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/development/current/main/10-Now.md

@@ -2,10 +2,10 @@
 
 ## Current Focus (next)
 
-- Phase 287（stabilization）: ビルド/テスト軽量化（quick が重すぎる）
-  - 目的: `tools/smokes/v2/run.sh --profile quick` を「開発中に回せる速さ」に戻す（意味論不変、分類/配置で解決）
-  - 入口: `docs/development/current/main/phases/phase-287/README.md`
-  - 手順: `docs/development/current/main/phases/phase-287/P1-INSTRUCTIONS.md`
+- Phase 288.1（dev-tools）: REPL session persistence + auto-display
+  - 目的: `hakorune --repl` で変数が行を跨いで生きる（暗黙local）＋式の自動表示（`_` を含む）
+  - 入口: `docs/development/current/main/phases/phase-288/README.md`
+  - 手順: `docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md`
 
 - Phase 284（design-first）: Return as ExitKind SSOT（patternに散らさない）
   - 目的: `return` を `ExitKind` + `compose::*` / `emit_frag()` に収束させ、pattern側の個別実装を増やさない

docs/development/current/main/30-Backlog.md

@@ -8,6 +8,11 @@ Related:
 
 ## 直近（JoinIR/selfhost）
 
+- **Phase 288（✅ P0–P3 complete）: REPL mode**
+  - 入口: `docs/development/current/main/phases/phase-288/README.md`
+  - SSOT: `docs/reference/language/repl.md`
+  - 次: Phase 288.1（session persistence / auto-display） `docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md`
+
 - **Phase 287（active, stabilization）: ビルド/テスト軽量化（quick が重すぎる）**
   - 目的: `tools/smokes/v2/run.sh --profile quick` を 45秒以内（目安）へ戻し、開発サイクルを軽くする
   - 入口: `docs/development/current/main/phases/phase-287/README.md`

docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md

@@ -0,0 +1,62 @@
+# Phase 288.1 P1: REPL Session Persistence + Auto-Display (instruction sheet)
+
+## Objective
+
+- Make REPL variables persist across input lines (`x = 1` then `print(x)` works).
+- Add minimal expression auto-display and `_` last-value binding (REPL-only).
+- Keep file mode semantics unchanged; quick smokes must remain green.
+
+SSOT:
+- `docs/reference/language/repl.md`
+
+## Constraints (non-negotiable)
+
+- No new env vars.
+- No file-mode behavior changes.
+- Keep REPL-specific state and logic isolated (Box-first).
+
+## Design (recommended)
+
+Do **not** persist `ValueId` across evaluations. Persist runtime values (VMValue/handle) in `ReplSessionBox`, and bridge them via a REPL-only rewrite step.
+
+### Bridge approach: REPL-only AST rewrite
+
+In REPL mode, rewrite variable reads/writes that are not declared in the current input line into calls against a REPL session object:
+
+- Read `x` → `__repl.get("x")`
+- Assignment `x = expr` → `__repl.set("x", expr)`
+- `_` is treated as a normal name in the session (written by auto-display).
+
+This keeps the parser unchanged and avoids contaminating the normal MIR builder scope model.
+
+### Session API (REPL-only)
+
+Provide a minimal host object `__repl` with:
+
+- `get(name: String) -> Any` (Fail-Fast if missing)
+- `set(name: String, value: Any) -> void`
+- `reset() -> void`
+
+Implementation options:
+
+- Rust VM only (initially): inject `__repl` as a built-in box/object available only in `--repl`.
+- LLVM parity is not required for Phase 288.1; REPL is a dev tool.
+
+## Step-by-step
+
+1) Add a REPL-only `__repl` host object and VM handlers for `get/set/reset`.
+2) Implement AST rewrite in the REPL runner before compilation:
+   - Collect “declared names” in the current line (`local name`, function params, etc.).
+   - Rewrite remaining identifier reads/writes to `__repl.get/set`.
+3) Implement auto-display:
+   - If the input is a pure expression, `print(result)` (or equivalent) in REPL only.
+   - Store result into session name `_` (skip if `void`).
+4) Add conformance checks (manual is OK if no test harness exists yet):
+   - `x = 1` (silent)
+   - `print(x)` prints `1`
+   - `y` (read) is NameError
+   - `1 + 1` prints `2` and `_` becomes `2`
+   - `.reset` clears variables (`print(x)` errors)
+5) Run regression gate:
+   - `./tools/smokes/v2/run.sh --profile quick` must stay `0 FAILED`.
+

docs/development/current/main/phases/phase-288/README.md

@@ -0,0 +1,33 @@
+# Phase 288: REPL mode (design-first, file-mode unaffected)
+
+Status: ✅ P0–P3 complete (2025-12-25) / ⏳ 288.1 next
+
+Goal: Add an interactive REPL for Nyash while keeping file mode semantics unchanged and keeping the language SSOT stable.
+
+SSOT:
+- REPL spec: `docs/reference/language/repl.md`
+
+## Scope
+
+- CLI entry: `hakorune --repl` / `-i`
+- REPL commands: `.help`, `.exit/.quit`, `.reset`
+- Fail-Fast: undefined reads are errors
+- File mode: no behavior changes (quick smokes remain green)
+
+## Completed (P0–P3)
+
+- P0: SSOT doc established/updated (`docs/reference/language/repl.md`)
+- P1: CLI entry point (`--repl` / `-i`)
+- P2: REPL session state isolated (Box-first; runtime-value based)
+- P3: Minimal UX and docs polish
+
+## Next (Phase 288.1)
+
+The MVP intentionally deferred these:
+
+- Session variable **persistence across lines** (bridge session → compilation/runtime)
+- Expression auto-display + `_` last-value binding
+- Multi-line input handling (continuations)
+
+Entry: `docs/development/current/main/phases/phase-288/P1-INSTRUCTIONS.md`
+