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+# Failure Handling Model Specification
+
+**Document Type:** Normative System Specification  
+**Scope:** Sensor Hub (Sub-Hub) Fault Detection, Classification, and Recovery  
+**Traceability:** SR-DIAG-001 through SR-DIAG-011, SR-SYS-002, SR-SYS-004
+
+## 1. Purpose
+
+This document defines the fault taxonomy, escalation rules, recovery behaviors, and integration with the system state machine. All components SHALL adhere to this failure handling model.
+
+## 2. Fault Taxonomy
+
+### 2.1 Severity Levels
+
+| Severity | Code | Description | State Impact | Recovery Behavior |
+|----------|------|-------------|--------------|-------------------|
+| **INFO** | `DIAG_SEV_INFO` | Informational event, no action required | None | Log only |
+| **WARNING** | `DIAG_SEV_WARNING` | Non-critical fault, degraded operation | `RUNNING` → `WARNING` | Continue with reduced functionality |
+| **ERROR** | `DIAG_SEV_ERROR` | Critical fault, feature disabled | Feature-specific | Feature isolation, retry logic |
+| **FATAL** | `DIAG_SEV_FATAL` | System-critical fault, core functionality disabled | `RUNNING` → `FAULT` | Controlled teardown, recovery attempt |
+
+### 2.2 Fault Categories
+
+| Category | Description | Examples | Typical Severity |
+|----------|-------------|----------|------------------|
+| **SENSOR** | Sensor hardware or communication failure | Disconnection, out-of-range, non-responsive | WARNING (single), ERROR (multiple), FATAL (all) |
+| **COMMUNICATION** | Network or protocol failure | Link loss, timeout, authentication failure | WARNING (temporary), ERROR (persistent), FATAL (critical) |
+| **STORAGE** | Persistence or storage medium failure | SD card failure, NVM corruption, write failure | WARNING (degraded), ERROR (persistent), FATAL (critical) |
+| **SECURITY** | Security violation or authentication failure | Secure boot failure, key corruption, unauthorized access | FATAL (always) |
+| **SYSTEM** | System resource or configuration failure | Memory exhaustion, task failure, configuration error | ERROR (recoverable), FATAL (unrecoverable) |
+| **OTA** | Firmware update failure | Validation failure, transfer error, flash error | ERROR (retry), FATAL (rollback) |
+| **CALIBRATION** | Calibration or machine constants failure | Invalid MC, calibration error, sensor mismatch | WARNING (single), ERROR (critical) |
+
+## 3. Diagnostic Code Structure
+
+### 3.1 Diagnostic Code Format
+
+```
+DIAG-<CATEGORY>-<COMPONENT>-<NUMBER>
+```
+
+- **CATEGORY:** Two-letter code (SN, CM, ST, SC, SY, OT, CL)
+- **COMPONENT:** Component identifier (e.g., TEMP, HUM, CO2, NET, SD, OTA)
+- **NUMBER:** Unique fault number (0001-9999)
+
+### 3.2 Diagnostic Code Registry
+
+| Code | Severity | Category | Component | Description |
+|------|----------|----------|-----------|-------------|
+| `DIAG-SN-TEMP-0001` | WARNING | SENSOR | Temperature | Temperature sensor disconnected |
+| `DIAG-SN-TEMP-0002` | ERROR | SENSOR | Temperature | Temperature sensor out of range |
+| `DIAG-SN-TEMP-0003` | FATAL | SENSOR | Temperature | All temperature sensors failed |
+| `DIAG-CM-NET-0001` | WARNING | COMMUNICATION | Network | Main Hub link temporarily lost |
+| `DIAG-CM-NET-0002` | ERROR | COMMUNICATION | Network | Main Hub link persistently lost |
+| `DIAG-ST-SD-0001` | WARNING | STORAGE | SD Card | SD card write failure (retry successful) |
+| `DIAG-ST-SD-0002` | ERROR | STORAGE | SD Card | SD card persistent write failure |
+| `DIAG-ST-SD-0003` | FATAL | STORAGE | SD Card | SD card corruption detected |
+| `DIAG-SC-BOOT-0001` | FATAL | SECURITY | Secure Boot | Secure boot verification failed |
+| `DIAG-SY-MEM-0001` | ERROR | SYSTEM | Memory | Memory allocation failure |
+| `DIAG-OT-FW-0001` | ERROR | OTA | Firmware | Firmware integrity validation failed |
+| `DIAG-CL-MC-0001` | WARNING | CALIBRATION | Machine Constants | Invalid sensor slot configuration |
+
+## 4. Fault Detection Rules
+
+### 4.1 Sensor Fault Detection
+
+| Condition | Detection Method | Severity Assignment |
+|-----------|------------------|-------------------|
+| Sensor disconnected | Hardware presence signal | WARNING (if other sensors available) |
+| Sensor non-responsive | Communication timeout (3 retries) | ERROR (if critical sensor) |
+| Sensor out of range | Value validation against limits | WARNING (if single occurrence), ERROR (if persistent) |
+| All sensors failed | Count of failed sensors = total | FATAL |
+
+### 4.2 Communication Fault Detection
+
+| Condition | Detection Method | Severity Assignment |
+|-----------|------------------|-------------------|
+| Link temporarily lost | Heartbeat timeout (< 30s) | WARNING |
+| Link persistently lost | Heartbeat timeout (> 5 minutes) | ERROR |
