feat: 生成图片提示词agent结构封装

api/app/agents/image_prompt/prompt_agent.py

@@ -0,0 +1,50 @@
+"""
+PromptGenerationAgent：生成回忆录配图的 image-generation prompt。
+接收 chapter_title、chapter_category、description、context_excerpt，
+调用 LLM 或 fallback 生成 {prompt, style, size}。
+底层委托 MemoirImagePromptService，保持对外接口兼容。
+"""
+from __future__ import annotations
+
+from typing import Any, Optional
+
+from app.features.memoir.memoir_images.prompting import MemoirImagePromptService
+from app.features.memoir.memoir_images.settings import MemoirImageSettings
+
+
+class PromptGenerationAgent:
+    """
+    图片提示词生成 Specialist Agent。
+    封装 MemoirImagePromptService，提供 build_prompt / build_cover_prompt 接口。
+    """
+
+    def __init__(self, llm: Optional[Any], settings: MemoirImageSettings) -> None:
+        self._service = MemoirImagePromptService(llm=llm, settings=settings)
+
+    def build_prompt(
+        self,
+        chapter_title: str,
+        chapter_category: str,
+        description: str,
+        context_excerpt: str,
+    ) -> dict[str, str]:
+        """生成正文配图的 image-generation prompt。"""
+        return self._service.build_prompt(
+            chapter_title=chapter_title,
+            chapter_category=chapter_category,
+            description=description,
+            context_excerpt=context_excerpt,
+        )
+
+    def build_cover_prompt(
+        self,
+        chapter_title: str,
+        chapter_category: str,
+        context_excerpt: str,
+    ) -> dict[str, str]:
+        """生成章节封面图的 image-generation prompt。"""
+        return self._service.build_cover_prompt(
+            chapter_title=chapter_title,
+            chapter_category=chapter_category,
+            context_excerpt=context_excerpt,
+        )