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draft/Features_old/Cross-Feature Constraints.md

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+## 1\. Purpose
+
+This document defines **cross-feature constraints** that apply across multiple system features and components. These constraints ensure consistent behavior, prevent architectural violations, and reduce integration risk.
+
+Cross-feature constraints are **mandatory rules** that all future software design and implementation must comply with.
+
+## 2\. Architectural Constraints
+
+### CFC-ARCH-01: Layered Architecture Enforcement
+
+*   Application logic shall not access hardware directly.
+    
+*   All hardware access shall be performed via Drivers and OSAL layers.
+    
+*   Persistence access shall only be performed through the DP component.
+    
+
+**Impacted Features:**  
+DAQ, DQC, DATA, DIAG, SYS, OTA, SEC
+
+### CFC-ARCH-02: State-Aware Feature Execution
+
+*   All features shall be aware of the current system state.
+    
+*   Features shall not execute actions that are invalid for the current state.
+    
+
+**Examples:**
+
+*   DAQ shall not start sampling during OTA\_UPDATE.
+    
+*   Communication shall be limited during TEARDOWN.
+    
+
+**Impacted Features:**  
+SYS, DAQ, COM, OTA, DATA
+
+## 3\. Concurrency & Timing Constraints
+
+### CFC-TIME-01: Non-Blocking Operation
+
+*   Sensor acquisition, communication, and UI updates shall be non-blocking.
+    
+*   Blocking operations shall be isolated in controlled system services (e.g., persistence task).
+    
+
+**Impacted Features:**  
+DAQ, COM, SYS
+
+### CFC-TIME-02: Deterministic Task Behavior
+
+*   Time-critical tasks (sensor acquisition, watchdog servicing) shall have deterministic execution time.
+    
+*   Dynamic memory allocation during runtime shall be minimized or prohibited in critical paths.
+    
+
+**Impacted Features:**  
+DAQ, SYS, DIAG
+
+## 4\. Data & Persistence Constraints
+
+### CFC-DATA-01: Single Source of Truth
+
+*   Runtime and persistent data shall be owned and managed by the DP component.
+    
+*   No feature shall maintain private persistent copies of shared system data.
+    
+
+**Impacted Features:**  
+DATA, DAQ, DIAG, SYS, OTA
+
+### CFC-DATA-02: Data Consistency During Transitions
+
+*   No data write operations shall occur during teardown unless explicitly authorized by the System Manager.
+    
+*   Persistence completion shall be confirmed before state transitions.
+    
+
+**Impacted Features:**  
+SYS, DATA, OTA
+
+## 5\. Security Constraints
+
+### CFC-SEC-01: Security First Initialization
+
+*   Secure boot and flash protection shall be enabled before any application-level logic executes.
+    
+
+**Impacted Features:**  
+SEC, SYS
+
+### CFC-SEC-02: Encrypted Channels Only
+
+*   OTA, diagnostics, and data transmission shall only occur over encrypted and authenticated channels.
+    
+
+**Impacted Features:**  
+COM, OTA, DIAG, SEC
+
+## 6\. HMI & Debug Constraints
+
+### CFC-HMI-01: Read-Only Local UI
+
+*   The OLED HMI shall not allow configuration changes that affect system safety or security.
+    
+*   Configuration updates shall only be accepted via authenticated communication channels.
+    
+
+**Impacted Features:**  
+SYS, SEC
+
+### CFC-DBG-01: Debug Isolation
+
+*   Debug and engineering sessions shall not interfere with normal system operation.
+    
+*   Debug commands shall respect system state restrictions.
+    
+
+**Impacted Features:**  
+SYS, DIAG, SEC