Add: windows mvp - transparent bugs not fixed

skills/m03-mutability/SKILL.md

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+---
+name: m03-mutability
+description: "CRITICAL: Use for mutability issues. Triggers: E0596, E0499, E0502, cannot borrow as mutable, already borrowed as immutable, mut, &mut, interior mutability, Cell, RefCell, Mutex, RwLock, 可变性, 内部可变性, 借用冲突"
+user-invocable: false
+---
+
+# Mutability
+
+> **Layer 1: Language Mechanics**
+
+## Core Question
+
+**Why does this data need to change, and who can change it?**
+
+Before adding interior mutability, understand:
+- Is mutation essential or accidental complexity?
+- Who should control mutation?
+- Is the mutation pattern safe?
+
+---
+
+## Error → Design Question
+
+| Error | Don't Just Say | Ask Instead |
+|-------|----------------|-------------|
+| E0596 | "Add mut" | Should this really be mutable? |
+| E0499 | "Split borrows" | Is the data structure right? |
+| E0502 | "Separate scopes" | Why do we need both borrows? |
+| RefCell panic | "Use try_borrow" | Is runtime check appropriate? |
+
+---
+
+## Thinking Prompt
+
+Before adding mutability:
+
+1. **Is mutation necessary?**
+   - Maybe transform → return new value
+   - Maybe builder → construct immutably
+
+2. **Who controls mutation?**
+   - External caller → `&mut T`
+   - Internal logic → interior mutability
+   - Concurrent access → synchronized mutability
+
+3. **What's the thread context?**
+   - Single-thread → Cell/RefCell
+   - Multi-thread → Mutex/RwLock/Atomic
+
+---
+
+## Trace Up ↑
+
+When mutability conflicts persist:
+
+```
+E0499/E0502 (borrow conflicts)
+    ↑ Ask: Is the data structure designed correctly?
+    ↑ Check: m09-domain (should data be split?)
+    ↑ Check: m07-concurrency (is async involved?)
+```
+
+| Persistent Error | Trace To | Question |
+|-----------------|----------|----------|
+| Repeated borrow conflicts | m09-domain | Should data be restructured? |
+| RefCell in async | m07-concurrency | Is Send/Sync needed? |
+| Mutex deadlocks | m07-concurrency | Is the lock design right? |
+
+---
+
+## Trace Down ↓
+
+From design to implementation:
+
+```
+"Need mutable access from &self"
+    ↓ T: Copy → Cell<T>
+    ↓ T: !Copy → RefCell<T>
+
+"Need thread-safe mutation"
+    ↓ Simple counters → AtomicXxx
+    ↓ Complex data → Mutex<T> or RwLock<T>
+
+"Need shared mutable state"
+    ↓ Single-thread: Rc<RefCell<T>>
+    ↓ Multi-thread: Arc<Mutex<T>>
+```
+
+---
+
+## Borrow Rules
+
+```
+At any time, you can have EITHER:
+├─ Multiple &T (immutable borrows)
+└─ OR one &mut T (mutable borrow)
+
+Never both simultaneously.
+```
+
+## Quick Reference
+
+| Pattern | Thread-Safe | Runtime Cost | Use When |
+|---------|-------------|--------------|----------|
+| `&mut T` | N/A | Zero | Exclusive mutable access |
+| `Cell<T>` | No | Zero | Copy types, no refs needed |
+| `RefCell<T>` | No | Runtime check | Non-Copy, need runtime borrow |
+| `Mutex<T>` | Yes | Lock contention | Thread-safe mutation |
+| `RwLock<T>` | Yes | Lock contention | Many readers, few writers |
+| `Atomic*` | Yes | Minimal | Simple types (bool, usize) |
+
+## Error Code Reference
+
+| Error | Cause | Quick Fix |
+|-------|-------|-----------|
+| E0596 | Borrowing immutable as mutable | Add `mut` or redesign |
+| E0499 | Multiple mutable borrows | Restructure code flow |
+| E0502 | &mut while & exists | Separate borrow scopes |
+
+---
+
+## Interior Mutability Decision
+
+| Scenario | Choose |
+|----------|--------|
+| T: Copy, single-thread | `Cell<T>` |
+| T: !Copy, single-thread | `RefCell<T>` |
+| T: Copy, multi-thread | `AtomicXxx` |
+| T: !Copy, multi-thread | `Mutex<T>` or `RwLock<T>` |
+| Read-heavy, multi-thread | `RwLock<T>` |
+| Simple flags/counters | `AtomicBool`, `AtomicUsize` |
+
+---
+
+## Anti-Patterns
+
+| Anti-Pattern | Why Bad | Better |
+|--------------|---------|--------|
+| RefCell everywhere | Runtime panics | Clear ownership design |
+| Mutex for single-thread | Unnecessary overhead | RefCell |
+| Ignore RefCell panic | Hard to debug | Handle or restructure |
+| Lock inside hot loop | Performance killer | Batch operations |
+
+---
+
+## Related Skills
+
+| When | See |
+|------|-----|
+| Smart pointer choice | m02-resource |
+| Thread safety | m07-concurrency |
+| Data structure design | m09-domain |
+| Anti-patterns | m15-anti-pattern |