_drain_queued_prompt attaches the transport pinned to the queued envelope, but the client that queued the prompt may have disconnected while the prompt sat in the queue. Attaching it then pins a dead peer into the session's fan-out, where it costs one failed write before the fan-out prunes it. That is not a regression — the line this replaced rebound the whole slot to that same dead transport, which cost the session for the entire drained turn rather than one write — but the guard is one condition, so it goes in.
_transport_is_dead is the predicate already used by the reaper and the orphan check: the parked drop sentinel, or a transport carrying _closed. Drain semantics are otherwise unchanged. The prompt still runs, and the clients already attached keep their stream; only the dead peer's attachment is skipped.
tests/tui_gateway/test_multi_client_fanout.py pins that the drained prompt still dispatches while the disconnected queuer stays out of the slot, alongside the existing case where a live queuer is attached and the single-client control where the queuer takes an unoccupied slot.
Raised by the automated review on #86784.
A session held exactly one transport, and prompt.submit, session.resume, session.activate, and the queued-prompt drain all rebound that slot. A second client therefore took the stream away from the first: the earlier client stopped receiving the turn it was already rendering, and either client disconnecting parked the whole session on the drop sentinel.
FanoutTransport goes in the same slot and satisfies the same Transport protocol, so write_json and every other reader of the slot are unchanged. It delivers each frame to a snapshot of its peers, concurrently when more than one peer is attached and the caller is not on an event loop, and prunes any peer that returns False or raises. A dead client is dropped; a slow one costs the emitter at most one write timeout per frame rather than one per peer. Request/response RPCs are unaffected: they still answer on the request's context-bound transport, so a client only ever sees replies to its own calls.
The rebind sites become attach sites through _attach_session_transport, whose ladder keeps the single-client shape identical. The same object already in the slot is a no-op; an empty, stdio, or parked slot is taken outright; only the arrival of a second live client wraps both. The queued-prompt drain is included because it pinned the drained turn to the queuer and silenced everyone else. A non-peer newcomer such as stdio or the drop sentinel never displaces a live client, so an activate dispatched without a bound websocket cannot silence the socket that owns the session.
Disconnect detaches first. A session that retains another client keeps streaming and is neither parked nor reaped, and only the clientless ones follow the existing close_on_disconnect and park-sentinel path, so a single-client disconnect, the orphan reaper, and its grace window behave as before. _ws_session_is_orphaned is unchanged: it still asks whether the drop sentinel is in the slot, and a fan-out is never the sentinel, so a session that still has a peer is never reported as orphaned.
Attach performs no entitlement check: any authenticated peer may mirror any session.
The fan-out architecture follows the approach in #40822 by @OmarB97.
What the slot's later history forces. _close_sessions_for_transport drops the #83716 rebind-to-the-most-recent-surviving-viewer, which fan-out membership subsumes — a pop-out window is a peer, so a session that still shows in one is never returned as clientless — and keeps the #77129 revalidation before parking, now expressed as a liveness check under _session_transport_lock so it is race-free against attach and detach. _transport_is_live_peer defers its last answer to _transport_is_dead: a socket that already latched _closed is a departed client, and admitting it would keep a session out of both the park and the reap. _transport_is_dead also learns the fan-out: a FanoutTransport with no live peer is dead, so a session whose peers were all pruned by failed writes cannot outlive the TTL and LRU reapers. The upstream test that pinned the #83716 rebind, test_close_transport_rebinds_session_to_remaining_viewer, is re-expressed in fan-out terms: both windows attached, the pop-out closes, the session stays with the main window unparked and still receiving frames.
Adapt FalconOrtiz's owner-mailbox proposal from #101564 onto the current
notification poller and topical modules. The durable mailbox is cross-process
ingress only: the existing owner admits its normal prompt turn after the
current turn and human FIFO clear. Retain immutable receipts, stable admission
identities, capability and lease fencing, compression lineage, and disable
blind recovery replay of imported turns.
The original stale server hunks and expiring receipt protocol were rebuilt
rather than cherry-picked: the current facade decomposition and durable busy
admission contract differ. Credit the earlier owner-mailbox work in #100544
and durable producer work in #100319.
Co-authored-by: fangliquanflq <fangliquan@qq.com>
Co-authored-by: 686f6c61 <github@00b.tech>
For each issue anchor present in BASE 63279301bc non-test .py and absent on HEAD, the BASE comment/docstring block was re-attached at the HEAD location of the code it explained (matched by the distinctive code line / enclosing def). Sentences already covered by an existing HEAD comment were deduped; the issue number always survives. Insert-only: no code lines changed.
Ryan Tucker