Retire GET /workstreams/workplan-index with 410; railiance01 deploy runbook

Return 410 Gone for legacy workplan-index route (replacement /workplans/index).
Add tests, update transition backlog, operator deploy evidence doc, and
STATE-WP-0070 progress notes.

tests/test_legacy_meter.py

@@ -165,6 +165,20 @@ class TestWorkplanAliasesAndLegacyMeter:
         }
         assert items.get("event_subject:org.statehub.workstream.completed") is None
 
+    async def test_legacy_workplan_index_returns_410(self, client):
+        r = await client.get(
+            "/workstreams/workplan-index",
+            headers={"X-StateHub-Component": "old-index-client"},
+        )
+        assert r.status_code == 410
+        assert "retired" in r.json()["detail"]
+        assert r.headers["X-StateHub-Replacement"] == "/workplans/index"
+
+        summary = (await client.get("/legacy-meter/summary")).json()
+        item = _summary_by_key(summary)["rest_api:GET /workstreams/workplan-index"]
+        assert item["window"]["calls"] == 1
+        assert item["window"]["components"] == {"old-index-client": 1}
+
     async def test_legacy_delete_workstream_returns_410(self, client):
         await _create_domain(client)
         topic = await _create_topic(client)

tests/test_routers_core.py

@@ -189,8 +189,12 @@ class TestWorkstreams:
 
     async def test_workplan_index_route(self, client):
         r = await client.get("/workstreams/workplan-index")
+        assert r.status_code == 410
+        assert r.headers["X-StateHub-Replacement"] == "/workplans/index"
+
+        r = await client.get("/workplans/index")
         assert r.status_code == 200
-        assert "workstreams" in r.json()
+        assert "workplans" in r.json()
 
     async def test_workplan_bindings_sync_populates_index(self, client, tmp_path):
         await _create_domain(client)