Robustness: detect retryable HTTP errors from structured SDK fields, not message strings

[zjshen14]

Problem

Both GeminiClient and AnthropicClient classify retryable errors by scanning the error message string:

// src/model/gemini.ts:63
const isRetryable =
  msg.includes("429") || msg.includes("500") || msg.includes("RESOURCE_EXHAUSTED");

// src/model/anthropic.ts:69
const isRetryable =
  msg.includes("429") || msg.includes("500") || msg.includes("overloaded");

Error message text is not a stable API — SDK version bumps, proxy wrappers, or locale changes can alter the message format. A retry that should fire won't, and hard errors may be silently retried.

Expected behavior

Retry classification should use the structured status field on the SDK error object, which is stable across SDK versions.

Fix

Use the SDK's typed error classes:

// Anthropic
import Anthropic from "@anthropic-ai/sdk";
const isRetryable =
  err instanceof Anthropic.APIError && [429, 500, 502, 529].includes(err.status);

// Gemini — GoogleGenerativeAIError exposes .status
import { GoogleGenerativeAIError } from "@google/generative-ai";
const isRetryable =
  err instanceof GoogleGenerativeAIError && [429, 500, 502, 503].includes(err.status ?? 0);

Location

• src/model/gemini.ts:63
• src/model/anthropic.ts:69

[zjshen14]

Fixed in PR #72 (squash-merged to main, commit 23fff42).

What changed:

• src/providers/gemini.ts: imports ApiError from @google/genai and checks err instanceof ApiError && [429, 500, 502, 503].includes(err.status) instead of scanning error message strings.
• src/providers/anthropic.ts: imports APIError from @anthropic-ai/sdk and checks err instanceof APIError && err.status !== undefined && [429, 500, 502, 529].includes(err.status) instead of scanning error message strings.
• Both test files updated to throw properly typed SDK error instances so tests exercise the real retry path; also added coverage for the new 503 (Gemini) and 529 (Anthropic) status codes, and a case verifying that plain (non-SDK) errors are not retried.

---

Generated by Claude Code