refactor: Remove FlowError and move noTasksToExecute to StoreError

[takeshishimada]

Summary

Removes FlowError entirely and moves noTasksToExecute to StoreError, clarifying the separation between framework-level and application-level errors.

Problem

FlowError violated separation of concerns by mixing:

• Framework errors: noTasksToExecute (API misuse detection)
• Application errors: validationFailed, networkError, stateError (domain logic)

This design forced applications to use framework-defined error types instead of defining their own domain-specific errors.

Solution

1. Removed FlowError completely

Application-domain errors (validationFailed, networkError, stateError, etc.) should be defined by each application, not by the framework.

2. Created dedicated StoreError.swift

Moved noTasksToExecute from FlowError to StoreError. StoreError now contains only framework-level errors:

• deallocated: Store lifecycle error
• cancelled: Task cancellation
• noTasksToExecute: API misuse detection

3. Updated Examples with custom error types

Demonstrates proper application error design:

• RetryNetworkFeature: RetryError (maxRetriesExceeded, networkFailure)
• MultiStepWizardFeature: WizardError (validationFailed, submissionFailed)
• PaginatedListFeature: PaginationError (fetchFailed)

4. Updated documentation

• Examples/AdvancedPatterns/README.md now shows custom error type patterns
• Removed all FlowError references

Changes

Deleted

• ❌ Sources/Flow/Store/FlowError.swift
• ❌ Tests/UnitTests/Store/FlowErrorTests.swift

Added

• ✅ Sources/Flow/Store/StoreError.swift with comprehensive documentation

Modified

• 📝 Sources/Flow/Store/ActionTask.swift - Updated documentation references
• 📝 Sources/Flow/Store/Store.swift - Removed inline StoreError definition, updated comments
• 📝 Examples/AdvancedPatterns/NetworkingWithRetry/RetryNetworkFeature.swift - Added RetryError
• 📝 Examples/AdvancedPatterns/MultiStepWizard/MultiStepWizardFeature.swift - Added WizardError
• 📝 Examples/AdvancedPatterns/PaginatedList/PaginatedListFeature.swift - Added PaginationError
• 📝 Examples/AdvancedPatterns/README.md - Updated best practices section

Benefits

✅ Clear separation of concerns: Framework errors vs Application errors
✅ Better flexibility: Applications define their own domain-specific errors
✅ Follows single responsibility principle: StoreError focuses on framework concerns only
✅ Improved examples: Demonstrates proper application error design patterns

Migration Guide

Applications using FlowError should define their own error types:

// Before
@Observable
final class State {
    var error: FlowError?
}

// After
enum MyError: Error, LocalizedError {
    case validationFailed(String)
    case networkError(Error)
    
    var errorDescription: String? {
        switch self {
        case .validationFailed(let reason):
            return "Validation failed: \(reason)"
        case .networkError(let underlying):
            return "Network error: \(underlying.localizedDescription)"
        }
    }
}

@Observable
final class State {
    var error: MyError?
}

Testing

• ✅ All tests passing (289/289)
• ✅ Build successful
• ✅ No FlowError references remaining in codebase

Breaking Changes

⚠️ BREAKING: FlowError has been removed. Applications must define their own error types.

🤖 Generated with Claude Code