subagent.steer resolves authority by comparing the request's context-bound transport with the session's transport slot. Once a session mirrors to more than one client that slot holds a FanoutTransport, so the comparison fails for every client, the peer that commissioned the subagent included, and every steer is rejected. Fan-out without this check ships that regression, and no existing test catches it because the suite only exercises single-client sessions.
Authority now asks whether the request's transport is attached to the session, directly or through the fan-out. The single-client case is unchanged: a bare slot still compares by identity.
This widens authority. Any client attached to a mirrored session can steer that session's subagents, not only the peer that commissioned them. Narrowing it back to the commissioning peer requires recording that peer per subagent, which this change does not do. tests/tui_gateway/test_multi_client_fanout.py pins the commissioning peer's authority inside a fan-out, pins the widened case, and keeps a single-client control in which an unattached client is still refused.
The four browser.controller.* handlers gate on the session transport slot exactly as subagent.steer did, through one shared gate in the _controller_method decorator, and the conversion missed them. Once a session mirrors to more than one client the slot holds a FanoutTransport, which is identical to no peer's WSTransport, so browser.controller.register, .result, .heartbeat and .detach all answer "session is not owned by this transport" for every client, the peer that registered the controller included. Browser control is therefore unusable on any mirrored session. No existing test catches it because the browser-control suite only exercises single-client sessions.
All four now ask the same question steer asks: is the request's transport attached to this session, directly or through the fan-out. The single-client case is unchanged, because a bare slot still compares by identity.
Only registration widens. On .result, .heartbeat and .detach the broker's is_owner check sits below the session gate and compares controller.owner is owner against the transport recorded at attach time (gateway/browser_control_broker.py), so a mirrored peer that did not register the controller is still refused there, now with "controller is not owned by this transport" instead of the session message. browser.controller.register has no such check, so any client attached to a mirrored session may register a controller for it; the broker's principal lane keeps that inside one authenticated identity, and a second identity in the same lane hard-replaces the first. tests/tui_gateway/test_multi_client_fanout.py pins the registering peer's access inside a fan-out, pins the widened and broker-refused cases, and keeps a single-client control in which an unattached client is still refused on all three scope-gated handlers.
Ryan Tucker
68ed3ffd10