clide:// deep link handler — open files at a line (T-56)

clide://open?path=&line= translates (in parseArgv) to editor.open, so an OS
scheme invocation routes through the existing CLI→IPC path into the running
window — single-instance for free, no new code path. Registered the scheme:
linux/clide.desktop MimeType x-scheme-handler/clide (Exec already passes %U) and
macOS Info.plist CFBundleURLTypes. Parser validates the action/path/line.

Linux works end to end (the OS passes the URL as argv). macOS URL DELIVERY (the
AppDelegate openURLs callback → forward into this path) is a follow-up — the
scheme is registered, but the native hook needs a real macOS machine to verify,
so it's not shipped blind. Also drops a stray import in clide_markdown_test.

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

test/cli/argv_to_request_test.dart

@@ -149,4 +149,38 @@ void main() {
       expect(r.args['positional'], ['README.md']);
     });
   });
+
+  group('parseArgv — clide:// deep links (T-56)', () {
+    test('clide://open?path= maps to editor.open', () {
+      final req = _expectOk(parseArgv(['clide://open?path=/repo/x.md'], requestId: '1'));
+      expect(req.cmd, 'editor.open');
+      expect(req.args['positional'], ['/repo/x.md']);
+    });
+
+    test('a &line= becomes the second positional', () {
+      final req = _expectOk(parseArgv(['clide://open?path=/repo/x.md&line=42'], requestId: '2'));
+      expect(req.cmd, 'editor.open');
+      expect(req.args['positional'], ['/repo/x.md', '42']);
+    });
+
+    test('an encoded path is decoded', () {
+      final req = _expectOk(parseArgv(['clide://open?path=/a%20b/c.dart'], requestId: '3'));
+      expect(req.args['positional'], ['/a b/c.dart']);
+    });
+
+    test('missing path errors', () {
+      final err = _expectErr(parseArgv(['clide://open'], requestId: '4'));
+      expect(err.error?.message, contains('requires a ?path'));
+    });
+
+    test('a non-positive or non-numeric line errors', () {
+      expect(_expectErr(parseArgv(['clide://open?path=/x&line=0'], requestId: '5')).error?.message, contains('positive integer'));
+      expect(_expectErr(parseArgv(['clide://open?path=/x&line=abc'], requestId: '6')).error?.message, contains('positive integer'));
+    });
+
+    test('an unknown action errors', () {
+      final err = _expectErr(parseArgv(['clide://frobnicate?x=1'], requestId: '7'));
+      expect(err.error?.message, contains('unknown clide:// action'));
+    });
+  });
 }

test/widgets/src/clide_markdown_test.dart

@@ -3,7 +3,6 @@
 library;
 
 import 'package:clide/widgets/widgets.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../../helpers/kernel_fixture.dart';