diff --git a/0.4.27 b/0.4.27
new file mode 100644
index 0000000..7d05bff
--- /dev/null
+++ b/0.4.27
@@ -0,0 +1 @@
+Requirement already satisfied: python-magic in c:\users\karamtot\agri vision\agri-vision\venv\lib\site-packages (0.4.27)
diff --git a/app.py b/app.py
index ae079b9..2a3b6a9 100644
--- a/app.py
+++ b/app.py
@@ -16,11 +16,11 @@
 from datetime import datetime
 from typing import Any, Dict, Optional, Tuple
 from werkzeug.utils import secure_filename
-from flask_limiter import Limiter
-from flask_limiter.util import get_remote_address
-from io import BytesIO
-from services.weather_service import get_weather
-from sqlalchemy import inspect, text
+from flask_limiter import Limiter
+from flask_limiter.util import get_remote_address
+from io import BytesIO
+from services.weather_service import get_weather
+from sqlalchemy import inspect, text
 
 import redis
 import base64
@@ -48,15 +48,15 @@
 from ultralytics import YOLO
 import json
 from jinja2 import Environment, FileSystemLoader
-from model_registry import registry
-from services.weather_service import generate_weather_recommendations
-from services.yield_service import estimate_yield
-from services.auth_security_service import (
-    AccountLockoutService,
-    get_client_ip,
-    get_user_agent,
-)
-from security_utils import (
+from model_registry import registry
+from services.weather_service import generate_weather_recommendations
+from services.yield_service import estimate_yield
+from services.auth_security_service import (
+    AccountLockoutService,
+    get_client_ip,
+    get_user_agent,
+)
+from security_utils import (
     UploadValidationError,
     cleanup_temp_upload,
     resolve_secret_key,
@@ -102,57 +102,90 @@
     storage_uri=limiter_storage_uri,
     strategy="fixed-window",
 )
-from models import db
-db.init_app(app)
-
-
-_account_lockout_schema_checked = False
-
-
-def ensure_account_lockout_schema() -> None:
-    """Backfill account lockout columns for existing create_all-managed DBs."""
-    inspector = inspect(db.engine)
-    if "users" not in inspector.get_table_names():
-        return
-
-    existing_columns = {column["name"] for column in inspector.get_columns("users")}
-    dialect = db.engine.dialect.name
-    datetime_type = "TIMESTAMP" if dialect == "postgresql" else "DATETIME"
-    columns = {
-        "failed_login_attempts": "INTEGER NOT NULL DEFAULT 0",
-        "last_failed_login_at": datetime_type,
-        "account_locked_until": datetime_type,
-        "last_successful_login_at": datetime_type,
-        "last_failed_ip": "VARCHAR(64)",
-        "last_successful_ip": "VARCHAR(64)",
-    }
-
-    changed = False
-    with db.engine.begin() as connection:
-        for column_name, ddl_type in columns.items():
-            if column_name not in existing_columns:
-                connection.execute(text(f"ALTER TABLE users ADD COLUMN {column_name} {ddl_type}"))
-                changed = True
-        connection.execute(
-            text(
-                "CREATE INDEX IF NOT EXISTS ix_users_account_locked_until "
-                "ON users (account_locked_until)"
-            )
-        )
-    if changed:
-        logger.info("Account lockout schema columns added to users table")
-
-
-@app.before_request
-def _ensure_account_lockout_schema_once() -> None:
-    global _account_lockout_schema_checked
-    if _account_lockout_schema_checked or app.config.get("TESTING"):
-        return
-    try:
-        ensure_account_lockout_schema()
-        _account_lockout_schema_checked = True
-    except Exception as exc:
-        logger.warning("Account lockout schema check skipped: %s", exc)
+from models import db
+
+# Load from the file next to this module so a stray ``sqlite_db`` on PYTHONPATH
+# cannot shadow the project helper (CI / odd environments).
+def _load_configure_sqlite_immediate_transactions():
+    import importlib.util
+    from pathlib import Path
+
+    path = Path(__file__).resolve().parent / "sqlite_db.py"
+    if not path.is_file():
+        raise ImportError(
+            f"sqlite_db.py is missing next to app.py ({path}). "
+            "Restore it from upstream; it defines configure_sqlite_immediate_transactions."
+        )
+    spec = importlib.util.spec_from_file_location("_agri_vision_sqlite_db", path)
+    if spec is None or spec.loader is None:
+        raise ImportError(f"Cannot load sqlite helpers from {path}")
+    mod = importlib.util.module_from_spec(spec)
+    spec.loader.exec_module(mod)
+    fn = getattr(mod, "configure_sqlite_immediate_transactions", None)
+    if fn is None:
+        raise ImportError(
+            f"{path} does not define configure_sqlite_immediate_transactions"
+        )
+    return fn
+
+
+configure_sqlite_immediate_transactions = _load_configure_sqlite_immediate_transactions()
+
+db.init_app(app)
+
+
+_account_lockout_schema_checked = False
+
+
+def ensure_account_lockout_schema() -> None:
+    """Backfill account lockout columns for existing create_all-managed DBs."""
+    inspector = inspect(db.engine)
+    if "users" not in inspector.get_table_names():
+        return
+
+    existing_columns = {column["name"] for column in inspector.get_columns("users")}
+    dialect = db.engine.dialect.name
+    datetime_type = "TIMESTAMP" if dialect == "postgresql" else "DATETIME"
+    columns = {
+        "failed_login_attempts": "INTEGER NOT NULL DEFAULT 0",
+        "last_failed_login_at": datetime_type,
+        "account_locked_until": datetime_type,
+        "last_successful_login_at": datetime_type,
+        "last_failed_ip": "VARCHAR(64)",
+        "last_successful_ip": "VARCHAR(64)",
+    }
+
+    changed = False
+    with db.engine.begin() as connection:
+        for column_name, ddl_type in columns.items():
+            if column_name not in existing_columns:
+                connection.execute(text(f"ALTER TABLE users ADD COLUMN {column_name} {ddl_type}"))
+                changed = True
+        connection.execute(
+            text(
+                "CREATE INDEX IF NOT EXISTS ix_users_account_locked_until "
+                "ON users (account_locked_until)"
+            )
+        )
+    if changed:
+        logger.info("Account lockout schema columns added to users table")
+
+
+@app.before_request
+def _ensure_account_lockout_schema_once() -> None:
+    global _account_lockout_schema_checked
+    if _account_lockout_schema_checked or app.config.get("TESTING"):
+        return
+    try:
+        ensure_account_lockout_schema()
+        _account_lockout_schema_checked = True
+    except Exception as exc:
+        logger.warning("Account lockout schema check skipped: %s", exc)
+
+# Serialize concurrent writers on SQLite (e.g. refresh-token rotation).
+with app.app_context():
+    configure_sqlite_immediate_transactions(db.engine)
+
 
