diff --git a/app/src/lib/i18n/ar.ts b/app/src/lib/i18n/ar.ts
index 9776fefee..9827f441f 100644
--- a/app/src/lib/i18n/ar.ts
+++ b/app/src/lib/i18n/ar.ts
@@ -2993,6 +2993,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'استدعاءات الأدوات',
   'conversations.subagent.working': 'يعمل…',
   'conversations.subagent.noOutputYet': 'لا يوجد ناتج بعد',
+  'conversations.subagent.input': 'المدخلات',
+  'conversations.subagent.output': 'المخرجات',
+  'conversations.subagent.noOutput': 'لم يتم إرجاع أي مخرجات',
   'conversations.subagent.close': 'إغلاق',
   'conversations.subagent.cancel': 'إلغاء المهمة',
   'conversations.subagent.cancelling': 'جارٍ الإلغاء…',
diff --git a/app/src/lib/i18n/bn.ts b/app/src/lib/i18n/bn.ts
index 9794b7c6a..821301f69 100644
--- a/app/src/lib/i18n/bn.ts
+++ b/app/src/lib/i18n/bn.ts
@@ -3057,6 +3057,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'টুল কল',
   'conversations.subagent.working': 'কাজ করছে…',
   'conversations.subagent.noOutputYet': 'এখনও কোনো আউটপুট নেই',
+  'conversations.subagent.input': 'ইনপুট',
+  'conversations.subagent.output': 'আউটপুট',
+  'conversations.subagent.noOutput': 'কোনো আউটপুট ফেরত আসেনি',
   'conversations.subagent.close': 'বন্ধ করুন',
   'conversations.subagent.cancel': 'কাজ বাতিল করুন',
   'conversations.subagent.cancelling': 'বাতিল করা হচ্ছে…',
diff --git a/app/src/lib/i18n/de.ts b/app/src/lib/i18n/de.ts
index c24fef911..25fb5ffd8 100644
--- a/app/src/lib/i18n/de.ts
+++ b/app/src/lib/i18n/de.ts
@@ -3129,6 +3129,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Tool-Aufrufe',
   'conversations.subagent.working': 'Arbeitet…',
   'conversations.subagent.noOutputYet': 'Noch keine Ausgabe',
+  'conversations.subagent.input': 'Eingabe',
+  'conversations.subagent.output': 'Ausgabe',
+  'conversations.subagent.noOutput': 'Keine Ausgabe zurückgegeben',
   'conversations.subagent.close': 'Schließen',
   'conversations.subagent.cancel': 'Aufgabe abbrechen',
   'conversations.subagent.cancelling': 'Wird abgebrochen…',
diff --git a/app/src/lib/i18n/en.ts b/app/src/lib/i18n/en.ts
index 7a1b370a5..607b0ad30 100644
--- a/app/src/lib/i18n/en.ts
+++ b/app/src/lib/i18n/en.ts
@@ -3587,6 +3587,9 @@ const en: TranslationMap = {
   'conversations.subagent.toolCalls': 'Tool calls',
   'conversations.subagent.working': 'Working…',
   'conversations.subagent.noOutputYet': 'No output yet',
+  'conversations.subagent.input': 'Input',
+  'conversations.subagent.output': 'Output',
+  'conversations.subagent.noOutput': 'No output returned',
   'conversations.subagent.close': 'Close',
   'conversations.subagent.cancel': 'Cancel task',
   'conversations.subagent.cancelling': 'Cancelling…',
diff --git a/app/src/lib/i18n/es.ts b/app/src/lib/i18n/es.ts
index 982f40f6f..7fe5a8b09 100644
--- a/app/src/lib/i18n/es.ts
+++ b/app/src/lib/i18n/es.ts
@@ -3108,6 +3108,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Llamadas a herramientas',
   'conversations.subagent.working': 'Trabajando…',
   'conversations.subagent.noOutputYet': 'Aún no hay resultados',
+  'conversations.subagent.input': 'Entrada',
+  'conversations.subagent.output': 'Salida',
+  'conversations.subagent.noOutput': 'No se devolvió ninguna salida',
   'conversations.subagent.close': 'Cerrar',
   'conversations.subagent.cancel': 'Cancelar tarea',
   'conversations.subagent.cancelling': 'Cancelando…',
diff --git a/app/src/lib/i18n/fr.ts b/app/src/lib/i18n/fr.ts
index 845fd9035..bcad3d08a 100644
--- a/app/src/lib/i18n/fr.ts
+++ b/app/src/lib/i18n/fr.ts
@@ -3123,6 +3123,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Appels d’outils',
   'conversations.subagent.working': 'En cours…',
   'conversations.subagent.noOutputYet': 'Aucun résultat pour l’instant',
+  'conversations.subagent.input': 'Entrée',
+  'conversations.subagent.output': 'Sortie',
+  'conversations.subagent.noOutput': 'Aucune sortie renvoyée',
   'conversations.subagent.close': 'Fermer',
   'conversations.subagent.cancel': 'Annuler la tâche',
   'conversations.subagent.cancelling': 'Annulation…',
diff --git a/app/src/lib/i18n/hi.ts b/app/src/lib/i18n/hi.ts
index eb2f76949..714211c4d 100644
--- a/app/src/lib/i18n/hi.ts
+++ b/app/src/lib/i18n/hi.ts
@@ -3058,6 +3058,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'टूल कॉल',
