diff --git a/build.ts b/build.ts
index 85b2b20..e63498c 100644
--- a/build.ts
+++ b/build.ts
@@ -1,5 +1,6 @@
 import { readdir, readFile, writeFile } from "fs/promises";
 import { join } from "path";
+import { getMacroDefines } from "./scripts/defines.ts";
 
 const outdir = "dist";
 
@@ -13,6 +14,7 @@ const result = await Bun.build({
     outdir,
     target: "bun",
     splitting: true,
+    define: getMacroDefines(),
 });
 
 if (!result.success) {
diff --git a/package.json b/package.json
index 8ed6f2d..feba267 100644
--- a/package.json
+++ b/package.json
@@ -36,7 +36,7 @@
   ],
   "scripts": {
     "build": "bun run build.ts",
-    "dev": "bun run src/entrypoints/cli.tsx",
+    "dev": "bun run scripts/dev.ts",
     "prepublishOnly": "bun run build",
     "lint": "biome lint src/",
     "lint:fix": "biome lint --fix src/",
diff --git a/scripts/defines.ts b/scripts/defines.ts
new file mode 100644
index 0000000..33ed2b5
--- /dev/null
+++ b/scripts/defines.ts
@@ -0,0 +1,18 @@
+/**
+ * Shared MACRO define map used by both dev.ts (runtime -d flags)
+ * and build.ts (Bun.build define option).
+ *
+ * Each value is a JSON-stringified expression that replaces the
+ * corresponding MACRO.* identifier at transpile / bundle time.
+ */
+export function getMacroDefines(): Record<string, string> {
+    return {
+        "MACRO.VERSION": JSON.stringify("2.1.888"),
+        "MACRO.BUILD_TIME": JSON.stringify(new Date().toISOString()),
+        "MACRO.FEEDBACK_CHANNEL": JSON.stringify(""),
+        "MACRO.ISSUES_EXPLAINER": JSON.stringify(""),
+        "MACRO.NATIVE_PACKAGE_URL": JSON.stringify(""),
+        "MACRO.PACKAGE_URL": JSON.stringify(""),
+        "MACRO.VERSION_CHANGELOG": JSON.stringify(""),
+    };
+}
diff --git a/scripts/dev.ts b/scripts/dev.ts
new file mode 100644
index 0000000..5a9ec8f
--- /dev/null
+++ b/scripts/dev.ts
@@ -0,0 +1,21 @@
+#!/usr/bin/env bun
+/**
+ * Dev entrypoint — launches cli.tsx with MACRO.* defines injected
+ * via Bun's -d flag (bunfig.toml [define] doesn't propagate to
+ * dynamically imported modules at runtime).
+ */
+import { getMacroDefines } from "./defines.ts";
+
+const defines = getMacroDefines();
+
+const defineArgs = Object.entries(defines).flatMap(([k, v]) => [
+    "-d",
+    `${k}:${v}`,
+]);
+
+const result = Bun.spawnSync(
+    ["bun", "run", ...defineArgs, "src/entrypoints/cli.tsx", ...process.argv.slice(2)],
+    { stdio: ["inherit", "inherit", "inherit"] },
+);
+
+process.exit(result.exitCode ?? 0);
diff --git a/src/entrypoints/cli.tsx b/src/entrypoints/cli.tsx
index 2a008c5..0ee6ff3 100644
--- a/src/entrypoints/cli.tsx
+++ b/src/entrypoints/cli.tsx
@@ -1,21 +1,5 @@
 #!/usr/bin/env bun
-// Runtime polyfill for bun:bundle (build-time macros)
-const feature = (_name: string) => false;
-if (typeof globalThis.MACRO === "undefined") {
-    (globalThis as any).MACRO = {
-        VERSION: "2.1.888",
-        BUILD_TIME: new Date().toISOString(),
-        FEEDBACK_CHANNEL: "",
-        ISSUES_EXPLAINER: "",
-        NATIVE_PACKAGE_URL: "",
-        PACKAGE_URL: "",
-        VERSION_CHANGELOG: "",
-    };
-}
-// Build-time constants — normally replaced by Bun bundler at compile time
-(globalThis as any).BUILD_TARGET = "external";
-(globalThis as any).BUILD_ENV = "production";
-(globalThis as any).INTERFACE_TYPE = "stdio";
+import { feature } from 'bun:bundle'
 
 // Bugfix for corepack auto-pinning, which adds yarnpkg to peoples' package.jsons
 // eslint-disable-next-line custom-rules/no-top-level-side-effects
diff --git a/src/types/global.d.ts b/src/types/global.d.ts
index ceb2f55..bff3970 100644
--- a/src/types/global.d.ts
+++ b/src/types/global.d.ts
@@ -4,9 +4,8 @@
  */
 
 // ============================================================================
-// MACRO — Bun compile-time macro function (from bun:bundle)
-// Expands the function body at build time and removes the call in production.
-// Also supports property access like MACRO.VERSION (compile-time constants).
+// MACRO — Bun compile-time constants injected via bunfig.toml [define] (dev)
+// and Bun.build({ define }) (production). See bunfig.toml & build.ts.
 declare namespace MACRO {
   export const VERSION: string
   export const BUILD_TIME: string
@@ -16,7 +15,6 @@ declare namespace MACRO {
   export const PACKAGE_URL: string
   export const VERSION_CHANGELOG: string
 }
-declare function MACRO<T>(fn: () => T): T
 
 // ============================================================================
 // Internal Anthropic-only identifiers (dead-code eliminated in open-source)
@@ -62,11 +60,7 @@ declare type T = unknown
 declare function TungstenPill(props?: { key?: string; selected?: boolean }): JSX.Element | null
 
 // ============================================================================
-// Build-time constants — replaced by Bun bundler, polyfilled at runtime
-// Using `string` (not literal types) so comparisons don't produce TS2367
-declare const BUILD_TARGET: string
-declare const BUILD_ENV: string
-declare const INTERFACE_TYPE: string
+// Build-time constants BUILD_TARGET/BUILD_ENV/INTERFACE_TYPE — removed (zero runtime usage)
 
 // ============================================================================
 // Ink custom JSX intrinsic elements — see src/types/ink-jsx.d.ts
diff --git a/src/types/internal-modules.d.ts b/src/types/internal-modules.d.ts
index bf1d214..95ff7a0 100644
--- a/src/types/internal-modules.d.ts
+++ b/src/types/internal-modules.d.ts
@@ -9,7 +9,6 @@
 // ============================================================================
 declare module "bun:bundle" {
     export function feature(name: string): boolean;
-    export function MACRO<T>(fn: () => T): T;
 }
 
 declare module "bun:ffi" {