feat: layered precise generation for A4 report images

3-phase pipeline to solve LLM prompt overflow from too many OCR elements:
Phase 1 (generate_skeleton): compressed layout schema → skeleton JRXML
Phase 2 (refine_layout): sampled coordinates → pixel-level position tuning
Phase 3 (map_fields): OCR field names → replace $F{field_N} placeholders

Only triggered when layout_schema.total_rows > 0 on initial_generation intent.
Text requests and all other intents are unaffected (zero behavior change).

agent/graph.py

@@ -16,6 +16,9 @@ from agent.nodes import (
     classify_intent,
     retrieve,
     generate,
+    generate_skeleton,
+    refine_layout,
+    map_fields,
     modify_jrxml,
     handle_consult,
     handle_undo,
@@ -87,6 +90,15 @@ def route_by_intent(state: AgentState) -> Literal[
         return "retrieve"
 
 
+@_log_route("route_after_retrieve")
+def route_after_retrieve(state: AgentState) -> Literal["generate", "generate_skeleton"]:
+    """当 layout_schema 存在时走三层精确生成，否则走原有 1-shot。"""
+    layout_schema = state.get("layout_schema")
+    if layout_schema and isinstance(layout_schema, dict) and layout_schema.get("total_rows", 0) > 0:
+        return "generate_skeleton"
+    return "generate"
+
+
 @_log_route("route_after_generate")
 def route_after_generate(state: AgentState) -> Literal["save_session"]:
     return "save_session"
@@ -158,6 +170,11 @@ def build_graph() -> StateGraph:
     workflow.add_node("handle_undo", handle_undo)
     workflow.add_node("handle_reset", handle_reset)
 
+    # 新增节点：分层精确生成（阶段一~三）
+    workflow.add_node("generate_skeleton", generate_skeleton)
+    workflow.add_node("refine_layout", refine_layout)
+    workflow.add_node("map_fields", map_fields)
+
     # ---- 入口和前置流程 ----
     workflow.set_entry_point("load_session")
     workflow.add_edge("load_session", "process_input")
@@ -180,12 +197,28 @@ def build_graph() -> StateGraph:
     )
 
     # ---- 初始生成分支 ----
-    workflow.add_edge("retrieve", "generate")
+    workflow.add_conditional_edges(
+        "retrieve",
+        route_after_retrieve,
+        {
+            "generate": "generate",
+            "generate_skeleton": "generate_skeleton",
+        },
+    )
+    # 原有 1-shot 路径
     workflow.add_conditional_edges(
         "generate",
         route_after_generate,
         {"save_session": "save_session"},
     )
+    # 分层精确生成 3 阶段路径
+    workflow.add_edge("generate_skeleton", "refine_layout")
+    workflow.add_edge("refine_layout", "map_fields")
+    workflow.add_conditional_edges(
+        "map_fields",
+        route_after_generate,
+        {"save_session": "save_session"},
+    )
 
     # ---- 修改分支 ----
     workflow.add_conditional_edges(
@@ -264,4 +297,6 @@ def create_initial_state() -> AgentState:
         jrxml_versions=[],
         last_error_case={},
         pending_failure_context={},
+        layout_schema={},
+        ocr_elements=[],
     )