   'conversations.subagent.working': 'काम कर रहा है…',
   'conversations.subagent.noOutputYet': 'अभी तक कोई आउटपुट नहीं',
+  'conversations.subagent.input': 'इनपुट',
+  'conversations.subagent.output': 'आउटपुट',
+  'conversations.subagent.noOutput': 'कोई आउटपुट नहीं मिला',
   'conversations.subagent.close': 'बंद करें',
   'conversations.subagent.cancel': 'कार्य रद्द करें',
   'conversations.subagent.cancelling': 'रद्द किया जा रहा है…',
diff --git a/app/src/lib/i18n/id.ts b/app/src/lib/i18n/id.ts
index 3ec5b61e0..30a1b9df0 100644
--- a/app/src/lib/i18n/id.ts
+++ b/app/src/lib/i18n/id.ts
@@ -3061,6 +3061,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Panggilan alat',
   'conversations.subagent.working': 'Bekerja…',
   'conversations.subagent.noOutputYet': 'Belum ada keluaran',
+  'conversations.subagent.input': 'Masukan',
+  'conversations.subagent.output': 'Keluaran',
+  'conversations.subagent.noOutput': 'Tidak ada keluaran',
   'conversations.subagent.close': 'Tutup',
   'conversations.subagent.cancel': 'Batalkan tugas',
   'conversations.subagent.cancelling': 'Membatalkan…',
diff --git a/app/src/lib/i18n/it.ts b/app/src/lib/i18n/it.ts
index adcfcfcbd..c115ed21c 100644
--- a/app/src/lib/i18n/it.ts
+++ b/app/src/lib/i18n/it.ts
@@ -3102,6 +3102,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Chiamate agli strumenti',
   'conversations.subagent.working': 'In corso…',
   'conversations.subagent.noOutputYet': 'Ancora nessun output',
+  'conversations.subagent.input': 'Input',
+  'conversations.subagent.output': 'Output',
+  'conversations.subagent.noOutput': 'Nessun output restituito',
   'conversations.subagent.close': 'Chiudi',
   'conversations.subagent.cancel': 'Annulla attività',
   'conversations.subagent.cancelling': 'Annullamento…',
diff --git a/app/src/lib/i18n/ko.ts b/app/src/lib/i18n/ko.ts
index 10668f88b..bc9652fbb 100644
--- a/app/src/lib/i18n/ko.ts
+++ b/app/src/lib/i18n/ko.ts
@@ -3033,6 +3033,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': '도구 호출',
   'conversations.subagent.working': '작업 중…',
   'conversations.subagent.noOutputYet': '아직 출력이 없습니다',
+  'conversations.subagent.input': '입력',
+  'conversations.subagent.output': '출력',
+  'conversations.subagent.noOutput': '반환된 출력 없음',
   'conversations.subagent.close': '닫기',
   'conversations.subagent.cancel': '작업 취소',
   'conversations.subagent.cancelling': '취소 중…',
diff --git a/app/src/lib/i18n/pl.ts b/app/src/lib/i18n/pl.ts
index 651c3ef2e..3e715e767 100644
--- a/app/src/lib/i18n/pl.ts
+++ b/app/src/lib/i18n/pl.ts
@@ -3089,6 +3089,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Wywołania narzędzi',
   'conversations.subagent.working': 'Pracuje…',
   'conversations.subagent.noOutputYet': 'Brak wyników',
+  'conversations.subagent.input': 'Wejście',
+  'conversations.subagent.output': 'Wyjście',
+  'conversations.subagent.noOutput': 'Brak zwróconych danych wyjściowych',
   'conversations.subagent.close': 'Zamknij',
   'conversations.subagent.cancel': 'Anuluj zadanie',
   'conversations.subagent.cancelling': 'Anulowanie…',
diff --git a/app/src/lib/i18n/pt.ts b/app/src/lib/i18n/pt.ts
index d224cb948..af3ad1825 100644
--- a/app/src/lib/i18n/pt.ts
+++ b/app/src/lib/i18n/pt.ts
@@ -3107,6 +3107,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Chamadas de ferramentas',
   'conversations.subagent.working': 'Trabalhando…',
   'conversations.subagent.noOutputYet': 'Ainda sem resultado',
+  'conversations.subagent.input': 'Entrada',
+  'conversations.subagent.output': 'Saída',
+  'conversations.subagent.noOutput': 'Nenhuma saída retornada',
   'conversations.subagent.close': 'Fechar',
   'conversations.subagent.cancel': 'Cancelar tarefa',
   'conversations.subagent.cancelling': 'Cancelando…',
diff --git a/app/src/lib/i18n/ru.ts b/app/src/lib/i18n/ru.ts
index 9429307a2..1fd79939a 100644
--- a/app/src/lib/i18n/ru.ts
+++ b/app/src/lib/i18n/ru.ts
@@ -3080,6 +3080,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': 'Вызовы инструментов',
   'conversations.subagent.working': 'Выполняется…',
   'conversations.subagent.noOutputYet': 'Пока нет результата',
+  'conversations.subagent.input': 'Ввод',
+  'conversations.subagent.output': 'Вывод',
