fix(setup): wizard errors copyable above the dialog, CLI skew explained, exec transparency

Field test of the setup wizard surfaced three trust breaks in one run:
an unexplained macOS Documents permission prompt, a perceived crash,
and an error message whose copy button could not be reached.

Root causes and fixes:
- chain init failures were shown as a SnackBar, which lands BEHIND the
  wizard's modal barrier: dimmed, clipped, copy unreachable — and the
  click aimed at it hit the barrier, dismissing the whole wizard with
  all answers (the perceived crash). Errors now open a modal dialog
  ABOVE the wizard via showChainErrorDialog with a copyable detail
  block, and the wizard is no longer barrier-dismissible.
- When the resolved chain binary is older than Studio and rejects
  --plan-json, the wizard now explains the version skew in plain
  language (binary path + update path) instead of leaking a raw clap
  usage error. A missing binary gets its own localized story.
- Step 3 announces which chain binary the preview will execute; when
  that binary physically lives (symlinks resolved) in a TCC-protected
  folder, the wizard pre-explains the macOS folder prompt.

Supporting changes: FriendlyError passes through friendlyError()
unchanged so call sites can ship precise localized stories through the
shared presentation; SystemActions gains resolvedChainBinary() plus
run/resolve test seams; ChainErrorBox hugs its content instead of
filling an unbounded dialog; the wizard's answers file is written
synchronously (the async dart:io variants never complete under the
widget-test fake-async zone).

Verified: flutter analyze clean, 53 tests green (6 new wizard error-
path tests incl. clipboard round-trip), plus a live GUI walk on macOS
in dark + light with a stale binary (skew dialog, copy verified via
clipboard) and with the real binary (TCC pre-explanation with the
resolved path, full plan preview).

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

lib/l10n/app_de.arb

@@ -1778,6 +1778,20 @@
   "setupFreeTextPrivacyRemote": "Ihre Beschreibung wird an die eingerichtete System-KI gesendet: {model} ({provider}).",
   "@setupFreeTextPrivacyRemote": {"placeholders": {"model": {"type": "String"}, "provider": {"type": "String"}}},
   "setupFreeTextUnavailable": "Für den Freitext-Weg braucht Ch∆In eine eingerichtete System-KI (Einstellungen → System-KI). Die Auswahl oben funktioniert immer — ganz ohne KI.",
+  "setupExecHint": "Für Vorschau und Einrichtung führt Studio das Programm „chain“ aus: {path}",
+  "@setupExecHint": {"placeholders": {"path": {"type": "String"}}},
+  "setupExecHintTcc": "Das Programm liegt unter {path} — macOS fragt dafür eventuell einmalig nach Zugriff auf diesen Ordner (z. B. „Dokumente“). Das ist zu erwarten und in Ordnung.",
+  "@setupExecHintTcc": {"placeholders": {"path": {"type": "String"}}},
+  "setupNoBinaryStepHint": "Das Programm „chain“ wurde auf diesem Rechner nicht gefunden — die Vorschau im nächsten Schritt wird fehlschlagen. Unter „Diagnose“ können Sie es auswählen oder Ch∆In installieren.",
+  "setupNoBinary": "Das Programm „chain“ wurde auf diesem Rechner nicht gefunden.",
+  "setupNoBinaryHint": "Ohne das Programm kann der Assistent die Einrichtung nicht anwenden. Wählen Sie es unter „Diagnose“ aus oder installieren Sie Ch∆In neu.",
+  "setupCliTooOld": "Das installierte „chain“-Programm ist älter als Studio und kennt diesen Assistenten noch nicht.",
+  "setupCliTooOldHint": "Gefunden wurde: {path}. Bitte Ch∆In aktualisieren (Seite „Diagnose“ → Update, oder im Terminal: chain update apply) und den Assistenten danach erneut öffnen.",
+  "@setupCliTooOldHint": {"placeholders": {"path": {"type": "String"}}},
+  "setupPreviewFailed": "Die Plan-Vorschau konnte nicht erstellt werden — das Programm „chain“ meldet einen Fehler.",
+  "setupApplyFailed": "Die Einrichtung konnte nicht angewendet werden — das Programm „chain“ meldet einen Fehler.",
+  "setupCliUsedBinary": "Ausgeführt wurde: {path}",
+  "@setupCliUsedBinary": {"placeholders": {"path": {"type": "String"}}},
   "setupFreeTextParseError": "Die System-KI hat keinen verwertbaren Vorschlag geliefert. Wählen Sie oben aus dem Menü — oder versuchen Sie es noch einmal.",
   "setupReflectionTitle": "So verstehe ich Ihre Aufgabe",
   "setupReflectionScenario": "Worum es geht: {label}",

