feat(chat): open cost modal from token usage

src/components/chat/hooks/useChatComposerState.ts

@@ -311,7 +311,7 @@ export function useChatComposerState({
   }, [addMessage]);
 
   const executeCommand = useCallback(
-    async (command: SlashCommand, rawInput?: string) => {
+    async (command: SlashCommand, rawInput?: string, options?: { preserveInput?: boolean }) => {
       if (!command || !selectedProject) {
         return;
       }
@@ -368,8 +368,10 @@ export function useChatComposerState({
         const result = (await response.json()) as CommandExecutionResult;
         if (result.type === 'builtin') {
           handleBuiltInCommand(result);
-          setInput('');
-          inputValueRef.current = '';
+          if (!options?.preserveInput) {
+            setInput('');
+            inputValueRef.current = '';
+          }
         } else if (result.type === 'custom') {
           await handleCustomCommand(result);
         }
@@ -400,6 +402,19 @@ export function useChatComposerState({
     ],
   );
 
+  const showCostModal = useCallback(() => {
+    executeCommand(
+      {
+        name: '/cost',
+        description: 'Display token usage information',
+        namespace: 'builtin',
+        metadata: { type: 'builtin' },
+      } as SlashCommand,
+      '/cost',
+      { preserveInput: true },
+    );
+  }, [executeCommand]);
+
   const {
     slashCommands,
     slashCommandsCount,
@@ -1049,5 +1064,6 @@ export function useChatComposerState({
     isInputFocused,
     commandModalPayload,
     closeCommandModal,
+    showCostModal,
   };
 }

src/components/chat/view/ChatInterface.tsx

@@ -178,6 +178,7 @@ function ChatInterface({
     isInputFocused: _isInputFocused,
     commandModalPayload,
     closeCommandModal,
+    showCostModal,
   } = useChatComposerState({
     selectedProject,
     selectedSession,
@@ -368,6 +369,7 @@ function ChatInterface({
           permissionMode={permissionMode}
           onModeSwitch={cyclePermissionMode}
           tokenBudget={tokenBudget}
+          onShowTokenUsage={showCostModal}
           slashCommandsCount={slashCommandsCount}
           onToggleCommandMenu={handleToggleCommandMenu}
           hasInput={Boolean(input.trim())}

src/components/chat/view/subcomponents/ChatComposer.tsx

@@ -58,6 +58,7 @@ interface ChatComposerProps {
   permissionMode: PermissionMode | string;
   onModeSwitch: () => void;
   tokenBudget: Record<string, unknown> | null;
+  onShowTokenUsage: () => void;
   slashCommandsCount: number;
   onToggleCommandMenu: () => void;
   hasInput: boolean;
@@ -111,6 +112,7 @@ export default function ChatComposer({
   permissionMode,
   onModeSwitch,
   tokenBudget,
+  onShowTokenUsage,
   slashCommandsCount,
   onToggleCommandMenu,
   hasInput,
@@ -353,7 +355,7 @@ export default function ChatComposer({
               </div>
             </button>
 
-            <TokenUsageSummary usage={tokenBudget} />
+            <TokenUsageSummary usage={tokenBudget} onClick={onShowTokenUsage} />
 
             <PromptInputButton
               tooltip={{ content: t('input.showAllCommands') }}

src/components/chat/view/subcomponents/TokenUsageSummary.tsx

@@ -2,6 +2,7 @@ import { ActivityIcon } from 'lucide-react';
 
 type TokenUsageSummaryProps = {
   usage: Record<string, unknown> | null;
+  onClick?: () => void;
 };
 
 const formatTokenCount = (value: number) => {
@@ -29,7 +30,7 @@ const readUsageNumber = (value: unknown) => {
   return Number.isFinite(parsed) ? parsed : 0;
 };
 
-export default function TokenUsageSummary({ usage }: TokenUsageSummaryProps) {
+export default function TokenUsageSummary({ usage, onClick }: TokenUsageSummaryProps) {
   const breakdown =
     usage?.breakdown && typeof usage.breakdown === 'object'
       ? usage.breakdown as Record<string, unknown>
@@ -39,15 +40,18 @@ export default function TokenUsageSummary({ usage }: TokenUsageSummaryProps) {
   const usedTokens = readUsageNumber(usage?.used) || inputTokens + outputTokens;
 
   return (
-    <div
-      className="inline-flex h-9 items-center gap-1.5 rounded-lg border border-border/70 bg-background/70 px-2 text-xs text-muted-foreground shadow-sm transition-colors hover:border-primary/25 hover:text-foreground sm:gap-2 sm:px-2.5"
+    <button
+      type="button"
+      onClick={onClick}
+      className="inline-flex h-9 items-center gap-1.5 rounded-lg border border-border/70 bg-background/70 px-2 text-xs text-muted-foreground shadow-sm transition-colors hover:border-primary/25 hover:text-foreground focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 sm:gap-2 sm:px-2.5"
       title={`${usedTokens.toLocaleString()} tokens used`}
+      aria-label="Show token usage"
     >
       <span className="grid h-5 w-5 place-items-center rounded-md bg-primary/10 text-primary">
         <ActivityIcon className="h-3.5 w-3.5" />
       </span>
       <span className="font-medium text-foreground">{formatTokenCount(usedTokens)}</span>
       <span className="hidden text-muted-foreground/70 sm:inline">tokens</span>
-    </div>
+    </button>
   );
 }