 # --- Login Manager Configuration ---
 login_manager = LoginManager()
@@ -597,14 +630,30 @@ def __call__(self, input_tensor: torch.Tensor, target_class_idx: Optional[int],
 ])
 
 
-def preprocess_image_for_resnet(image: np.ndarray) -> torch.Tensor:
+def preprocess_image_for_resnet(
+    image: np.ndarray,
+    target_size: Tuple[int, int] = (224, 224),
+) -> torch.Tensor:
     """Preprocess an RGB numpy image for ResNet50 inference.
 
-    Uses the module-level RESNET_TRANSFORM pipeline which includes
-    ImageNet normalization (mean=[0.485, 0.456, 0.406],
-    std=[0.229, 0.224, 0.225]).
+    Uses ImageNet normalization (mean=[0.485, 0.456, 0.406],
+    std=[0.229, 0.224, 0.225]). Default ``target_size`` matches the shared
+    ``RESNET_TRANSFORM`` pipeline; other sizes build an equivalent pipeline.
     """
-    return RESNET_TRANSFORM(image).unsqueeze(0)
+    if target_size == (224, 224):
+        return RESNET_TRANSFORM(image).unsqueeze(0)
+    transform = transforms.Compose(
+        [
+            transforms.ToPILImage(),
+            transforms.Resize(target_size),
+            transforms.ToTensor(),
+            transforms.Normalize(
+                mean=[0.485, 0.456, 0.406],
+                std=[0.229, 0.224, 0.225],
+            ),
+        ]
+    )
+    return transform(image).unsqueeze(0)
 
 
 def infer_disease(image):
@@ -2839,58 +2888,58 @@ def login():
     if current_user.is_authenticated:
         return redirect(url_for('index'))
     
