fix(code-runtime): bound hostile output accounting

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

@@ -1,5 +1,7 @@
 /** JSON string-prefix accounting for the outer-output ledger. @module @deepseek-ai/dsh-code-runtime-worker/output-json */
 
+import type { CodeJsonValue } from '@deepseek-ai/dsh-code-runtime'
+
 /** Control characters with a two-byte short JSON escape instead of `\u00XX`. */
 const SHORT_ESCAPE_CODES = new Set([0x08, 0x09, 0x0a, 0x0c, 0x0d])
 
@@ -13,6 +15,69 @@ function serializedCharacterBytes(character: string): number {
   return Buffer.byteLength(character, 'utf8')
 }
 
+/**
+ * Measure one JSON string without materializing its complete escaped form.
+ * @param text - the candidate string.
+ * @param maxBytes - largest serialized size the caller can admit.
+ * @returns Exact serialized bytes, or `undefined` as soon as the cap is crossed.
+ */
+export function jsonStringBytesUpTo(text: string, maxBytes: number): number | undefined {
+  if (maxBytes < 2) return undefined
+  let bytes = 2
+  for (const character of text) {
+    bytes += serializedCharacterBytes(character)
+    if (bytes > maxBytes) return undefined
+  }
+  return bytes
+}
+
+/**
+ * Measure one lossless JSON value without allocating its serialized form.
+ * @param value - already validated lossless JSON.
+ * @param maxBytes - largest serialized size the caller can admit.
+ * @returns Exact serialized bytes, or `undefined` as soon as the cap is crossed.
+ */
+export function jsonValueBytesUpTo(value: CodeJsonValue, maxBytes: number): number | undefined {
+  if (value === null) return maxBytes >= 4 ? 4 : undefined
+  if (typeof value === 'string') return jsonStringBytesUpTo(value, maxBytes)
+  if (typeof value === 'number') {
+    const bytes = Buffer.byteLength(String(value), 'utf8')
+    return bytes <= maxBytes ? bytes : undefined
+  }
+  if (typeof value === 'boolean') {
+    const bytes = value ? 4 : 5
+    return bytes <= maxBytes ? bytes : undefined
+  }
+
+  let bytes = 2
+  if (bytes > maxBytes) return undefined
+  if (Array.isArray(value)) {
+    for (let index = 0; index < value.length; index++) {
+      if (index > 0 && ++bytes > maxBytes) return undefined
+      const item = value[index]
+      if (item === undefined) return undefined
+      const itemBytes = jsonValueBytesUpTo(item, maxBytes - bytes)
+      if (itemBytes === undefined) return undefined
+      bytes += itemBytes
+    }
+    return bytes
+  }
+
+  let entries = 0
+  for (const [key, item] of Object.entries(value)) {
+    if (entries > 0 && ++bytes > maxBytes) return undefined
+    const keyBytes = jsonStringBytesUpTo(key, maxBytes - bytes)
+    if (keyBytes === undefined) return undefined
+    bytes += keyBytes + 1
+    if (bytes > maxBytes) return undefined
+    const itemBytes = jsonValueBytesUpTo(item, maxBytes - bytes)
+    if (itemBytes === undefined) return undefined
+    bytes += itemBytes
+    entries += 1
+  }
+  return bytes
+}
+
 /**
  * Return the longest code-point-aligned prefix whose JSON string encoding,
  * including its surrounding quotes, fits `maxBytes`.
@@ -23,7 +88,6 @@ function serializedCharacterBytes(character: string): number {
  */
 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) {
@@ -32,5 +96,5 @@ export function truncateJsonStringBytes(text: string, maxBytes: number): string
     bytes += cost
     end += character.length
   }
-  return text.slice(0, end)
+  return end === text.length ? text : text.slice(0, end)
 }