fix(settings): quote numeric-shaped YAML keys so hash-keyed settings survive reload

The emitter wrote block-map keys raw while only values went through
quoting. A workspace-hash key segment that happens to be all digits
with a leading zero (or digits-e-digits) reloaded as an int/float —
leading zero dropped, or collapsed to Infinity — orphaning the stored
value. Hit ~1 in 1200 repos, deterministically and permanently: the
PATH preset (D-106) and the pre-existing Claude account binding for
such a repo vanished on every restart with no diagnostics. Same defect
class as the T-376 value-corruption fixes in this file; found by the
T-511 review pass, confirmed against the live store.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -44,6 +44,10 @@ heading, and (b) bumping `pubspec.yaml` `version:` in the same commit.
 
 ### Fixed
 
+- Hash-keyed settings (per-workspace PATH presets, Claude account bindings)
+  with a number-shaped hash suffix were silently lost on restart — YAML map
+  keys are now quoted on write.
+
 ## [2.9.0] — 2026-06-30
 
 ### Added

lib/kernel/src/settings.dart

@@ -282,7 +282,14 @@ void _emit(StringBuffer buf, Object? v, int indent) {
       return;
     }
     v.forEach((k, vv) {
-      buf.write('$pad$k:');
+      // Keys go through the same quoting as values: a numeric-shaped key —
+      // e.g. an all-digit FNV workspace-hash suffix (`app.env.pathPrepend.
+      // 0123…`, `app.claude.account.<hash>`) — would otherwise reload as an
+      // int/float and silently corrupt the key (leading zero dropped, or
+      // `1e…` collapsing to Infinity), orphaning the stored value.
+      buf.write(pad);
+      _emitScalar(buf, '$k');
+      buf.write(':');
       if (vv is Map && vv.isNotEmpty) {
         buf.writeln();
         _emit(buf, vv, indent + 1);

test/kernel/src/settings_test.dart

@@ -37,6 +37,20 @@ void main() {
       loaded.dispose();
     });
 
+    test('numeric-shaped key segments round-trip unmangled (workspace-hash keys)', () async {
+      // FNV workspace-hash suffixes (app.env.pathPrepend.<hash>, the account
+      // bindings) can be number-shaped; an unquoted YAML key would reload as
+      // an int (leading zero dropped) or a float ('1e…' → Infinity) and
+      // silently orphan the stored value.
+      await store.set<List<String>>('app.env.pathPrepend.0123456789012345', const ['/opt/go/bin']);
+      await store.set<String>('app.claude.account.1e23456789012345', 'work');
+      final loaded = SettingsStore(appDir: tmp);
+      await loaded.load();
+      expect(loaded.get<List<dynamic>>('app.env.pathPrepend.0123456789012345'), ['/opt/go/bin']);
+      expect(loaded.get<String>('app.claude.account.1e23456789012345'), 'work');
+      loaded.dispose();
+    });
+
     test('app.* scope supports bool + int + list', () async {
       await store.set<bool>('app.extensions.git.enabled', false);
       await store.set<int>('app.layout.width', 240);