feat(engine): add faction power system with event triggers

- Add FactionData model with power and members fields
- Add FactionEventResult model for faction event responses
- Add faction field to AgentState
- Implement faction classification based on emotion
- Add faction event triggers (festival/panic) when power >= 5
- Update StepResponse to include triggered_faction_event
- Add tests for new faction system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

engine-python/app/factions.py

@@ -1,40 +1,138 @@
 """派系系统 - 基于立场分类角色并影响世界"""
-from typing import Dict
-from .models import WorldState, AgentState, Factions
+from typing import Dict, Tuple
+from .models import (
+    WorldState, AgentState, Factions, FactionData,
+    FactionEventResult, WorldEffect, Emotion
+)
 
 # 派系分类阈值
 OPTIMIST_THRESHOLD = 0.6
 FEARFUL_THRESHOLD = 0.6
 
+# 阵营技能触发阈值
+FACTION_POWER_THRESHOLD = 5
+
+# 阵营事件对情绪的影响
+FACTION_EVENT_EFFECTS = {
+    "festival": 0.2,   # 乐观派事件提升情绪
+    "panic": -0.3,     # 恐惧派事件降低情绪
+}
+
 
 def classify_faction(agent: AgentState) -> str:
-    """根据 stance 分类角色所属派系"""
-    if agent.stance.optimism > OPTIMIST_THRESHOLD:
+    """根据 emotion 分类角色所属派系
+
+    规则：
+    - emotion 偏正 (happy) → optimists
+    - emotion 偏负 (anxious) → fearful
+    - 其它 (calm) → neutral
+    """
+    if agent.emotion == Emotion.HAPPY:
         return "optimists"
-    elif agent.stance.fear > FEARFUL_THRESHOLD:
+    elif agent.emotion == Emotion.ANXIOUS:
         return "fearful"
     else:
         return "neutral"
 
 
 def update_factions(state: WorldState) -> None:
-    """统计各派系人数并更新 world_state"""
-    counts = {"optimists": 0, "fearful": 0, "neutral": 0}
+    """统计各派系并更新 world_state
 
-    for agent in state.agents.values():
+    流程：
+    1. 清空 factions.members
+    2. 遍历所有 agents，根据 emotion 分类
+    3. 更新 agent.faction 字段
+    4. 将 agent 加入对应 faction.members
+    5. 每个 agent 为 faction 增加 power += 1
+    """
+    # 重置 factions
+    state.factions = Factions(
+        optimists=FactionData(power=0, members=[]),
+        fearful=FactionData(power=0, members=[])
+    )
+
+    for agent_id, agent in state.agents.items():
         faction = classify_faction(agent)
-        counts[faction] += 1
+        agent.faction = faction
 
-    state.factions = Factions(**counts)
+        if faction == "optimists":
+            state.factions.optimists.members.append(agent_id)
+            state.factions.optimists.power += 1
+        elif faction == "fearful":
+            state.factions.fearful.members.append(agent_id)
+            state.factions.fearful.power += 1
+        # neutral 不加入任何派系
 
 
 def apply_faction_influence(state: WorldState) -> None:
-    """派系分布影响世界情绪"""
-    optimists = state.factions.optimists
-    fearful = state.factions.fearful
+    """派系分布影响世界情绪（保留原有逻辑）"""
+    optimists = state.factions.optimists.power
+    fearful = state.factions.fearful.power
 
     if optimists > fearful:
         state.town_mood = min(10, state.town_mood + 1)
     elif fearful > optimists:
         state.town_mood = max(-10, state.town_mood - 1)
-    # 平局时不变化
+
+
+def check_and_trigger_faction_event(state: WorldState) -> FactionEventResult:
+    """检查并触发阵营事件
+
+    规则：
+    - 当 faction.power >= 5 时，触发对应世界事件
+    - optimists → festival（提升情绪）
+    - fearful → panic（降低情绪）
+    - 触发后该 faction.power 归零
+    """
+    result = FactionEventResult(type=None, source_faction=None)
+
+    # 检查乐观派
+    if state.factions.optimists.power >= FACTION_POWER_THRESHOLD:
+        result = FactionEventResult(type="festival", source_faction="optimists")
+        _apply_faction_event(state, "festival")
+        state.factions.optimists.power = 0
+
+    # 检查恐惧派
+    elif state.factions.fearful.power >= FACTION_POWER_THRESHOLD:
+        result = FactionEventResult(type="panic", source_faction="fearful")
+        _apply_faction_event(state, "panic")
+        state.factions.fearful.power = 0
+
+    return result
+
+
+def _apply_faction_event(state: WorldState, event_type: str) -> None:
+    """应用阵营事件效果
+
+    1. 创建 WorldEffect 写入 world_state.world_effects
+    2. 影响所有 agent 的 emotion
+    """
+    # 创建持续影响效果
+    if event_type == "festival":
+        effect = WorldEffect(
+            type="faction_event",
+            name="节日庆典",
+            intensity=1,
+            remaining_ticks=3,
+            mood_modifier=1
+        )
+    else:  # panic
+        effect = WorldEffect(
+            type="faction_event",
+            name="恐慌蔓延",
+            intensity=1,
+            remaining_ticks=3,
+            mood_modifier=-1
+        )
+
+    state.world_effects.append(effect)
+
+    # 影响所有 agent 的 stance（间接影响下一轮 emotion）
+    emotion_delta = FACTION_EVENT_EFFECTS.get(event_type, 0)
+    for agent in state.agents.values():
+        if emotion_delta > 0:
+            agent.stance.optimism = min(1.0, agent.stance.optimism + emotion_delta)
+            agent.stance.fear = max(0.0, agent.stance.fear - emotion_delta * 0.5)
+        else:
+            agent.stance.fear = min(1.0, agent.stance.fear + abs(emotion_delta))
+            agent.stance.optimism = max(0.0, agent.stance.optimism - abs(emotion_delta) * 0.5)