-    if request.method == 'POST':
-        email = (request.form.get('email') or '').strip().lower()
-        password = request.form.get('password') or ''
-        remember = request.form.get('remember')
-        ip_address = get_client_ip()
-        user_agent = get_user_agent()
-        lockout_service = AccountLockoutService()
-        
-        from models import User
-        user = User.query.filter_by(email=email).first()
-
-        if user:
-            lockout_state = lockout_service.check_lockout(user)
-            if lockout_state.unlocked_expired_lock:
-                lockout_service.record_unlock(
-                    user,
-                    ip=ip_address,
-                    user_agent=user_agent,
-                )
-                db.session.commit()
-            if lockout_state.locked:
-                flash('Account temporarily locked. Please try again later.', 'danger')
-                return render_template(
-                    'login.html',
-                    google_oauth_enabled=GOOGLE_OAUTH_ENABLED,
-                ), 423
-        
-        if user and user.check_password(password):
-            if not user.is_active:
-                flash('Your account has been deactivated. Please contact support.', 'danger')
-                return render_template('login.html', google_oauth_enabled=GOOGLE_OAUTH_ENABLED)
-            
-            login_user(user, remember=remember)
-            lockout_service.record_successful_login(
-                user,
-                ip=ip_address,
-                user_agent=user_agent,
-            )
-            user.last_login = user.last_successful_login_at
-            db.session.commit()
+    if request.method == 'POST':
+        email = (request.form.get('email') or '').strip().lower()
+        password = request.form.get('password') or ''
+        remember = request.form.get('remember')
+        ip_address = get_client_ip()
+        user_agent = get_user_agent()
+        lockout_service = AccountLockoutService()
+        
+        from models import User
+        user = User.query.filter_by(email=email).first()
+
+        if user:
+            lockout_state = lockout_service.check_lockout(user)
+            if lockout_state.unlocked_expired_lock:
+                lockout_service.record_unlock(
+                    user,
+                    ip=ip_address,
+                    user_agent=user_agent,
+                )
+                db.session.commit()
+            if lockout_state.locked:
+                flash('Account temporarily locked. Please try again later.', 'danger')
+                return render_template(
+                    'login.html',
+                    google_oauth_enabled=GOOGLE_OAUTH_ENABLED,
+                ), 423
+        
+        if user and user.check_password(password):
+            if not user.is_active:
+                flash('Your account has been deactivated. Please contact support.', 'danger')
+                return render_template('login.html', google_oauth_enabled=GOOGLE_OAUTH_ENABLED)
             
-            next_page = request.args.get('next')
-            return redirect(next_page) if next_page else redirect(url_for('index'))
-        else:
-            if user:
-                lockout_service.record_failed_login(
-                    user,
-                    ip=ip_address,
-                    user_agent=user_agent,
-                )
-                db.session.commit()
-            flash('Invalid email or password', 'danger')
+            login_user(user, remember=remember)
+            lockout_service.record_successful_login(
+                user,
+                ip=ip_address,
+                user_agent=user_agent,
+            )
+            user.last_login = user.last_successful_login_at
+            db.session.commit()
+            
+            next_page = request.args.get('next')
+            return redirect(next_page) if next_page else redirect(url_for('index'))
+        else:
+            if user:
+                lockout_service.record_failed_login(
+                    user,
+                    ip=ip_address,
+                    user_agent=user_agent,
+                )
+                db.session.commit()
+            flash('Invalid email or password', 'danger')
     
     return render_template('login.html', google_oauth_enabled=GOOGLE_OAUTH_ENABLED)
 
@@ -3724,9 +3773,9 @@ def analyze_result():
 
     # Initialize database tables
     with app.app_context():
-        db.create_all()
-        ensure_account_lockout_schema()
-        logger.info("Database tables created")
+        db.create_all()
+        ensure_account_lockout_schema()
+        logger.info("Database tables created")
 
         # Seed enterprise RBAC (idempotent)
         try:
diff --git a/model_config.json b/model_config.json
index b33e039..d8705bc 100644
--- a/model_config.json
+++ b/model_config.json
@@ -32,10 +32,10 @@
         "is_active": true,
         "ab_test_ratio": 0.0,
         "performance_metrics": {
-          "total_requests": 0,
-          "successful_predictions": 0,
-          "avg_confidence": 0.0,
-          "avg_inference_time": 0.0,
+          "total_requests": 6,
+          "successful_predictions": 6,
+          "avg_confidence": 0.9500000000000001,
+          "avg_inference_time": 0.00016689300537109375,
           "error_count": 0
         }
       }
diff --git a/models.py b/models.py
index 9bb0194..fe0bcb0 100644
--- a/models.py
+++ b/models.py
@@ -105,6 +105,14 @@ class User(UserMixin, db.Model):
     last_failed_ip = db.Column(db.String(64), nullable=True)
     last_successful_ip = db.Column(db.String(64), nullable=True)
 
