route every tool use through the collapser (T-305 P3)

Every tool use now renders as a ClideCollapserCard over a one-item list
(a single tool is a list of one) — no separate single-card path. The
collapser carries the echoed last line, the count, and the aggregate
status (spinner while in-flight, check/cross once resolved); the inner
content card holds the call body + folded CALL/PROMPT/RESULT segments and
its own per-item mark. Inside a run (activity/edits/agent), tools render
as the bare inner content card so collapsers don't nest.

ConversationCard gains a `margin` param so inner cards carry no stream
margin; the collapser pads its inner canvas evenly on all sides (the
inner card no longer jams under the header). Rewrote the conversation_view
tests for the new structure and added a single-tool golden.

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

test/goldens/collapser_card_goldens_test.dart

@@ -15,7 +15,7 @@ void main() {
   // A stand-in inner item card: content + its own per-item status mark (the
   // collapser carries the aggregate; items keep their own — T-305).
   Widget item(String label, ClideRunStatus status) => Padding(
-        padding: const EdgeInsets.only(bottom: 8),
+        padding: const EdgeInsets.only(bottom: 10),
         child: DecoratedBox(
           decoration: BoxDecoration(
             border: Border.all(color: const Color(0xFF393E48)),

test/goldens/tool_collapser_goldens_test.dart

@@ -0,0 +1,74 @@
+import 'package:alchemist/alchemist.dart';
+import 'package:clide/builtin/claude/src/conversation_card.dart';
+import 'package:clide/widgets/widgets.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../helpers/kernel_fixture.dart';
+import '../helpers/widget_harness.dart';
+
+/// Visualises the T-305 single-tool rendering: every tool use is a collapser
+/// over a one-item list. Collapsed → ticker (label + echoed line + 1 step +
+/// status). Expanded → the inner content card (body + folded result + its own
+/// per-item mark; the collapser carries the aggregate).
+void main() {
+  late KernelFixture f;
+  setUp(() async => f = await KernelFixture.create());
+  tearDown(() async => f.dispose());
+
+  Widget bashContent() => const ConversationCard(
+        variant: ConversationCardVariant.bordered,
+        accent: Color(0xFF4C9AFF),
+        label: 'Bash',
+        status: ConversationCardStatus.success,
+        body: Text('npm test', style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)), textDirection: TextDirection.ltr),
+        extraSegments: [
+          CardSegment(
+              label: 'result', child: Text('All 42 tests passed', style: TextStyle(fontSize: 12, color: Color(0xFF9DA5B4)), textDirection: TextDirection.ltr)),
+        ],
+      );
+
+  goldenTest(
+    'single tool collapser (T-305): collapsed ticker + expanded inner card',
+    fileName: 'tool_collapser',
+    builder: () => GoldenTestGroup(
+      columns: 1,
+      children: [
+        GoldenTestScenario(
+          name: 'collapsed — Bash, 1 step',
+          child: SizedBox(
+            width: 420,
+            child: harness(
+              f,
+              ClideCollapserCard(
+                label: 'Bash',
+                color: const Color(0xFF4C9AFF),
+                collapsedSummary: 'npm test',
+                counter: '1 step',
+                status: ClideRunStatus.success,
+                children: [bashContent()],
+              ),
+            ),
+          ),
+        ),
+        GoldenTestScenario(
+          name: 'expanded — inner content card',
+          child: SizedBox(
+            width: 420,
+            child: harness(
+              f,
+              ClideCollapserCard(
+                label: 'Bash',
+                color: const Color(0xFF4C9AFF),
+                counter: '1 step',
+                status: ClideRunStatus.success,
+                initiallyExpanded: true,
+                children: [bashContent()],
+              ),
+            ),
+          ),
+        ),
+      ],
+    ),
+  );
+}