- Add OpenAI-compat executor-time normalization for `tool` message content, converting non-string tool results to plain text and replacing image parts with a clear unsupported marker for models configured with text-only `input-modalities`. - Apply normalization in both regular and streaming OpenAI-compat execution paths before prompt-cache processing. - Update config example to document `[text]` `input-modalities` for upstreams that reject multimodal tool-result content. Closes: #4737