PART 3
State Machine Architecture
Edge Case Resolution
Race Condition Fix → Session Persistence Edge Case
How architectural fixes reveal state persistence bugs and lead to bulletproof state machines
Series ProgressPart 3 of 5
StartComplete
production-demo
Launch App →State Machine Engineering: Theory to Production
Deep technical discussion on finite state machines, edge case handling, and production debugging strategies
Audio Discussion • 22:18
0:0022:18
Audio Placeholder
⚠Production Edge Case: Session Persistence Bug
Bug Reproduction Criteria
User completes study session
Navigates away (tab close/browser refresh)
Returns later (same session/device)
Browser storage intact
Result: Phantom "Session Complete" screen
State Corruption Analysis
javascript
// Problematic state inference logic
const StudySessionManager = () => {
const { sessionId, isComplete, flashcards } = useStudySession();
// PROBLEM: Multiple variables determining state
if (isComplete && sessionId) {
return <StudySessionResults />; // FALSE POSITIVE
}
// STATE CORRUPTION SCENARIO:
// sessionId: "prev_session_123" (persisted)
// isComplete: true (from previous session)
// flashcards: [] (not loaded yet)
// Result: Wrong component rendered
}Root Cause: Variable-Based State Logic
The application was inferring state from multiple boolean/object variables instead of maintaining an explicit state machine. This created ambiguous combinations where the intended state was unclear.
Anti-pattern identified:
→ State = f(sessionId, isComplete, flashcards, error)
→ 2^n possible combinations (many invalid)
→ Impossible to debug all edge cases
Technical Impact Assessment
User Experience
Phantom screensCritical
User confusionHigh
App abandonment riskMedium
Development
Debug complexityVery High
Test coverage gapsHigh
Feature development riskMedium
Business
Support ticketsIncreasing
User retentionAt risk
Technical debtHigh