+| Authentication failure | Security layer rejection | FATAL |
+| Protocol error | Message parsing failure (3 consecutive) | ERROR |
+
+### 4.3 Storage Fault Detection
+
+| Condition | Detection Method | Severity Assignment |
+|-----------|------------------|-------------------|
+| Write failure (retry successful) | Write operation with retry | WARNING |
+| Write failure (persistent) | Write operation failure (3 retries) | ERROR |
+| SD card corruption | File system check failure | FATAL |
+| Storage full | Available space < threshold | WARNING |
+
+### 4.4 Security Fault Detection
+
+| Condition | Detection Method | Severity Assignment |
+|-----------|------------------|-------------------|
+| Secure boot failure | Boot verification failure | FATAL (always) |
+| Key corruption | Cryptographic key validation failure | FATAL |
+| Unauthorized access | Authentication failure (3 attempts) | FATAL |
+| Message tampering | Integrity check failure | ERROR (if persistent → FATAL) |
+
+## 5. Escalation Rules
+
+### 5.1 Severity Escalation
+
+| Current Severity | Escalation Trigger | New Severity | State Transition |
+|------------------|-------------------|--------------|-----------------|
+| INFO | N/A | N/A | None |
+| WARNING | Same fault persists > 5 minutes | ERROR | `WARNING` → `WARNING` (feature degraded) |
+| WARNING | Multiple warnings (≥3) | ERROR | `WARNING` → `WARNING` (feature degraded) |
+| WARNING | Critical feature affected | FATAL | `WARNING` → `FAULT` |
+| ERROR | Same fault persists > 10 minutes | FATAL | `RUNNING` → `FAULT` |
+| ERROR | Cascading failures (≥2 features) | FATAL | `RUNNING` → `FAULT` |
+| FATAL | N/A | N/A | `RUNNING` → `FAULT` |
+
+### 5.2 Cascading Failure Detection
+
+A cascading failure is detected when:
+- Multiple independent features fail simultaneously
+- Failure in one feature causes failure in another
+- System resource exhaustion (memory, CPU, storage)
+
+**Response:** Immediate escalation to FATAL, transition to `FAULT` state.
+
+## 6. Recovery Behaviors
+
+### 6.1 Recovery Strategies by Severity
+
+| Severity | Recovery Strategy | Retry Logic | State Impact |
+|----------|------------------|-------------|--------------|
+| **INFO** | None | N/A | None |
+| **WARNING** | Automatic retry, degraded operation | 3 retries with exponential backoff | Continue in `WARNING` state |
+| **ERROR** | Feature isolation, automatic retry | 3 retries, then manual intervention | Feature disabled, system continues |
+| **FATAL** | Controlled teardown, recovery attempt | Single recovery attempt, then manual | `FAULT` → `TEARDOWN` → `INIT` |
+
+### 6.2 Recovery Time Limits
+
+| Fault Type | Maximum Recovery Time | Recovery Action |
+|------------|----------------------|----------------|
+| Sensor (WARNING) | 5 minutes | Automatic retry, sensor exclusion |
+| Communication (WARNING) | 30 seconds | Automatic reconnection |
+| Storage (WARNING) | 10 seconds | Retry write operation |
+| Sensor (ERROR) | Manual intervention | Sensor marked as failed |
+| Communication (ERROR) | Manual intervention | Communication feature disabled |
+| Storage (ERROR) | Manual intervention | Persistence disabled, system continues |
+| FATAL (any) | 60 seconds | Controlled teardown and recovery attempt |
+
+### 6.3 Latching Behavior
+
+| Severity | Latching Rule | Clear Condition |
+|----------|--------------|----------------|
+| **INFO** | Not latched | Overwritten by new event |
+| **WARNING** | Latched until cleared | Fault condition cleared + manual clear OR automatic clear after 1 hour |
+| **ERROR** | Latched until cleared | Manual clear via diagnostic session OR system reset |
+| **FATAL** | Latched until cleared | Manual clear via diagnostic session OR system reset |
+
+## 7. Fault Reporting
+
+### 7.1 Reporting Channels
+
+| Severity | Local HMI | Diagnostic Log | Main Hub | Diagnostic Session |
+|----------|-----------|----------------|----------|-------------------|
+| **INFO** | Optional | Yes | No | Yes |
+| **WARNING** | Yes (status indicator) | Yes | Yes (periodic) | Yes |
+| **ERROR** | Yes (status indicator) | Yes | Yes (immediate) | Yes |
+| **FATAL** | Yes (status indicator) | Yes | Yes (immediate) | Yes |
+
+### 7.2 Diagnostic Event Structure
+
+```c
+typedef struct {
+    uint32_t diagnostic_code;      // Unique diagnostic code
+    diag_severity_t severity;      // INFO, WARNING, ERROR, FATAL
+    uint64_t timestamp;              // System timestamp (microseconds)
+    const char* source_component;   // Component identifier
+    uint32_t occurrence_count;     // Number of occurrences
+    bool is_latched;                // Latching status
+    fault_category_t category;      // SENSOR, COMMUNICATION, etc.
