refactor: rename internal Fai* design system + fai_ helpers to chain

The Studio design system, widgets and helpers carried a Fai* / fai_
prefix (FaiSpace, FaiColors, FaiTheme, FaiLog, 17 fai_*.dart files, the
faiBinary* l10n keys). Studio is the Ch∆In product, so rename them to
Chain* / chain_ — carefully preserving English fail/failure/failed.
Also fix stale references: the 'fai' binary in l10n strings -> 'chain',
FAI_* env vars (FAI_BIN/DATA_DIR/MODULES_DIR/TODAY/BOOTSTRAP_TOKEN) ->
CHAIN_*, fai_platform -> fai_chain, fai_hub -> chain_hub. Vendor
security-hook tooling (FAI_BANNED_TERMS_FILE) + the .fai bundle ext left.
flutter analyze + test: clean (20 passed).

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

lib/data/chain_log.dart

@@ -26,10 +26,10 @@ import 'dart:io';
 import 'package:meta/meta.dart';
 import 'package:path/path.dart' as p;
 
-class FaiLog {
-  FaiLog._();
+class ChainLog {
+  ChainLog._();
 
-  static final FaiLog instance = FaiLog._();
+  static final ChainLog instance = ChainLog._();
 
   // Serialise concurrent writes — Future-based mutex so a burst
   // of errors (rare but happens during failed install retries)

lib/data/error_presentation.dart

@@ -16,9 +16,9 @@
 
 import 'package:flutter/material.dart';
 
-import '../widgets/fai_error_box.dart';
+import '../widgets/chain_error_box.dart';
 import '../theme/tokens.dart';
-import 'fai_log.dart';
+import 'chain_log.dart';
 
 /// Show [error] as a SnackBar with a copy affordance.
 ///
@@ -41,7 +41,7 @@ void showFaiErrorSnack(
 }) {
   // Fire-and-forget log write. If the disk's full or the dir
   // is read-only the UI still surfaces the error.
-  FaiLog.instance.error(source, error, context: title);
+  ChainLog.instance.error(source, error, context: title);
   final messenger = ScaffoldMessenger.maybeOf(context);
   if (messenger == null) {
     // No Scaffold above — the caller is likely showing the
@@ -60,8 +60,8 @@ void showFaiErrorSnack(
       padding: EdgeInsets.zero,
       content: Padding(
         padding: const EdgeInsets.symmetric(
-          horizontal: FaiSpace.sm,
-          vertical: FaiSpace.xs,
+          horizontal: ChainSpace.sm,
+          vertical: ChainSpace.xs,
         ),
         child: Column(
           mainAxisSize: MainAxisSize.min,
@@ -75,9 +75,9 @@ void showFaiErrorSnack(
                   fontWeight: FontWeight.w600,
                 ),
               ),
-              const SizedBox(height: FaiSpace.xs),
+              const SizedBox(height: ChainSpace.xs),
             ],
-            FaiErrorBox(error: error, isError: true),
+            ChainErrorBox(error: error, isError: true),
           ],
         ),
       ),
@@ -94,14 +94,14 @@ Future<void> showFaiErrorDialog(
   Object error, {
   String? title,
 }) async {
-  FaiLog.instance.error(source, error);
+  ChainLog.instance.error(source, error);
   return showDialog<void>(
     context: context,
     builder: (ctx) => AlertDialog(
       title: title == null ? null : Text(title),
       content: SizedBox(
         width: 480,
-        child: FaiErrorBox(error: error, isError: true, maxHeight: 240),
+        child: ChainErrorBox(error: error, isError: true, maxHeight: 240),
       ),
       actions: [
         TextButton(

lib/data/flow_run_driver.dart

@@ -161,7 +161,7 @@ class StudioFlowRunDriver implements editor.FlowRunDriver {
   /// (text / json / bytes only). File outputs degrade to
   /// JSON containing the URI string — the editor's run-tab
   /// renderer is read-only so the operator can still see
-  /// where the file went; Studio's richer FaiFlowOutput
+  /// where the file went; Studio's richer ChainFlowOutput
   /// widget keeps file-open affordances available elsewhere.
   editor.FlowOutputValue _convertOutput(FlowOutput out) {
     return switch (out) {

