docs(repl): Phase 288 documentation cleanup

Updated documentation to reflect actual implementation status:
- docs/reference/language/repl.md: Corrected examples (variable persistence TODO)
- docs/development/current/main/10-Now.md: Phase 288 completion noted
- docs/development/current/main/30-Backlog.md: Updated with Phase 288.1 tasks
- docs/development/current/main/phases/phase-288/: Added phase documentation

Accurate REPL behavior examples:
- x = 1 works (implicit local)
- print(x) errors (persistence in Phase 288.1)
- Expression auto-display deferred

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

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

docs/reference/language/repl.md

@@ -1,6 +1,6 @@
 # REPL Mode (Read–Eval–Print Loop) — Specification (SSOT)
 
-**Status**: Phase 288 MVP Implementation (2025-12-25)
+**Status**: Phase 288 MVP Implementation (2025-12-25) — partial (dev tool)
 
 ## Philosophy: Two Execution Contexts, One Language
 
@@ -75,8 +75,8 @@ static box Main {
 >>> x = 1           // ✅ Implicitly creates session-level local
 >>>
 
->>> print(x)        // ✅ Reads from session scope
-1
+>>> print(x)        // ⏳ Phase 288.1: session→eval bridge needed
+Error: Undefined variable 'x'
 
 >>> y               // ❌ ERROR: Undefined variable (Fail-Fast)
 Error: Undefined variable 'y'
@@ -88,11 +88,9 @@ Hint: Variable not defined. Assign a value first.
 >>> print(z)
 3
 
->>> 1 + 1           // ✅ Expression auto-display (Phase 288.1+)
-2
+>>> 1 + 1           // ⏳ Phase 288.1: expression auto-display
 
->>> _               // ✅ Last value stored in _ variable
-2
+>>> _               // ⏳ Phase 288.1: last value binding
 
 >>> .reset          // ✅ Clear session
 Session reset
@@ -108,6 +106,18 @@ Error: Undefined variable 'x'
 - Reads of undefined names are errors (Fail-Fast; no silent `void`)
 - **Implementation**: Session stores runtime values (`VMValue`), not MIR IDs
 
+## Implementation Status (MVP vs planned)
+
+Implemented in Phase 288 MVP:
+- `hakorune --repl` / `-i`
+- `.help`, `.exit/.quit`, `.reset`
+- REPL-only session object exists (runtime-value based)
+- File mode regression gate remains green
+
+Planned for Phase 288.1:
+- Session variables visible to subsequent compiled lines (`x = 1` then `print(x)`)
+- Expression auto-display and `_` last-value binding
+
 ## 2) Binding Rules in REPL Mode
 
 ### 2.1 Implicit local on assignment (key feature)