test(docker): fix svstat 'want up' assertion in profile-gateway lifecycle test

After the supervise-perms fix lands, the s6 lifecycle actually works
for the hermes user — hermes -p <profile> gateway start now genuinely
brings the supervised gateway up rather than silently no-op'ing on
EACCES. That exposes a latent bug in this test's assertion: it
expected 'want up' to appear literally in s6-svstat output, but
s6-svstat elides redundancies — when the slot is currently up AND
s6 wants it up, the output is just 'up (pid N pgid N) X seconds';
the explicit 'want up' token only appears when current ≠ wanted
(e.g. 'down (exitcode 1) … , want up' on a crash-loop).

Add a small helper _svstat_wants_up() that reads the want-state
correctly across both spellings:
  * 'up …'                       → wanted up (unless explicit 'want down')
  * 'down …, want up'            → wanted up explicitly
  * 'down …'                     → wanted down

Both stop and start assertions now use the helper. Also rewords
the module docstring to acknowledge that the supervised process
may succeed OR crash-loop depending on environment, but the want-
state contract holds either way.

(cherry picked from commit 02c933aedc)

tests/docker/test_profile_gateway.py

@@ -8,11 +8,14 @@ with the pre-Phase-4 informational message.
 These tests were marked ``xfail(strict=True)`` through Phase 0–3 and
 flip to plain ``test_…`` once Phase 4 lands (now).
 
-NB: The harness profile created here has no model/auth configured,
-so the gateway process itself will exit with code 1 on every start
-attempt (s6 will keep restarting it). We assert against s6's
-``want up`` / ``want down`` state — which reflects the lifecycle
-command's intent, not the supervised process's health.
+NB: The harness profile has no model/auth configured. Depending on
+how the gateway run script handles missing config, the supervised
+process may either spin up successfully (and svstat reports ``up``)
+or exit fast and get throttled by s6 (and svstat reports ``down …,
+want up``). Both states are valid "user asked for gateway up" results
+— what we assert is the *want* intent the lifecycle command set, NOT
+the supervised process's health. ``s6-svc -u`` records ``want up`` in
+the supervise/status file regardless of the run-script outcome.
 
 Every ``docker exec`` here runs as the unprivileged ``hermes`` user
 (via :func:`docker_exec_sh` in conftest); see the conftest module
@@ -42,6 +45,27 @@ def _svstat(container: str) -> str:
     return r.stdout if r.returncode == 0 else ""
 
 
+def _svstat_wants_up(container: str) -> bool:
+    """Read the slot's want-state from s6-svstat output.
+
+    s6-svstat formats the output to elide redundancies — when the
+    service is currently up AND s6 wants it up, the literal token
+    ``want up`` doesn't appear (it's implicit from the leading ``up``).
+    When the service is down but s6 wants it back up, ``, want up``
+    appears explicitly. So a comprehensive "is the want-intent set to
+    up" check has to accept both spellings.
+    """
+    state = _svstat(container)
+    if not state:
+        return False
+    head = state.split()[0] if state.split() else ""
+    if head == "up":
+        # Currently up implies wanted-up unless ``want down`` is set.
+        return "want down" not in state
+    # Currently down — ``want up`` only shows up when explicitly set.
+    return "want up" in state
+
+
 def test_profile_create_then_gateway_start(
     built_image: str, container_name: str,
 ) -> None:
@@ -66,17 +90,23 @@ def test_profile_create_then_gateway_start(
 
     # After start, s6's intent is "up" — even if the supervised gateway
     # process spin-fails (no model/auth in the test profile), the
-    # supervision-state contract holds.
+    # supervision-state contract holds. See ``_svstat_wants_up`` for
+    # why we accept both ``up …`` (currently up) and ``down …, want
+    # up`` (down but s6 wants up).
     time.sleep(2)
-    state = _svstat(container_name)
-    assert "want up" in state, f"want up not in svstat: {state!r}"
+    assert _svstat_wants_up(container_name), (
+        f"slot want-state is not up after gateway start: "
+        f"{_svstat(container_name)!r}"
+    )
 
     r = _sh(container_name, f"hermes -p {PROFILE} gateway stop", timeout=30)
     assert r.returncode == 0
 
     time.sleep(2)
-    state = _svstat(container_name)
-    assert "want up" not in state, f"want up still in svstat: {state!r}"
+    assert not _svstat_wants_up(container_name), (
+        f"slot want-state still up after gateway stop: "
+        f"{_svstat(container_name)!r}"
+    )
 
 
 def test_profile_delete_stops_gateway(