+} diagnostic_event_t;
+```
+
+## 8. Integration with State Machine
+
+### 8.1 Fault-to-State Mapping
+
+| Fault Severity | Current State | Target State | Transition Trigger |
+|----------------|---------------|--------------|-------------------|
+| INFO | Any | Same | None (no state change) |
+| WARNING | `RUNNING` | `WARNING` | First WARNING fault |
+| WARNING | `WARNING` | `WARNING` | Additional WARNING (latched) |
+| ERROR | `RUNNING` | `RUNNING` | Feature isolation, continue |
+| ERROR | `WARNING` | `WARNING` | Feature isolation, continue |
+| FATAL | `RUNNING` | `FAULT` | First FATAL fault |
+| FATAL | `WARNING` | `FAULT` | Escalation to FATAL |
+| FATAL | `FAULT` | `FAULT` | Additional FATAL (latched) |
+
+### 8.2 State-Dependent Fault Handling
+
+| State | Fault Handling Behavior |
+|-------|------------------------|
+| `INIT` | Boot-time faults → `BOOT_FAILURE` if security-related |
+| `RUNNING` | Full fault detection and handling |
+| `WARNING` | Fault escalation monitoring, recovery attempts |
+| `FAULT` | Fault logging only, recovery attempt preparation |
+| `OTA_PREP` | OTA-related faults only, others deferred |
+| `OTA_UPDATE` | OTA progress faults only |
+| `TEARDOWN` | Fault logging only, no new fault detection |
+| `SERVICE` | Fault inspection only, no new fault detection |
+
+## 9. Error Handler Responsibilities
+
+The Error Handler component SHALL:
+1. Receive fault reports from all components
+2. Classify faults according to taxonomy
+3. Determine severity and escalation
+4. Trigger state transitions when required
+5. Manage fault latching and clearing
+6. Coordinate recovery attempts
+7. Report faults to diagnostics and Main Hub
+
+## 10. Traceability
+
+- **SR-DIAG-001:** Implemented via diagnostic code framework
+- **SR-DIAG-002:** Implemented via unique diagnostic code assignment
+- **SR-DIAG-003:** Implemented via severity classification
+- **SR-DIAG-004:** Implemented via timestamp and source association
+- **SR-SYS-002:** Implemented via fault-to-state mapping
+- **SR-SYS-004:** Implemented via FATAL fault → TEARDOWN transition
+
+## 11. Mermaid Fault Escalation Diagram
+
+```mermaid
+flowchart TD
+    FaultDetected[Fault Detected] --> ClassifySeverity{Classify Severity}
+    ClassifySeverity -->|INFO| LogOnly[Log Only]
+    ClassifySeverity -->|WARNING| CheckState1{Current State?}
+    ClassifySeverity -->|ERROR| IsolateFeature[Isolate Feature]
+    ClassifySeverity -->|FATAL| TriggerFaultState[Trigger FAULT State]
+    
+    CheckState1 -->|RUNNING| TransitionWarning[Transition to WARNING]
+    CheckState1 -->|WARNING| LatchWarning[Latch Warning]
+    
+    IsolateFeature --> RetryLogic{Retry Logic}
+    RetryLogic -->|Success| ClearError[Clear Error]
+    RetryLogic -->|Failure| EscalateToFatal{Escalate?}
+    EscalateToFatal -->|Yes| TriggerFaultState
+    EscalateToFatal -->|No| ManualIntervention[Manual Intervention]
+    
+    TriggerFaultState --> TeardownSequence[Initiate Teardown]
+    TeardownSequence --> RecoveryAttempt{Recovery Attempt}
+    RecoveryAttempt -->|Success| ResetToInit[Reset to INIT]
+    RecoveryAttempt -->|Failure| ManualIntervention
+```
--- a/system_design/specifications/System
+++ b/system_design/specifications/System
@@ -0,0 +1,304 @@
+# System Review Checklist
+
+**Project:** Sensor Hub – Poultry Farm Automation  
+**Scope:** Sensor Hub (Sub-Hub Only)  
+**Purpose:** Verify system readiness before FRD/SAD generation and AI-assisted implementation
+
+## 1\. Requirements Completeness Review
+
+### 1.1 Feature Coverage
+
+✔ All major functional domains defined:
+
+*   ☐ Data Acquisition (DAQ)
+    
+*   ☐ Data Quality &amp; Calibration (DQC)
+    
+*   ☐ Communication (COM)
+    
+*   ☐ Diagnostics &amp; Health (DIAG)
+    
+*   ☐ Persistence &amp; Data Management (DATA)
+    
+*   ☐ OTA Update (OTA)
+    
+*   ☐ Security &amp; Safety (SEC)
+    
+*   ☐ System Management &amp; HMI (SYS)
+    
+
+**Acceptance Criteria:**  
+No functional behavior is undocumented or implicit.
