docs(repl): Update Phase 288 P3 completion status

Updated implementation status to reflect actual working features:
- ✅ print() output displays
- ✅ .reset command works
- ✅ Implicit local binding compiles
- ⏳ Variable persistence (deferred to Phase 288.1+)

Known limitations documented:
- Variable access across lines not yet working
- _ variable stored but not accessible yet
- Expression auto-display deferred

Accurate current behavior examples added.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

docs/reference/language/repl.md

@@ -287,45 +287,57 @@ Recommended file-mode errors:
 
 ## 9) Phase 288 MVP Implementation Status
 
-### Completed (Phase 288 P0-P3)
+### Completed (Phase 288 P0-P3) - 2025-12-25
 
 ✅ **CLI Entry** (`--repl` / `-i` flags)
 ✅ **REPL Loop** (`.help`, `.exit`, `.reset` commands)
 ✅ **ReplSessionBox** (VMValue-based session state)
-✅ **Implicit Local Binding** (`x = 1` creates session variable)
-✅ **print() Output** (ExternCall output displays)
-✅ **`_` Variable** (last value stored)
-✅ **Session Persistence** (VMValue persists across lines)
-✅ **Fail-Fast** (undefined reads error immediately)
+✅ **Implicit Local Binding** (`x = 1` compiles without error)
+✅ **print() Output** (ExternCall output displays correctly)
+✅ **`_` Variable** (last value stored in session)
+✅ **Session Reset** (`.reset` command clears state)
+✅ **Main Box Entry Point** (VM execution fixed)
 
-### Deferred to Phase 288.1
+### Deferred to Phase 288.1+
 
+⏳ **Variable Persistence** (session variables accessible across lines)
 ⏳ **Expression Auto-Display** (`1+1` → `2` automatic output)
 ⏳ **Complex Expression Detection** (distinguish expression vs statement)
-⏳ **REPL Variable Injection** (session variables accessible in compilation)
+⏳ **REPL Variable Injection** (session → compilation context bridge)
 
-### Current Behavior (Phase 288 MVP)
+### Current Behavior (Phase 288 P3 MVP)
 
 ```nyash
+>>> .help
+Commands:
+  .exit / .quit - Exit REPL
+  .reset - Clear session
+  .help - Show this help
+
 >>> x = 42
->>>                    # Silent (no auto-display)
+>>>                    # Silent (implicit local creation)
 
->>> print(x)
-42                     # print() output only
+>>> print("Hello REPL!")
+Hello REPL!            # print() output displays
 
->>> print(_)
-42                     # _ holds last value
+>>> print(42 + 1)
+43                     # Arithmetic works
 
 >>> 1 + 1
->>>                    # Silent (expression detection in Phase 288.1)
+>>>                    # Silent (expression auto-display in Phase 288.1)
 
 >>> .reset
 Session reset
 
->>> print(x)
-Error: Undefined variable 'x'
+>>> print("After reset")
+After reset            # REPL continues after reset
 ```
 
+**Known Limitations** (Phase 288 MVP):
+- Variable persistence not yet implemented (`x = 1` then `print(x)` errors)
+- `_` variable stored but not accessible in user code yet
+- No expression auto-display (deferred to Phase 288.1)
+
 **Design Philosophy**: Follow 80/20 rule - deliver working REPL first, polish UX later.
 
 ---