fix(anthropic-auto-compact): handle empty messages at arbitrary indices

- Add messageIndex field to ParsedTokenLimitError type for tracking message position
- Extract message index from 'messages.N' format in error messages using regex
- Update fixEmptyMessages to accept optional messageIndex parameter
- Target specific empty message by index instead of fixing all empty messages
- Apply replaceEmptyTextParts before injectTextPart for better coverage
- Remove experimental flag requirement - non-empty content errors now auto-recover by default
- Fixes issue where compaction could create empty messages at positions other than the last message

🤖 GENERATED WITH ASSISTANCE OF [OhMyOpenCode](https://github.com/code-yeongyu/oh-my-opencode)

src/hooks/anthropic-auto-compact/parser.ts

@@ -28,6 +28,8 @@ const TOKEN_LIMIT_KEYWORDS = [
   "non-empty content",
 ]
 
+const MESSAGE_INDEX_PATTERN = /messages\.(\d+)/
+
 function extractTokensFromMessage(message: string): { current: number; max: number } | null {
   for (const pattern of TOKEN_LIMIT_PATTERNS) {
     const match = message.match(pattern)
@@ -40,6 +42,14 @@ function extractTokensFromMessage(message: string): { current: number; max: numb
   return null
 }
 
+function extractMessageIndex(text: string): number | undefined {
+  const match = text.match(MESSAGE_INDEX_PATTERN)
+  if (match) {
+    return parseInt(match[1], 10)
+  }
+  return undefined
+}
+
 function isTokenLimitError(text: string): boolean {
   const lower = text.toLowerCase()
   return TOKEN_LIMIT_KEYWORDS.some((kw) => lower.includes(kw.toLowerCase()))
@@ -52,6 +62,7 @@ export function parseAnthropicTokenLimitError(err: unknown): ParsedTokenLimitErr
         currentTokens: 0,
         maxTokens: 0,
         errorType: "non-empty content",
+        messageIndex: extractMessageIndex(err),
       }
     }
     if (isTokenLimitError(err)) {
@@ -155,6 +166,7 @@ export function parseAnthropicTokenLimitError(err: unknown): ParsedTokenLimitErr
       currentTokens: 0,
       maxTokens: 0,
       errorType: "non-empty content",
+      messageIndex: extractMessageIndex(combinedText),
     }
   }