diff --git a/codeflow_engine/__init__.py b/codeflow_engine/__init__.py
index 0de48ba..8d9fb51 100644
--- a/codeflow_engine/__init__.py
+++ b/codeflow_engine/__init__.py
@@ -34,9 +34,16 @@
 )
 from codeflow_engine.integrations.base import Integration
 from codeflow_engine.quality.metrics_collector import MetricsCollector
-from codeflow_engine.security.authorization.enterprise_manager import (
-    EnterpriseAuthorizationManager,
-)
+
+# Security - guarded import
+EnterpriseAuthorizationManager: type[Any] | None = None
+try:
+    from codeflow_engine.security.authorization.enterprise_manager import (
+        EnterpriseAuthorizationManager,
+    )
+except (ImportError, OSError):
+    pass
+
 from codeflow_engine.workflows.base import Workflow
 from codeflow_engine.workflows.engine import WorkflowEngine
 
diff --git a/codeflow_engine/actions/__init__.py b/codeflow_engine/actions/__init__.py
index 5b38a41..5178031 100644
--- a/codeflow_engine/actions/__init__.py
+++ b/codeflow_engine/actions/__init__.py
@@ -17,19 +17,66 @@
 
 from codeflow_engine.actions.registry import ActionRegistry
 
-# Import category modules
-from codeflow_engine.actions import (
-    ai_actions,
-    analysis,
-    base,
-    generation,
-    git,
-    issues,
-    maintenance,
-    platform,
-    quality,
-    scripts,
-)
+# Import category modules with error handling for optional dependencies
+ai_actions = None
+try:
+    from codeflow_engine.actions import ai_actions
+except (ImportError, OSError):
+    pass
+
+analysis = None
+try:
+    from codeflow_engine.actions import analysis
+except (ImportError, OSError):
+    pass
+
+base = None
+try:
+    from codeflow_engine.actions import base
+except (ImportError, OSError):
+    pass
+
+generation = None
+try:
+    from codeflow_engine.actions import generation
+except (ImportError, OSError):
+    pass
+
+git = None
+try:
+    from codeflow_engine.actions import git
+except (ImportError, OSError):
+    pass
+
+issues = None
+try:
+    from codeflow_engine.actions import issues
+except (ImportError, OSError):
+    pass
+
+maintenance = None
+try:
+    from codeflow_engine.actions import maintenance
+except (ImportError, OSError):
+    pass
+
+platform = None
+try:
+    from codeflow_engine.actions import platform
+except (ImportError, OSError):
+    pass
+
+quality = None
+try:
+    from codeflow_engine.actions import quality
+except (ImportError, OSError):
+    pass
+
+scripts = None
+try:
+    from codeflow_engine.actions import scripts
+except (ImportError, OSError):
+    pass
 
 # Re-export commonly used actions for backward compatibility
 # Analysis
diff --git a/codeflow_engine/actions/ai_actions/__init__.py b/codeflow_engine/actions/ai_actions/__init__.py
index ac2d9cb..db90918 100644
--- a/codeflow_engine/actions/ai_actions/__init__.py
+++ b/codeflow_engine/actions/ai_actions/__init__.py
@@ -37,8 +37,18 @@
 except ImportError:
     pass
 
-# Submodule exports
-from codeflow_engine.actions.ai_actions import autogen, llm
+# Submodule exports with guarded imports
+autogen = None
+try:
+    from codeflow_engine.actions.ai_actions import autogen
+except (ImportError, OSError):
+    pass
+
+llm = None
+try:
+    from codeflow_engine.actions.ai_actions import llm
+except (ImportError, OSError):
+    pass
 
 __all__ = [
     "AutoGenAgentSystem",
diff --git a/codeflow_engine/actions/issues/__init__.py b/codeflow_engine/actions/issues/__init__.py
index 6371e92..213ea44 100644
--- a/codeflow_engine/actions/issues/__init__.py
+++ b/codeflow_engine/actions/issues/__init__.py
@@ -43,8 +43,15 @@
 except ImportError:
     pass
 
+FindStaleIssuesOrPRs: type[Any] | None = None
+try:
+    from codeflow_engine.actions.issues.find_stale_issues_or_prs import FindStaleIssuesOrPRs
+except ImportError:
+    pass
+
 __all__ = [
     "CreateOrUpdateIssue",
+    "FindStaleIssuesOrPRs",
     "IssueCreator",
     "LabelPR",
     "LabelPRBySize",
diff --git a/codeflow_engine/models/base.py b/codeflow_engine/models/base.py
index ece7c6e..6a06f65 100644
--- a/codeflow_engine/models/base.py
+++ b/codeflow_engine/models/base.py
@@ -6,7 +6,7 @@
 
 from abc import ABC
 from dataclasses import dataclass, field
-from datetime import datetime
+from datetime import datetime, timezone
 from typing import Any
 
 
@@ -15,7 +15,7 @@ class BaseModel(ABC):
     """Base class for all CodeFlow models with common functionality."""
 
     id: str | None = None
-    created_at: datetime = field(default_factory=datetime.utcnow)
+    created_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
     updated_at: datetime | None = None
 
     def to_dict(self) -> dict[str, Any]:
@@ -33,14 +33,18 @@ def to_dict(self) -> dict[str, Any]:
 
 @dataclass
 class TimestampMixin:
-    """Mixin for models that need timestamp tracking."""
+    """Mixin for models that need timestamp tracking.
+    
+    Note: Defines created_at and updated_at fields (same as BaseModel).
+    Be cautious when using with BaseModel in multiple inheritance to avoid conflicts.
+    """
 
