    # Cite the source on the birth event.
+    cite = await client.post(
+        f"/api/v1/trees/{tree_id}/citations",
+        json={"source_id": source_id, "event_id": event, "page": "p. 4"},
+        headers=h,
+    )
+    assert cite.status_code == 201, cite.text
+    citation_id = cite.json()["id"]
+
+    citations = (await client.get(f"/api/v1/trees/{tree_id}/citations", headers=h)).json()
+    assert len(citations) == 1
+    assert citations[0]["event_id"] == event
+    assert citations[0]["source_id"] == source_id
+
+    resp = await client.delete(f"/api/v1/trees/{tree_id}/citations/{citation_id}", headers=h)
+    assert resp.status_code == 204
+    assert len((await client.get(f"/api/v1/trees/{tree_id}/citations", headers=h)).json()) == 0
+
+
+async def test_citation_needs_exactly_one_target(client):
+    h, tree_id, person, event = await _setup(client, "src2@example.com")
+    source_id = (
+        await client.post(
+            f"/api/v1/trees/{tree_id}/sources", json={"title": "X"}, headers=h
+        )
+    ).json()["id"]
+
+    # No target.
+    r = await client.post(
+        f"/api/v1/trees/{tree_id}/citations", json={"source_id": source_id}, headers=h
+    )
+    assert r.status_code == 409
+    # Two targets.
+    r = await client.post(
+        f"/api/v1/trees/{tree_id}/citations",
+        json={"source_id": source_id, "person_id": person, "event_id": event},
+        headers=h,
+    )
+    assert r.status_code == 409
+
+
+async def test_citation_unknown_source_404(client):
+    h, tree_id, person, _ = await _setup(client, "src3@example.com")
+    r = await client.post(
+        f"/api/v1/trees/{tree_id}/citations",
+        json={"source_id": str(uuid.uuid4()), "person_id": person},
+        headers=h,
+    )
+    assert r.status_code == 404
+
+
+async def test_non_member_cannot_create_source(client):
+    h, tree_id, _, _ = await _setup(client, "src4@example.com")
+    other = auth(await register(client, "src-intruder@example.com"))
+    r = await client.post(
+        f"/api/v1/trees/{tree_id}/sources", json={"title": "nope"}, headers=other
+    )
+    assert r.status_code == 403