/<database>/-/foreign-key-targets API endpoint

Returns a list of tables with a single primary key, and for each one
the name of that primary key column and its SQLite type affinity.

This will be used by the create table UI to suggest foreign keys.

tests/test_api_write.py

@@ -1144,6 +1144,81 @@ async def test_foreign_key_suggestions_fail_open(ds_write, monkeypatch):
     assert columns["age"]["suggestions"] == []
 
 
+@pytest.mark.asyncio
+async def test_foreign_key_targets(ds_write):
+    token = write_token(ds_write, permissions=["ct"])
+    db = ds_write.get_database("data")
+    await db.execute_write("create table owners (id integer primary key)")
+    await db.execute_write("create table categories (slug varchar(30) primary key)")
+    await db.execute_write("create table blob_things (hash blob primary key)")
+    await db.execute_write(
+        "create table numeric_codes (code decimal(10,5) primary key)"
+    )
+    await db.execute_write(
+        'create table floating_point (value "FLOATING POINT" primary key)'
+    )
+    await db.execute_write(
+        "create table compound (a integer, b integer, primary key (a, b))"
+    )
+    await db.execute_write("create table no_pk (name text)")
+
+    response = await ds_write.client.get(
+        "/data/-/foreign-key-targets",
+        headers=_headers(token),
+    )
+    assert response.status_code == 200, response.text
+    assert response.json() == {
+        "ok": True,
+        "database": "data",
+        "targets": [
+            {
+                "fk_table": "blob_things",
+                "fk_column": "hash",
+                "type": "blob",
+            },
+            {
+                "fk_table": "categories",
+                "fk_column": "slug",
+                "type": "text",
+            },
+            {
+                "fk_table": "docs",
+                "fk_column": "id",
+                "type": "integer",
+            },
+            {
+                "fk_table": "floating_point",
+                "fk_column": "value",
+                "type": "integer",
+            },
+            {
+                "fk_table": "numeric_codes",
+                "fk_column": "code",
+                "type": "numeric",
+            },
+            {
+                "fk_table": "owners",
+                "fk_column": "id",
+                "type": "integer",
+            },
+        ],
+    }
+
+
+@pytest.mark.asyncio
+async def test_foreign_key_targets_permission_denied(ds_write):
+    token = write_token(ds_write, permissions=["ir"])
+    response = await ds_write.client.get(
+        "/data/-/foreign-key-targets",
+        headers=_headers(token),
+    )
+    assert response.status_code == 403
+    assert response.json() == {
+        "ok": False,
+        "errors": ["Permission denied: need create-table"],
+    }
+
+
 @pytest.mark.asyncio
 async def test_alter_table_permission_denied(ds_write):
     token = write_token(ds_write, permissions=["ir"])