A synchronous SHOW in onWebClientStarted permanently blocks every later form open on that connection

[CrushBy]

A synchronous SHOW in onWebClientStarted permanently blocks every later form open on that connection

Environment

• lsFusion 7.0-SNAPSHOT (server build 392), client war of the same build
• Apache Tomcat 9.0.121, Java 17.0.9, PostgreSQL 18, Windows 10
• Browser: Chromium (verified headless via Playwright; same behavior in the regular web client)

Minimal reproduction

MODULE Repro;

REQUIRE SystemEvents;

FORM home 'Home'
    OBJECTS h = INTEGER
    PROPERTIES VALUE(h)
;

FORM other 'Other'
    OBJECTS o = INTEGER
    PROPERTIES VALUE(o)
;

NAVIGATOR {
    NEW other FIRST;
}

// opens at web client start — WITHOUT NOWAIT (synchronous)
onWebClientStarted() + {
    SHOW home DOCKED;
}

Steps:

1. Open the web client — home renders fine (docked).
2. Click Other in the navigator.
3. The tab appears with a "Loading" spinner (loading-async-icon) and stays there forever.
4. Every other navigator entry behaves the same, until the browser tab is closed.

What makes it hard to diagnose:

• No errors in the server log.
• No browser console errors.
• No failed or hanging HTTP requests — the client keeps polling POST /main/dispatch, each answered with an empty ClientMessageResult.

Server-side diagnosis

jstack of the app server while the client is stuck shows the per-connection navigator thread parked for the whole life of the form opened by the launch handler:

"pool-97-navigator-pausable-daemon-1" ... in Object.wait()
  at lsfusion.server.logics.action.controller.context.ExecutionContext.requestFormUserInteraction(ExecutionContext.java:733)
  at lsfusion.server.logics.action.controller.context.ExecutionContext.createAndRequestFormInstance(ExecutionContext.java:827)
  at lsfusion.server.logics.form.open.interactive.FormInteractiveAction.executeInternal(FormInteractiveAction.java:172)
  at lsfusion.server.logics.form.open.FormAction.executeInternal(FormAction.java:109)
  ...
  at lsfusion.server.logics.navigator.controller.remote.RemoteNavigator.runAction(RemoteNavigator.java:833)

So the synchronous SHOW never completes (it waits for home to close), and all subsequent remote actions of that connection serialize behind the paused invocation. The client shows the async-loading panel and silently waits.

Expected behavior

At least one of:

1. Docs: Launch_events / the onWebClientStarted handler and the SHOW operator docs should state that a synchronous SHOW inside a launch-event handler blocks every later form open on that connection, and that NOWAIT must be used there. Right now the WAIT/NOWAIT heuristic ("the operator works synchronously when the current session may still be used afterwards") picks the synchronous mode silently, and nothing hints at the failure mode.
2. Platform: treat launch-event handlers as implicitly async (equivalent of forcing NOWAIT there), or don't serialize the connection's action queue behind an invocation that is parked waiting for a form it just opened.

Workaround

onWebClientStarted() + {
    SHOW home DOCKED NOWAIT;
}

With NOWAIT everything works: the form opens, and subsequent navigator opens proceed normally (verified on the same build — flipping only this keyword un-hangs the client).