fix zai context window (functionally [advertised context window] - [max output tokens]) and properly pass in max tokens so Z.ai doesn't default to 65k for GLM-5
Multiple OpenAI-compatible LLM clients (Azure, Deepseek, Groq, Together, XAI, ZAI)
and Anthropic-compatible clients (Anthropic, MiniMax, Google Vertex) were overriding
request_async/stream_async without calling sanitize_unicode_surrogates, causing
UnicodeEncodeError when message content contained lone UTF-16 surrogates.
Root cause: Child classes override parent methods but omit the sanitization step that
the base OpenAIClient includes. This allows corrupted Unicode (unpaired surrogates
from malformed emoji) to reach the httpx layer, which rejects it during UTF-8 encoding.
Fix: Import and call sanitize_unicode_surrogates in all overridden request methods.
Also removed duplicate sanitize_unicode_surrogates definition from openai_client.py
that shadowed the canonical implementation in letta.helpers.json_helpers.
🐾 Generated with [Letta Code](https://letta.com)
Co-Authored-By: Letta <noreply@letta.com>
Issue-ID: 10c0f2e4-f87b-11f0-b91c-da7ad0900000
* feat: add zai provider support
* add zai_api_key secret to deploy-core
* add to justfile
* add testing, provider integration skill
* enable zai key
* fix zai test
* clean up skill a little
* small changes
