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_050.md

@@ -0,0 +1,55 @@
+# Task ID: 50
+
+**Title:** Implement progressive tool exposure for gated sessions
+
+**Status:** done
+
+**Dependencies:** 48 ✓, 49 ✓
+
+**Priority:** high
+
+**Description:** Modify tools/list behavior to only expose begin_session while gated, and expose all tools plus read_prompts after ungating.
+
+**Details:**
+
+1. Update tools/list handling in `/src/mcplocal/src/router.ts`:
+   ```typescript
+   async handleToolsList(sessionId: string): Promise<Tool[]> {
+     const state = this.getSessionState(sessionId);
+     
+     if (state.gated) {
+       // Only show begin_session while gated
+       return [this.getBeginSessionTool()];
+     }
+     
+     // After ungating: all upstream tools + read_prompts
+     const upstreamTools = await this.discoverTools();
+     return [...upstreamTools, this.getReadPromptsTool()];
+   }
+   ```
+
+2. Block direct tool calls while gated:
+   ```typescript
+   async handleToolCall(sessionId: string, toolName: string, args: any): Promise<any> {
+     const state = this.getSessionState(sessionId);
+     
+     if (state.gated && toolName !== 'begin_session') {
+       // Intercept: extract keywords, match prompts, inject briefing
+       return this.handleInterceptedCall(sessionId, toolName, args);
+     }
+     
+     // Normal routing
+     return this.routeToolCall(toolName, args);
+   }
+   ```
+
+3. Ensure notifications/tools/list_changed is sent after ungating
+
+**Test Strategy:**
+
+- Unit test: tools/list while gated returns only begin_session
+- Unit test: tools/list after ungating returns all tools + read_prompts
+- Unit test: begin_session not visible after ungating
+- Unit test: Tool call while gated (not begin_session) triggers intercept
+- Unit test: Tool call after ungating routes normally
+- Unit test: notifications/tools/list_changed sent on ungate