STATE-WP-0070 T03: remove legacy workstream MCP aliases

Meter-gated removal (7 consecutive zero-usage windows reached). Deletes:
- MCP tools: create_workstream, list_workstreams, update_workstream,
  update_workstream_status
- MCP resource: state://workstreams/{topic_slug}
- Dead helpers: _LEGACY_MCP_* maps, _legacy_mcp_deprecation,
  _meter_legacy_mcp, _attach_legacy_deprecation, _update_workplan_legacy_impl

TOOLS.md keeps a retired→preferred migration map (per backlog). Removed the
now-dead STATEHUB_MCP_LEGACY_METER guard in conftest. Retargeted the
create_workplan error-skip test to the preferred tool; dropped alias-only tests.

Staged on branch state-wp-0070-legacy-retirement — do not merge until the 7th
documented zero-usage window is captured.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_mcp_write_tools.py

@@ -56,43 +56,6 @@ class TestMCPWriteTools:
         assert calls[1][1]["workplan_id"] == "wp-1"
         assert calls[1][1]["event_type"] == "workplan_created"
 
-    async def test_create_workstream_legacy_alias_uses_workplans_endpoint(self, monkeypatch):
-        calls: list[tuple[str, dict[str, Any]]] = []
-
-        def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
-            calls.append((path, body))
-            if path == "/workplans":
-                return {"id": "wp-1", "repo_id": body["repo_id"], "title": body["title"], "slug": body["slug"], "status": "active"}
-            if path == "/progress":
-                return {"id": "event-1", **body}
-            raise AssertionError(f"unexpected POST {path}")
-
-        monkeypatch.setattr(server, "_post", fake_post)
-
-        body = await _call_tool(
-            "create_workstream",
-            {"repo_id": "repo-1", "title": "Legacy alias"},
-        )
-
-        assert body["id"] == "wp-1"
-        assert body["_deprecation"]["replacement"] == "create_workplan"
-        assert [path for path, _ in calls] == ["/workplans", "/progress"]
-
-    async def test_list_workstreams_legacy_alias_wraps_deprecation(self, monkeypatch):
-        monkeypatch.setattr(
-            server,
-            "_get",
-            lambda path, params=None: [{"id": "wp-1", "title": "Example"}]
-            if path == "/workplans"
-            else [],
-        )
-
-        body = await _call_tool("list_workstreams", {})
-
-        assert body["_deprecation"]["replacement"] == "list_workplans"
-        assert body["workplans"] == [{"id": "wp-1", "title": "Example"}]
-        assert body["workstreams"] == body["workplans"]
-
     async def test_create_task_returns_rest_shape_and_emits_progress(self, monkeypatch):
         calls: list[tuple[str, dict[str, Any]]] = []
 
@@ -306,7 +269,7 @@ class TestMCPWriteTools:
         assert calls[1][1]["decision_id"] == "decision-1"
         assert calls[1][1]["event_type"] == "decision_recorded"
 
-    async def test_create_workstream_api_error_skips_progress(self, monkeypatch):
+    async def test_create_workplan_api_error_skips_progress(self, monkeypatch):
         calls: list[tuple[str, dict[str, Any]]] = []
 
         def fake_post(path: str, body: dict[str, Any]) -> dict[str, Any]:
@@ -316,11 +279,11 @@ class TestMCPWriteTools:
         monkeypatch.setattr(server, "_post", fake_post)
 
         body = await _call_tool(
-            "create_workstream",
+            "create_workplan",
             {"repo_id": "bad-repo", "title": "No progress on failure"},
         )
 
-        assert body["tool"] == "create_workstream"
+        assert body["tool"] == "create_workplan"
         assert body["error"] == "API 422: invalid repo"
         assert [path for path, _ in calls] == ["/workplans"]