Implement lemonade provider for Codex

[sawansri]

Resolves #1504

Also introduces --agent-args allowing users to pass in arguments to their agents, similar to how we used to do --llamacpp-args. This enables features such as session resumption in both Claude Code and Codex.

[jeremyfowers]

server log

2026-04-01 15:16:07.111 [Info] (Router) Model loaded successfully. Total loaded: 1
2026-04-01 15:16:07.111 [Info] (Server) Model loaded successfully: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:07.111 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:07.119 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:07.119 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:07.119 [Error] (StreamingProxy) Backend returned error: 500
2026-04-01 15:16:07.333 [Info] (Server) Model already loaded: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:07.333 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:07.340 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:07.340 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:07.340 [Error] (StreamingProxy) Backend returned error: 500
2026-04-01 15:16:07.770 [Info] (Server) Model already loaded: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:07.770 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:07.776 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:07.776 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:07.776 [Error] (StreamingProxy) Backend returned error: 500
2026-04-01 15:16:08.660 [Info] (Server) Model already loaded: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:08.660 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:08.666 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:08.666 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:08.666 [Error] (StreamingProxy) Backend returned error: 500
2026-04-01 15:16:10.128 [Info] (Server) Model already loaded: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:10.128 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:10.134 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:10.134 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:10.134 [Error] (StreamingProxy) Backend returned error: 500
2026-04-01 15:16:13.647 [Info] (Server) Model already loaded: user.Qwen3.5-35B-A3B-NoThinking
2026-04-01 15:16:13.647 [Info] (Server) POST /api/v1/responses - Streaming
2026-04-01 15:16:13.652 [Error] (Process) srv    operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 85, column 32 in source:\n...first %}↵            {{- raise_exception('System message must be at the beginnin...\n                                           ^\nError: Jinja Exception: System message must be at the beginning.","type":"server_error"}}
2026-04-01 15:16:13.652 [Info] (Process) srv  log_server_r: done request: POST /v1/responses 127.0.0.1 500
2026-04-01 15:16:13.652 [Error] (StreamingProxy) Backend returned error: 500

Codex isnt working for me, any tips?

[sawansri]

Appears to be related to: ggml-org/llama.cpp#20733. There's a draft PR open to address this: ggml-org/llama.cpp#21174.

Looks like an upstream issue with the qwen3.5 model family. I've been testing with GLM 4.7 Flash and Nemotron 3 Nano, which probably explains why I haven't hit this issue.