fix(classification): harden registration updates

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a02b22-9638-76d2-bbff-b7ea1770b118

tests/test_routers_core.py

@@ -108,6 +108,29 @@ class TestRepos:
         assert r.status_code == 201
         assert r.json()["host_paths"] == {"workstation": "/srv/hosted-repo"}
 
+    async def test_patch_reclassifies_primary_domain(self, client):
+        await _create_domain(client, slug="infotech", name="Infotech")
+        await _create_domain(client, slug="financials", name="Financials")
+        await _create_repo(client, domain_slug="infotech", slug="reclassified-repo")
+
+        r = await client.patch(
+            "/repos/reclassified-repo",
+            json={
+                "domain_slug": "financials",
+                "category": "product",
+                "secondary_domains": [],
+                "capability_tags": ["accounting"],
+                "business_stake": [],
+                "business_mechanics": [],
+                "classified_at": "2026-08-23",
+                "classified_by": "human",
+                "standard_version": "1.0",
+            },
+        )
+
+        assert r.status_code == 200, r.text
+        assert r.json()["domain_slug"] == "financials"
+
 
 # ---------------------------------------------------------------------------
 # Topic tests