feat(narrative): add narrative API blueprint

Five endpoints under /api/narrative/*:
- GET  /story/<sim_id>                — full story so far
- GET  /story/<sim_id>/round/<num>    — single round
- POST /translate                     — translate a round on demand
- GET  /characters/<sim_id>           — roster with emotional state
- POST /characters/<sim_id>/init      — bootstrap from OASIS profiles

Blueprint registered alongside existing graph/simulation/report
blueprints following the established pattern. Smoke-tested via Flask
test client.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/__init__.py

@@ -63,10 +63,11 @@ def create_app(config_class=Config):
         return response
     
     # 注册蓝图
-    from .api import graph_bp, simulation_bp, report_bp
+    from .api import graph_bp, simulation_bp, report_bp, narrative_bp
     app.register_blueprint(graph_bp, url_prefix='/api/graph')
     app.register_blueprint(simulation_bp, url_prefix='/api/simulation')
     app.register_blueprint(report_bp, url_prefix='/api/report')
+    app.register_blueprint(narrative_bp, url_prefix='/api/narrative')
     
     # 健康检查
     @app.route('/health')

backend/app/api/__init__.py

@@ -7,8 +7,10 @@ from flask import Blueprint
 graph_bp = Blueprint('graph', __name__)
 simulation_bp = Blueprint('simulation', __name__)
 report_bp = Blueprint('report', __name__)
+narrative_bp = Blueprint('narrative', __name__)
 
 from . import graph  # noqa: E402, F401
 from . import simulation  # noqa: E402, F401
 from . import report  # noqa: E402, F401
+from . import narrative  # noqa: E402, F401
 

backend/app/api/narrative.py

@@ -0,0 +1,82 @@
+"""Narrative Layer API endpoints.
+
+Routes are attached to the narrative_bp blueprint defined in api/__init__.py.
+All endpoints are prefixed with /api/narrative (see app/__init__.py).
+"""
+import os
+import json
+from flask import jsonify, request
+
+from . import narrative_bp
+from ..config import Config
+from ..services.narrative.story_store import StoryStore
+from ..services.narrative.narrative_translator import translate_round
+from ..services.narrative.character_engine import CharacterEngine
+
+
+def _sim_dir(sim_id: str) -> str:
+    """Resolve a simulation ID to its on-disk directory."""
+    return os.path.join(Config.OASIS_SIMULATION_DATA_DIR, sim_id)
+
+
+@narrative_bp.route('/story/<sim_id>', methods=['GET'])
+def get_full_story(sim_id):
+    """Return every story beat generated so far for this simulation."""
+    store = StoryStore(_sim_dir(sim_id))
+    return jsonify({"sim_id": sim_id, "beats": store.get_all_beats()})
+
+
+@narrative_bp.route('/story/<sim_id>/round/<int:round_num>', methods=['GET'])
+def get_round_story(sim_id, round_num):
+    """Return a single round's story beat, or 404 if not yet translated."""
+    store = StoryStore(_sim_dir(sim_id))
+    beat = store.get_beat_by_round(round_num)
+    if not beat:
+        return jsonify({"error": "Round not translated yet"}), 404
+    return jsonify(beat)
+
+
+@narrative_bp.route('/translate', methods=['POST'])
+def translate():
+    """Translate a specific round on demand.
+
+    Body: {"sim_id": str, "round": int, "platform": str = "twitter", "tone": str = "neutral"}
+    """
+    data = request.get_json() or {}
+    sim_id = data.get('sim_id')
+    round_num = data.get('round')
+    platform = data.get('platform', 'twitter')
+    tone = data.get('tone', 'neutral')
+
+    if not sim_id or round_num is None:
+        return jsonify({"error": "sim_id and round are required"}), 400
+
+    try:
+        beat = translate_round(_sim_dir(sim_id), platform, int(round_num), tone)
+        return jsonify(beat)
+    except Exception as e:
+        return jsonify({"error": str(e)}), 500
+
+
+@narrative_bp.route('/characters/<sim_id>', methods=['GET'])
+def get_characters(sim_id):
+    """Return the extended character roster (with emotional state)."""
+    store = StoryStore(_sim_dir(sim_id))
+    return jsonify({"characters": store.load_characters()})
+
+
+@narrative_bp.route('/characters/<sim_id>/init', methods=['POST'])
+def initialize_characters(sim_id):
+    """Bootstrap narrative character profiles from the simulation's OASIS profiles."""
+    sim_dir = _sim_dir(sim_id)
+    profiles_path = os.path.join(sim_dir, 'profiles.json')
+    if not os.path.exists(profiles_path):
+        return jsonify({"error": "profiles.json not found for this simulation"}), 404
+
+    with open(profiles_path, 'r', encoding='utf-8') as f:
+        profiles = json.load(f)
+
+    store = StoryStore(sim_dir)
+    engine = CharacterEngine(store)
+    characters = engine.initialize_from_profiles(profiles)
+    return jsonify({"count": len(characters), "characters": characters})