fix(coding-agent): warn on Anthropic subscription auth

packages/coding-agent/src/modes/interactive/interactive-mode.ts

@@ -129,6 +129,13 @@ type CompactionQueuedMessage = {
 	mode: "steer" | "followUp";
 };
 
+const ANTHROPIC_SUBSCRIPTION_AUTH_WARNING =
+	"Anthropic subscription auth is active. Third-party usage now draws from extra usage and is billed per token, not your Claude plan limits. Manage extra usage at https://claude.ai/settings/usage.";
+
+function isAnthropicSubscriptionAuthKey(apiKey: string | undefined): boolean {
+	return typeof apiKey === "string" && apiKey.startsWith("sk-ant-oat");
+}
+
 /**
  * Options for InteractiveMode initialization.
  */
@@ -175,6 +182,7 @@ export class InteractiveMode {
 	private lastEscapeTime = 0;
 	private changelogMarkdown: string | undefined = undefined;
 	private startupNoticesShown = false;
+	private anthropicSubscriptionWarningShown = false;
 
 	// Status line tracking (for mutating immediately-sequential status updates)
 	private lastStatusSpacer: Spacer | undefined = undefined;
@@ -431,7 +439,7 @@ export class InteractiveMode {
 
 	private shouldShowEarendilAnnouncement(): boolean {
 		const now = new Date();
-		return now.getFullYear() === 2026 && now.getMonth() === 3 && now.getDate() === 8;
+		return now.getFullYear() === 2026 && now.getMonth() === 3 && (now.getDate() === 8 || now.getDate() === 9);
 	}
 
 	private showStartupNoticesIfNeeded(): void {
@@ -631,6 +639,8 @@ export class InteractiveMode {
 			this.showWarning(modelFallbackMessage);
 		}
 
+		void this.maybeWarnAboutAnthropicSubscriptionAuth();
+
 		// Process initial messages
 		if (initialMessage) {
 			try {
@@ -2980,6 +2990,7 @@ export class InteractiveMode {
 				const thinkingStr =
 					result.model.reasoning && result.thinkingLevel !== "off" ? ` (thinking: ${result.thinkingLevel})` : "";
 				this.showStatus(`Switched to ${result.model.name || result.model.id}${thinkingStr}`);
+				void this.maybeWarnAboutAnthropicSubscriptionAuth(result.model);
 			}
 		} catch (error) {
 			this.showError(error instanceof Error ? error.message : String(error));
@@ -3476,6 +3487,7 @@ export class InteractiveMode {
 				this.footer.invalidate();
 				this.updateEditorBorderColor();
 				this.showStatus(`Model: ${model.id}`);
+				void this.maybeWarnAboutAnthropicSubscriptionAuth(model);
 				this.checkDaxnutsEasterEgg(model);
 			} catch (error) {
 				this.showError(error instanceof Error ? error.message : String(error));
@@ -3511,6 +3523,35 @@ export class InteractiveMode {
 		this.footerDataProvider.setAvailableProviderCount(uniqueProviders.size);
 	}
 
+	private async maybeWarnAboutAnthropicSubscriptionAuth(
+		model: Model<any> | undefined = this.session.model,
+	): Promise<void> {
+		if (this.anthropicSubscriptionWarningShown) {
+			return;
+		}
+		if (!model || model.provider !== "anthropic") {
+			return;
+		}
+
+		const storedCredential = this.session.modelRegistry.authStorage.get("anthropic");
+		if (storedCredential?.type === "oauth") {
+			this.anthropicSubscriptionWarningShown = true;
+			this.showWarning(ANTHROPIC_SUBSCRIPTION_AUTH_WARNING);
+			return;
+		}
+
+		try {
+			const apiKey = await this.session.modelRegistry.getApiKeyForProvider(model.provider);
+			if (!isAnthropicSubscriptionAuthKey(apiKey)) {
+				return;
+			}
+			this.anthropicSubscriptionWarningShown = true;
+			this.showWarning(ANTHROPIC_SUBSCRIPTION_AUTH_WARNING);
+		} catch {
+			// Ignore auth lookup failures for warning-only checks.
+		}
+	}
+
 	private showModelSelector(initialSearchInput?: string): void {
 		this.showSelector((done) => {
 			const selector = new ModelSelectorComponent(
@@ -3526,6 +3567,7 @@ export class InteractiveMode {
 						this.updateEditorBorderColor();
 						done();
 						this.showStatus(`Model: ${model.id}`);
+						void this.maybeWarnAboutAnthropicSubscriptionAuth(model);
 						this.checkDaxnutsEasterEgg(model);
 					} catch (error) {
 						done();