merge: AgentProject membership — the junction is now load-bearing

Merges feat/agent-project-membership (task 166/152). An agent can finally join
many projects: membership routes, per-membership role and optional brain
override, chat resolving context from the membership, and CLI attach-agent /
detach-agent / get memberships. The legacy Agent.projectId fallback is kept for
this release as the schema comment promises.

Conflict resolved in main.ts: that branch added its RBAC case to
mapUrlToPermission inline, while this branch had extracted the function to
middleware/url-permission.ts so it could be tested. Kept the extraction and
ported the case into it — joining a team is `edit:agents:<name>`, not
`create:agents`, which is the authority to mint a whole agent.

Also fixes something the extraction makes possible. security.test.ts contained a
hand-copied reproduction of mapUrlToPermission, because main.ts self-invokes
main() and nothing in it was importable. A security test asserting against a
copy stops testing the system the moment the real one changes, and this copy had
already drifted. It now imports the real function; all 18 assertions still pass,
against the code that actually runs.

Local: build clean, workspace 2550 passed, lint unchanged at 794 errors.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4wNHWf7xSwnZCWpJcyv9p

.taskmaster/tasks/task_098.md

@@ -0,0 +1,79 @@
+# Task ID: 98
+
+**Title:** Implement Persistent File Cache for Stages
+
+**Status:** done
+
+**Dependencies:** 73 ✓
+
+**Priority:** high
+
+**Description:** Extend CacheProvider with file-based persistence in ~/.mcpctl/cache/proxymodel/ for cross-session caching.
+
+**Details:**
+
+Create `src/mcplocal/src/proxymodel/file-cache.ts`:
+
+```typescript
+import { mkdir, readFile, writeFile, readdir, stat, unlink } from 'fs/promises';
+import { join } from 'path';
+import { createHash } from 'crypto';
+import type { CacheProvider } from './types';
+
+const CACHE_DIR = join(process.env.HOME ?? '', '.mcpctl', 'cache', 'proxymodel');
+
+export class FileCacheProvider implements CacheProvider {
+  private memCache = new Map<string, string>();
+  private maxSizeBytes: number;
+  
+  constructor(options: { maxSizeBytes?: number } = {}) {
+    this.maxSizeBytes = options.maxSizeBytes ?? 100 * 1024 * 1024; // 100MB default
+  }
+  
+  hash(content: string): string {
+    return createHash('sha256').update(content).digest('hex').slice(0, 16);
+  }
+  
+  private keyToPath(key: string): string {
+    const safeKey = key.replace(/[^a-zA-Z0-9-_]/g, '_');
+    return join(CACHE_DIR, safeKey);
+  }
+  
+  async get(key: string): Promise<string | null> {
+    // Check memory first
+    if (this.memCache.has(key)) return this.memCache.get(key)!;
+    
+    // Check file
+    try {
+      const content = await readFile(this.keyToPath(key), 'utf-8');
+      this.memCache.set(key, content); // Warm memory cache
+      return content;
+    } catch {
+      return null;
+    }
+  }
+  
+  async set(key: string, value: string): Promise<void> {
+    await mkdir(CACHE_DIR, { recursive: true });
+    this.memCache.set(key, value);
+    await writeFile(this.keyToPath(key), value);
+    await this.enforceMaxSize();
+  }
+  
+  async getOrCompute(key: string, compute: () => Promise<string>): Promise<string> {
+    const cached = await this.get(key);
+    if (cached !== null) return cached;
+    const value = await compute();
+    await this.set(key, value);
+    return value;
+  }
+  
+  private async enforceMaxSize(): Promise<void> {
+    // LRU eviction based on file mtime when cache exceeds maxSizeBytes
+  }
+}
+```
+
+**Test Strategy:**
+
+Unit tests: file-based persistence survives process restart, memory cache is warmed on file read, LRU eviction works when size exceeded, concurrent access is safe. Integration test with real filesystem.