Column transition validation and enhanced search filters (DEW-0013, DEW-0014)

DEW-0013: Enhanced search filters (already implemented in DEW-0011 pass)
- dew kanban search already had --column/--type/--label/--milestone filters
- Closed ticket

DEW-0014: Column transition validation
- ColumnConfig gains optional allowedTransitions: List<String>
- Parsed from allowed_transitions YAML list on each column entry
- MoveCommand validates current column's allowedTransitions before moving;
  unconfigured (empty list) = all transitions allowed (existing behaviour)
- Test: transition validation integration test with constrained + unconstrained columns

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

packages/kanban/lib/src/commands/move_command.dart

@@ -40,7 +40,23 @@ class MoveCommand extends DewCommand with DewToolCommand {
       prefix: config.prefix,
     );
 
-    final ticket = await store.update(id, column: column);
-    return 'Moved ${ticket.id} to "$column".';
+    final ticket = await store.findById(id);
+    if (ticket == null) throw ArgumentError('Ticket $id not found.');
+
+    // Check allowed_transitions if configured on the current column.
+    final currentColConfig = config.columns.firstWhere(
+      (c) => c.id == ticket.column,
+      orElse: () => ColumnConfig(id: ticket.column, name: ticket.column, color: ''),
+    );
+    if (currentColConfig.allowedTransitions.isNotEmpty &&
+        !currentColConfig.allowedTransitions.contains(column)) {
+      throw ArgumentError(
+        'Column "${ticket.column}" does not allow transitions to "$column". '
+        'Allowed: ${currentColConfig.allowedTransitions.join(', ')}',
+      );
+    }
+
+    final updated = await store.update(id, column: column);
+    return 'Moved ${updated.id} to "$column".';
   }
 }

packages/kanban/lib/src/kanban_config.dart

@@ -13,7 +13,16 @@ class ColumnConfig {
   final String name;
   final String color;
 
-  const ColumnConfig({required this.id, required this.name, required this.color});
+  /// Optional list of column IDs that this column can transition to.
+  /// If null/empty, all transitions are allowed.
+  final List<String> allowedTransitions;
+
+  const ColumnConfig({
+    required this.id,
+    required this.name,
+    required this.color,
+    this.allowedTransitions = const [],
+  });
 }
 
 class KanbanConfig {
@@ -44,6 +53,10 @@ extension KanbanDewConfig on DewConfig {
                   id: c['id'] as String,
                   name: c['name'] as String,
                   color: c['color'] as String,
+                  allowedTransitions: (c['allowed_transitions'] as YamlList?)
+                          ?.map((t) => t as String)
+                          .toList() ??
+                      const [],
                 ),
               )
               .toList(),

packages/kanban/test/dew_kanban_test.dart

@@ -129,6 +129,83 @@ dew:
     });
   });
 
+  group('MoveCommand transition validation', () {
+    test('move respects allowed_transitions when configured', () async {
+      final tempDir = await Directory.systemTemp.createTemp('kanban_transitions_test_');
+      final origDir = Directory.current;
+      try {
+        await Directory(p.join(tempDir.path, '.project', 'kanban')).create(recursive: true);
+        await File(p.join(tempDir.path, '.project', 'dew.yaml')).writeAsString('''
+dew:
+  mcp:
+    host: localhost
+    port: 9090
+  kanban:
+    prefix: T
+    ticket_types:
+      - id: task
+        name: Task
+    columns:
+      - id: backlog
+        name: Backlog
+        color: grey
+        allowed_transitions:
+          - doing
+      - id: doing
+        name: Doing
+        color: blue
+        allowed_transitions:
+          - done
+          - backlog
+      - id: done
+        name: Done
+        color: green
+''');
+        Directory.current = tempDir;
+        final registry = CommandRegistry();
+        registerCommands(registry);
+        final tools = {for (final t in registry.mcpTools) t.name: t};
+
+        await tools['kanban_create_ticket']!.handler({
+          'title': 'Flow test',
+          'type': 'task',
+        });
+
+        // Allowed: backlog → doing
+        await expectLater(
+          tools['kanban_move_ticket']!.handler({'id': 'T-0001', 'column': 'doing'}),
+          completes,
+        );
+
+        // Disallowed: doing → done is allowed, but doing → backlog is also
+        // allowed; skip to testing a rejected transition:
+        // "done" has no allowed_transitions (unconstrained), but let's test
+        // that "backlog" column can't go directly to "done".
+        // Reset to backlog first.
+        await tools['kanban_move_ticket']!.handler({'id': 'T-0001', 'column': 'backlog'});
+
+        // backlog → done should throw (not in allowed_transitions).
+        await expectLater(
+          tools['kanban_move_ticket']!.handler({'id': 'T-0001', 'column': 'done'}),
+          throwsA(isA<ArgumentError>()),
+        );
+
+        // Unconstrained column (done) — any target is valid.
+        await tools['kanban_move_ticket']!.handler({'id': 'T-0001', 'column': 'doing'});
+        await tools['kanban_move_ticket']!.handler({'id': 'T-0001', 'column': 'done'});
+        // done → backlog: done has no constraints, so it's allowed.
+        final result = await tools['kanban_move_ticket']!.handler({
+          'id': 'T-0001',
+          'column': 'backlog',
+        });
+        expect(result, contains('T-0001'));
+      } finally {
+        Directory.current = origDir;
+        await tempDir.delete(recursive: true);
+      }
+    });
+  });
+
   group('Ticket', () {
     test('roundtrip serialisation', () {
       final t = Ticket(