+  'conversations.subagent.noOutput': 'Вывод отсутствует',
   'conversations.subagent.close': 'Закрыть',
   'conversations.subagent.cancel': 'Отменить задачу',
   'conversations.subagent.cancelling': 'Отмена…',
diff --git a/app/src/lib/i18n/zh-CN.ts b/app/src/lib/i18n/zh-CN.ts
index 016b51a66..b0560ae66 100644
--- a/app/src/lib/i18n/zh-CN.ts
+++ b/app/src/lib/i18n/zh-CN.ts
@@ -2910,6 +2910,9 @@ const messages: TranslationMap = {
   'conversations.subagent.toolCalls': '工具调用',
   'conversations.subagent.working': '处理中…',
   'conversations.subagent.noOutputYet': '暂无输出',
+  'conversations.subagent.input': '输入',
+  'conversations.subagent.output': '输出',
+  'conversations.subagent.noOutput': '无输出返回',
   'conversations.subagent.close': '关闭',
   'conversations.subagent.cancel': '取消任务',
   'conversations.subagent.cancelling': '正在取消…',
diff --git a/app/src/pages/conversations/components/SubagentDrawer.tsx b/app/src/pages/conversations/components/SubagentDrawer.tsx
index 25c69c17e..bc7615eca 100644
--- a/app/src/pages/conversations/components/SubagentDrawer.tsx
+++ b/app/src/pages/conversations/components/SubagentDrawer.tsx
@@ -369,34 +369,9 @@ export function SubagentDrawer({
                   );
                 }
 
-                const callTone =
-                  item.status === 'running'
-                    ? 'text-amber-700 dark:text-amber-300'
-                    : item.status === 'success'
-                      ? 'text-sage-700 dark:text-sage-300'
-                      : 'text-coral-700 dark:text-coral-300';
-                const statusLabel =
-                  item.status === 'running'
-                    ? t('conversations.subagent.statusRunning')
-                    : item.status === 'success'
-                      ? t('conversations.subagent.statusCompleted')
-                      : t('conversations.subagent.statusFailed');
                 return (
                   <ItemWrapper key={`tl-${item.callId}`} divider={turnDivider}>
-                    <div
-                      className="flex items-center gap-2 rounded-md border border-stone-200 bg-stone-50 px-2.5 py-1.5 text-xs dark:border-neutral-800 dark:bg-neutral-800/60"
-                      data-testid="subagent-drawer-tool-call">
-                      <span className={callTone}>🔧</span>
-                      <span className="font-mono text-stone-700 dark:text-neutral-200">
-                        {item.toolName}
-                      </span>
-                      <span className={`ml-auto ${callTone}`}>{statusLabel}</span>
-                      {item.elapsedMs != null && item.status !== 'running' ? (
-                        <span className="text-[10px] text-stone-400 dark:text-neutral-500">
-                          {formatElapsed(item.elapsedMs)}
-                        </span>
-                      ) : null}
-                    </div>
+                    <ToolCallRow item={item} />
                   </ItemWrapper>
                 );
               })}
@@ -417,3 +392,115 @@ function ItemWrapper({ divider, children }: { divider: ReactNode; children: Reac
     </>
   );
 }
+
+type SubagentToolItem = Extract<SubagentTranscriptItem, { kind: 'tool' }>;
+
+/**
+ * Pretty-print a tool's input arguments for display. Objects/arrays are
+ * rendered as indented JSON; a string is shown verbatim. Returns `null` when
+ * there are no arguments to show (e.g. a tool called with no input, or a
+ * transcript reopened from memory where args weren't persisted).
+ */
+function formatArgs(args: unknown): string | null {
+  if (args == null) return null;
+  if (typeof args === 'string') return args.length > 0 ? args : null;
+  try {
+    return JSON.stringify(args, null, 2);
+  } catch {
+    return String(args);
+  }
+}
+
+/**
+ * One child tool call in the drawer transcript, expandable to reveal exactly
+ * *what happened*: the input arguments the sub-agent passed and the raw output
+ * the tool returned. Collapsed by default to keep the transcript scannable;
+ * the chevron only appears once there's detail to reveal (args present, or the
+ * call completed with a captured result). Reopened-from-memory transcripts
+ * carry no args/result, so those rows stay non-expandable.
