外部 API skill 文档同步 style 的提示词注入语义

requests-and-outputs.md 把 style 描述为只控制 deterministic post-processing，
缺了本分支加的另一半——pixelArt 会在发给 provider 的提示词末尾追加一行约束。

是文档漂移不是遗漏：OpenAPI 的两处 schema 一直是对的，连子句都写了；master
把 api-selection.md 拆成四篇时是从注入之前的版本重写的。我上轮合并只 grep 了
旧错误说法有没有复活，确认没有就收工——验证旧错误的缺席不等于验证新事实的在场。

改动限于三行，与 OpenAPI 对齐，不新造措辞。刻意不复制子句字面文本：Rust 常量
是真值源、OpenAPI 已复制一份，再抄第三份就是把同一事实摊到三处，这次漂移正是
这么发生的。文档改为指向 OpenAPI 并写明是刻意不复制。

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.codex/skills/genarrative-external-editor-api/references/requests-and-outputs.md

@@ -138,10 +138,10 @@ Carry the current art spec in `generationInputs.artSpec` and reflect important c
 }
 ```
 
-The top-level `style` field is not the art spec's visual-style prose. It controls deterministic post-processing:
+The top-level `style` field is not the art spec's visual-style prose. It appends a short server-side clause to the prompt sent to the provider and enables deterministic post-processing:
 
-- Omitted, `null`, empty string, or `"none"`: disable post-processing without warning.
-- `"pixelArt"`: enable pixel-art snapping for ordinary image generation, `kind: "character"`, and icon spritesheet generation.
+- Omitted, `null`, empty string, or `"none"`: no clause is appended and no post-processing runs, without warning.
+- `"pixelArt"`: append one short pixel-art line to the end of the prompt sent to the provider, and enable pixel-art snapping, for ordinary image generation, `kind: "character"`, and icon spritesheet generation. The line is appended, not substituted — the rest of your prompt is unchanged. For the exact per-kind wording, read the `style` field description in the OpenAPI document; it is the contract, and this guide deliberately does not copy it.
 - Unknown strings, or `"pixelArt"` on unsupported kinds such as `spec`, `quick-edit`, `ui-design`, or `publication-material`: continue without style processing and return `warning.code: "unsupported-image-style"`.
 - Non-string JSON values: malformed request, HTTP `400`.