Fix BorderedLoader to pass theme to DynamicBorder

BorderedLoader receives theme as a parameter but was creating
DynamicBorder() without passing it, causing DynamicBorder to
fall back to the global theme variable which is undefined when
loaded via jiti (separate module cache).

Added doc comment to DynamicBorder explaining the jiti issue.

packages/coding-agent/src/modes/interactive/components/dynamic-border.ts

@@ -2,15 +2,17 @@ import type { Component } from "@mariozechner/pi-tui";
 import { theme } from "../theme/theme.js";
 
 /**
- * Dynamic border component that adjusts to viewport width
+ * Dynamic border component that adjusts to viewport width.
+ *
+ * Note: When used from hooks loaded via jiti, the global `theme` may be undefined
+ * because jiti creates a separate module cache. Always pass an explicit color
+ * function when using DynamicBorder in components exported for hook use.
  */
 export class DynamicBorder implements Component {
 	private color: (str: string) => string;
 
-	constructor(color?: (str: string) => string) {
-		// Use provided color function, or default to theme border color
-		// Theme may not be initialized at construction time, so we check at render time
-		this.color = color ?? ((str) => (theme ? theme.fg("border", str) : str));
+	constructor(color: (str: string) => string = (str) => theme.fg("border", str)) {
+		this.color = color;
 	}
 
 	invalidate(): void {