Summary

• Updated README.md and README_jp.md to align with the "5 Core Principles" structure from MEDIUM_ARTICLE_EN.md
• This creates consistency across all documentation (README, CoreConcepts.md, Medium articles)

The 5 Core Principles

1. Unidirectional Data Flow (newly added ✨)

• What: Explains Action → Handler → State → View
• Why: This fundamental principle was missing from README
• Benefit: Users immediately understand Flow's architecture

2. View-Local State (evolved from "No Global Store")

• Before: "No Global Store" - focused on what it doesn't have
• After: "View-Local State" - emphasizes SwiftUI alignment
• Improvement: Clearer philosophical alignment with SwiftUI

3. Result-Returning Actions (simplified)

• Before: Long parent-child communication example
• After: Concise save/navigate example
• Improvement: Easier to grasp quickly

4. MainActor Isolation (evolved from "Swift 6 Concurrency")

• Before: "Swift 6 Concurrency" - technical feature name
• After: "MainActor Isolation" - emphasizes the benefit
• Improvement: Highlights Flow's distinctive feature (direct state updates)

5. @observable Support (simplified)

• Before: Listed detailed benefits
• After: Concise 3-point summary
• Improvement: Matches README's concise style

What Was Removed

❌ "Observable Actions" (Middleware)

• Not a core principle of Flow's architecture
• Middleware is a useful feature but secondary
• Users can discover it through full documentation

Consistency Achieved

This PR creates consistency across:

• ✅ README.md - Now uses "5 Core Principles"
• ✅ README_jp.md - Now uses "5つのコア原則"
• ✅ CoreConcepts.md - Already updated (PR docs: Improve CoreConcepts.md structure with '5 Core Principles' #20)
• ✅ MEDIUM_ARTICLE_EN.md - Reference source
• ✅ MEDIUM_ARTICLE_JP.md - Reference source

All documents now tell the same story with the same structure.

Statistics

• Lines changed: 123 insertions, 238 deletions
• Net reduction: 115 lines (more concise!)
• Principles covered: 5 (was missing Unidirectional Data Flow)

Before & After

Before

## Key Features
### No Global Store
### Result-Returning Actions
### @Observable Support
### Swift 6 Concurrency
### Observable Actions

After

## The 5 Core Principles
### 1. Unidirectional Data Flow
### 2. View-Local State
### 3. Result-Returning Actions
### 4. MainActor Isolation
### 5. @Observable Support

Test Plan

• Review alignment with MEDIUM_ARTICLE_EN.md
• Verify README.md and README_jp.md match in structure
• Check that all code examples are correct
• Confirm consistency with CoreConcepts.md

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