+
+### 1.2 Requirement Quality
+
+For **each system requirement**, verify:
+
+*   ☐ Uses “SHALL”
+    
+*   ☐ Is testable
+    
+*   ☐ Is unambiguous
+    
+*   ☐ Has a unique ID
+    
+*   ☐ Is traceable to a feature
+    
+
+**Red Flags:**
+
+*   Vague timing (“fast”, “real-time”)
+    
+*   Mixed requirements (“shall… and …”)
+    
+*   Implementation leakage (“using mutex”)
+    
+
+## 2\. Architectural Soundness Review
+
+### 2.1 Layering &amp; Separation of Concerns
+
+*   ☐ Hardware access isolated
+    
+*   ☐ No feature bypasses System Manager
+    
+*   ☐ Persistence accessed only via DP
+    
+*   ☐ HMI does not modify safety-critical configuration
+    
+
+**Fail Condition:**  
+Any feature directly accesses hardware or storage without abstraction.
+
+### 2.2 State Machine Validity
+
+*   ☐ All system states defined
+    
+*   ☐ Valid transitions documented
+    
+*   ☐ Illegal transitions blocked
+    
+*   ☐ Feature behavior defined per state
+    
+
+**States to Verify:**
+
+*   INIT
+    
+*   IDLE
+    
+*   RUNNING
+    
+*   DEGRADED
+    
+*   OTA\_UPDATE
+    
+*   TEARDOWN
+    
+*   ERROR
+    
+
+## 3\. Cross-Feature Constraint Compliance
+
+### 3.1 Constraint Awareness
+
+*   ☐ Each feature respects cross-feature constraints
+    
+*   ☐ No constraint contradicts a requirement
+    
+*   ☐ Constraints are globally enforceable
+    
+
+### 3.2 Conflict Resolution
+
+Check for conflicts such as:
+
+*   ☐ OTA vs DAQ timing
+    
+*   ☐ Persistence vs Power Loss
+    
+*   ☐ Diagnostics vs Real-Time Tasks
+    
+*   ☐ Debug vs Secure Boot
+    
+
+**Acceptance:**  
+Conflicts resolved via priority rules or system state restrictions.
+
+## 4\. Timing &amp; Performance Review
+
+### 4.1 Real-Time Constraints
+
+*   ☐ High-frequency sampling bounded
+    
+*   ☐ Worst-case execution time considered
+    
+*   ☐ Non-blocking design enforced
+    
+
+### 4.2 Resource Usage
+
+*   ☐ CPU usage bounded
+    
+*   ☐ RAM usage predictable
+    
+*   ☐ Stack sizes justified
+    
+*   ☐ Heap usage minimized in runtime
+    
+
+## 5\. Reliability &amp; Fault Handling Review
+
+### 5.1 Fault Detection
+
+*   ☐ Sensor failure detection defined
+    
+*   ☐ Communication failure detection defined
+    
+*   ☐ Storage failure detection defined
+    
+
+### 5.2 Fault Response
+
+*   ☐ Graceful degradation defined
+    
+*   ☐ Diagnostics logged
+    
+*   ☐ System state updated appropriately
+    
+
+## 6\. Security Review
+
+### 6.1 Boot &amp; Firmware
+
+*   ☐ Secure boot enforced
+    
+*   ☐ Firmware integrity verified
+    
+*   ☐ Rollback prevention defined
+    
+
+### 6.2 Communication
+
+*   ☐ Encryption mandatory
+    
+*   ☐ Authentication required
+    
+*   ☐ Key management strategy defined
+    
+
+### 6.3 Debug Access
+
+*   ☐ Debug sessions authenticated
+    
+*   ☐ Debug disabled in production unless authorized
+    
+*   ☐ Debug cannot bypass security or safety
+    
+
+## 7\. Data Management Review
+
+### 7.1 Data Ownership
+
+*   ☐ Single source of truth enforced
+    
+*   ☐ Clear ownership per data type
+    
+*   ☐ No duplicated persistent data
+    
+
+### 7.2 Persistence Safety
+
+*   ☐ Safe writes during state transitions
+    
+*   ☐ Power-loss tolerance defined
+    
+*   ☐ Data recovery defined
+    
+
+## 8\. HMI &amp; Usability Review (OLED + Buttons)
+
+### 8.1 Display Content
+
+*   ☐ Connectivity status
+    
+*   ☐ System status
+    
+*   ☐ Connected sensors
+    
+*   ☐ Time &amp; date
+    
+
+### 8.2 Navigation Logic
+
+*   ☐ Menu hierarchy defined
+    
+*   ☐ Button behavior consistent
+    
+*   ☐ No destructive action via UI
+    
+
+## 9\. Standards &amp; Compliance Readiness
+
+### 9.1 IEC 61499 Mapping Readiness
+
+*   ☐ Functional blocks identifiable
+    
+*   ☐ Event/data separation respected
+    
+*   ☐ Distributed execution possible
+    
+
+### 9.2 ISA-95 Alignment Readiness
+
+*   ☐ Sensor Hub maps to Level 1/2
+    
+*   ☐ Clear boundary to Level 3/4
+    
+*   ☐ No business logic leakage
+    
+
+## 10\. AI Readiness Review
+
+### 10.1 Prompt Compatibility
+
+*   ☐ Features modular
+    
+*   ☐ Requirements structured
