feat(hooks): add setWidget API for multi-line status displays

- ctx.ui.setWidget(key, lines) for multi-line displays above editor
- Widgets appear below 'Working...' indicator, above editor
- Supports ANSI styling including strikethrough
- Added theme.strikethrough() method
- Plan-mode hook now shows todo list with checkboxes
- Completed items show checked box and strikethrough text

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

@@ -131,6 +131,17 @@ export async function runRpcMode(session: AgentSession): Promise<never> {
 			} as RpcHookUIRequest);
 		},
 
+		setWidget(key: string, lines: string[] | undefined): void {
+			// Fire and forget - host can implement widget display
+			output({
+				type: "hook_ui_request",
+				id: crypto.randomUUID(),
+				method: "setWidget",
+				widgetKey: key,
+				widgetLines: lines,
+			} as RpcHookUIRequest);
+		},
+
 		async custom() {
 			// Custom UI not supported in RPC mode
 			return undefined as never;

packages/coding-agent/src/modes/rpc/rpc-types.ts

@@ -189,6 +189,13 @@ export type RpcHookUIRequest =
 			notifyType?: "info" | "warning" | "error";
 	  }
 	| { type: "hook_ui_request"; id: string; method: "setStatus"; statusKey: string; statusText: string | undefined }
+	| {
+			type: "hook_ui_request";
+			id: string;
+			method: "setWidget";
+			widgetKey: string;
+			widgetLines: string[] | undefined;
+	  }
 	| { type: "hook_ui_request"; id: string; method: "set_editor_text"; text: string };
 
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