AgentQA used to trust request.AgentEnabled even when
resolveAgent() returned nil (no agent_id, or unresolvable id) — the
request reached the async goroutine, AgentQA service errored with
'custom agent configuration is required', and the user saw a broken
SSE stream with no actionable error.
Most likely root cause is a stale frontend settings store where
isAgentEnabled stayed true after selectedAgentId got blanked
(typically a cross-tenant switch where the previously selected
agent isn't visible in the new tenant). The frontend fix lives in
selectAgent() syncing both flags, but the handler shouldn't trust
that contract.
Add an early 400 with a clear message before executeQA dispatches.
Logs the actual request.AgentID (sanitized) so future stuck-state
reports are diagnosable from a single log line.
wizardchen
8c0510f2e1