+ */
+function ToolCallRow({ item }: { item: SubagentToolItem }) {
+  const { t } = useT();
+  const [expanded, setExpanded] = useState(false);
+
+  const callTone =
+    item.status === 'running'
+      ? 'text-amber-700 dark:text-amber-300'
+      : item.status === 'success'
+        ? 'text-sage-700 dark:text-sage-300'
+        : item.status === 'cancelled'
+          ? 'text-stone-600 dark:text-neutral-300'
+          : item.status === 'awaiting_user'
+            ? 'text-amber-700 dark:text-amber-300'
+            : 'text-coral-700 dark:text-coral-300';
+  const statusLabel =
+    item.status === 'running'
+      ? t('conversations.subagent.statusRunning')
+      : item.status === 'success'
+        ? t('conversations.subagent.statusCompleted')
+        : item.status === 'cancelled'
+          ? t('conversations.subagent.statusCancelled')
+          : item.status === 'awaiting_user'
+            ? t('conversations.subagent.statusAwaitingUser')
+            : t('conversations.subagent.statusFailed');
+
+  const argsText = formatArgs(item.args);
+  const hasOutput = item.result != null;
+  const expandable = argsText != null || hasOutput;
+
+  const detailPre =
+    'max-h-60 overflow-auto whitespace-pre-wrap break-words rounded bg-white px-2 py-1.5 ' +
+    'font-mono text-[11px] leading-relaxed text-stone-600 dark:bg-neutral-900 dark:text-neutral-300';
+  const detailLabel =
+    'mb-1 text-[10px] font-semibold uppercase tracking-wide text-stone-400 dark:text-neutral-500';
+
+  return (
+    <div
+      className="rounded-md border border-stone-200 bg-stone-50 text-xs dark:border-neutral-800 dark:bg-neutral-800/60"
+      data-testid="subagent-drawer-tool-call">
+      <button
+        type="button"
+        disabled={!expandable}
+        onClick={() => setExpanded(v => !v)}
+        aria-expanded={expandable ? expanded : undefined}
+        data-testid="subagent-tool-call-toggle"
+        className="flex w-full items-center gap-2 px-2.5 py-1.5 text-left disabled:cursor-default">
+        {expandable ? (
+          <span className="shrink-0 text-[9px] text-stone-400 dark:text-neutral-500">
+            {expanded ? '▾' : '▸'}
+          </span>
+        ) : (
+          <span className="w-[9px] shrink-0" aria-hidden />
+        )}
+        <span className={callTone}>🔧</span>
+        <span className="font-mono text-stone-700 dark:text-neutral-200">{item.toolName}</span>
+        <span className={`ml-auto ${callTone}`}>{statusLabel}</span>
+        {item.elapsedMs != null && item.status !== 'running' ? (
+          <span className="text-[10px] text-stone-400 dark:text-neutral-500">
+            {formatElapsed(item.elapsedMs)}
+          </span>
+        ) : null}
+      </button>
+      {expandable && expanded ? (
+        <div className="space-y-2 border-t border-stone-200 px-2.5 py-2 dark:border-neutral-800">
+          {argsText != null ? (
+            <div data-testid="subagent-tool-call-input">
+              <div className={detailLabel}>{t('conversations.subagent.input')}</div>
+              <pre className={detailPre}>{argsText}</pre>
+            </div>
+          ) : null}
+          {hasOutput ? (
+            <div data-testid="subagent-tool-call-output">
+              <div className={detailLabel}>{t('conversations.subagent.output')}</div>
+              <pre className={detailPre}>
+                {item.result && item.result.length > 0
+                  ? item.result
+                  : t('conversations.subagent.noOutput')}
+              </pre>
+            </div>
+          ) : null}
+        </div>
+      ) : null}
+    </div>
+  );
+}
diff --git a/app/src/pages/conversations/components/__tests__/SubagentDrawer.test.tsx b/app/src/pages/conversations/components/__tests__/SubagentDrawer.test.tsx
index d74fb7324..c5ecdc8f0 100644
--- a/app/src/pages/conversations/components/__tests__/SubagentDrawer.test.tsx
+++ b/app/src/pages/conversations/components/__tests__/SubagentDrawer.test.tsx
@@ -242,4 +242,75 @@ describe('SubagentDrawer', () => {
     // Case-robust: the label may be rendered as "Cancelled" or "cancelled".
     expect(screen.getByTestId('subagent-drawer').textContent?.toLowerCase()).toContain('cancelled');
   });
+
+  it('expands a tool call to reveal its input args and output', async () => {
+    const transcript: SubagentTranscriptItem[] = [
+      {
+        kind: 'tool',
+        iteration: 1,
+        callId: 'c1',
+        toolName: 'web_search',
+        status: 'success',
+        elapsedMs: 1200,
+        args: { query: 'Q3 revenue drivers' },
+        result: 'Found 3 results about revenue.',
+      },
+    ];
+    render(
+      <SubagentDrawer subagent={activity({ transcript })} status="success" onClose={() => {}} />
+    );
+
+    // Collapsed by default — neither input nor output is rendered yet.
+    expect(screen.queryByTestId('subagent-tool-call-input')).toBeNull();
+    expect(screen.queryByTestId('subagent-tool-call-output')).toBeNull();
+
+    await userEvent.click(screen.getByTestId('subagent-tool-call-toggle'));
+
+    expect(screen.getByTestId('subagent-tool-call-input').textContent).toContain(
+      'Q3 revenue drivers'
+    );
+    expect(screen.getByTestId('subagent-tool-call-output').textContent).toContain(
+      'Found 3 results about revenue.'