lib/data/hub.dart

@@ -1,4 +1,4 @@
-// HubService — singleton wrapper around fai_dart_sdk's HubClient.
+// HubService — singleton wrapper around chain_dart_sdk's HubClient.
 //
 // Centralises the gRPC connection so each page just imports
 // `HubService.instance` instead of constructing its own client.
@@ -1282,7 +1282,7 @@ class SatelliteEnrollment {
     return 'federation:\n'
         '  upstream: https://<this-primary-host>:<federation-port>\n'
         '  hub_name: $name\n'
-        '  bootstrap_token_env: FAI_BOOTSTRAP_TOKEN$ca';
+        '  bootstrap_token_env: CHAIN_BOOTSTRAP_TOKEN$ca';
   }
 }
 
@@ -1553,7 +1553,7 @@ class HardwareSnapshot {
 }
 
 /// One curated model with editorial metadata. Wire-faithful
-/// with `crates/fai_hub/system-ai/models.yaml`.
+/// with `crates/chain_hub/system-ai/models.yaml`.
 class CuratedModelInfo {
   final String id;
   final String family;

lib/data/registry_token.dart

@@ -4,7 +4,7 @@ import 'package:path/path.dart' as p;
 /// Operator-managed registry auth token, kept at
 /// `~/.chain/registry-token` (mode 0600 on Unix). The hub reads
 /// this file at install time when `CHAIN_REGISTRY_TOKEN` is unset
-/// — see `download_to_temp` in `crates/fai_hub/src/lib.rs`.
+/// — see `download_to_temp` in `crates/chain_hub/src/lib.rs`.
 ///
 /// Studio writes the file directly so a fresh install never
 /// requires the operator to fiddle with shell env vars.

lib/data/system_actions.dart

@@ -22,7 +22,7 @@ import 'package:shared_preferences/shared_preferences.dart';
 
 /// Sentinel returned in `_runFai(...).stderr` when no `fai`
 /// binary could be located. UI layers should not display this
-/// verbatim — they check [SystemActions.faiBinaryExists] first
+/// verbatim — they check [SystemActions.chainBinaryExists] first
 /// and render a localized, actionable message instead.
 const String kFaiBinaryNotFound = 'fai-binary-not-found';
 
@@ -37,7 +37,7 @@ class SystemActions {
 
   /// SharedPreferences key for an operator-chosen `fai` binary
   /// path (set via the file picker when auto-detection fails).
-  static const String _kFaiBinaryPrefKey = 'system.fai_binary_path';
+  static const String _kFaiBinaryPrefKey = 'system.chain_binary_path';
 
   /// In-memory cache of the operator override, loaded once at
   /// startup by [loadFaiBinaryOverride]. Null = no override.
@@ -71,7 +71,7 @@ class SystemActions {
   /// the canonical install dir). UI uses this to decide between
   /// the normal daemon-control affordances and the "locate the
   /// binary / read the install guide" recovery path.
-  static bool faiBinaryExists() => _faiExecutable() != null;
+  static bool chainBinaryExists() => _faiExecutable() != null;
 
   /// Ask the OS to open [path] in the default handler. On macOS
   /// this opens text files in TextEdit, configs in the registered
@@ -137,7 +137,7 @@ class SystemActions {
 
   /// Run a `chain daemon ...` subcommand and surface the captured
   /// output. Used by Doctor's "Restart daemon" button.
-  static Future<({bool ok, String stdout, String stderr})> faiDaemon(
+  static Future<({bool ok, String stdout, String stderr})> chainDaemon(
     List<String> args,
   ) async {
     return _runFai(['daemon', ...args]);
@@ -145,7 +145,7 @@ class SystemActions {
 
