LLM provider SDK lacks retry logic for transient API errors #11705

Summary

The LLM provider integration lacks retry logic for transient API errors (rate limits, temporary failures), treating all errors as permanent failures.

Location

packages/opencode/src/provider/provider.ts (overall architecture)
packages/opencode/src/provider/sdk/copilot/openai-compatible-error.ts

Issue

The provider SDK:

1. Has no exponential backoff for 429 (rate limit) responses
2. Doesn't parse or respect `Retry-After` headers
3. Treats all API errors as permanent failures
4. Has no retry budget or max attempts configuration
5. Error structures don't implement `isRetryable` checks

// Current error handling doesn't distinguish retryable from permanent errors
const errorStructure = config.errorStructure ?? defaultOpenAICompatibleErrorStructure

Impact

• Severity: Medium
• Type: Reliability
• Effect:
  • Rate limit errors immediately fail instead of backing off
  • Temporary network issues cause permanent failures
  • Higher error rates during API instability

Suggested Fix

1. Add retry configuration to provider options:

interface ProviderRetryConfig {
  maxAttempts?: number
  initialDelayMs?: number
  maxDelayMs?: number
  retryableStatusCodes?: number[]
}

2. Implement exponential backoff with jitter:

async function fetchWithRetry(url, options, retryConfig) {
  let attempt = 0
  while (attempt < retryConfig.maxAttempts) {
    try {
      const response = await fetch(url, options)
      if (response.status === 429 || response.status >= 500) {
        const retryAfter = response.headers.get('Retry-After')
        const delay = retryAfter 
          ? parseInt(retryAfter) * 1000 
          : calculateBackoff(attempt, retryConfig)
        await sleep(delay)
        attempt++
        continue
      }
      return response
    } catch (e) {
      if (!isRetryableError(e) || attempt >= retryConfig.maxAttempts - 1) throw e
      await sleep(calculateBackoff(attempt, retryConfig))
      attempt++
    }
  }
}

3. Add `isRetryable` to error structures to distinguish between:
   • Rate limit (429) - retry with backoff
   • Server error (5xx) - retry with backoff
   • Client error (4xx except 429) - don't retry
   • Network error - retry with backoff