feat: implement workspace sync with Mutagen (Phase 2)

[VAIBHAVSING]

Summary

Implements Phase 2: Workspace Sync for Remote Coasts using Mutagen for reliable file synchronization between local development machine and remote VMs.

This PR builds on coast-guard#168 (Phase 0) and adds complete workspace synchronization functionality.

What's New

🔄 Mutagen Integration

• Full Mutagen sync session lifecycle management
• Unidirectional sync (local → remote) using one-way-safe mode
• Automatic Mutagen agent installation on remote (~10MB)
• Session naming: coast-<project>-<branch>-<remote>
• Remote workspace path: ~/coast-workspaces/<project>/<branch>/

🎯 CLI Commands

# Create sync session
coast sync create <project> <remote> --local-path <path> --branch <branch>

# Check status
coast sync status [project]

# Control sync
coast sync pause <project>
coast sync resume <project>
coast sync flush <project>

# Cleanup
coast sync terminate <project>

📁 Features

• .coastignore support - Respects ignore patterns (node_modules, .git, *.log, etc.)
• Real-time sync - Changes detected and synced automatically
• Pause/Resume - Control when sync happens
• Status tracking - Monitor sync state (Initial, Syncing, Paused, Error)
• Multiple projects - Sync multiple projects to same remote simultaneously

🏗️ Architecture

• MutagenManager in coast-daemon/src/remote/mutagen.rs (697 lines)
• CLI commands in coast-cli/src/commands/sync.rs (406 lines)
• Protocol extensions in coast-core/src/protocol/remote.rs
• State persistence in sync_sessions table
• Handler integration with analytics support

🧪 Testing

• Comprehensive test scripts (test_sync_simple.sh, test_sync_quick.sh)
• Setup automation (setup_test.sh, install_mutagen.sh)
• Detailed guides (QUICK_TEST.md, TEST_SYNC.md)
• Tests cover: initial sync, real-time updates, ignore patterns, pause/resume

Technical Details

Mutagen Requirements:

• Local: ~100MB (one-time install)
• Remote: ~10MB agent (auto-installed via SSH)

Sync Behavior:

• Mode: one-way-safe (local → remote only)
• Transport: SSH with optional key configuration
• Conflict handling: Local always wins
• Delete propagation: Safe deletes only

State Management:

• In-memory session cache for fast lookups
• SQLite persistence in sync_sessions table
• Status tracking: last_sync_at, status, mutagen_session_id

Testing Instructions

Prerequisites

1. A VM with SSH access
2. Mutagen installed locally (or use ./install_mutagen.sh)
3. Coast built in release mode

Quick Test

# Setup
./setup_test.sh
export PATH="$HOME/.local/bin:$(pwd)/target/release:$PATH"

# Run test (replace with your VM)
./test_sync_simple.sh ubuntu@192.168.1.100

# Or with SSH key
./test_sync_simple.sh ubuntu@192.168.1.100 ~/.ssh/id_rsa

See QUICK_TEST.md for detailed instructions.

Changes

New Files

• coast-daemon/src/remote/mutagen.rs - Mutagen manager implementation
• coast-cli/src/commands/sync.rs - CLI sync commands
• QUICK_TEST.md - Quick testing guide
• TEST_SYNC.md - Comprehensive manual testing guide
• install_mutagen.sh - Mutagen installation script
• setup_test.sh - One-command test setup
• test_sync_simple.sh - Automated test script

Modified Files

• coast-core/src/protocol/remote.rs - Add sync request/response types
• coast-daemon/src/handlers/remote.rs - Add sync handlers (6 variants)
• coast-daemon/src/state/remotes.rs - Add sync session state methods
• coast-daemon/src/server.rs - Initialize MutagenManager
• coast-daemon/src/analytics.rs - Track sync operations
• coast-cli/src/lib.rs - Add Sync command

Stack

• Phase 0: feat: add remote coasts infrastructure (Phase 0) coast-guard/coasts#168 (base) - Remote infrastructure
• Phase 2: This PR - Workspace sync with Mutagen
• Phase 3: Next - Remote build/run operations

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