lib/l10n/app_en.arb

@@ -1817,6 +1817,20 @@
   "setupFreeTextPrivacyRemote": "Your description is sent to the configured system AI: {model} ({provider}).",
   "@setupFreeTextPrivacyRemote": {"placeholders": {"model": {"type": "String"}, "provider": {"type": "String"}}},
   "setupFreeTextUnavailable": "The free-text path needs a configured system AI (Settings → System AI). The choices above always work — no AI required.",
+  "setupExecHint": "For the preview and setup, Studio runs the “chain” program: {path}",
+  "@setupExecHint": {"placeholders": {"path": {"type": "String"}}},
+  "setupExecHintTcc": "The program lives at {path} — macOS may ask once for access to that folder (e.g. “Documents”). That is expected and fine.",
+  "@setupExecHintTcc": {"placeholders": {"path": {"type": "String"}}},
+  "setupNoBinaryStepHint": "The “chain” program could not be found on this machine — the preview in the next step will fail. You can pick it under “Doctor”, or install Ch∆In.",
+  "setupNoBinary": "The “chain” program could not be found on this machine.",
+  "setupNoBinaryHint": "Without it the assistant cannot apply the setup. Pick it under “Doctor”, or reinstall Ch∆In.",
+  "setupCliTooOld": "The installed “chain” program is older than Studio and does not know this assistant yet.",
+  "setupCliTooOldHint": "Found: {path}. Please update Ch∆In (“Doctor” page → update, or in a terminal: chain update apply) and reopen the assistant afterwards.",
+  "@setupCliTooOldHint": {"placeholders": {"path": {"type": "String"}}},
+  "setupPreviewFailed": "The plan preview could not be created — the “chain” program reported an error.",
+  "setupApplyFailed": "The setup could not be applied — the “chain” program reported an error.",
+  "setupCliUsedBinary": "Executed: {path}",
+  "@setupCliUsedBinary": {"placeholders": {"path": {"type": "String"}}},
   "setupFreeTextParseError": "The system AI did not return a usable suggestion. Pick from the menu above — or try again.",
   "setupReflectionTitle": "This is how I read your task",
   "setupReflectionScenario": "What it is about: {label}",

lib/l10n/app_localizations.dart

@@ -5479,6 +5479,66 @@ abstract class AppLocalizations {
   /// **'The free-text path needs a configured system AI (Settings → System AI). The choices above always work — no AI required.'**
   String get setupFreeTextUnavailable;
 
+  /// No description provided for @setupExecHint.
+  ///
+  /// In en, this message translates to:
+  /// **'For the preview and setup, Studio runs the “chain” program: {path}'**
+  String setupExecHint(String path);
+
+  /// No description provided for @setupExecHintTcc.
+  ///
+  /// In en, this message translates to:
+  /// **'The program lives at {path} — macOS may ask once for access to that folder (e.g. “Documents”). That is expected and fine.'**
+  String setupExecHintTcc(String path);
+
+  /// No description provided for @setupNoBinaryStepHint.
+  ///
+  /// In en, this message translates to:
+  /// **'The “chain” program could not be found on this machine — the preview in the next step will fail. You can pick it under “Doctor”, or install Ch∆In.'**
+  String get setupNoBinaryStepHint;
+
+  /// No description provided for @setupNoBinary.
+  ///
+  /// In en, this message translates to:
+  /// **'The “chain” program could not be found on this machine.'**
+  String get setupNoBinary;
+
+  /// No description provided for @setupNoBinaryHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Without it the assistant cannot apply the setup. Pick it under “Doctor”, or reinstall Ch∆In.'**
+  String get setupNoBinaryHint;
+
+  /// No description provided for @setupCliTooOld.
+  ///
+  /// In en, this message translates to:
+  /// **'The installed “chain” program is older than Studio and does not know this assistant yet.'**
+  String get setupCliTooOld;
+
+  /// No description provided for @setupCliTooOldHint.
+  ///
+  /// In en, this message translates to:
+  /// **'Found: {path}. Please update Ch∆In (“Doctor” page → update, or in a terminal: chain update apply) and reopen the assistant afterwards.'**
+  String setupCliTooOldHint(String path);
+
+  /// No description provided for @setupPreviewFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'The plan preview could not be created — the “chain” program reported an error.'**
+  String get setupPreviewFailed;
+
+  /// No description provided for @setupApplyFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'The setup could not be applied — the “chain” program reported an error.'**
+  String get setupApplyFailed;
+
+  /// No description provided for @setupCliUsedBinary.
+  ///
+  /// In en, this message translates to:
+  /// **'Executed: {path}'**
+  String setupCliUsedBinary(String path);
+
   /// No description provided for @setupFreeTextParseError.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -3238,6 +3238,50 @@ class AppLocalizationsDe extends AppLocalizations {
   String get setupFreeTextUnavailable =>
       'Für den Freitext-Weg braucht Ch∆In eine eingerichtete System-KI (Einstellungen → System-KI). Die Auswahl oben funktioniert immer — ganz ohne KI.';
 
