The `effective_max_output_tokens` heuristic defaults to 64K for any model
not in the known-context-window table. This is fine for DeepSeek's hosted
API (1M context) but causes immediate HTTP 400s on self-hosted providers
with tight `max-model-len`.
Example: vLLM serving Qwen3.6 with `--max-model-len 65536` rejects
requests because 64000 (output) + ~1500 (input) exceeds the limit by 1
token.
This change lets the operator set `DEEPSEEK_MAX_OUTPUT_TOKENS=16384` (or
whatever fits their deployment) to override the heuristic. The env var
takes precedence over the model-table lookup when set to a positive
integer; otherwise the existing behavior is preserved.
No new config struct field — env-only override keeps the public API
unchanged. Useful for embedded users (e.g. pinvou3) who need to control
output budget without forking the engine config schema.
Co-authored-by: hexin <he.xin@h3c.com>
hexin
4f3a0c3cfc