fix(code-runtime): validate arguments before worker dispatch

packages/code-runtime/code-runtime-worker/src/output-json.ts

@@ -0,0 +1,36 @@
+/** JSON string-prefix accounting for the outer-output ledger. @module @deepseek-ai/dsh-code-runtime-worker/output-json */
+
+/** Control characters with a two-byte short JSON escape instead of `\u00XX`. */
+const SHORT_ESCAPE_CODES = new Set([0x08, 0x09, 0x0a, 0x0c, 0x0d])
+
+/** Serialized bytes contributed by one complete Unicode code point inside JSON quotes. */
+function serializedCharacterBytes(character: string): number {
+  if (character.length === 2) return 4
+  if (character === '"' || character === '\\') return 2
+  const code = character.charCodeAt(0)
+  if (code >= 0xd800 && code <= 0xdfff) return 6
+  if (code < 0x20) return SHORT_ESCAPE_CODES.has(code) ? 2 : 6
+  return Buffer.byteLength(character, 'utf8')
+}
+
+/**
+ * Return the longest code-point-aligned prefix whose JSON string encoding,
+ * including its surrounding quotes, fits `maxBytes`.
+ *
+ * @param text - the candidate string.
+ * @param maxBytes - serialized JSON-string bytes available.
+ * @returns the fitting prefix, or an empty string when even useful content cannot fit.
+ */
+export function truncateJsonStringBytes(text: string, maxBytes: number): string {
+  if (maxBytes < 2) return ''
+  if (Buffer.byteLength(JSON.stringify(text), 'utf8') <= maxBytes) return text
+  let bytes = 2
+  let end = 0
+  for (const character of text) {
+    const cost = serializedCharacterBytes(character)
+    if (bytes + cost > maxBytes) break
+    bytes += cost
+    end += character.length
+  }
+  return text.slice(0, end)
+}