feat(agents): Scope B A1 — 4 竞品生成器 schema/spec + 2 上下文 builder

续写/扩写/降AI率/拆书 4 个生成器的声明（preview-only writes=[]，只声明 tier #2）：
- schemas.py: ContinuationResult/PolishResult/DeAiResult/BookTeardownResult
- specs.py: continue(writer)/expand(writer)/de-ai(analyst)/teardown(analyst)，各配 system_prompt
- generation_node.py: build_continuation_context(续写读前文)/build_text_input_context(原文输入)
- 单测: 4 spec/schema 契约 + 2 builder 纯函数（确定性/空值降级）

守不变量 #2(只声明 tier)/#3(纯预览不写库)/#9(system_prompt 进缓存前缀)。

packages/agents/tests/test_competitor_specs.py

@@ -0,0 +1,89 @@
+"""Scope B 竞品快赢 · 4 个生成器的 spec/schema 契约测试。
+
+校验每个 spec 的 name/tier/reads/writes/output_schema/scope/input_schema，
+对齐不变量 #2（只声明 tier）/ #3（4 生成器一律纯预览 writes=[]）。不联网、无 DB。
+"""
+
+from __future__ import annotations
+
+import pytest
+from ww_agents import (
+    AgentSpec,
+    BookTeardownResult,
+    ContinuationResult,
+    DeAiResult,
+    PolishResult,
+    continue_spec,
+    de_ai_spec,
+    expand_spec,
+    teardown_spec,
+)
+
+# (spec, name, tier, reads, output_schema)
+_COMPETITOR_SPECS = [
+    (continue_spec, "continue", "writer", ["projects", "outline", "chapters"], ContinuationResult),
+    (expand_spec, "expand", "writer", ["projects"], PolishResult),
+    (de_ai_spec, "de-ai", "analyst", ["projects"], DeAiResult),
+    (teardown_spec, "teardown", "analyst", ["projects"], BookTeardownResult),
+]
+
+
+@pytest.mark.parametrize(
+    ("spec", "name", "tier", "reads", "output_schema"),
+    _COMPETITOR_SPECS,
+)
+def test_competitor_spec_declares_expected_contract(
+    spec: AgentSpec,
+    name: str,
+    tier: str,
+    reads: list[str],
+    output_schema: type,
+) -> None:
+    assert spec.name == name
+    assert spec.tier == tier
+    assert spec.reads == reads
+    assert spec.writes == []  # 不变量 #3：4 生成器一律纯预览
+    assert spec.output_schema is output_schema
+    assert spec.scope == "builtin"
+    assert spec.input_schema is None  # 注入材料为序列化文本，非结构化入参
+
+
+@pytest.mark.parametrize("spec", [row[0] for row in _COMPETITOR_SPECS])
+def test_competitor_spec_has_nonempty_system_prompt(spec: AgentSpec) -> None:
+    assert spec.system_prompt.strip()
+
+
+# ---- schema 解析/默认值契约 ----
+
+
+def test_continuation_result_parses_text() -> None:
+    parsed = ContinuationResult.model_validate({"text": "雷光再起，他迈步向前。"})
+    assert parsed.text == "雷光再起，他迈步向前。"
+
+
+def test_polish_result_parses_text() -> None:
+    parsed = PolishResult.model_validate({"text": "夜色更浓，风穿过断壁。"})
+    assert parsed.text == "夜色更浓，风穿过断壁。"
+
+
+def test_de_ai_result_parses_text() -> None:
+    parsed = DeAiResult.model_validate({"text": "他咧嘴一笑，没多说什么。"})
+    assert parsed.text == "他咧嘴一笑，没多说什么。"
+
+
+def test_book_teardown_result_parses_and_lists_default_empty() -> None:
+    empty = BookTeardownResult(structure="开篇立钩→铺垫→爆发")
+    assert empty.themes == []
+    assert empty.archetypes == []
+    assert empty.hooks == []
+    parsed = BookTeardownResult.model_validate(
+        {
+            "themes": ["逆袭", "复仇"],
+            "archetypes": ["废柴主角", "腹黑反派"],
+            "structure": "黄金三章立爽点，逐卷升级",
+            "hooks": ["章末反转", "扮猪吃虎"],
+        }
+    )
+    assert parsed.themes == ["逆袭", "复仇"]
+    assert parsed.structure == "黄金三章立爽点，逐卷升级"
+    assert parsed.hooks == ["章末反转", "扮猪吃虎"]