feat(code): add context usage indicator

apps/code/src/renderer/features/message-editor/components/ContextUsageIndicator.tsx

@@ -0,0 +1,41 @@
+import { Text, Tooltip } from "@radix-ui/themes";
+import { useContextUsageForTask } from "@renderer/features/sessions/hooks/useSession";
+
+const CONTEXT_WARNING_THRESHOLD_PCT = 40;
+
+interface ContextUsageIndicatorProps {
+  taskId?: string;
+}
+
+export function ContextUsageIndicator({ taskId }: ContextUsageIndicatorProps) {
+  const contextUsage = useContextUsageForTask(taskId);
+  if (!contextUsage || contextUsage.size <= 0) return null;
+
+  const percent = Math.round((contextUsage.used / contextUsage.size) * 100);
+
+  if (percent < CONTEXT_WARNING_THRESHOLD_PCT) return null;
+
+  return (
+    <Tooltip
+      content={`Context: ${percent}% used (${Math.round(contextUsage.used / 1000)}k / ${Math.round(contextUsage.size / 1000)}k tokens)`}
+    >
+      <Text
+        size="1"
+        style={{
+          color: getContextColor(percent),
+          fontFamily: "var(--font-mono)",
+          padding: "4px 10px",
+          cursor: "default",
+        }}
+      >
+        {percent}%
+      </Text>
+    </Tooltip>
+  );
+}
+
+function getContextColor(percent: number): string {
+  if (percent >= 80) return "var(--red-9)";
+  if (percent >= 50) return "var(--yellow-11)";
+  return "var(--green-9)";
+}

apps/code/src/renderer/features/message-editor/components/EditorToolbar.tsx

@@ -3,6 +3,7 @@ import { Paperclip } from "@phosphor-icons/react";
 import { Flex, IconButton, Tooltip } from "@radix-ui/themes";
 import { useRef } from "react";
 import type { FileAttachment } from "../utils/content";
+import { ContextUsageIndicator } from "./ContextUsageIndicator";
 
 interface EditorToolbarProps {
   disabled?: boolean;
@@ -69,6 +70,7 @@ export function EditorToolbar({
       {!hideSelectors && (
         <ModelSelector taskId={taskId} adapter={adapter} disabled={disabled} />
       )}
+      <ContextUsageIndicator taskId={taskId} />
     </Flex>
   );
 }

apps/code/src/renderer/features/sessions/hooks/useSession.ts

@@ -147,6 +147,25 @@ export const useThoughtLevelConfigOptionForTask = (
   return useConfigOptionForTask(taskId, "thought_level");
 };
 
+/** Get context window usage for a task (used / size) */
+export const useContextUsageForTask = (
+  taskId: string | undefined,
+): { used: number; size: number } | undefined => {
+  return useSessionStore((s) => {
+    if (!taskId) return undefined;
+    const taskRunId = s.taskIdIndex[taskId];
+    if (!taskRunId) return undefined;
+    const session = s.sessions[taskRunId];
+    if (
+      session?.contextUsed === undefined ||
+      session?.contextSize === undefined
+    ) {
+      return undefined;
+    }
+    return { used: session.contextUsed, size: session.contextSize };
+  });
+};
+
 /** Get the adapter type for a task */
 export const useAdapterForTask = (
   taskId: string | undefined,

apps/code/src/renderer/features/sessions/service/service.ts

@@ -911,6 +911,23 @@ export class SessionService {
         setPersistedConfigOptions(taskRunId, configOptions);
         log.info("Session config options updated", { taskRunId });
       }
+
+      // Handle context usage updates
+      if (params?.update?.sessionUpdate === "usage_update") {
+        const update = params.update as {
+          used?: number;
+          size?: number;
+        };
+        if (
+          typeof update.used === "number" &&
+          typeof update.size === "number"
+        ) {
+          sessionStoreSetters.updateSession(taskRunId, {
+            contextUsed: update.used,
+            contextSize: update.size,
+          });
+        }
+      }
     }
 
     // Handle _posthog/sdk_session notifications for adapter info

apps/code/src/renderer/features/sessions/stores/sessionStore.ts

@@ -73,6 +73,10 @@ export interface AgentSession {
   /** Number of session/prompt events to skip from polled logs (set during resume) */
   skipPolledPromptCount?: number;
   optimisticItems: OptimisticItem[];
+  /** Context window tokens used (from usage_update) */
+  contextUsed?: number;
+  /** Context window total size in tokens (from usage_update) */
+  contextSize?: number;
 }
 
 // --- Config Option Helpers ---

packages/agent/src/adapters/claude/claude-agent.ts

@@ -346,6 +346,11 @@ export class ClaudeAcpAgent extends BaseAcpAgent {
                 ? Math.min(...contextWindows)
                 : getDefaultContextWindow(this.session.modelId ?? "");
 
+            this.session.contextSize = contextWindowSize;
+            if (lastAssistantTotalUsage !== null) {
+              this.session.contextUsed = lastAssistantTotalUsage;
+            }
+
             // Send usage_update notification
             if (lastAssistantTotalUsage !== null) {
               await this.client.sessionUpdate({

packages/agent/src/adapters/claude/types.ts

@@ -53,6 +53,10 @@ export type Session = BaseSession & {
   effort?: EffortLevel;
   configOptions: SessionConfigOption[];
   accumulatedUsage: AccumulatedUsage;
+  /** Latest context window usage (total tokens from last assistant message) */
+  contextUsed?: number;
+  /** Context window size in tokens */
+  contextSize?: number;
   promptRunning: boolean;
   pendingMessages: Map<string, PendingMessage>;
   nextPendingOrder: number;