Importing tui_gateway.entry from a worker thread raised
'ValueError: signal only works in main thread of the main interpreter'
because signal.signal() was called unconditionally at import time.
On the Desktop/WebSocket path, server._build() runs in a daemon thread and
does 'from tui_gateway.entry import ensure_mcp_discovery_started' as the
first import of entry (entry.main() is never run there), which crashed and
aborted MCP discovery startup — every session then lost its MCP servers
(e.g. Dart-mcp) with ClosedResourceError.
signal handlers are process-global, so installing them only when the module
is first imported in the main thread is sufficient; importing from a worker
thread becomes a safe no-op.
Fixes#72667
brein
8b11249755