# Task ID: 79

**Title:** Implement Stage Registry and Dynamic Loader

**Status:** done

**Dependencies:** 71 ✓, 75 ✓, 76 ✓, 77 ✓

**Priority:** high

**Description:** Create the stage registry that resolves stage names to handlers, loading from ~/.mcpctl/stages/ for custom stages and falling back to built-ins.

**Details:**

Create `src/mcplocal/src/proxymodel/stage-registry.ts`:

```typescript
import { readdir, stat } from 'fs/promises';
import { join } from 'path';
import type { StageHandler } from './types';

const STAGES_DIR = join(process.env.HOME ?? '', '.mcpctl', 'stages');

const builtInStages: Map<string, StageHandler> = new Map();
const customStages: Map<string, StageHandler> = new Map();

// Register built-ins at module load
import passthrough from './stages/passthrough';
import paginate from './stages/paginate';
import sectionSplit from './stages/section-split';
import summarizeTree from './stages/summarize-tree';

builtInStages.set('passthrough', passthrough);
builtInStages.set('paginate', paginate);
builtInStages.set('section-split', sectionSplit);
builtInStages.set('summarize-tree', summarizeTree);

export async function loadCustomStages(): Promise<void> {
  customStages.clear();
  try {
    const files = await readdir(STAGES_DIR);
    for (const file of files.filter(f => f.endsWith('.ts') || f.endsWith('.js'))) {
      const name = file.replace(/\.(ts|js)$/, '');
      const module = await import(join(STAGES_DIR, file));
      customStages.set(name, module.default);
    }
  } catch { /* directory doesn't exist */ }
}

export function getStage(name: string): StageHandler | null {
  return customStages.get(name) ?? builtInStages.get(name) ?? null;
}

export function listStages(): { name: string; source: 'built-in' | 'local' }[] {
  const result: { name: string; source: 'built-in' | 'local' }[] = [];
  for (const name of builtInStages.keys()) {
    result.push({ name, source: customStages.has(name) ? 'local' : 'built-in' });
  }
  for (const name of customStages.keys()) {
    if (!builtInStages.has(name)) result.push({ name, source: 'local' });
  }
  return result;
}
```

**Test Strategy:**

Unit tests: built-in stages are registered, getStage() returns correct handler, custom stages override built-ins, listStages() shows correct sources, missing stages return null. Integration test with actual stage files in temp directory.