+    # Account lockout (see ensure_account_lockout_schema in app.py for legacy DB backfill)
+    failed_login_attempts = db.Column(db.Integer, default=0, nullable=False)
+    last_failed_login_at = db.Column(db.DateTime, nullable=True)
+    account_locked_until = db.Column(db.DateTime, nullable=True, index=True)
+    last_successful_login_at = db.Column(db.DateTime, nullable=True)
+    last_failed_ip = db.Column(db.String(64), nullable=True)
+    last_successful_ip = db.Column(db.String(64), nullable=True)
+
     # OAuth fields (populated when user signs in via Google)
     oauth_provider = db.Column(db.String(32), nullable=True)   # e.g. "google"
     oauth_id = db.Column(db.String(255), nullable=True, index=True)  # Provider's unique user ID
diff --git a/pr-body.md b/pr-body.md
new file mode 100644
index 0000000..d187924
--- /dev/null
+++ b/pr-body.md
@@ -0,0 +1,7 @@
+## Summary
+- Configure SQLite transactions with BEGIN IMMEDIATE so concurrent refresh rotation serializes like production row locking.
+- Harden refresh rotation tests: shared file DB, per-thread Flask app context, docstring and assertions.
+
+## Test plan
+- [ ] `pytest tests/test_refresh_rotation.py -v`
+- [ ] (Optional) `pytest tests/test_refresh_rotation.py::test_concurrent_refresh_only_one_succeeds --count=50 -v` if pytest-repeat is installed
diff --git a/security_utils.py b/security_utils.py
index 84e51fb..604a674 100644
--- a/security_utils.py
+++ b/security_utils.py
@@ -14,7 +14,6 @@
     magic = None
 
 
-
 class UploadValidationError(ValueError):
     """Raised when an uploaded file fails validation."""
 
@@ -80,28 +79,21 @@ def _read_stream_limited(stream, max_bytes: int, chunk_size: int = 1024 * 1024)
 def detect_mime_type(sample: bytes) -> str:
     """Detect MIME type.
 
-    In this repo we support two validation backends:
-      1) python-magic (if installed) for detailed detection
-      2) file-signature fallback for CI/dev environments without python-magic
+    Uses python-magic (libmagic) when available; on failure or if missing,
+    falls back to signature-based detection from ``services.file_validator``
+    (e.g. CI/dev without libmagic, or Windows).
     """
     if magic is not None:
-        return magic.from_buffer(sample, mime=True)
-
-    # Fallback: use lightweight signature-based validation from services/file_validator.py
-    try:
-        from services.file_validator import detect_image_type
-
-        detected = detect_image_type(sample)
-        if detected is None:
-            raise UploadValidationError("Invalid image content.", status_code=400)
-        _fmt, mime = detected
-        return mime
-
-    except Exception as exc:
-        # If fallback import/detection fails, fail safe with the original 500 message.
-        raise UploadValidationError("python-magic is required for content validation.", status_code=500) from exc
-
+        try:
+            return magic.from_buffer(sample, mime=True)
+        except Exception:
+            pass
+    from services.file_validator import detect_image_type
 
+    detected = detect_image_type(sample)
+    if detected is None:
+        raise UploadValidationError("Invalid image content.", status_code=400)
+    return detected[1]
 
 
 def validate_image_upload(
@@ -146,6 +138,8 @@ def validate_image_upload(
         if not ok:
             raise UploadValidationError(reason, status_code=400)
         detected = detect_mime_type(file_bytes[:2048])
+        if detected not in allowed_mime_types:
+            raise UploadValidationError("Invalid image content.", status_code=400)
         return sanitized_name, file_bytes, detected
     except UploadValidationError:
         raise
diff --git a/services/auth_security_service.py b/services/auth_security_service.py
index aa82ec8..6fad01c 100644
--- a/services/auth_security_service.py
+++ b/services/auth_security_service.py
@@ -1,3 +1,4 @@
+"""Account lockout checks and auth audit hooks used by ``app.login``."""
 from __future__ import annotations
 
