fix(e2b): harden remote startup and teardown

packages/e2b/subprocess-e2b/src/environment.ts

@@ -1,7 +1,31 @@
 /** Shared remote-environment scrubbing for E2B process and terminal launchers. */
 
+import { Buffer } from 'node:buffer'
+import type { Sandbox } from '@deepseek-ai/dsh-e2b'
 import { SENSITIVE_ENV_PATTERN } from '@deepseek-ai/dsh-subprocess'
 
+const BASE64 = /^(?:[A-Za-z0-9+/]{4})*(?:[A-Za-z0-9+/]{2}==|[A-Za-z0-9+/]{3}=)?$/
+
+/**
+ * Read the remote environment through ASCII base64 so SDK callback chunking cannot corrupt UTF-8.
+ * @param sandbox - shared E2B execution world.
+ * @param signal - optional cancellation for the control-plane request.
+ * @returns the complete NUL-delimited UTF-8 environment.
+ */
+export async function readRemoteEnvironment(sandbox: Sandbox, signal?: AbortSignal): Promise<string> {
+  const result = await sandbox.commands.run(
+    'set -o pipefail; env -0 | base64 -w 0',
+    signal === undefined ? {} : { signal },
+  )
+  const encoded = result.stdout.trim()
+  if (!BASE64.test(encoded)) throw new Error('subprocess-e2b: remote environment transport returned invalid base64')
+  try {
+    return new TextDecoder('utf-8', { fatal: true }).decode(Buffer.from(encoded, 'base64'))
+  } catch (error: unknown) {
+    throw new Error('subprocess-e2b: remote environment is not valid UTF-8', { cause: error })
+  }
+}
+
 /**
  * Parse an E2B NUL-delimited environment while removing harness-private and credential-shaped names.
  * @param raw - The complete NUL-delimited remote environment.