fix(studio): daemon-start probes health first + shows a readable error

'Tap to start' on an already-running hub reported 'daemon could not be
started' (the start failed because it was already up) then flashed the
error away as a SnackBar — confusing next to the sidebar's 'connected'.
Now: on a failed start, probe the hub; if it answers, just connect (no
false error). If it is genuinely down, show the daemon's stderr in a
persistent, copyable dialog (showFaiProcessErrorDialog) instead of a
SnackBar that vanishes before the operator can read or copy it.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/error_presentation.dart

@@ -109,6 +109,27 @@ void showFaiProcessError(
   );
 }
 
+/// Like [showFaiProcessError] but as a persistent modal dialog. Use for
+/// failures the operator needs time to read and copy (a daemon that
+/// won't start) — a SnackBar flashes away before they can act on it.
+Future<void> showFaiProcessErrorDialog(
+  BuildContext context,
+  String source,
+  String stdout,
+  String stderr, {
+  String? title,
+}) {
+  final detail = [stderr.trim(), stdout.trim()]
+      .where((s) => s.isNotEmpty)
+      .join('\n\n');
+  return showFaiErrorDialog(
+    context,
+    source,
+    detail.isEmpty ? 'process exited non-zero (no output)' : detail,
+    title: title,
+  );
+}
+
 /// Show [error] as a centered modal dialog. Use this when the
 /// failure blocks meaningful interaction (auth missing, hub
 /// unreachable) — a SnackBar would be too easy to dismiss.

lib/main.dart

@@ -275,20 +275,29 @@ class StudioShellState extends State<StudioShell> {
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(content: Text(l.daemonStartRequested)),
       );
-    } else {
-      // Surface the daemon's stderr/stdout as a copyable error — this
-      // is the message the operator most often needs to paste back.
-      showFaiProcessError(
-        context,
-        'daemon.start',
-        r.stdout,
-        r.stderr,
-        title: l.daemonStartFailed(''),
-      );
+      Future.delayed(const Duration(seconds: 1), _checkHealth);
+      return;
     }
-    // Probe again shortly so the UI flips to "connected" without
-    // waiting for the next 5 s tick.
-    Future.delayed(const Duration(seconds: 1), _checkHealth);
+    // The start command reported failure — but very often the daemon is
+    // simply already running (port in use). Probe before crying error,
+    // so "tap to start" on an already-up hub just connects.
+    final alive =
+        await HubService.instance.healthy().catchError((_) => false);
+    if (!mounted) return;
+    if (alive) {
+      await _checkHealth();
+      return;
+    }
+    // Genuinely down: a persistent, copyable dialog — a SnackBar flashes
+    // away before the operator can read or copy the daemon's stderr.
+    await showFaiProcessErrorDialog(
+      context,
+      'daemon.start',
+      r.stdout,
+      r.stderr,
+      title: l.daemonStartFailed(''),
+    );
+    if (mounted) Future.delayed(const Duration(seconds: 1), _checkHealth);
   }
 
   /// Switch the sidebar's selected page by its registered id
@@ -702,17 +711,23 @@ class _SidebarState extends State<_Sidebar>
       ScaffoldMessenger.of(context).showSnackBar(
         SnackBar(content: Text(l.daemonStartRequested)),
       );
-    } else {
-      // Surface the daemon's stderr/stdout as a copyable error — this
-      // is the message the operator most often needs to paste back.
-      showFaiProcessError(
-        context,
-        'daemon.start',
-        r.stdout,
-        r.stderr,
-        title: l.daemonStartFailed(''),
-      );
+      return;
     }
+    // The daemon may already be running (port in use) — probe before
+    // showing an error, so this just connects on an already-up hub.
+    final alive =
+        await HubService.instance.healthy().catchError((_) => false);
+    if (!context.mounted) return;
+    if (alive) return;
+    // Genuinely down: persistent, copyable dialog (a SnackBar flashes
+    // away before the operator can read or copy the daemon's stderr).
+    await showFaiProcessErrorDialog(
+      context,
+      'daemon.start',
+      r.stdout,
+      r.stderr,
+      title: l.daemonStartFailed(''),
+    );
   }
 
   @override