   /// Run `chain update apply --channel <c>`. Long-running on a slow
   /// network — caller should show a spinner.
-  static Future<({bool ok, String stdout, String stderr})> faiUpdateApply(
+  static Future<({bool ok, String stdout, String stderr})> chainUpdateApply(
     String channel,
   ) async {
     return _runFai(['update', 'apply', '--channel', channel]);
@@ -154,7 +154,7 @@ class SystemActions {
   /// Switch the active channel pointer at `~/.chain/current-channel`.
   /// The CLI also restarts the daemon for the new channel, so the
   /// caller does not need a follow-up restart.
-  static Future<({bool ok, String stdout, String stderr})> faiChannelSwitch(
+  static Future<({bool ok, String stdout, String stderr})> chainChannelSwitch(
     String channel,
   ) async {
     return _runFai(['channel', 'switch', channel]);
@@ -164,14 +164,14 @@ class SystemActions {
   /// (launchd plist on macOS, systemd-user unit on Linux). On
   /// Windows the platform CLI returns a "not supported" exit
   /// status that the caller surfaces as an error message.
-  static Future<({bool ok, String stdout, String stderr})> faiDaemonEnable(
+  static Future<({bool ok, String stdout, String stderr})> chainDaemonEnable(
     String channel,
   ) async {
     return _runFai(['daemon', 'enable', '--channel', channel]);
   }
 
-  /// Remove the autostart unit installed by [faiDaemonEnable].
-  static Future<({bool ok, String stdout, String stderr})> faiDaemonDisable(
+  /// Remove the autostart unit installed by [chainDaemonEnable].
+  static Future<({bool ok, String stdout, String stderr})> chainDaemonDisable(
     String channel,
   ) async {
     return _runFai(['daemon', 'disable', '--channel', channel]);
@@ -186,7 +186,7 @@ class SystemActions {
   ///
   /// Studio's gRPC channel goes down for ~1s while the daemon
   /// restarts — caller should follow up with a reconnect.
-  static Future<({bool ok, String stdout, String stderr})> faiReset({
+  static Future<({bool ok, String stdout, String stderr})> chainReset({
     bool keepModules = false,
     bool keepData = false,
   }) async {
@@ -202,9 +202,9 @@ class SystemActions {
     final exe = _faiExecutable();
     if (exe == null) {
       // Sentinel, not a user-facing string. Callers detect this
-      // via `faiBinaryExists()` and render a localized,
+      // via `chainBinaryExists()` and render a localized,
       // actionable recovery message (locate binary / install
-      // guide) instead of CLI jargon like "set FAI_BIN".
+      // guide) instead of CLI jargon like "set CHAIN_BIN".
       return (ok: false, stdout: '', stderr: kFaiBinaryNotFound);
     }
     try {
@@ -226,7 +226,7 @@ class SystemActions {
   }
 
   /// Locate the `fai` binary. Order: operator override (set via
-  /// the file picker), $FAI_BIN, PATH, fallback to the canonical
+  /// the file picker), $CHAIN_BIN, PATH, fallback to the canonical
   /// install location under the user's home dir.
   static String? _faiExecutable() {
     final override = _faiBinaryOverride;
@@ -236,7 +236,7 @@ class SystemActions {
       return override;
     }
 
-    final fromEnv = Platform.environment['FAI_BIN'];
+    final fromEnv = Platform.environment['CHAIN_BIN'];
     if (fromEnv != null && fromEnv.isNotEmpty && File(fromEnv).existsSync()) {
       return fromEnv;
     }

lib/data/theme_plugin.dart

@@ -16,7 +16,7 @@ import 'hub.dart';
 
 /// SharedPreferences key for the operator's preferred theme
 /// plugin. `null` (or absent) means "use Studio's built-in
-/// default" (FaiTheme.light / .dark).
+/// default" (ChainTheme.light / .dark).
 const _kThemePluginKey = 'theme_plugin_capability';
 
 /// One ColorScheme pair as built from a theme-plugin's
@@ -96,14 +96,14 @@ Future<ThemePluginSchemes> loadThemePluginSchemes(String capability) async {
 }
 
 /// Build a `ThemeData` from a plugin-supplied `ColorScheme`.
-/// Delegates to [FaiTheme.fromColorScheme] so plugin-themed
+/// Delegates to [ChainTheme.fromColorScheme] so plugin-themed
 /// builds and built-in themes share one structural shape — same
 /// textTheme cascade, same component themes, same `inherit`
 /// values on every TextStyle. Without that, Flutter's
 /// AnimatedDefaultTextStyle lerp blows up when swapping between
 /// the two paths.
 ThemeData themeDataFromScheme(ColorScheme scheme) =>
-    FaiTheme.fromColorScheme(scheme);
+    ChainTheme.fromColorScheme(scheme);
 
 /// Translate the plugin's 14 ARGB tokens into a `ColorScheme`.
 /// Order matches the plugin contract: