fix(e2b): harden remote process lifecycle

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

@@ -3,6 +3,64 @@
 import { Buffer } from 'node:buffer'
 import type { SubprocessOutputRead, SubprocessOutputReader } from '@deepseek-ai/dsh-subprocess'
 
+const BASE64_TEXT = /^[A-Za-z0-9+/]+={0,2}$/u
+
+/** Reserved non-base64 frame proving that one remote encoder reached clean EOF. */
+export const E2B_OUTPUT_COMPLETE_FRAME = '!dsh-e2b-output-complete!'
+
+/** Incrementally decode newline-delimited base64 frames emitted by one remote encoder. */
+export class E2BBase64Decoder {
+  private pending = ''
+  private complete = false
+
+  /**
+   * Decode every complete newline-delimited frame in one arbitrarily split SDK callback.
+   * @param text - ASCII base64 frames from E2B's decoded callback.
+   * @returns the complete raw bytes made available by this callback.
+   */
+  push(text: string): Buffer {
+    if (text.length === 0) return Buffer.alloc(0)
+    this.pending += text
+    const decoded: Buffer[] = []
+    for (;;) {
+      const boundary = this.pending.indexOf('\n')
+      if (boundary < 0) break
+      const frame = this.pending.slice(0, boundary)
+      this.pending = this.pending.slice(boundary + 1)
+      if (frame === E2B_OUTPUT_COMPLETE_FRAME) {
+        if (this.complete) throw new Error('subprocess-e2b: duplicate output transport completion')
+        this.complete = true
+        continue
+      }
+      if (this.complete) throw new Error('subprocess-e2b: output transport continued after completion')
+      if (!BASE64_TEXT.test(frame)) {
+        throw new Error('subprocess-e2b: invalid base64 output transport')
+      }
+      const bytes = Buffer.from(frame, 'base64')
+      if (bytes.toString('base64') !== frame) {
+        throw new Error('subprocess-e2b: invalid base64 output transport')
+      }
+      decoded.push(bytes)
+    }
+    return Buffer.concat(decoded)
+  }
+
+  /**
+   * Validate clean encoder completion, or discard an interrupted trailing frame after requested termination.
+   * @param requireComplete - Whether natural completion requires the reserved EOF frame.
+   */
+  finish(requireComplete = true): void {
+    if (!requireComplete) {
+      this.pending = ''
+      return
+    }
+    if (this.pending.length > 0) {
+      throw new Error('subprocess-e2b: truncated base64 output transport')
+    }
+    if (!this.complete) throw new Error('subprocess-e2b: incomplete output transport')
+  }
+}
+
 /** Offset reader used for one collect-mode E2B stream. */
 export class E2BOutputReader implements SubprocessOutputReader {
   private chunks: Buffer[] = []
@@ -27,12 +85,12 @@ export class E2BOutputReader implements SubprocessOutputReader {
   }
 
   /**
-   * Append one decoded SDK output event.
-   * @param text - Event text delivered by E2B.
+   * Append one byte-faithful decoded transport event.
+   * @param bytes - Raw command bytes recovered from the ASCII SDK transport.
    */
-  push(text: string): void {
-    if (text.length === 0) return
-    const chunk = Buffer.from(text)
+  push(bytes: Uint8Array): void {
+    if (bytes.length === 0) return
+    const chunk = Buffer.from(bytes)
     this.totalBytes += chunk.length
     this.chunks.push(chunk)
     this.retainedBytes += chunk.length