diff --git a/backend/app/api/simulation.py b/backend/app/api/simulation.py
index 008a6089..d63cc15b 100644
--- a/backend/app/api/simulation.py
+++ b/backend/app/api/simulation.py
@@ -8,6 +8,7 @@ import traceback
 from flask import request, jsonify, send_file
 
 from . import simulation_bp
+from .. import get_storage
 from ..config import Config
 from ..services.zep_entity_reader import ZepEntityReader
 from ..services.oasis_profile_generator import OasisProfileGenerator
@@ -190,7 +191,7 @@ def create_simulation():
                 "error": t('api.projectNotFound', id=project_id)
             }), 404
         
-        graph_id = data.get('graph_id') or project.graph_id
+        graph_id = data.get('graph_id') or project.get("graph_id")
         if not graph_id:
             return jsonify({
                 "success": False,
@@ -436,7 +437,7 @@ def prepare_simulation():
             }), 404
         
         # Get simulation requirement
-        simulation_requirement = project.simulation_requirement or ""
+        simulation_requirement = project.get("simulation_requirement") or ""
         if not simulation_requirement:
             return jsonify({
                 "success": False,
@@ -444,7 +445,7 @@ def prepare_simulation():
             }), 400
 
         # Get document text
-        document_text = ProjectManager.get_extracted_text(state.project_id) or ""
+        document_text = ProjectManager.get_extracted_text(state.project_id, get_storage()) or ""
         
         entity_types_list = data.get('entity_types')
         use_llm_for_profiles = data.get('use_llm_for_profiles', True)
@@ -718,7 +719,7 @@ def get_prepare_status():
                 "error": t('api.taskNotFound', id=task_id)
             }), 404
         
-        task_dict = task.to_dict()
+        task_dict = task
         task_dict["already_prepared"] = False
         
         return jsonify({
@@ -932,10 +933,10 @@ def get_simulation_history():
             