+    );
+  });
+
+  it('shows the no-output placeholder when the tool returned an empty result', async () => {
+    const transcript: SubagentTranscriptItem[] = [
+      { kind: 'tool', iteration: 1, callId: 'c1', toolName: 'noop', status: 'success', result: '' },
+    ];
+    render(
+      <SubagentDrawer subagent={activity({ transcript })} status="success" onClose={() => {}} />
+    );
+    await userEvent.click(screen.getByTestId('subagent-tool-call-toggle'));
+    expect(screen.getByTestId('subagent-tool-call-output').textContent?.toLowerCase()).toContain(
+      'no output'
+    );
+  });
+
+  it('renders cancelled/awaiting_user tool-call statuses with their own label (not "failed")', () => {
+    const transcript: SubagentTranscriptItem[] = [
+      { kind: 'tool', iteration: 1, callId: 'c1', toolName: 'web_search', status: 'cancelled' },
+      { kind: 'tool', iteration: 1, callId: 'c2', toolName: 'composio', status: 'awaiting_user' },
+    ];
+    render(
+      <SubagentDrawer subagent={activity({ transcript })} status="cancelled" onClose={() => {}} />
+    );
+    const rows = screen.getAllByTestId('subagent-drawer-tool-call');
+    expect(rows[0].textContent?.toLowerCase()).toContain('cancelled');
+    expect(rows[0].textContent?.toLowerCase()).not.toContain('failed');
+    expect(rows[1].textContent?.toLowerCase()).toContain('awaiting');
+  });
+
+  it('does not offer expansion for a tool call with no captured args or result', () => {
+    const transcript: SubagentTranscriptItem[] = [
+      { kind: 'tool', iteration: 1, callId: 'c1', toolName: 'web_search', status: 'success' },
+    ];
+    render(
+      <SubagentDrawer subagent={activity({ transcript })} status="success" onClose={() => {}} />
+    );
+    const toggle = screen.getByTestId('subagent-tool-call-toggle') as HTMLButtonElement;
+    expect(toggle.disabled).toBe(true);
+    expect(screen.queryByTestId('subagent-tool-call-input')).toBeNull();
+    expect(screen.queryByTestId('subagent-tool-call-output')).toBeNull();
+  });
 });
diff --git a/app/src/providers/ChatRuntimeProvider.tsx b/app/src/providers/ChatRuntimeProvider.tsx
index 9e0911bc1..33ec6c6ca 100644
--- a/app/src/providers/ChatRuntimeProvider.tsx
+++ b/app/src/providers/ChatRuntimeProvider.tsx
@@ -641,6 +641,7 @@ const ChatRuntimeProvider = ({ children }: { children: React.ReactNode }) => {
                 toolName: event.tool_name,
                 status: 'running',
                 iteration: event.subagent?.child_iteration,
+                args: event.args,
               },
             ],
           },
@@ -655,6 +656,7 @@ const ChatRuntimeProvider = ({ children }: { children: React.ReactNode }) => {
             callId: event.tool_call_id,
             toolName: event.tool_name,
             iteration: event.subagent?.child_iteration,
+            args: event.args,
           })
         );
       },
@@ -676,6 +678,7 @@ const ChatRuntimeProvider = ({ children }: { children: React.ReactNode }) => {
           status: event.success ? 'success' : 'error',
           elapsedMs: event.subagent?.elapsed_ms ?? updatedCalls[callIdx].elapsedMs,
           outputChars: event.subagent?.output_chars ?? updatedCalls[callIdx].outputChars,
+          result: event.output ?? updatedCalls[callIdx].result,
         };
         const next = [...existing];
         next[idx] = { ...entry, subagent: { ...entry.subagent, toolCalls: updatedCalls } };
@@ -688,6 +691,7 @@ const ChatRuntimeProvider = ({ children }: { children: React.ReactNode }) => {
             success: event.success,
             elapsedMs: event.subagent?.elapsed_ms,
             outputChars: event.subagent?.output_chars,
+            result: event.output,
           })
         );
       },
diff --git a/app/src/services/chatService.ts b/app/src/services/chatService.ts
index 8b067d67f..c15bcea21 100644
--- a/app/src/services/chatService.ts
+++ b/app/src/services/chatService.ts
@@ -301,6 +301,12 @@ export interface ChatSubagentToolCallEvent {
   skill_id: string;
   /** Provider-assigned tool call id. */
   tool_call_id: string;
+  /**
+   * Full arguments the sub-agent invoked the tool with, so the processing
+   * drawer can show *what exactly* the child did. Absent for tools called
+   * with no/`null` arguments.
+   */
+  args?: unknown;
   subagent?: SubagentProgressDetail;
 }
 
@@ -313,7 +319,11 @@ export interface ChatSubagentToolResultEvent {
   skill_id: string;
   tool_call_id: string;
   success: boolean;
-  /** Stringified JSON `{ output_chars, elapsed_ms }` matching `tool_result`. */
+  /**
+   * The child tool's actual output text, so the drawer can show what came
+   * back. Size/timing still arrive via `subagent.output_chars` /
+   * `subagent.elapsed_ms`.
+   */
   output?: string;
   subagent?: SubagentProgressDetail;
 }
diff --git a/app/src/store/chatRuntimeSlice.ts b/app/src/store/chatRuntimeSlice.ts
index 609e50053..a9a300cae 100644
--- a/app/src/store/chatRuntimeSlice.ts
+++ b/app/src/store/chatRuntimeSlice.ts
@@ -133,6 +133,10 @@ export type SubagentTranscriptItem =
       status: ToolTimelineEntryStatus;
       elapsedMs?: number;
       outputChars?: number;
+      /** Arguments the child invoked the tool with (set on start). */
+      args?: unknown;
+      /** The tool's actual output text (set on completion). */
+      result?: string;
     };
 
 /** One child tool call performed by a running sub-agent. */
@@ -148,6 +152,10 @@ export interface SubagentToolCallEntry {
   elapsedMs?: number;
   /** Character length of the tool result (set on completion). */
