hakorune/docs/development/current/PLUGIN_LOADER_MIGRATION_PLAN.md

Plugin Loader Migration Plan

Status: Migration plan memo（継続検討用の設計メモ）
Note: 実際の進捗と優先度は CURRENT_TASK.md と roadmap 側を正として管理し、このファイルはプラグインローダ統合の設計メモ・タスクリストとして扱います。

Overview

Consolidate three plugin loader implementations into a single unified system.

Current State

1. plugin_loader_v2.rs (906 lines) - Main BID-FFI plugin system
2. plugin_loader.rs (1217 lines) - Builtin box dynamic loading
3. plugin_loader_legacy.rs (299 lines) - Legacy host vtable system

Total: ~2400 lines of code with significant duplication

Target State

• plugin_loader_unified.rs - Single unified loader (~800 lines)
• plugin_ffi_common.rs - Shared FFI utilities (~300 lines)
• Total: ~1100 lines (55% reduction)

Migration Steps

Phase 1: Infrastructure (DONE)

• Create plugin_loader_unified.rs skeleton
• Create plugin_ffi_common.rs for shared types
• Update runtime/mod.rs
• Basic compilation check

Phase 2: Common Pattern Extraction

• Extract TLV encoding/decoding to plugin_ffi_common
• Extract handle management patterns
• Extract memory management utilities
• Extract error handling patterns

Phase 3: BID Plugin Migration

• Port PluginBoxV2 implementation
• Port BID FFI invoke mechanism
• Port plugin loading logic
• Port configuration parsing
• Migrate tests

Phase 4: Builtin Plugin Migration

• Port FileBoxProxy and related proxies
• Port dynamic library loading for builtins
• Port builtin-specific FFI patterns
• Migrate feature flags handling

Phase 5: Legacy Plugin Migration

• Port host vtable implementation
• Port legacy box creation
• Decide on deprecation timeline

Phase 6: Integration

• Update all references to old loaders
• Ensure backward compatibility
• Performance benchmarking
• Documentation update

Phase 7: Cleanup

• Remove old plugin loaders
• Remove redundant tests
• Update CLAUDE.md
• Final code review

Technical Decisions

Unified Plugin Type Detection

fn detect_plugin_type(path: &str) -> PluginType {
    // 1. Check file extension (.bid, .legacy, .builtin)
    // 2. Check nyash-box.toml for type field
    // 3. Probe for known symbols
    // 4. Default to BID
}

Handle Management Strategy

• Use generic PluginHandle<T> for all plugin types
• Centralized handle registry in plugin_ffi_common
• Reference counting with Arc<Mutex>

Error Handling

• Convert all errors to Result<T, String> at boundaries
• Plugin-specific errors wrapped with context
• Consistent error messages across all plugin types

Risk Mitigation

Backward Compatibility

• Keep old loaders under feature flags during migration
• Provide compatibility shims if needed
• Extensive testing with existing plugins

Performance

• Benchmark before and after migration
• Profile hot paths (box creation, method dispatch)
• Optimize only after correctness verified

Testing Strategy

1. Unit tests for each component
2. Integration tests with real plugins
3. E2E tests with full applications
4. Regression tests for edge cases

Success Metrics

• Code reduction: 50%+ fewer lines
• All existing tests pass
• No performance regression
• Cleaner API surface
• Better error messages
• Easier to add new plugin types

Timeline

• Phase 1-2: Day 1 (Today)
• Phase 3-4: Day 2-3
• Phase 5-6: Day 4
• Phase 7: Day 5

Total: 5 days for complete migration