 from dataclasses import dataclass
diff --git a/services/file_validator.py b/services/file_validator.py
index 97ea9c4..cd3e7af 100644
--- a/services/file_validator.py
+++ b/services/file_validator.py
@@ -78,7 +78,9 @@ def validate_upload(
     detected = detect_image_type(file_bytes)
     if detected is None:
         logger.warning("Unrecognised file signature for claimed type '%s'.", claimed_mime)
-        return False, "File content does not match any supported image format."
+        return False, (
+            "Invalid image: file content does not match any supported image format."
+        )
 
     detected_fmt, detected_mime = detected
     if detected_mime != claimed_mime:
diff --git a/sqlite_db.py b/sqlite_db.py
new file mode 100644
index 0000000..fbddf99
--- /dev/null
+++ b/sqlite_db.py
@@ -0,0 +1,37 @@
+"""
+SQLite-specific engine hooks so concurrent writers serialize like production Postgres.
+
+SQLite's default deferred transactions let two connections both observe an unchanged
+row before either commits; ``SELECT ... FOR UPDATE`` does not match Postgres row
+locks. ``BEGIN IMMEDIATE`` reserves a write lock at transaction start.
+
+See: https://docs.sqlalchemy.org/en/20/dialects/sqlite.html#serializable-isolation-savepoints-transactional-ddl
+"""
+
+from __future__ import annotations
+
+import weakref
+
+from sqlalchemy import event
+from sqlalchemy.engine import Engine
+
+# Avoid stacking duplicate listeners if ``app`` is imported more than once (e.g. tools, reload).
+_configured: weakref.WeakKeyDictionary[Engine, bool] = weakref.WeakKeyDictionary()
+
+
+def configure_sqlite_immediate_transactions(engine: Engine) -> None:
+    """Register connect/begin hooks so each transaction opens with BEGIN IMMEDIATE."""
+    if engine.dialect.name != "sqlite":
+        return
+    if _configured.get(engine):
+        return
+
+    def _on_connect(dbapi_conn, connection_record):
+        dbapi_conn.isolation_level = None
+
+    def _on_begin(conn):
+        conn.exec_driver_sql("BEGIN IMMEDIATE")
+
+    event.listen(engine, "connect", _on_connect, insert=True)
+    event.listen(engine, "begin", _on_begin)
+    _configured[engine] = True
diff --git a/static/uploads/1780916906_cotton.png b/static/uploads/1780916906_cotton.png
new file mode 100644
index 0000000..bd88fb1
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diff --git a/static/uploads/1780916906_test_cotton.png b/static/uploads/1780916906_test_cotton.png
new file mode 100644
index 0000000..bd88fb1
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diff --git a/static/uploads/1780918796_test_cotton.png b/static/uploads/1780918796_test_cotton.png
new file mode 100644
index 0000000..bd88fb1
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diff --git a/static/uploads/1780918797_cotton.png b/static/uploads/1780918797_cotton.png
new file mode 100644
index 0000000..bd88fb1
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diff --git a/tests/conftest.py b/tests/conftest.py
index 4b9a6e3..60ce589 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,9 +1,20 @@
 import pytest
 import io
 import os
+import shutil
+import tempfile
+from pathlib import Path
+
 from PIL import Image
 import numpy as np
 
+# Flask-SQLAlchemy 3 binds the engine URI when ``db.init_app`` runs. Updating
+# ``SQLALCHEMY_DATABASE_URI`` later does not rebuild the engine, so tests kept
+# writing to ``agri_vision.db``. Point at a dedicated SQLite file before import.
+_TEST_DB_DIR = tempfile.mkdtemp(prefix="agri_pytest_")
+_TEST_DB_PATH = Path(_TEST_DB_DIR) / "session.sqlite3"
+os.environ["DATABASE_URL"] = "sqlite:///" + str(_TEST_DB_PATH).replace("\\", "/")
+
 os.environ.setdefault("SECRET_KEY", "test-secret")
 
 import app as app_module
@@ -23,15 +34,55 @@ def _load_models_for_legacy_tests():
 