   outputChars?: number;
+  /** Arguments the child invoked the tool with (set on start). */
+  args?: unknown;
+  /** The tool's actual output text (set on completion). */
+  result?: string;
 }
 
 export interface ToolTimelineEntry {
@@ -630,14 +638,15 @@ const chatRuntimeSlice = createSlice({
         callId: string;
         toolName: string;
         iteration?: number;
+        args?: unknown;
       }>
     ) => {
-      const { threadId, rowId, callId, toolName, iteration } = action.payload;
+      const { threadId, rowId, callId, toolName, iteration, args } = action.payload;
       const entry = state.toolTimelineByThread[threadId]?.find(e => e.id === rowId);
       if (!entry?.subagent) return;
       const transcript = (entry.subagent.transcript ??= []);
       if (transcript.some(i => i.kind === 'tool' && i.callId === callId)) return;
-      transcript.push({ kind: 'tool', iteration, callId, toolName, status: 'running' });
+      transcript.push({ kind: 'tool', iteration, callId, toolName, status: 'running', args });
     },
     /**
      * Flip a transcript `tool` item to its terminal status when the child
@@ -653,15 +662,17 @@ const chatRuntimeSlice = createSlice({
         success: boolean;
         elapsedMs?: number;
         outputChars?: number;
+        result?: string;
       }>
     ) => {
-      const { threadId, rowId, callId, success, elapsedMs, outputChars } = action.payload;
+      const { threadId, rowId, callId, success, elapsedMs, outputChars, result } = action.payload;
       const entry = state.toolTimelineByThread[threadId]?.find(e => e.id === rowId);
       const item = entry?.subagent?.transcript?.find(i => i.kind === 'tool' && i.callId === callId);
       if (!item || item.kind !== 'tool') return;
       item.status = success ? 'success' : 'error';
       if (elapsedMs != null) item.elapsedMs = elapsedMs;
       if (outputChars != null) item.outputChars = outputChars;
+      if (result != null) item.result = result;
     },
     setTaskBoardForThread: (
       state,
diff --git a/src/bin/harness_subagent_audit.rs b/src/bin/harness_subagent_audit.rs
index fa0940766..aa114437b 100644
--- a/src/bin/harness_subagent_audit.rs
+++ b/src/bin/harness_subagent_audit.rs
@@ -555,6 +555,7 @@ async fn drain_progress(
                 task_id,
                 call_id,
                 tool_name,
+                arguments: _,
                 iteration,
             } => {
                 eprintln!(
@@ -581,6 +582,7 @@ async fn drain_progress(
                 tool_name,
                 success,
                 output_chars,
+                output: _,
                 elapsed_ms,
                 iteration,
             } => {
diff --git a/src/openhuman/agent/harness/engine/progress.rs b/src/openhuman/agent/harness/engine/progress.rs
index 605ef5264..aa0a67326 100644
--- a/src/openhuman/agent/harness/engine/progress.rs
+++ b/src/openhuman/agent/harness/engine/progress.rs
@@ -40,7 +40,7 @@ pub(crate) trait ProgressReporter: Send + Sync {
         _call_id: &str,
         _tool_name: &str,
         _success: bool,
-        _output_chars: usize,
+        _output: &str,
         _elapsed_ms: u64,
         _iteration: u32,
     ) {
@@ -158,7 +158,7 @@ impl ProgressReporter for TurnProgress {
         call_id: &str,
         tool_name: &str,
         success: bool,
-        output_chars: usize,
+        output: &str,
         elapsed_ms: u64,
         iteration: u32,
     ) {
@@ -169,7 +169,7 @@ impl ProgressReporter for TurnProgress {
                     call_id: call_id.to_string(),
                     tool_name: tool_name.to_string(),
                     success,
-                    output_chars,
+                    output_chars: output.chars().count(),
                     elapsed_ms,
                     iteration,
                 },
@@ -217,7 +217,7 @@ impl ProgressReporter for SubagentProgress {
         &self,
         call_id: &str,
         tool_name: &str,
-        _arguments: &serde_json::Value,
+        arguments: &serde_json::Value,
         iteration: u32,
     ) {
         if let Some(ref sink) = self.sink {
@@ -228,6 +228,7 @@ impl ProgressReporter for SubagentProgress {
                     task_id: self.task_id.clone(),
                     call_id: call_id.to_string(),
                     tool_name: tool_name.to_string(),
+                    arguments: arguments.clone(),
                     iteration,
                 },
             );
@@ -239,7 +240,7 @@ impl ProgressReporter for SubagentProgress {
         call_id: &str,
         tool_name: &str,
         success: bool,
-        output_chars: usize,
+        output: &str,
         elapsed_ms: u64,
         iteration: u32,
     ) {
@@ -252,7 +253,8 @@ impl ProgressReporter for SubagentProgress {
                     call_id: call_id.to_string(),
                     tool_name: tool_name.to_string(),
                     success,
-                    output_chars,
+                    output_chars: output.chars().count(),
+                    output: output.to_string(),
                     elapsed_ms,
                     iteration,
                 },
diff --git a/src/openhuman/agent/harness/engine/tools.rs b/src/openhuman/agent/harness/engine/tools.rs
index 9ed91893f..9e1a0ca3b 100644
--- a/src/openhuman/agent/harness/engine/tools.rs
+++ b/src/openhuman/agent/harness/engine/tools.rs
@@ -71,14 +71,14 @@ pub(crate) async fn run_one_tool(
     // (denied / CliRpcOnly / unknown) so the client row flips to `error`
     // instead of staying running.
