Phase 12: Tool registry — governed business actions for AI agents

- ToolRegistry: named tools with parameter validation and audit logging
- 6 built-in staffing tools:
  search_candidates (skills, city, state, experience, availability)
  get_candidate (by ID)
  revenue_by_client (top N by billed revenue)
  recruiter_performance (placements, revenue per recruiter)
  cold_leads (called N+ times, never placed)
  open_jobs (by vertical, city)
- Each tool: name, description, params, permission level (read/write/admin)
- SQL template with validated parameter substitution
- Full audit trail: every invocation logged with agent, params, result
- Endpoints: GET /tools (list), GET /tools/{name} (schema),
  POST /tools/{name}/call (execute), GET /tools/audit (log)
- Per ADR-015: governed interface before raw SQL for agents

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/gateway/src/main.rs

@@ -1,5 +1,6 @@
 mod auth;
 mod observability;
+mod tools;
 
 use axum::{Router, extract::DefaultBodyLimit, routing::get};
 use proto::lakehouse::catalog_service_server::CatalogServiceServer;
@@ -51,7 +52,7 @@ async fn main() {
         .route("/health", get(health))
         .nest("/storage", storaged::service::router(store.clone()))
         .nest("/catalog", catalogd::service::router(registry.clone()))
-        .nest("/query", queryd::service::router(engine))
+        .nest("/query", queryd::service::router(engine.clone()))
         .nest("/ai", aibridge::service::router(ai_client.clone()))
         .nest("/ingest", ingestd::service::router(ingestd::service::IngestState {
             store: store.clone(),
@@ -68,7 +69,15 @@ async fn main() {
             }
         }))
         .nest("/workspaces", queryd::workspace_service::router(workspace_mgr))
-        .nest("/journal", journald::service::router(journal));
+        .nest("/journal", journald::service::router(journal))
+        .nest("/tools", tools::service::router({
+            let tool_reg = tools::registry::ToolRegistry::new_with_defaults();
+            tool_reg.register_defaults().await;
+            tools::ToolState {
+                registry: tool_reg,
+                query_fn: tools::QueryExecutor::new(engine.clone()),
+            }
+        }));
 
     // Auth middleware (if enabled)
     if config.auth.enabled {