feat(auth): add retry with exponential backoff to refreshClaudeOAuthToken

[iceteaSA]

Summary

Adds resilient retry logic to refreshClaudeOAuthToken:

• Exponential backoff: Up to 3 attempts (configurable via maxRetries) with delays of 0ms, 500ms, 1000ms (configurable via baseDelayMs)
• 5xx retry: Server errors automatically retry after canceling the response body
• Network error retry: Retries on ECONNRESET, ECONNREFUSED, ETIMEDOUT, UND_ERR_CONNECT_TIMEOUT, and generic "fetch failed"
• 4xx immediate throw: Client errors (including ClaudeOAuthRefreshError) are not retried
• Non-breaking: New parameters are optional with sensible defaults. Existing callers get retry automatically.

Motivation

Currently a single transient error during token refresh (e.g., a Cloudflare 502 or a momentary network blip) causes the entire session to fail. This is especially impactful for long-running sessions where a brief infrastructure hiccup shouldn't require re-authentication.

Testing

All existing tests pass. The retry logic handles both FallbackAccountManager.refreshAccountNow() (which calls this function) and the main account refresh path in the OpenCode plugin.

[ualtinok]

@cubic-dev-ai review this

[cubic-dev-ai]

@cubic-dev-ai review this

@ualtinok I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[ualtinok]

Thanks for putting this together — the transient retry behavior is useful. I reworked it slightly on main in 0131669 so the shared OAuth helper retries transient network/5xx failures, while the OpenCode main-account path disables the helper retry and keeps its existing outer retry/backoff/file-lock layer single-sourced. That avoids multiplying refresh attempts against Anthropic's OAuth endpoint while still covering fallback/Pi/helper callers.\n\nClosing this PR as superseded by the reworked implementation on main. Appreciate the contribution!

[ualtinok]

Closed as superseded by the reworked implementation merged on main in 0131669. Thanks again!

[iceteaSA]

Closed as superseded by the reworked implementation merged on main in 0131669. Thanks again!

Awesome! I saw you made a more robust mechanism for refreshes. Already rebased onto my Frankenstein's Fork