     let emit_failed_completion = |message: &str| {
-        let output_chars = message.chars().count();
+        let message = message.to_string();
         async move {
             progress
                 .tool_completed(
                     progress_call_id,
                     &call.name,
                     false,
-                    output_chars,
+                    &message,
                     0,
                     iteration_u32,
                 )
@@ -361,7 +361,7 @@ pub(crate) async fn run_one_tool(
             progress_call_id,
             &call.name,
             success,
-            result_text.chars().count(),
+            &result_text,
             elapsed_ms,
             iteration_u32,
         )
diff --git a/src/openhuman/agent/harness/session/agent_tool_exec.rs b/src/openhuman/agent/harness/session/agent_tool_exec.rs
index 18480a8b9..b8f7bc8d7 100644
--- a/src/openhuman/agent/harness/session/agent_tool_exec.rs
+++ b/src/openhuman/agent/harness/session/agent_tool_exec.rs
@@ -279,7 +279,7 @@ pub(super) async fn run_agent_tool_call(
             &call_id,
             &call.name,
             success,
-            result.chars().count(),
+            &result,
             elapsed_ms,
             (iteration + 1) as u32,
         )
diff --git a/src/openhuman/agent/harness/subagent_runner/ops/tool_source.rs b/src/openhuman/agent/harness/subagent_runner/ops/tool_source.rs
index 09a5d7565..97c265e0f 100644
--- a/src/openhuman/agent/harness/subagent_runner/ops/tool_source.rs
+++ b/src/openhuman/agent/harness/subagent_runner/ops/tool_source.rs
@@ -86,14 +86,7 @@ impl super::super::super::engine::ToolSource for SubagentToolSource<'_> {
                 available.join(", ")
             );
             progress
-                .tool_completed(
-                    progress_call_id,
-                    &call.name,
-                    false,
-                    text.chars().count(),
-                    0,
-                    iteration_u32,
-                )
+                .tool_completed(progress_call_id, &call.name, false, &text, 0, iteration_u32)
                 .await;
             return super::super::super::engine::ToolRunResult {
                 text,
diff --git a/src/openhuman/agent/progress.rs b/src/openhuman/agent/progress.rs
index 754d7077e..1e1aee668 100644
--- a/src/openhuman/agent/progress.rs
+++ b/src/openhuman/agent/progress.rs
@@ -149,6 +149,10 @@ pub enum AgentProgress {
         task_id: String,
         call_id: String,
         tool_name: String,
+        /// Full arguments the child invoked the tool with, so the parent
+        /// thread's UI can show *what exactly* the sub-agent did (not just
+        /// the tool name). Mirrors the top-level `ToolCallStarted.arguments`.
+        arguments: serde_json::Value,
         /// 1-based child iteration index this call belongs to.
         iteration: u32,
     },
@@ -161,6 +165,10 @@ pub enum AgentProgress {
         tool_name: String,
         success: bool,
         output_chars: usize,
+        /// Full text the tool returned, so the UI can show the sub-agent's
+        /// actual result/output. `output_chars` is kept as a cheap size hint
+        /// for consumers that only want the length.
+        output: String,
         elapsed_ms: u64,
         /// 1-based child iteration index.
         iteration: u32,
diff --git a/src/openhuman/agent/progress_tracing/tests.rs b/src/openhuman/agent/progress_tracing/tests.rs
index a860b4139..8d9a2b599 100644
--- a/src/openhuman/agent/progress_tracing/tests.rs
+++ b/src/openhuman/agent/progress_tracing/tests.rs
@@ -265,6 +265,7 @@ fn subagent_lifecycle_nests_under_the_turn() {
                 task_id: "task-1".to_string(),
                 call_id: "sc-1".to_string(),
                 tool_name: "read_file".to_string(),
+                arguments: serde_json::Value::Null,
                 iteration: 1,
             },
             30,
@@ -277,6 +278,7 @@ fn subagent_lifecycle_nests_under_the_turn() {
                 tool_name: "read_file".to_string(),
                 success: true,
                 output_chars: 99,
+                output: "file contents".to_string(),
                 elapsed_ms: 40,
                 iteration: 1,
             },
diff --git a/src/openhuman/channels/providers/web/progress_bridge.rs b/src/openhuman/channels/providers/web/progress_bridge.rs
index 19de45351..4228bcb9b 100644
--- a/src/openhuman/channels/providers/web/progress_bridge.rs
+++ b/src/openhuman/channels/providers/web/progress_bridge.rs
@@ -15,6 +15,40 @@ fn unix_epoch_ms() -> u64 {
         .unwrap_or(0)
 }
 
+/// Upper bound on the sub-agent tool output forwarded to the drawer over
+/// Socket.IO. The `SubagentToolCallCompleted` event carries the *pre-handoff*
+/// tool result (the result-handoff path that stashes large toolkit payloads
+/// behind a short placeholder runs later, in `SubagentToolSource`), so a raw
+/// multi-MB integration result would otherwise ship in full to the socket /
+/// Redux / DOM. Cap it here on a UTF-8 boundary with a truncation marker so the
+/// drawer payload stays bounded while still showing what the tool returned.
+const MAX_WIRE_SUBAGENT_OUTPUT: usize = 256 * 1024;
+
+/// Bytes reserved within the cap for the truncation marker so the *final*
+/// payload (content + marker) never exceeds [`MAX_WIRE_SUBAGENT_OUTPUT`].
+/// Generous upper bound for `…[truncated <N> bytes of tool output]` at any
+/// plausible `N` (the "…" is 3 UTF-8 bytes).
+const TRUNCATION_MARKER_BUDGET: usize = 80;
+
+/// Truncate `output` so the returned string stays within
+/// [`MAX_WIRE_SUBAGENT_OUTPUT`] bytes, slicing on a char boundary and
+/// appending a marker (which is itself counted against the cap) when content
+/// was dropped. Returns the input unchanged when it's already within the cap.
