Problem

Z.AI (智谱 GLM) vision models (glm-4v-flash, glm-4v-plus, glm-4v, etc.) fail when used as the auxiliary.vision provider due to two compatibility issues:

Issue 1: Error 1210 — max_tokens rejected on multimodal calls

Z.AI rejects the max_tokens parameter for vision model requests with error code 1210 ("API 调用参数有误"). The error string does not contain "max_tokens", so the existing unsupported-parameter retry logic in call_llm() never fires. This results in a hard failure with no recovery.

Issue 2: Wrong endpoint inheritance (silent failure)

When the main runtime provider uses Z.AI's Anthropic-compatible endpoint (open.bigmodel.cn/api/anthropic), the vision client inherits this endpoint via resolve_vision_provider_client(). Z.AI's Anthropic wire cannot properly handle image content — models silently fail with responses like "I can't see the image" (received base64 data but couldn't process it through the Anthropic translation layer). This is a silent failure with no HTTP error, making it extremely hard to diagnose.

Changes

1. resolve_vision_provider_client() — Force Z.AI vision to use the OpenAI-compatible endpoint (open.bigmodel.cn/api/paas/v4) instead of inheriting the Anthropic wire from the main runtime provider.

2. _build_call_kwargs() — Skip max_tokens for Z.AI vision models (detected by 4v/5v/-v suffix in model name).

3. _AnthropicCompletionsAdapter — Support _skip_zai_max_tokens flag for cases where the adapter is still used.

4. _to_openai_base_url() — Rewrite Z.AI Anthropic URLs to OpenAI-compatible path (handles edge case URL rewriting).

5. call_llm() retry — Detect Z.AI-specific error 1210 and strip max_tokens before retrying.

Testing

• Verified with glm-4v-flash on Z.AI free tier — vision analysis works correctly
• Main runtime (GLM-4/GLM-5 text models) unaffected — changes only activate for Z.AI vision models
• vision_analyze tool returns correct descriptions of test images

Config used for testing

auxiliary:
  vision:
    provider: zai
    model: glm-4v-flash

Main provider: zai with base_url: https://open.bigmodel.cn/api/anthropic