Refuse browser fixture success when supervisor failed to initialize

docs/inventories/DATA_LAYOUT_INVENTORY.md

@@ -2,7 +2,7 @@
 
 Machine extraction of the `docs/ARCHITECTURE.md` "Data layout (`~/Ouroboros/`)" tree — the durable-file orientation carrier (this tree's counterpart of the reference PERSISTENCE_OWNERS derivation checklist) — regenerated by `python scripts/regenerate_inventories.py`. Do not edit. Every entry is probed against reality: repo entries must exist as tracked paths; data-plane entries must appear as a literal in the runtime sources that construct them. A durable file renamed or removed in code while its tree row survives = red (`tests/test_generated_inventories.py`).
 
-Source: `docs/architecture/01-high-level-architecture.md`, physical LF lines 597-686; UTF-8 SHA-256 `026d6d93423e4fcd321a0ff78e46d779f96f305fa48320152523e1a63e1f90a7`.
+Source: `docs/architecture/01-high-level-architecture.md`, physical LF lines 597-686; UTF-8 SHA-256 `773a6c53f7985e35274ee4c319b0ff50cfe5478592c79775a05db741e9f42081`.
 
 - entries: **79** (code-ref: 72, repo-dir: 6, repo-path: 1)
 

tests/candidate_checkout.py

@@ -57,6 +57,11 @@ def _fetch(url, timeout=5):
         return response.read()
 
 
+def require_running_supervisor(state):
+    if state.get("supervisor_error") or not state.get("supervisor_ready") or not state.get("workers_total"):
+        raise CandidateError(f"CANDIDATE_SERVER_UNAVAILABLE: {state.get('supervisor_error') or 'no worker pool'}")
+
+
 def assert_served_candidate(url, checkout, data_dir, pid, candidate):
     """Bind a healthy server to its owned PID, this checkout's bytes and its Python.
 
@@ -74,6 +79,7 @@ def assert_served_candidate(url, checkout, data_dir, pid, candidate):
     from ouroboros.server_process import read_service_bindings
 
     binding = read_service_bindings(data_dir)["main"]
+    require_running_supervisor(json.loads(_fetch(url + "/api/state")))
     assert binding["pid"] == pid, "health answered by a different server process"
     assert url == f"http://127.0.0.1:{binding['port']}"
     for relative, route in (("web/index.html", "/"),

tests/test_candidate_checkout.py

@@ -10,6 +10,14 @@ from tests import candidate_checkout as candidate
 pytestmark = pytest.mark.serial
 
 
+def test_ready_flag_does_not_hide_failed_supervisor():
+    candidate.require_running_supervisor({"supervisor_ready": True, "workers_total": 1})
+    for state in ({"supervisor_ready": True, "workers_total": 0},
+                  {"supervisor_ready": True, "workers_total": 1, "supervisor_error": "init failed"}):
+        with pytest.raises(candidate.CandidateError, match="CANDIDATE_SERVER_UNAVAILABLE"):
+            candidate.require_running_supervisor(state)
+
+
 def test_installed_project_cannot_supply_code_missing_from_candidate(monkeypatch):
     from importlib import metadata
     from types import SimpleNamespace