+    
+*   ☐ Architecture explicit
+    
+
+### 10.2 Tool Handoff Readiness
+
+*   ☐ Claude can generate FRD/SAD
+    
+*   ☐ Mermaid diagrams derivable
+    
+*   ☐ DeepSeek can critique logic
+    
+*   ☐ Cursor rules enforce constraints
+    
+
+## Final Gate Decision
+
+### GO / NO-GO Criteria
+
+**GO** if:
+
+*   All sections ≥ 90% checked
+    
+*   No critical architectural violation
+    
+*   Security constraints enforced
+    
+
+**NO-GO** if:
+
+*   Missing system states
+    
+*   Undefined failure behavior
+    
+*   Security gaps
+    
+*   Persistence inconsistency
--- a/system_design/specifications/System_State_Machine_Specification.md
+++ b/system_design/specifications/System_State_Machine_Specification.md
@@ -0,0 +1,314 @@
+# System State Machine Specification
+
+**Document Type:** Normative System Specification  
+**Scope:** Sensor Hub (Sub-Hub) Operational States  
+**Traceability:** SR-SYS-001, SR-SYS-002, SR-SYS-003
+
+## 1. Purpose
+
+This document defines the complete finite state machine (FSM) governing the Sensor Hub's operational lifecycle. All system components SHALL respect state-based operation restrictions as defined herein.
+
+## 2. State Definitions
+
+### 2.1 State Enumeration
+
+| State ID | State Name | Description | Entry Condition |
+|----------|------------|-------------|-----------------|
+| `INIT` | Initialization | Hardware and software initialization phase | Power-on, reset, or post-teardown |
+| `BOOT_FAILURE` | Boot Failure | Secure boot verification failed | Secure boot check failure during INIT |
+| `RUNNING` | Normal Operation | Active sensor acquisition and communication | Successful initialization |
+| `WARNING` | Degraded Operation | Non-fatal fault detected, degraded functionality | Non-critical fault detected during RUNNING |
+| `FAULT` | Fatal Error | Critical fault, core functionality disabled | Fatal error or cascading failures |
+| `OTA_PREP` | OTA Preparation | Preparing for firmware update | OTA request accepted, validation pending |
+| `OTA_UPDATE` | OTA Update Active | Firmware update in progress | Firmware transfer and flashing |
+| `MC_UPDATE` | Machine Constants Update | Machine constants update in progress | MC update request accepted |
+| `TEARDOWN` | Controlled Shutdown | Safe shutdown sequence execution | Update, fault recovery, or manual command |
+| `SERVICE` | Service Mode | Engineering/diagnostic interaction | Debug session active |
+| `SD_DEGRADED` | SD Card Degraded | SD card failure detected, fallback mode | SD card access failure |
+
+### 2.2 State Characteristics
+
+#### INIT
+- **Duration:** Bounded (max 5 seconds)
+- **Allowed Operations:** Hardware initialization, secure boot verification, MC loading
+- **Forbidden Operations:** Sensor acquisition, communication, persistence writes
+- **Exit Conditions:** Success → RUNNING, Secure boot failure → BOOT_FAILURE
+
+#### BOOT_FAILURE
+- **Duration:** Indefinite (requires manual intervention)
+- **Allowed Operations:** Diagnostic reporting, secure boot retry (limited)
+- **Forbidden Operations:** All application features
+- **Exit Conditions:** Manual reset, secure boot success → INIT
+
+#### RUNNING
+- **Duration:** Indefinite (normal operation)
+- **Allowed Operations:** All features (DAQ, DQC, COM, DIAG, DATA, HMI)
+- **Forbidden Operations:** OTA, MC update (must transition via TEARDOWN)
+- **Exit Conditions:** Fault → WARNING/FAULT, OTA request → OTA_PREP, MC update → MC_UPDATE, Debug session → SERVICE
+
+#### WARNING
+- **Duration:** Until fault cleared or escalated
+- **Allowed Operations:** Degraded DAQ, COM, DIAG (limited), DATA (read-only)
+- **Forbidden Operations:** OTA, MC update
+- **Exit Conditions:** Fault cleared → RUNNING, Fault escalated → FAULT
+
+#### FAULT
+- **Duration:** Until recovery attempt or manual intervention
+- **Allowed Operations:** Diagnostic reporting, error logging, controlled teardown
+- **Forbidden Operations:** Sensor acquisition, communication (except diagnostics)
+- **Exit Conditions:** Recovery attempt → TEARDOWN, Manual reset → INIT
+
+#### OTA_PREP
+- **Duration:** Bounded (max 2 seconds)