             # Get associated project's file list (up to 3)
             project = ProjectManager.get_project(sim.project_id)
-            if project and hasattr(project, 'files') and project.files:
+            if project and project.get("files"):
                 sim_dict["files"] = [
                     {"filename": f.get("filename", "Unknown file")}
-                    for f in project.files[:3]
+                    for f in project.get("files", [])[:3]
                 ]
             else:
                 sim_dict["files"] = []
@@ -1573,8 +1574,8 @@ def start_simulation():
                 # Try to get from project
                 project = ProjectManager.get_project(state.project_id)
                 if project:
-                    graph_id = project.graph_id
-            
+                    graph_id = project.get("graph_id")
+
             if not graph_id:
                 return jsonify({
                     "success": False,
@@ -2699,3 +2700,29 @@ def close_simulation_env():
             "error": str(e),
             "traceback": traceback.format_exc()
         }), 500
+
+
+# ============== F2-A: Agent CRUD endpoints ==============
+
+@simulation_bp.route('/<simulation_id>/agent/<int:user_id>', methods=['PATCH'])
+def patch_agent(simulation_id: str, user_id: int):
+    """Update an agent profile (Fase A/B fields). Sets manually_edited=True."""
+    try:
+        fields = request.get_json() or {}
+        if not fields:
+            return jsonify({"success": False, "error": t('api.requireFields')}), 400
+
+        manager = SimulationManager()
+        try:
+            updated = manager.patch_agent_profile(simulation_id, user_id, fields)
+        except ValueError as e:
+            return jsonify({"success": False, "error": str(e)}), 404
+        except PermissionError as e:
+            return jsonify({"success": False, "error": str(e)}), 403
+        except LookupError as e:
+            return jsonify({"success": False, "error": str(e)}), 404
+
+        return jsonify({"success": True, "data": updated})
+    except Exception as e:
+        logger.error(f"patch_agent failed: {e}")
+        return jsonify({"success": False, "error": str(e), "traceback": traceback.format_exc()}), 500
diff --git a/backend/app/services/simulation_manager.py b/backend/app/services/simulation_manager.py
index df05edf5..5630d1e3 100644
--- a/backend/app/services/simulation_manager.py
+++ b/backend/app/services/simulation_manager.py
@@ -539,3 +539,57 @@ class SimulationManager:
                 f"   - Both platforms in parallel: python {scripts_dir}/run_parallel_simulation.py --config {config_path}"
             )
         }
+
+    def patch_agent_profile(self, simulation_id: str, user_id: int, fields: dict) -> dict:
+        """
+        Update an agent's profile fields and set manually_edited=True.
+        Raises ValueError if simulation not found.
+        Raises PermissionError if simulation status is running or completed.
+        Raises LookupError if agent user_id not found.
+        Uses atomic write: backup → write → delete backup on success, restore on failure.
+        """
+        state = self.get_simulation(simulation_id)
+        if not state:
+            raise ValueError(f"Simulation {simulation_id} not found")
+
+        immutable = {SimulationStatus.RUNNING, SimulationStatus.COMPLETED}
+        if state.status in immutable:
+            raise PermissionError(f"Cannot edit agent while simulation is {state.status.value}")
+
+        sim_dir = self._get_simulation_dir(simulation_id)
+        profiles_file = os.path.join(sim_dir, "reddit_profiles.json")
+        backup_file = profiles_file + ".bak"
+
+        if not os.path.exists(profiles_file):
+            raise FileNotFoundError(f"reddit_profiles.json not found for {simulation_id}")
+
+        with open(profiles_file, 'r', encoding='utf-8') as f:
+            profiles = json.load(f)
+
+        target = next((p for p in profiles if p.get("user_id") == user_id), None)
+        if target is None:
+            raise LookupError(f"Agent user_id={user_id} not found in simulation {simulation_id}")
+
+        allowed = {
+            "name", "bio", "persona", "age", "gender", "mbti",
+            "country", "profession", "interested_topics", "stance", "sentiment_bias",
+            "posts_per_hour", "comments_per_hour", "active_hours",
+            "response_delay_min", "response_delay_max", "activity_level", "influence_weight",
+        }
+        for k, v in fields.items():
+            if k in allowed:
+                target[k] = v
+        target["manually_edited"] = True
+
+        import shutil
+        shutil.copy2(profiles_file, backup_file)
+        try:
+            with open(profiles_file, 'w', encoding='utf-8') as f:
+                json.dump(profiles, f, ensure_ascii=False, indent=2)
+            os.remove(backup_file)
+        except Exception:
+            shutil.copy2(backup_file, profiles_file)
+            os.remove(backup_file)
+            raise
+
+        return target
diff --git a/backend/tests/test_simulation_agent_api.py b/backend/tests/test_simulation_agent_api.py
new file mode 100644
index 00000000..fc1889a0
--- /dev/null
+++ b/backend/tests/test_simulation_agent_api.py
@@ -0,0 +1,86 @@
+import json
+import os
+import pytest
+from flask import Flask
+
+
+@pytest.fixture
+def app():
+    os.environ.setdefault("SECRET_KEY", "test")
+    from backend.app import create_app
+    application = create_app({'TESTING': True, 'WTF_CSRF_ENABLED': False})
+    return application
+
+
+@pytest.fixture
+def client(app):
+    with app.test_client() as c:
+        yield c
+
+
+@pytest.fixture
+def sim_with_profiles(tmp_path, monkeypatch):
+    """Creates a simulation directory with a minimal state.json and reddit_profiles.json"""
+    from backend.app.services import simulation_manager as sm_module
+    monkeypatch.setattr(sm_module.SimulationManager, 'SIMULATION_DATA_DIR', str(tmp_path))
+
+    sim_id = "sim_test001"
+    sim_dir = tmp_path / sim_id
+    sim_dir.mkdir()
+
+    state = {
+        "simulation_id": sim_id,
+        "project_id": "proj_test",
+        "graph_id": "g1",
+        "status": "profiles_ready",
+        "entities_count": 2,
+        "profiles_count": 2,
+        "entity_types": [],
+        "config_generated": False,
+        "config_reasoning": "",
+        "current_round": 0,
+        "twitter_status": "not_started",
+        "reddit_status": "not_started",
+        "created_at": "2026-01-01T00:00:00",
+        "updated_at": "2026-01-01T00:00:00",
+        "error": None,
+        "parent_simulation_id": None,
+        "graph_id_simulation": None,
+        "enable_twitter": True,
+        "enable_reddit": True,
+    }
+    (sim_dir / "state.json").write_text(json.dumps(state))
+
+    profiles = [
+        {"user_id": 0, "user_name": "alice", "name": "Alice", "bio": "Original bio",
+         "persona": "Curious", "manually_edited": False},
+        {"user_id": 1, "user_name": "bob", "name": "Bob", "bio": "Bob bio",
+         "persona": "Bold", "manually_edited": False},
+    ]
+    (sim_dir / "reddit_profiles.json").write_text(json.dumps(profiles))
+    return sim_id
+
+
+def test_patch_agent_updates_bio(client, sim_with_profiles):
+    sim_id = sim_with_profiles
+    resp = client.patch(f"/api/simulation/{sim_id}/agent/0", json={"bio": "Updated bio"})
+    assert resp.status_code == 200
+    data = resp.get_json()
+    assert data["success"] is True
+    assert data["data"]["bio"] == "Updated bio"
+    assert data["data"]["manually_edited"] is True
+
+
+def test_patch_agent_sets_manually_edited(client, sim_with_profiles, tmp_path):
+    sim_id = sim_with_profiles
+    client.patch(f"/api/simulation/{sim_id}/agent/0", json={"bio": "New bio"})
+    sim_dir = tmp_path / sim_id
+    profiles = json.loads((sim_dir / "reddit_profiles.json").read_text())
+    assert profiles[0]["manually_edited"] is True
+    assert profiles[1]["manually_edited"] is False  # untouched
+
+
+def test_patch_agent_not_found(client, sim_with_profiles):
+    sim_id = sim_with_profiles
+    resp = client.patch(f"/api/simulation/{sim_id}/agent/99", json={"bio": "x"})
+    assert resp.status_code == 404