+  @override
+  String setupExecHint(String path) {
+    return 'Für Vorschau und Einrichtung führt Studio das Programm „chain“ aus: $path';
+  }
+
+  @override
+  String setupExecHintTcc(String path) {
+    return 'Das Programm liegt unter $path — macOS fragt dafür eventuell einmalig nach Zugriff auf diesen Ordner (z. B. „Dokumente“). Das ist zu erwarten und in Ordnung.';
+  }
+
+  @override
+  String get setupNoBinaryStepHint =>
+      'Das Programm „chain“ wurde auf diesem Rechner nicht gefunden — die Vorschau im nächsten Schritt wird fehlschlagen. Unter „Diagnose“ können Sie es auswählen oder Ch∆In installieren.';
+
+  @override
+  String get setupNoBinary =>
+      'Das Programm „chain“ wurde auf diesem Rechner nicht gefunden.';
+
+  @override
+  String get setupNoBinaryHint =>
+      'Ohne das Programm kann der Assistent die Einrichtung nicht anwenden. Wählen Sie es unter „Diagnose“ aus oder installieren Sie Ch∆In neu.';
+
+  @override
+  String get setupCliTooOld =>
+      'Das installierte „chain“-Programm ist älter als Studio und kennt diesen Assistenten noch nicht.';
+
+  @override
+  String setupCliTooOldHint(String path) {
+    return 'Gefunden wurde: $path. Bitte Ch∆In aktualisieren (Seite „Diagnose“ → Update, oder im Terminal: chain update apply) und den Assistenten danach erneut öffnen.';
+  }
+
+  @override
+  String get setupPreviewFailed =>
+      'Die Plan-Vorschau konnte nicht erstellt werden — das Programm „chain“ meldet einen Fehler.';
+
+  @override
+  String get setupApplyFailed =>
+      'Die Einrichtung konnte nicht angewendet werden — das Programm „chain“ meldet einen Fehler.';
+
+  @override
+  String setupCliUsedBinary(String path) {
+    return 'Ausgeführt wurde: $path';
+  }
+
   @override
   String get setupFreeTextParseError =>
       'Die System-KI hat keinen verwertbaren Vorschlag geliefert. Wählen Sie oben aus dem Menü — oder versuchen Sie es noch einmal.';

lib/l10n/app_localizations_en.dart

@@ -3234,6 +3234,50 @@ class AppLocalizationsEn extends AppLocalizations {
   String get setupFreeTextUnavailable =>
       'The free-text path needs a configured system AI (Settings → System AI). The choices above always work — no AI required.';
 
+  @override
+  String setupExecHint(String path) {
+    return 'For the preview and setup, Studio runs the “chain” program: $path';
+  }
+
+  @override
+  String setupExecHintTcc(String path) {
+    return 'The program lives at $path — macOS may ask once for access to that folder (e.g. “Documents”). That is expected and fine.';
+  }
+
+  @override
+  String get setupNoBinaryStepHint =>
+      'The “chain” program could not be found on this machine — the preview in the next step will fail. You can pick it under “Doctor”, or install Ch∆In.';
+
+  @override
+  String get setupNoBinary =>
+      'The “chain” program could not be found on this machine.';
+
+  @override
+  String get setupNoBinaryHint =>
+      'Without it the assistant cannot apply the setup. Pick it under “Doctor”, or reinstall Ch∆In.';
+
+  @override
+  String get setupCliTooOld =>
+      'The installed “chain” program is older than Studio and does not know this assistant yet.';
+
+  @override
+  String setupCliTooOldHint(String path) {
+    return 'Found: $path. Please update Ch∆In (“Doctor” page → update, or in a terminal: chain update apply) and reopen the assistant afterwards.';
+  }
+
+  @override
+  String get setupPreviewFailed =>
+      'The plan preview could not be created — the “chain” program reported an error.';
+
+  @override
+  String get setupApplyFailed =>
+      'The setup could not be applied — the “chain” program reported an error.';
+
+  @override
+  String setupCliUsedBinary(String path) {
+    return 'Executed: $path';
+  }
+
   @override
   String get setupFreeTextParseError =>
       'The system AI did not return a usable suggestion. Pick from the menu above — or try again.';