+- **Allowed Operations:** OTA readiness validation, teardown initiation
+- **Forbidden Operations:** Sensor acquisition, new communication sessions
+- **Exit Conditions:** Ready → TEARDOWN, Rejected → RUNNING
+
+#### OTA_UPDATE
+- **Duration:** Bounded (max 10 minutes)
+- **Allowed Operations:** Firmware reception, validation, flashing
+- **Forbidden Operations:** Sensor acquisition, normal communication, persistence (except OTA data)
+- **Exit Conditions:** Success → RUNNING (after reboot), Failure → FAULT
+
+#### MC_UPDATE
+- **Duration:** Bounded (max 30 seconds)
+- **Allowed Operations:** MC reception, validation, teardown
+- **Forbidden Operations:** Sensor acquisition, normal communication
+- **Exit Conditions:** Success → TEARDOWN, Failure → RUNNING
+
+#### TEARDOWN
+- **Duration:** Bounded (max 500ms)
+- **Allowed Operations:** Data flush, resource release, state persistence
+- **Forbidden Operations:** New sensor acquisition, new communication sessions
+- **Exit Conditions:** Complete → INIT (reset), OTA → OTA_UPDATE, MC → MC_UPDATE
+
+#### SERVICE
+- **Duration:** Until session closed
+- **Allowed Operations:** Diagnostic access, read-only inspection, controlled commands
+- **Forbidden Operations:** Sensor acquisition (may be paused), OTA, MC update
+- **Exit Conditions:** Session closed → RUNNING
+
+#### SD_DEGRADED
+- **Duration:** Until SD recovery or manual intervention
+- **Allowed Operations:** Sensor acquisition (no persistence), communication, diagnostics
+- **Forbidden Operations:** Persistence writes (except critical diagnostics)
+- **Exit Conditions:** SD recovery → RUNNING, Manual intervention → SERVICE
+
+## 3. State Transition Table
+
+| From State | To State | Trigger | Guard Condition | Action | Authorized Caller |
+|------------|----------|---------|-----------------|--------|------------------|
+| `[*]` | `INIT` | Power-on, Reset | None | Initialize hardware, secure boot check | System |
+| `INIT` | `RUNNING` | Init success | Secure boot OK, MC loaded, sensors detected | Start DAQ, COM, DIAG tasks | System Manager |
+| `INIT` | `BOOT_FAILURE` | Secure boot fail | Secure boot verification failed | Log security fault, disable application | Secure Boot |
+| `BOOT_FAILURE` | `INIT` | Manual reset | None | Reset system | User/Engineer |
+| `RUNNING` | `WARNING` | Non-fatal fault | Diagnostic severity = WARNING | Degrade functionality, notify | Error Handler |
+| `RUNNING` | `FAULT` | Fatal fault | Diagnostic severity = FATAL | Stop critical features | Error Handler |
+| `RUNNING` | `OTA_PREP` | OTA request | OTA request received, system ready | Validate readiness | OTA Manager |
+| `RUNNING` | `MC_UPDATE` | MC update request | MC update received, authenticated | Validate MC | MC Manager |
+| `RUNNING` | `SERVICE` | Debug session | Debug session authenticated | Pause non-critical tasks | Debug Manager |
+| `RUNNING` | `SD_DEGRADED` | SD failure | SD card access failure detected | Disable persistence writes | Persistence |
+| `WARNING` | `RUNNING` | Fault cleared | Diagnostic cleared, system healthy | Restore full functionality | Error Handler |
+| `WARNING` | `FAULT` | Fault escalated | Multiple warnings or critical fault | Stop degraded features | Error Handler |
+| `FAULT` | `TEARDOWN` | Recovery attempt | Recovery command received | Initiate controlled shutdown | System Manager |
+| `OTA_PREP` | `TEARDOWN` | OTA ready | Readiness validated | Begin teardown | OTA Manager |
+| `OTA_PREP` | `RUNNING` | OTA rejected | Readiness check failed | Resume normal operation | OTA Manager |
+| `TEARDOWN` | `OTA_UPDATE` | Teardown complete (OTA) | OTA pending, data flushed | Enter OTA state | System Manager |
+| `TEARDOWN` | `MC_UPDATE` | Teardown complete (MC) | MC update pending, data flushed | Enter MC update | System Manager |
+| `TEARDOWN` | `INIT` | Teardown complete (reset) | Reset requested, data flushed | Reset system | System Manager |
+| `OTA_UPDATE` | `RUNNING` | OTA success | Firmware flashed, validated | Reboot into new firmware | OTA Manager |
+| `OTA_UPDATE` | `FAULT` | OTA failure | Firmware validation failed | Log error, enter fault | OTA Manager |