-    created_at: datetime = field(default_factory=datetime.utcnow)
+    created_at: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
     updated_at: datetime | None = None
 
     def touch(self) -> None:
         """Update the updated_at timestamp."""
-        self.updated_at = datetime.utcnow()
+        self.updated_at = datetime.now(timezone.utc)
 
 
 @dataclass
diff --git a/codeflow_engine/models/config.py b/codeflow_engine/models/config.py
index bf13d37..757f593 100644
--- a/codeflow_engine/models/config.py
+++ b/codeflow_engine/models/config.py
@@ -4,10 +4,11 @@
 This module contains data models for configuration objects used in the CodeFlow system.
 """
 
-from dataclasses import dataclass, field
 from enum import StrEnum
 from typing import Any
 
+from pydantic import BaseModel, Field, SecretStr, field_validator
+
 
 class LogLevel(StrEnum):
     """Logging levels for the application."""
@@ -28,59 +29,79 @@ class Environment(StrEnum):
     TESTING = "testing"
 
 
-@dataclass
-class DatabaseConfig:
-    """Database configuration model."""
+class DatabaseConfig(BaseModel):
+    """Database configuration model with validation."""
 
     url: str
-    pool_size: int = 5
-    max_overflow: int = 10
+    pool_size: int = Field(default=5, ge=0)
+    max_overflow: int = Field(default=10, ge=0)
     echo: bool = False
     ssl_required: bool = True
 
+    @field_validator("url")
+    @classmethod
+    def validate_url(cls, v: str) -> str:
+        """Validate database URL format."""
+        if not v:
+            raise ValueError("Database URL cannot be empty")
+        # Basic URL validation - must contain ://
+        if "://" not in v:
+            raise ValueError(
+                "Invalid database URL format. Expected format: dialect://user:password@host:port/database"
+            )
+        return v
+
 
-@dataclass
-class RedisConfig:
-    """Redis configuration model."""
+class RedisConfig(BaseModel):
+    """Redis configuration model with validation."""
 
     url: str
-    max_connections: int = 10
+    max_connections: int = Field(default=10, ge=0)
     ssl: bool = True
 
+    @field_validator("url")
+    @classmethod
+    def validate_url(cls, v: str) -> str:
+        """Validate Redis URL format."""
+        if not v:
+            raise ValueError("Redis URL cannot be empty")
+        # Basic URL validation - must contain ://
+        if "://" not in v:
+            raise ValueError(
+                "Invalid Redis URL format. Expected format: redis://host:port or rediss://host:port"
+            )
+        return v
+
 
-@dataclass
-class LLMConfig:
-    """LLM provider configuration model."""
+class LLMConfig(BaseModel):
+    """LLM provider configuration model with validation."""
 
     provider: str
-    api_key: str | None = None
+    api_key: SecretStr | None = None
     model: str  # Required; provider-specific (e.g., gpt-4, claude-3-opus, mistral-large)
-    temperature: float = 0.7
-    max_tokens: int = 4096
+    temperature: float = Field(default=0.7, ge=0.0, le=2.0)
+    max_tokens: int = Field(default=4096, gt=0)
 
 
-@dataclass
-class GitHubConfig:
-    """GitHub integration configuration model."""
+class GitHubConfig(BaseModel):
+    """GitHub integration configuration model with secrets protection."""
 
-    token: str | None = None
+    token: SecretStr | None = None
     app_id: str | None = None
-    private_key: str | None = None
-    webhook_secret: str | None = None
+    private_key: SecretStr | None = None
+    webhook_secret: SecretStr | None = None
 
 
-@dataclass
-class WorkflowConfig:
-    """Workflow execution configuration model."""
+class WorkflowConfig(BaseModel):
+    """Workflow execution configuration model with validation."""
 
-    max_concurrent: int = 10
-    timeout_seconds: int = 300
-    retry_attempts: int = 3
-    retry_delay_seconds: int = 5
+    max_concurrent: int = Field(default=10, gt=0)
+    timeout_seconds: int = Field(default=300, gt=0)
+    retry_attempts: int = Field(default=3, ge=0)
+    retry_delay_seconds: int = Field(default=5, gt=0)
 
 
-@dataclass
-class AppConfig:
+class AppConfig(BaseModel):
     """Main application configuration model."""
 
     environment: Environment = Environment.DEVELOPMENT
@@ -90,8 +111,8 @@ class AppConfig:
     redis: RedisConfig | None = None
     llm: LLMConfig | None = None
     github: GitHubConfig | None = None
-    workflow: WorkflowConfig = field(default_factory=WorkflowConfig)
-    custom_settings: dict[str, Any] = field(default_factory=dict)
+    workflow: WorkflowConfig = Field(default_factory=WorkflowConfig)
+    custom_settings: dict[str, Any] = Field(default_factory=dict)
 
 
 __all__ = [
diff --git a/codeflow_engine/models/events.py b/codeflow_engine/models/events.py
index c4144dd..ba31be1 100644
--- a/codeflow_engine/models/events.py
+++ b/codeflow_engine/models/events.py
@@ -5,7 +5,7 @@
 """
 
 from dataclasses import dataclass, field
-from datetime import datetime
+from datetime import datetime, timezone
 from enum import StrEnum
 from typing import Any
 
@@ -133,7 +133,7 @@ class WebhookEvent:
     sender: User
     installation_id: int | None = None
     payload: dict[str, Any] = field(default_factory=dict)
-    timestamp: datetime = field(default_factory=datetime.utcnow)
+    timestamp: datetime = field(default_factory=lambda: datetime.now(timezone.utc))
 
     # Optional specific event data
     pull_request: PullRequest | None = None