feat(env): supporter-binary resolver — explicit override → PATH → well-known (T-495)

SupporterBinaries resolves claude/d2/etc. to absolute paths (D-104): an
explicit override map first, then the login-shell/process PATH, then the
well-known bin dirs incl. Homebrew-on-Linux — the dir the standard PATH
expansion omits and a .bashrc-only brew shellenv misses (the D-104 gap).
detect() probes those to seed the override map (pinned, not re-probed each
launch); isStalePin flags a moved tool. Pure Dart, dart test (11 cases).
Settings storage + first-run detect wire on next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/src/env/supporter_binaries_test.dart

@@ -0,0 +1,62 @@
+import 'package:clide/src/env/supporter_binaries.dart';
+import 'package:test/test.dart';
+
+void main() {
+  SupporterBinaries make({Map<String, String> overrides = const {}, Set<String> files = const {}, String path = '/usr/bin:/bin', String home = '/home/u'}) =>
+      SupporterBinaries(overrides: overrides, exists: files.contains, searchPath: () => path, home: home);
+
+  group('resolve', () {
+    test('an explicit override wins', () {
+      final r = make(overrides: {'d2': '/opt/d2'}, files: {'/opt/d2', '/usr/bin/d2'});
+      expect(r.resolve('d2'), '/opt/d2');
+    });
+
+    test('a stale override falls through to the PATH', () {
+      final r = make(overrides: {'d2': '/gone/d2'}, files: {'/usr/bin/d2'});
+      expect(r.resolve('d2'), '/usr/bin/d2');
+    });
+
+    test('searches the PATH when there is no override', () {
+      final r = make(files: {'/bin/d2'});
+      expect(r.resolve('d2'), '/bin/d2');
+    });
+
+    test('finds a tool in linuxbrew via the well-known dirs (the D-104 gap)', () {
+      final r = make(files: {'/home/linuxbrew/.linuxbrew/bin/d2'});
+      expect(r.resolve('d2'), '/home/linuxbrew/.linuxbrew/bin/d2');
+    });
+
+    test('finds a tool in ~/.local/bin', () {
+      final r = make(files: {'/home/u/.local/bin/pql'}, path: '/usr/bin');
+      expect(r.resolve('pql'), '/home/u/.local/bin/pql');
+    });
+
+    test('returns null when unresolved', () {
+      expect(make().resolve('nope'), isNull);
+    });
+  });
+
+  group('isStalePin', () {
+    test('true when the override points at a missing file', () {
+      expect(make(overrides: {'d2': '/gone'}).isStalePin('d2'), isTrue);
+    });
+    test('false when the override exists', () {
+      expect(make(overrides: {'d2': '/ok'}, files: {'/ok'}).isStalePin('d2'), isFalse);
+    });
+    test('false when there is no override', () {
+      expect(make().isStalePin('d2'), isFalse);
+    });
+  });
+
+  group('detect', () {
+    test('finds tools across the PATH and well-known dirs', () {
+      final r = make(files: {'/usr/bin/claude', '/home/linuxbrew/.linuxbrew/bin/d2'}, path: '/usr/bin');
+      expect(r.detect(['claude', 'd2', 'missing']), {'claude': '/usr/bin/claude', 'd2': '/home/linuxbrew/.linuxbrew/bin/d2'});
+    });
+
+    test('prefers the earliest matching directory', () {
+      final r = make(files: {'/usr/bin/d2', '/home/linuxbrew/.linuxbrew/bin/d2'}, path: '/usr/bin');
+      expect(r.detect(['d2'])['d2'], '/usr/bin/d2');
+    });
+  });
+}