+| `MC_UPDATE` | `TEARDOWN` | MC update complete | MC validated, applied | Reinitialize system | MC Manager |
+| `SERVICE` | `RUNNING` | Session closed | Debug session terminated | Resume normal operation | Debug Manager |
+| `SD_DEGRADED` | `RUNNING` | SD recovered | SD card access restored | Re-enable persistence | Persistence |
+| `SD_DEGRADED` | `SERVICE` | Manual intervention | User intervention required | Enter service mode | User/Engineer |
+
+## 4. Per-State Feature Execution Rules
+
+### 4.1 DAQ (Data Acquisition) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | None | Sensor initialization only |
+| `RUNNING` | Full acquisition cycle | None |
+| `WARNING` | Degraded acquisition (reduced frequency) | Failed sensors excluded |
+| `FAULT` | None | Acquisition stopped |
+| `OTA_PREP` | None | Acquisition stopped |
+| `OTA_UPDATE` | None | Acquisition stopped |
+| `MC_UPDATE` | None | Acquisition stopped |
+| `TEARDOWN` | None | Acquisition stopped |
+| `SERVICE` | Paused (optional read-only) | No new samples |
+| `SD_DEGRADED` | Full acquisition | Data not persisted |
+| `BOOT_FAILURE` | None | Not applicable |
+
+### 4.2 DQC (Data Quality & Calibration) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | Sensor detection, MC loading | No calibration |
+| `RUNNING` | Full quality checks, calibration | None |
+| `WARNING` | Degraded quality checks | Reduced validation |
+| `FAULT` | Error reporting only | No quality checks |
+| `OTA_PREP` | None | Quality checks stopped |
+| `OTA_UPDATE` | None | Quality checks stopped |
+| `MC_UPDATE` | MC validation only | No sensor calibration |
+| `TEARDOWN` | None | Quality checks stopped |
+| `SERVICE` | Read-only inspection | No calibration |
+| `SD_DEGRADED` | Full quality checks | Results not persisted |
+| `BOOT_FAILURE` | None | Not applicable |
+
+### 4.3 COM (Communication) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | None | No communication |
+| `RUNNING` | Full bidirectional communication | None |
+| `WARNING` | Limited communication (diagnostics only) | Reduced bandwidth |
+| `FAULT` | Diagnostic reporting only | No data transmission |
+| `OTA_PREP` | OTA negotiation only | No other communication |
+| `OTA_UPDATE` | OTA data transfer only | No other communication |
+| `MC_UPDATE` | MC transfer only | No other communication |
+| `TEARDOWN` | Session closure only | No new sessions |
+| `SERVICE` | Debug session communication | No Main Hub communication |
+| `SD_DEGRADED` | Full communication | Data not persisted |
+| `BOOT_FAILURE` | Diagnostic reporting only | Limited communication |
+
+### 4.4 DIAG (Diagnostics) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | Boot diagnostics | Limited logging |
+| `RUNNING` | Full diagnostics | None |
+| `WARNING` | Full diagnostics | None |
+| `FAULT` | Full diagnostics | None |
+| `OTA_PREP` | OTA diagnostics | Limited scope |
+| `OTA_UPDATE` | OTA progress diagnostics | Limited scope |
+| `MC_UPDATE` | MC update diagnostics | Limited scope |
+| `TEARDOWN` | Teardown diagnostics | Limited scope |
+| `SERVICE` | Full diagnostics (read access) | No new diagnostics |
+| `SD_DEGRADED` | Full diagnostics | Persistence limited |
+| `BOOT_FAILURE` | Security diagnostics | Limited scope |
+
+### 4.5 DATA (Persistence) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | MC loading only | No writes |
+| `RUNNING` | Full persistence | None |
+| `WARNING` | Read-only, critical writes | Limited writes |
+| `FAULT` | Critical diagnostics only | No sensor data writes |
+| `OTA_PREP` | Read-only | No writes |
+| `OTA_UPDATE` | OTA data only | No sensor data writes |
+| `MC_UPDATE` | MC writes only | No sensor data writes |
+| `TEARDOWN` | Critical data flush only | Authorized writes only |
+| `SERVICE` | Read-only | No writes |
+| `SD_DEGRADED` | Read-only (if possible) | No writes |
+| `BOOT_FAILURE` | None | Not applicable |
+
+### 4.6 OTA Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | None | OTA not active |
+| `RUNNING` | OTA negotiation only | No transfer |
+| `WARNING` | None | OTA blocked |
+| `FAULT` | None | OTA blocked |
