feat: M1.4.3 - Beatrice REPL Implementation (Interactive Shell)

[LyeZinho]

Summary

Implements the complete Beatrice REPL (Read-Eval-Print Loop) for interactive user interaction with MiMi, following the M1.4.1 design specification.

Features Delivered

• Interactive REPL Shell - Continuous read-eval-print loop with line buffering
• Special Commands - Control commands (.help, .status, .clear, .config, .history, .exit, .quit)
• Shell Integration - Execute system commands via !command syntax
• Multi-line Input - Backslash continuation for complex commands
• Startup Scripts - Load and execute initialization commands from file
• History Management - In-memory command history with configurable size
• Prompt States - Context-aware prompts (default, debug, async task following)

Implementation Details

Task Breakdown

1. Task 1 - Module structure (5 files, special command parser)
2. Task 2 - REPL main loop (stdin reader, event dispatcher)
3. Task 3 - Multi-line input & startup scripts (12 integration tests)
4. Task 4 - Documentation (450 lines of comprehensive docs)

Test Results

✅ 25 Tests Passing

• 13 unit tests (config, prompts, command parsing)
• 12 integration tests (command-line args, feature flags)

Code Metrics

• Production: 431 lines (5 modules)
• Tests: 116 lines (12 integration tests)
• Documentation: 450 lines

Git Commits

1. feat: add REPL module structure with special commands
2. feat: implement REPL main loop with special command handling
3. test: add REPL integration tests for all features
4. docs: add comprehensive REPL implementation documentation

Architecture

repl/
├── mod.rs              → ReplConfig, PromptState
├── editor.rs           → History management (in-memory Phase 1)
├── completion.rs       → Completion stub (Phase 2)
├── special_commands.rs → .help, .status, .clear, .config, .history, .exit, !shell
└── loop.rs            → Main event loop, multiline handling, startup scripts

Usage

# Basic REPL
mimi repl

# With options
mimi repl --no-history --max-history 500 --startup-script setup.mimi

# Inside REPL
mimi> .help
mimi> .status
mimi> !ls -la
mimi> exec some command \
... continuation
mimi> .exit

Dependencies

• No new dependencies added (uses std only)
• dev-dependencies: assert_cmd, predicates, tempfile

Testing

# All tests
cargo test -p mimi-cli

# Just REPL tests
cargo test -p mimi-cli repl

Next Steps

• M1.4.3 Phase 2: rustyline integration, persistent history, tab completion
• M1.4.4: HTTP server
• M1.4.5: WebSocket support
• M1.4.6: Integration with Mimi state machine

Blockers / Notes

• M1.4.2 (CLI core) not yet merged into main - this branch depends on M1.4.2 implementation pattern
• Command execution deferred to M1.4.6 (state machine integration)

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Branch: feature/M1.4.3-repl-implementation
Base: main
Status: Ready for code review