diff --git a/sdks/cli-shared/package.json b/sdks/cli-shared/package.json
index 896c536..35e005d 100644
--- a/sdks/cli-shared/package.json
+++ b/sdks/cli-shared/package.json
@@ -15,7 +15,7 @@
   "exports": {
     ".": {
       "types": "./dist/index.d.ts",
-      "import": "./dist/index.mjs",
+      "import": "./dist/index.js",
       "require": "./dist/index.cjs"
     }
   },
diff --git a/sdks/cli-shared/src/index.ts b/sdks/cli-shared/src/index.ts
index 3696364..da2773f 100644
--- a/sdks/cli-shared/src/index.ts
+++ b/sdks/cli-shared/src/index.ts
@@ -10,18 +10,54 @@ export type NonExecutableBinaryMessageOptions = {
 	genericInstallCommands?: string[];
 };
 
+export type FsSubset = {
+	accessSync: (path: string, mode?: number) => void;
+	chmodSync: (path: string, mode: number) => void;
+	constants: { X_OK: number };
+};
+
 export function isBunRuntime(): boolean {
-  if (typeof process?.versions?.bun === "string") return true;
-  const userAgent = process?.env?.npm_config_user_agent || "";
-  return userAgent.includes("bun/");
+	if (typeof process?.versions?.bun === "string") return true;
+	const userAgent = process?.env?.npm_config_user_agent || "";
+	return userAgent.includes("bun/");
 }
 
 const PERMISSION_ERRORS = new Set(["EACCES", "EPERM", "ENOEXEC"]);
 
-export function isPermissionError(error: unknown): boolean {
-  if (!error || typeof error !== "object") return false;
-  const code = (error as { code?: unknown }).code;
-  return typeof code === "string" && PERMISSION_ERRORS.has(code);
+function isPermissionError(error: unknown): boolean {
+	if (!error || typeof error !== "object") return false;
+	const code = (error as { code?: unknown }).code;
+	return typeof code === "string" && PERMISSION_ERRORS.has(code);
+}
+
+/**
+ * Checks if a binary is executable and attempts to make it executable if not.
+ * Returns true if the binary is (or was made) executable, false if it couldn't
+ * be made executable due to permission errors. Throws for other errors.
+ *
+ * Requires fs to be passed in to avoid static imports that break browser builds.
+ */
+export function assertExecutable(binPath: string, fs: FsSubset): boolean {
+	if (process.platform === "win32") {
+		return true;
+	}
+
+	try {
+		fs.accessSync(binPath, fs.constants.X_OK);
+		return true;
+	} catch {
+		// Not executable, try to fix
+	}
+
+	try {
+		fs.chmodSync(binPath, 0o755);
+		return true;
+	} catch (error) {
+		if (isPermissionError(error)) {
+			return false;
+		}
+		throw error;
+	}
 }
 
 export function formatNonExecutableBinaryMessage(
diff --git a/sdks/cli/bin/sandbox-agent b/sdks/cli/bin/sandbox-agent
index 93cac38..66c1aac 100755
--- a/sdks/cli/bin/sandbox-agent
+++ b/sdks/cli/bin/sandbox-agent
@@ -1,8 +1,8 @@
 #!/usr/bin/env node
 const { execFileSync } = require("child_process");
 const {
+  assertExecutable,
   formatNonExecutableBinaryMessage,
-  isPermissionError,
 } = require("@sandbox-agent/cli-shared");
 const fs = require("fs");
 const path = require("path");
@@ -10,29 +10,27 @@ const path = require("path");
 const TRUST_PACKAGES =
   "@sandbox-agent/cli-linux-x64 @sandbox-agent/cli-darwin-arm64 @sandbox-agent/cli-darwin-x64 @sandbox-agent/cli-win32-x64";
 
