Wake-ups for kanban notifications and background delegation completions were
injected via handle_message() using a build_session_key()-derived key, which
can never match the raw X-Hermes-Session-Id key that api_server sessions run
under — so the wake landed in a session nobody was reading. On top of that,
ApiServerAdapter.send() reports failure without raising, and that was treated
as a successful delivery, so the notify cursor advanced past events that were
permanently lost; and background delegation was forced synchronous on
api_server since there was no way to wake the session afterward.
Fix: route wake-ups for non-push adapters through a self-post to
/v1/chat/completions with the original session id, treat non-raising send
failures as failures (rewind instead of advancing the cursor), and re-enable
background delegation whenever a session id is available to wake.
The origin session id is captured from the request-scoped api_server chat_id
binding rather than HERMES_SESSION_ID: constructing a child agent calls
set_current_session_id() with the subagent's internal id, clobbering that
variable right before dispatch would read it and misrouting the wake into
the subagent's own session.
Related: #56580, #64609, #53027, #63169, #56531, #50319, #64113
