[F029] websocket: remove broken /api/permissions/check loopback from channel stream

channel_stream called validate_channel_access, which HTTP-loopbacked to
GET /api/permissions/check — a route that does not exist. Every call 404'd
-> False -> the channel stream closed with WS_1008_POLICY_VIOLATION for
EVERY client, so the real-time channel stream was dead. Removed the
function, its call site, and the now-unused httpx + settings imports.

Post-F004 the panel-token gate is the channel-stream authorization (the
CEO panel is the sole WS client and may view every channel), so the
broken loopback is removed rather than replaced with an in-process check
the CEO always passes. The legitimate enforcement.validate_channel_access
(slugs, in-process static ACL) is a different function and is untouched.

F027 is resolved-by-F004 (no code change): all three per-agent streams
gate on _require_panel_token first, so only the authorized CEO panel can
connect — 'any viewer subscribes to any target' is closed.

TDD; ruff/mypy clean; 530 unit/api+enforcement+RBAC tests green.

tests/unit/api/test_websocket_auth.py

@@ -19,7 +19,12 @@ from uuid import uuid4
 import pytest
 from fastapi import WebSocketDisconnect, status
 from roboco.agents_config import CEO_AGENT_ID, issue_agent_token
-from roboco.api.websocket import agent_stream, notification_stream
+from roboco.api.websocket import (
+    ConnectionManager,
+    agent_stream,
+    channel_stream,
+    notification_stream,
+)
 
 if TYPE_CHECKING:
     import pytest as _pytest  # noqa: F401
@@ -119,3 +124,49 @@ async def test_agent_stream_rejects_missing_token_when_required(
     ws.close.assert_awaited_once()
     assert ws.close.await_args.kwargs["code"] == status.WS_1008_POLICY_VIOLATION
     ws.accept.assert_not_awaited()
+
+
+# ---------------------------------------------------------------------------
+# The channel stream must be usable by a panel-token holder. It previously
+# called validate_channel_access, which HTTP-loopbacked to a non-existent
+# /api/permissions/check endpoint — every connection 404'd → False → the stream
+# closed with WS_1008_POLICY_VIOLATION for every client (the channel live-stream
+# was dead). Post-F004 the panel-token gate IS the channel-stream authorization
+# (the CEO panel is the sole WS client and may view every channel), so the
+# broken loopback check is removed rather than replaced with theater.
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_channel_stream_accepts_panel_token_holder(
+    monkeypatch: pytest.MonkeyPatch,
+) -> None:
+    """A panel-token holder supplying an agent_id query param is accepted and
+    registered on the channel stream — not fail-closed by a dead permission
+    check that 404s against a non-existent endpoint."""
+    monkeypatch.setenv("ROBOCO_AGENT_AUTH_SECRET", _SECRET)
+    monkeypatch.setenv("ROBOCO_AGENT_AUTH_REQUIRED", "true")
+    token = issue_agent_token(CEO_AGENT_ID, "ceo", "")
+    channel_id = uuid4()
+    viewer_id = uuid4()
+    mgr = ConnectionManager()
+    ws = _mock_ws(
+        headers={"x-agent-token": token},
+        query={"agent_id": str(viewer_id)},
+    )
+    monkeypatch.setattr("roboco.api.websocket.manager", mgr)
+
+    await channel_stream(ws, channel_id)
+
+    ws.accept.assert_awaited_once()
+    # Not fail-closed by a dead permission check.
+    ws.close.assert_not_awaited()
+    # The "connected" confirmation is sent immediately after connect_channel
+    # registers the socket, and its subscriber_count proves the socket was in
+    # the channel's subscription set at confirmation time (the mock then raises
+    # WebSocketDisconnect so the finally disconnects it — the normal clean
+    # exit, not a fail-close).
+    confirmation = ws.send_json.await_args.args[0]
+    assert confirmation["type"] == "connected"
+    assert confirmation["channel_id"] == str(channel_id)
+    assert confirmation["subscriber_count"] == 1