fix(chat): propagate empty draft on target swap and dispose

Oracle re-review on PR #30 flagged that _ChatDetailViewState only
called onDraftChanged when _textCtl.text was non-empty. The empty
case is load-bearing: if the user restored a saved draft, deleted
the text, then switched target (or closed the panel), the parent's
draft map kept the stale entry and resurrected it on the next swap.

Fix: call onDraftChanged unconditionally in both didUpdateWidget
(target change) and dispose (tear-down), so the parent map learns
when a draft is now empty.

Adds a regression test exercising the restore-clear-swap sequence.

apps/chanora_flutter/lib/widgets/chat_views.dart

@@ -1144,9 +1144,12 @@ class _ChatDetailViewState extends State<ChatDetailView> {
   void didUpdateWidget(covariant ChatDetailView oldWidget) {
     super.didUpdateWidget(oldWidget);
     if (oldWidget.target != widget.target) {
-      if (oldWidget.onDraftChanged != null && _textCtl.text.isNotEmpty) {
-        oldWidget.onDraftChanged!(_textCtl.text);
-      }
+      // Propagate the OUTGOING draft unconditionally, including empty
+      // text. The empty case is load-bearing: if the user typed text,
+      // saved it, restored it, then deleted everything, the parent
+      // map must learn the draft is now empty — otherwise the stale
+      // entry resurrects on the next target swap.
+      oldWidget.onDraftChanged?.call(_textCtl.text);
       _textCtl.text = widget.restoredDraft ?? '';
       _lastRenderedTarget = null;
     }
@@ -1154,9 +1157,10 @@ class _ChatDetailViewState extends State<ChatDetailView> {
 
   @override
   void dispose() {
-    if (widget.onDraftChanged != null && _textCtl.text.isNotEmpty) {
-      widget.onDraftChanged!(_textCtl.text);
-    }
+    // Same unconditional flush on tear-down. The `isNotEmpty` guard
+    // here would silently drop "user cleared the field then closed
+    // the panel" into the same stale-entry bug class as didUpdateWidget.
+    widget.onDraftChanged?.call(_textCtl.text);
     _textCtl.dispose();
     _scrollCtl.dispose();
     super.dispose();

apps/chanora_flutter/test/widgets/chat_panel_test.dart

@@ -133,4 +133,69 @@ void main() {
       'server draft',
     );
   });
+
+  testWidgets(
+    'chat detail propagates empty draft when the user clears it before switching target',
+    (tester) async {
+      // Regression: previously, _ChatDetailViewState only emitted
+      // onDraftChanged when the text was non-empty. If the user
+      // restored a saved draft, deleted it, then switched target,
+      // the stale entry stayed in the parent's draft map and
+      // resurrected on the next target swap.
+      String? savedDraft = 'sentinel-unset';
+      final messages = <ChatEntry>[];
+
+      Widget detail({
+        required rust.BridgeMessageTarget target,
+        required String? restoredDraft,
+      }) {
+        return MaterialApp(
+          localizationsDelegates: AppL10n.localizationsDelegates,
+          supportedLocales: AppL10n.supportedLocales,
+          home: Scaffold(
+            body: ChatDetailView(
+              messages: messages,
+              snapshot: snapshot(),
+              target: target,
+              clientName: '',
+              currentChannelId: BigInt.from(10),
+              channelName: 'Lobby',
+              restoredDraft: restoredDraft,
+              onDraftChanged: (text) => savedDraft = text,
+            ),
+          ),
+        );
+      }
+
+      await tester.pumpWidget(
+        detail(
+          target: const rust.BridgeMessageTarget.channel(),
+          restoredDraft: 'previously saved channel draft',
+        ),
+      );
+
+      expect(
+        tester.widget<TextField>(find.byType(TextField)).controller!.text,
+        'previously saved channel draft',
+      );
+
+      // User clears the field, then switches target.
+      await tester.enterText(find.byType(TextField), '');
+      await tester.pumpWidget(
+        detail(
+          target: const rust.BridgeMessageTarget.server(),
+          restoredDraft: null,
+        ),
+      );
+
+      // The empty string MUST reach the parent so the stale entry
+      // is overwritten in the draft map. With the previous guarded
+      // implementation, savedDraft would still hold the sentinel.
+      expect(
+        savedDraft,
+        '',
+        reason: 'empty draft must overwrite stale entry on target swap',
+      );
+    },
+  );
 }