+fn cap_wire_output(output: String) -> String {
+    if output.len() <= MAX_WIRE_SUBAGENT_OUTPUT {
+        return output;
+    }
+    let mut end = MAX_WIRE_SUBAGENT_OUTPUT.saturating_sub(TRUNCATION_MARKER_BUDGET);
+    while end > 0 && !output.is_char_boundary(end) {
+        end -= 1;
+    }
+    let omitted = output.len() - end;
+    format!(
+        "{}\n…[truncated {omitted} bytes of tool output]",
+        &output[..end]
+    )
+}
+
 pub(super) fn ledger_upsert_agent_run(
     config: &crate::openhuman::config::Config,
     upsert: crate::openhuman::session_db::run_ledger::AgentRunUpsert,
@@ -689,6 +723,7 @@ pub(crate) fn spawn_progress_bridge(
                     task_id,
                     call_id,
                     tool_name,
+                    arguments,
                     iteration,
                 } => {
                     let count = child_tool_counts.entry(task_id.clone()).or_insert(0);
@@ -721,6 +756,14 @@ pub(crate) fn spawn_progress_bridge(
                         request_id: request_id.clone(),
                         tool_name: Some(tool_name),
                         skill_id: Some(task_id.clone()),
+                        // The child's tool arguments, so the UI can show what
+                        // the sub-agent actually did (issue: subagent drawer
+                        // detail). Skipped from the wire when `null`.
+                        args: if arguments.is_null() {
+                            None
+                        } else {
+                            Some(arguments)
+                        },
                         round: Some(round),
                         tool_call_id: Some(call_id),
                         subagent: Some(SubagentProgressDetail {
@@ -739,6 +782,7 @@ pub(crate) fn spawn_progress_bridge(
                     tool_name,
                     success,
                     output_chars,
+                    output,
                     elapsed_ms,
                     iteration,
                 } => {
@@ -768,10 +812,11 @@ pub(crate) fn spawn_progress_bridge(
                         success: Some(success),
                         round: Some(round),
                         tool_call_id: Some(call_id),
-                        output: Some(
-                            json!({"output_chars": output_chars, "elapsed_ms": elapsed_ms})
-                                .to_string(),
-                        ),
+                        // The child's actual tool output, so the drawer can show
+                        // *what came back* (not just a char count). Capped to a
+                        // bounded size for the wire (#4007); `output_chars` +
+                        // `elapsed_ms` still ride along in `subagent` below.
+                        output: Some(cap_wire_output(output)),
                         subagent: Some(SubagentProgressDetail {
                             child_iteration: Some(iteration),
                             agent_id: Some(agent_id),
@@ -1027,6 +1072,26 @@ pub(crate) fn spawn_progress_bridge(
 mod tests {
     use super::*;
 
+    #[test]
+    fn cap_wire_output_passes_through_small_payloads() {
+        let s = "small tool result".to_string();
+        assert_eq!(cap_wire_output(s.clone()), s);
+    }
+
+    #[test]
+    fn cap_wire_output_truncates_large_payloads_on_char_boundary() {
+        // A multibyte payload past the cap: result stays valid UTF-8, is shorter
+        // than the input, and carries the truncation marker.
+        let big = "é".repeat(MAX_WIRE_SUBAGENT_OUTPUT); // 2 bytes each → well over cap
+        let capped = cap_wire_output(big.clone());
+        assert!(capped.len() < big.len());
+        assert!(capped.contains("[truncated"));
+        // Truncation landed on a char boundary (no replacement char / panic).
+        assert!(capped.starts_with('é'));
+        // The final payload (content + marker) must honor the wire cap.
+        assert!(capped.len() <= MAX_WIRE_SUBAGENT_OUTPUT);
+    }
+
     #[test]
     fn worktree_detail_collapses_empty_changed_files_to_none() {
         // Non-isolated / clean worker: empty list → `None` so the renderer
diff --git a/src/openhuman/threads/turn_state/mirror_tests.rs b/src/openhuman/threads/turn_state/mirror_tests.rs
index b02b32404..9aa9b7843 100644
--- a/src/openhuman/threads/turn_state/mirror_tests.rs
+++ b/src/openhuman/threads/turn_state/mirror_tests.rs
@@ -238,6 +238,7 @@ fn subagent_lifecycle_records_and_clears_active() {
         task_id: "sub-1".into(),
         call_id: "ctc-1".into(),
         tool_name: "search".into(),
+        arguments: serde_json::Value::Null,
         iteration: 1,
     });
     let activity = m.snapshot().tool_timeline[0]
diff --git a/tests/memory_threads_raw_coverage_e2e.rs b/tests/memory_threads_raw_coverage_e2e.rs
index 9a51d8fe0..394a92138 100644
--- a/tests/memory_threads_raw_coverage_e2e.rs
+++ b/tests/memory_threads_raw_coverage_e2e.rs
@@ -3179,6 +3179,7 @@ fn turn_state_mirror_persists_progress_edges_from_public_events() {
         task_id: "task-1".into(),
         call_id: "child-call".into(),
         tool_name: "memory.read".into(),
+        arguments: serde_json::Value::Null,
         iteration: 1,
     }));
     assert!(!mirror.observe(&AgentProgress::SubagentToolCallCompleted {
@@ -3188,6 +3189,7 @@ fn turn_state_mirror_persists_progress_edges_from_public_events() {
         tool_name: "memory.read".into(),
         success: true,
         output_chars: 44,
+        output: "child tool output".into(),
         elapsed_ms: 22,
         iteration: 1,
     }));