Workers screen shows each agent's version and protocol, and who is behind

The hello carries the fluksio-worker version. An agent refused for an older
protocol stays listed as Needs upgrade until it attaches again. Docs gain an
Upgrading workers section.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx

backend/tests/api/routes/test_workers.py

@@ -38,6 +38,27 @@ def test_the_token_names_the_worker_and_its_labels(
     assert [(w["name"], w["labels"]) for w in attached] == [("gpu-box", ["gpu"])]
 
 
+def test_the_list_names_each_version_and_who_is_behind(
+    client: TestClient, superuser_token_headers: dict[str, str]
+) -> None:
+    issued = mint(client, superuser_token_headers)
+    url = f"{PREFIX}/attach?token={issued['token']}"
+
+    def listed() -> list[tuple[object, ...]]:
+        answer = client.get(PREFIX, headers=superuser_token_headers).json()
+        return [(w["protocol"], w["version"], w["behind"]) for w in answer]
+
+    with client.websocket_connect(url) as ws:
+        ws.send_json({**hello(), "protocol": PROTOCOL - 1, "version": "0.1.5"})
+        assert ws.receive_json()["op"] == "refused"
+    assert listed() == [(PROTOCOL - 1, "0.1.5", True)]
+
+    with client.websocket_connect(url) as ws:
+        ws.send_json({**hello(), "version": "0.2.0"})
+        ws.receive_json()
+        assert listed() == [(PROTOCOL, "0.2.0", False)]
+
+
 def test_a_worker_cannot_claim_a_label_its_token_lacks(
     client: TestClient, superuser_token_headers: dict[str, str]
 ) -> None: