fix: USE_MAGICK build flag - use define instead of bun:bundle

The bun:bundle module only exists at bundle time, not when running source
directly (dev/tests). This caused CI failures with:
  error: Cannot find package 'bundle'

Fix: Use Bun.build's define option to set __USE_MAGICK__ as a compile-time
constant. At dev/test time it's undefined (defaults to false/sharp).
At build time it's set based on USE_MAGICK env var.

👾 Generated with [Letta Code](https://letta.com)

Co-Authored-By: Letta <noreply@letta.com>

build.js

@@ -39,6 +39,7 @@ await Bun.build({
   define: {
     LETTA_VERSION: JSON.stringify(version),
     BUILD_TIME: JSON.stringify(new Date().toISOString()),
+    __USE_MAGICK__: useMagick ? "true" : "false",
   },
   // Load text files as strings (for markdown, etc.)
   loader: {

src/cli/helpers/imageResize.ts

@@ -1,6 +1,5 @@
 // Image resizing utilities for clipboard paste
 // Follows Codex CLI's approach (codex-rs/utils/image/src/lib.rs)
-import { feature } from "bun:bundle";
 
 export const MAX_IMAGE_WIDTH = 2000;
 export const MAX_IMAGE_HEIGHT = 2000;
@@ -14,7 +13,15 @@ export interface ResizeResult {
   resized: boolean;
 }
 
-// Import the correct implementation based on feature flag
-export const resizeImageIfNeeded = feature("USE_MAGICK")
+// Build-time constant for magick variant (set via Bun.build define when USE_MAGICK=1)
+// At dev/test time this is undefined, at build time it's true/false
+declare const __USE_MAGICK__: boolean | undefined;
+
+// Use magick implementation only when explicitly built with USE_MAGICK=1
+// typeof check handles dev/test case where __USE_MAGICK__ doesn't exist
+const useMagick =
+  typeof __USE_MAGICK__ !== "undefined" && __USE_MAGICK__ === true;
+
+export const resizeImageIfNeeded = useMagick
   ? (await import("./imageResize.magick.js")).resizeImageIfNeeded
   : (await import("./imageResize.sharp.js")).resizeImageIfNeeded;