ui: jobs with progress, refusals listed, datum preview, form filters and defaults

- A solve or a mesher runs as a job with one progress mechanism: the overlay
  shows the step, stage, count and elapsed time with a bar when bounded, OK
  waits while it runs, and the status sums it up (elements, smallest angle,
  time) (#322, #357).
- Over the control channel such a command is a job too: answered when it
  ends however long it runs, or at once with wait: false, then job.status,
  job.wait, job.cancel; ui.inspect gives job; MCP waits for it (#367).
- A command that cannot run yet lists what it misses in the context panel,
  each with a button to the command that provides it (#323).
- A cancelled or refused solve stays in its workspace (#324, test).
- A mesher form starts from the parameters of the mesh it would replace (#343).
- Seed Edges and edge/vertex/face datum points switch the selection filter
  while open and restore it (#341).
- Datum forms draw the datum live, the Partition form shows its datum, and
  new datums and partitions get the next free name (#347).

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

apps/fieldcraft/src/control_server.rs

@@ -115,6 +115,11 @@ fn serve(stream: TcpStream, tx: Sender<ControlRequest>, ctx: egui::Context) {
                 }
                 ctx.request_repaint();
                 let mut r = rrx.recv_timeout(REPLY_TIMEOUT).unwrap_or_else(|_| json!({"ok": false, "error": "timeout"}));
+                // A request waiting for a job (a solve, a mesher): its reply comes when the job
+                // ends, however long it runs; the job always answers, even when cancelled.
+                if r.get(fieldcraft_ui_egui::control::PENDING).is_some() {
+                    r = rrx.recv().unwrap_or_else(|_| json!({"ok": false, "error": "the job ended without a reply"}));
+                }
                 if let Some(o) = r.as_object_mut() {
                     o.insert("id".into(), id);
                 }