-function printExecutableHint(binPath) {
-  console.error(
-    formatNonExecutableBinaryMessage({
-      binPath,
-      trustPackages: TRUST_PACKAGES,
-      bunInstallBlocks: [
-        {
-          label: "Project install",
-          commands: [
-            `bun pm trust ${TRUST_PACKAGES}`,
-            "bun add @sandbox-agent/cli",
-          ],
-        },
-        {
-          label: "Global install",
-          commands: [
-            `bun pm -g trust ${TRUST_PACKAGES}`,
-            "bun add -g @sandbox-agent/cli",
-          ],
-        },
-      ],
-    }),
-  );
+function formatHint(binPath) {
+  return formatNonExecutableBinaryMessage({
+    binPath,
+    trustPackages: TRUST_PACKAGES,
+    bunInstallBlocks: [
+      {
+        label: "Project install",
+        commands: [
+          `bun pm trust ${TRUST_PACKAGES}`,
+          "bun add @sandbox-agent/cli",
+        ],
+      },
+      {
+        label: "Global install",
+        commands: [
+          `bun pm -g trust ${TRUST_PACKAGES}`,
+          "bun add -g @sandbox-agent/cli",
+        ],
+      },
+    ],
+  });
 }
 
 const PLATFORMS = {
@@ -53,29 +51,13 @@ try {
   const pkgPath = require.resolve(`${pkg}/package.json`);
   const bin = process.platform === "win32" ? "sandbox-agent.exe" : "sandbox-agent";
   const binPath = path.join(path.dirname(pkgPath), "bin", bin);
-  if (process.platform !== "win32") {
-    try {
-      fs.accessSync(binPath, fs.constants.X_OK);
-    } catch (error) {
-      try {
-        fs.chmodSync(binPath, 0o755);
-      } catch (chmodError) {
-        if (isPermissionError(chmodError)) {
-          printExecutableHint(binPath);
-        }
-        console.error(`Failed to make ${binPath} executable.`);
-        throw chmodError;
-      }
-    }
-  }
-  try {
-    execFileSync(binPath, process.argv.slice(2), { stdio: "inherit" });
-  } catch (execError) {
-    if (isPermissionError(execError)) {
-      printExecutableHint(binPath);
-    }
-    throw execError;
+
+  if (!assertExecutable(binPath, fs)) {
+    console.error(formatHint(binPath));
+    process.exit(1);
   }
+
+  execFileSync(binPath, process.argv.slice(2), { stdio: "inherit" });
 } catch (e) {
   if (e.status !== undefined) process.exit(e.status);
   throw e;
diff --git a/sdks/typescript/src/spawn.ts b/sdks/typescript/src/spawn.ts
index c879786..6323e08 100644
--- a/sdks/typescript/src/spawn.ts
+++ b/sdks/typescript/src/spawn.ts
@@ -1,8 +1,8 @@
 import type { ChildProcess } from "node:child_process";
 import type { AddressInfo } from "node:net";
 import {
+  assertExecutable,
   formatNonExecutableBinaryMessage,
-  isPermissionError,
 } from "@sandbox-agent/cli-shared";
 
 export type SandboxAgentSpawnLogMode = "inherit" | "pipe" | "silent";
@@ -73,29 +73,29 @@ export async function spawnSandboxAgent(
     throw new Error("sandbox-agent binary not found. Install @sandbox-agent/cli or set SANDBOX_AGENT_BIN.");
   }
 
-  if (process.platform !== "win32") {
-    try {
-      fs.accessSync(binaryPath, fs.constants.X_OK);
-    } catch (error) {
-      if (isPermissionError(error)) {
-        throw new Error(
-          formatNonExecutableBinaryMessage({
-            binPath: binaryPath,
-            trustPackages: TRUST_PACKAGES,
-            bunInstallBlocks: [
-              {
-                label: "Project install",
-                commands: [
-                  `bun pm trust ${TRUST_PACKAGES}`,
-                  "bun add sandbox-agent",
-                ],
-              },
+  if (!assertExecutable(binaryPath, fs)) {
+    throw new Error(
+      formatNonExecutableBinaryMessage({
+        binPath: binaryPath,
+        trustPackages: TRUST_PACKAGES,
+        bunInstallBlocks: [
+          {
+            label: "Project install",
+            commands: [
+              `bun pm trust ${TRUST_PACKAGES}`,
+              "bun add sandbox-agent",
             ],
-          }),
-        );
-      }
-      throw error;
-    }
+          },
+          {
+            label: "Global install",
+            commands: [
+              `bun pm -g trust ${TRUST_PACKAGES}`,
+              "bun add -g sandbox-agent",
+            ],
+          },
+        ],
+      }),
+    );
   }
 
   const stdio = logMode === "inherit" ? "inherit" : logMode === "silent" ? "ignore" : "pipe";