feat(run): host-injected native file picker for flow file inputs

The Run tab asked the operator to type an absolute path into a text
field — with no file dialog anywhere. FlowEditorPage now accepts an
onPickFile callback (PickedFileData: name + bytes) that hosts wire
to their native picker; the path-entry dialog remains only as the
no-host fallback. 0.23.0.

Signed-off-by: flemming-it <sf@flemming.it>

lib/chain_studio_flow_editor.dart

@@ -40,6 +40,8 @@ export 'src/run_driver.dart'
     show
         FlowRunDriver,
         FlowRunEvent,
+        PickedFileData,
+        PickFileCallback,
         StepStarted,
         StepCompleted,
         StepFailed,

lib/src/flow_editor_page.dart

@@ -101,6 +101,11 @@ class FlowEditorPage extends StatefulWidget {
   /// silent — no install button offered.
   final List<String> storeCapabilities;
 
+  /// Host-side native file picker for the Run tab's file inputs.
+  /// Studio passes a real file dialog; null keeps the manual
+  /// path-entry fallback.
+  final PickFileCallback? onPickFile;
+
   /// The host's active workspace/project slug (empty = "all
   /// projects", no active workspace). Used only to flag a
   /// mismatch when the open flow file declares a *different*
@@ -126,6 +131,7 @@ class FlowEditorPage extends StatefulWidget {
     this.storeCapabilities = const [],
     this.activeProject = '',
     this.onSwitchToFileProject,
+    this.onPickFile,
   });
 
   @override
@@ -658,6 +664,7 @@ outputs:
                 controller: _controller,
                 strings: _l,
                 driver: widget.runDriver,
+                onPickFile: widget.onPickFile,
               ),
             ],
           ),

lib/src/run_driver.dart

@@ -19,6 +19,19 @@
 
 import 'dart:typed_data';
 
+/// A file chosen by the host's native picker for a flow file input.
+class PickedFileData {
+  final String fileName;
+  final Uint8List bytes;
+  const PickedFileData({required this.fileName, required this.bytes});
+}
+
+/// Host-side native file picker. Returns null when the operator
+/// cancels. When a host does not supply one, the Run tab falls back
+/// to its manual path-entry dialog.
+typedef PickFileCallback = Future<PickedFileData?> Function();
+
+
 abstract class FlowRunDriver {
   /// Trigger a run of [flowName] with the supplied inputs.
   /// Text + file inputs come in separate maps so the host

lib/src/widgets/run_tab.dart

@@ -36,11 +36,17 @@ class RunTab extends StatefulWidget {
   final FlowEditorController controller;
   final FlowEditorStrings strings;
   final FlowRunDriver? driver;
+
+  /// Host-side native file picker; null keeps the manual
+  /// path-entry fallback dialog.
+  final PickFileCallback? onPickFile;
+
   const RunTab({
     super.key,
     required this.controller,
     required this.strings,
     this.driver,
+    this.onPickFile,
   });
 
   @override
@@ -469,11 +475,21 @@ class _RunTabState extends State<RunTab> {
   }
 
   Future<void> _pickFile(String name) async {
-    // For 0.2.0 the editor relies on the host to inject a
-    // file-picker via callback; minimal version uses
-    // dart:io directly for desktop. Studio uses file_picker;
-    // we fall back to a manual path entry dialog if no host
-    // picker is available.
+    // Host-injected native picker first — typing an absolute path
+    // by hand is a last resort, not an input method.
+    final hostPick = widget.onPickFile;
+    if (hostPick != null) {
+      final picked = await hostPick();
+      if (picked == null || !mounted) return;
+      setState(() {
+        _fileInputs[name] = _FilePick(
+          fileName: picked.fileName,
+          bytes: picked.bytes,
+        );
+      });
+      return;
+    }
+    // Fallback without a host picker: manual path entry.
     final controller = TextEditingController();
     final ctx = context;
     final result = await showDialog<String>(