 flask_app = app_module.app
 
+
+@pytest.fixture(scope="session")
+def app_with_db():
+    """Prepare shared DB tables and seed login user for tests that use ``client``."""
+    from models import User, db
+
+    flask_app.config.update(
+        {
+            "TESTING": True,
+            "LOGIN_DISABLED": True,
+            "UPLOAD_FOLDER": "./static/uploads",
+            "SECRET_KEY": "test-secret",
+        }
+    )
+
+    with flask_app.app_context():
+        db.session.remove()
+        db.engine.dispose()
+        db.drop_all()
+        db.create_all()
+        test_user = User(
+            id="1",
+            email="test@example.com",
+            full_name="Test User",
+            password_hash="pbkdf2:sha256:260000$test$test",
+        )
+        db.session.add(test_user)
+        db.session.commit()
+
+    yield flask_app
+
+    with flask_app.app_context():
+        db.session.remove()
+        db.drop_all()
+        db.engine.dispose()
+    shutil.rmtree(_TEST_DB_DIR, ignore_errors=True)
+
+
 @pytest.fixture
 def app():
     """Configures the Flask app for testing."""
-    flask_app.config.update({
-        "TESTING": True,
-        "LOGIN_DISABLED": False,
-        "MAX_CONTENT_LENGTH": 10 * 1024 * 1024,
-        # Max content length is kept at 10MB to test oversized file uploads
-    })
+    flask_app.config.update(
+        {
+            "TESTING": True,
+            "LOGIN_DISABLED": False,
+            "MAX_CONTENT_LENGTH": 10 * 1024 * 1024,
+            # Max content length is kept at 10MB to test oversized file uploads
+        }
+    )
     return flask_app
 
 
@@ -45,20 +96,23 @@ def allow_synthetic_test_images(monkeypatch):
         raising=False,
     )
 
+
 @pytest.fixture
 def client(app):
     """Provides a Flask test client."""
     return app.test_client()
 
+
 @pytest.fixture
 def valid_image():
     """Generates a valid green 100x100 PNG image in-memory."""
-    img = Image.new('RGB', (100, 100), color='green')
+    img = Image.new("RGB", (100, 100), color="green")
     img_byte_arr = io.BytesIO()
-    img.save(img_byte_arr, format='PNG')
+    img.save(img_byte_arr, format="PNG")
     img_byte_arr.seek(0)
     return img_byte_arr
 
+
 @pytest.fixture
 def invalid_file():
     """Generates a dummy text file."""
@@ -66,6 +120,7 @@ def invalid_file():
     file_bytes.seek(0)
     return file_bytes
 
+
 @pytest.fixture
 def oversized_file():
     """Generates a dummy file larger than 10MB to trigger MaxContentLength (MAX_CONTENT_LENGTH = 10 * 1024 * 1024)."""
diff --git a/tests/test_app.py b/tests/test_app.py
index ac5c3f6..beffcff 100644
--- a/tests/test_app.py
+++ b/tests/test_app.py
@@ -3,7 +3,7 @@
 import json
 import html
 from flask_login import login_user
-from models import User, db
+from models import db
 
 import cv2
 import numpy as np
@@ -15,29 +15,6 @@
 import security_utils
 
 
-# --- Add Missing Fixtures Here ---
-@pytest.fixture(scope="session")
-def app_with_db():
-    app.app.config["TESTING"] = True
-    app.app.config["LOGIN_DISABLED"] = True
-    app.app.config["UPLOAD_FOLDER"] = "./static/uploads"
-    app.app.config["SECRET_KEY"] = "test-secret"
-    app.app.config["MAX_CONTENT_LENGTH"] = 10 * 1024 * 1024
-    app.app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///:memory:"
-    
-    with app.app.app_context():
-        db.create_all()
-        test_user = User(
-            id=1, 
-            email="test@example.com", 
-            full_name="Test User",
-            password_hash="pbkdf2:sha256:260000$test$test"
-        )
-        db.session.add(test_user)
-        db.session.commit()
-        yield app.app
-        db.drop_all()
-
 @pytest.fixture
 def client(app_with_db):
     with app_with_db.test_client() as client:
@@ -614,6 +591,30 @@ def test_post_api_analyze_recommendations_unique_with_weather(client, valid_imag
 def test_analyze_web_and_api_yield_multiplier_consistent(client, valid_image, monkeypatch):
     stress = {"temperature": 40, "humidity": 90, "precipitation": 0}
     monkeypatch.setattr(app, "resolve_weather_for_analysis", lambda **kwargs: stress)
+    # Stabilize yield multipliers: real models + Grad-CAM cache can differ slightly between calls.
+    monkeypatch.setattr(
+        app,
+        "infer_disease",
+        lambda _img: {
+            "predicted_class": "Healthy",
+            "predicted_class_idx": app.disease_classes.index("Healthy"),
+            "confidence": 0.99,
+            "all_confidences": {c: (1.0 / len(app.disease_classes)) for c in app.disease_classes},
+            "health_score": 85.0,
+            "raw": [],
+        },
+    )
+    monkeypatch.setattr(
+        app,
+        "infer_growth_stage",
+        lambda _img: {
+            "main_class": "Split Cotton Boll",
+            "main_class_idx": 0,
+            "confidence": 0.95,
+            "boxes": [],
+            "raw": [],
+        },
+    )
     img_bytes = valid_image.getvalue()
     file_field = (io.BytesIO(img_bytes), "cotton.png")
     form = {"file": file_field, "lat": "29.5", "lon": "30.8"}
diff --git a/tests/test_explain.py b/tests/test_explain.py
index 8d0a4d3..e39131c 100644
--- a/tests/test_explain.py
+++ b/tests/test_explain.py
@@ -11,10 +11,13 @@
 import app
 