+| `OTA_PREP` | Readiness validation | No transfer |
+| `OTA_UPDATE` | Full OTA operations | None |
+| `MC_UPDATE` | None | OTA blocked |
+| `TEARDOWN` | None | OTA blocked |
+| `SERVICE` | None | OTA blocked |
+| `SD_DEGRADED` | None | OTA blocked |
+| `BOOT_FAILURE` | None | OTA blocked |
+
+### 4.7 SEC (Security) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | Secure boot verification | Must complete before app start |
+| `RUNNING` | Full security (encryption, authentication) | None |
+| `WARNING` | Full security | None |
+| `FAULT` | Security diagnostics | Limited operations |
+| `OTA_PREP` | OTA authentication | None |
+| `OTA_UPDATE` | Firmware verification | None |
+| `MC_UPDATE` | MC authentication | None |
+| `TEARDOWN` | Key protection | None |
+| `SERVICE` | Debug authentication | None |
+| `SD_DEGRADED` | Full security | None |
+| `BOOT_FAILURE` | Security fault handling | Limited operations |
+
+### 4.8 SYS (System Management) Feature
+
+| State | Allowed Operations | Restrictions |
+|-------|-------------------|--------------|
+| `INIT` | State management, initialization | Limited operations |
+| `RUNNING` | Full system management | None |
+| `WARNING` | Degraded management | Limited operations |
+| `FAULT` | Fault recovery management | Limited operations |
+| `OTA_PREP` | OTA state management | Limited operations |
+| `OTA_UPDATE` | OTA state management | Limited operations |
+| `MC_UPDATE` | MC state management | Limited operations |
+| `TEARDOWN` | Teardown execution | Limited operations |
+| `SERVICE` | Service mode management | Limited operations |
+| `SD_DEGRADED` | Degraded management | Limited operations |
+| `BOOT_FAILURE` | Boot failure management | Limited operations |
+
+## 5. State Transition Timing Requirements
+
+| Transition | Maximum Duration | Justification |
+|------------|------------------|---------------|
+| `[*]` → `INIT` | 100ms | Power-on initialization |
+| `INIT` → `RUNNING` | 5s | Hardware init, secure boot, MC load |
+| `INIT` → `BOOT_FAILURE` | 2s | Secure boot verification |
+| `RUNNING` → `WARNING` | 50ms | Fault detection and state change |
+| `RUNNING` → `FAULT` | 50ms | Critical fault detection |
+| `RUNNING` → `OTA_PREP` | 100ms | OTA request processing |
+| `OTA_PREP` → `TEARDOWN` | 2s | Readiness validation |
+| `TEARDOWN` → `OTA_UPDATE` | 500ms | Data flush and resource release |
+| `TEARDOWN` → `INIT` | 500ms | Data flush and reset |
+| `OTA_UPDATE` → `RUNNING` | 10 minutes | Firmware transfer and flashing |
+| `RUNNING` → `SERVICE` | 100ms | Debug session establishment |
+| `SERVICE` → `RUNNING` | 50ms | Debug session closure |
+
+## 6. State Notification Mechanism
+
+All state transitions SHALL notify registered components via the Event System:
+- **Event Type:** `SYSTEM_STATE_CHANGED`
+- **Payload:** Previous state, new state, transition reason
+- **Subscribers:** All feature managers (DAQ, DQC, COM, DIAG, DATA, OTA, SEC, SYS)
+
+## 7. Traceability
+
+- **SR-SYS-001:** Implemented via complete FSM definition
+- **SR-SYS-002:** Implemented via per-state feature execution rules
+- **SR-SYS-003:** Implemented via state notification mechanism
+
+## 8. Mermaid State Diagram
+
+```mermaid
+stateDiagram-v2
+    [*] --> INIT
+    INIT --> RUNNING: initSuccess
+    INIT --> BOOT_FAILURE: secureBootFail
+    BOOT_FAILURE --> INIT: manualReset
+    RUNNING --> WARNING: nonFatalFault
+    RUNNING --> FAULT: fatalFault
+    RUNNING --> OTA_PREP: otaRequest
+    RUNNING --> MC_UPDATE: mcUpdateRequest
+    RUNNING --> SERVICE: debugSession
+    RUNNING --> SD_DEGRADED: sdFailure
+    WARNING --> RUNNING: faultCleared
+    WARNING --> FAULT: faultEscalated
+    FAULT --> TEARDOWN: recoveryAttempt
+    OTA_PREP --> TEARDOWN: otaReady
+    OTA_PREP --> RUNNING: otaRejected
+    TEARDOWN --> OTA_UPDATE: otaPending
+    TEARDOWN --> MC_UPDATE: mcPending
+    TEARDOWN --> INIT: resetRequested
+    OTA_UPDATE --> RUNNING: otaSuccess
+    OTA_UPDATE --> FAULT: otaFailure
+    MC_UPDATE --> TEARDOWN: mcComplete
+    SERVICE --> RUNNING: sessionClosed
+    SD_DEGRADED --> RUNNING: sdRecovered
+    SD_DEGRADED --> SERVICE: manualIntervention
+```