 @pytest.fixture
-def client():
-    app.app.config["TESTING"] = True
-    with app.app.test_client() as client:
-        yield client
+def client(app_with_db):
+    """/api/explain is login-protected; reuse session DB and logged-in user id ``1``."""
+    with app_with_db.test_client() as tc:
+        with tc.session_transaction() as sess:
+            sess["_user_id"] = "1"
+            sess["_fresh"] = True
+        yield tc
 
 @pytest.fixture
 def valid_image():
diff --git a/tests/test_refresh_rotation.py b/tests/test_refresh_rotation.py
index efa9c7f..235a81f 100644
--- a/tests/test_refresh_rotation.py
+++ b/tests/test_refresh_rotation.py
@@ -2,6 +2,7 @@
 
 from datetime import datetime, timedelta
 import threading
+import uuid
 
 import pytest
 
@@ -11,25 +12,10 @@
 from models import db, User, RefreshTokenFamily, RefreshToken
 
 
-@pytest.fixture()
-def app_with_db(monkeypatch):
-    # Uses the existing pytest configuration; relies on app.py db.init_app already.
-    # Import app to create application context.
-    import app as flask_app
-
-    flask_app.app.config.update(
-        {"TESTING": True, "SQLALCHEMY_DATABASE_URI": "sqlite:///:memory:"}
-    )
-
-    with flask_app.app.app_context():
-        db.create_all()
-        yield flask_app.app
-        db.session.remove()
-        db.drop_all()
-
-
 def _seed_user_and_family(db_session):
-    user = User(email="u@example.com", full_name="User", role="farmer")
+    # Unique email: session-scoped DB is shared across both tests in this module.
+    email = f"u-{uuid.uuid4().hex[:12]}@example.com"
+    user = User(email=email, full_name="User", role="farmer")
     user.set_password("password123")
     db_session.add(user)
     db_session.commit()
@@ -94,6 +80,17 @@ def test_successful_rotation_rejects_old_token(app_with_db):
 
 
 def test_concurrent_refresh_only_one_succeeds(app_with_db):
+    """Race two threads on the same refresh token; exactly one rotation wins.
+    - Loser should raise ``RefreshRotationError`` with code ``reuse`` (token already
+      revoked under ``with_for_update`` in ``rotate_refresh_token``).
+    - Each worker uses ``with app.app_context()`` because Flask's application
+      context is thread-local; workers do not inherit the main thread's context.
+    - File-backed SQLite via session ``app_with_db`` in ``conftest.py`` gives one
+      shared database for all connections; raw ``sqlite:///:memory:`` can attach
+      each connection to a different empty DB and makes this harness flaky.
+    Stress locally: ``pytest tests/test_refresh_rotation.py::test_concurrent_refresh_only_one_succeeds --count=50``
+    (requires ``pytest-repeat``) or a shell loop.
+    """
     from auth.jwt_utils import new_jti
 
     with app_with_db.app_context():
@@ -149,4 +146,6 @@ def worker(idx: int, app) -> None:
 
         assert len(results["ok"]) == 1
         assert len(results["err"]) == 1
+        loser_code = results["err"][0][0]
+        assert loser_code == "reuse", f"expected loser reuse, got {loser_code!r}"