feat(mcp): implement resilience middleware pipeline

Author: Shanyu-Dabbiru

apps/sim/lib/mcp/resilience/pipeline.ts

@@ -0,0 +1,42 @@
+import type { McpExecutionContext, McpMiddleware, McpMiddlewareNext } from './types'
+import type { McpToolResult } from '@/lib/mcp/types'
+
+export class ResiliencePipeline {
+    private middlewares: McpMiddleware[] = []
+
+    /**
+     * Add a middleware to the pipeline chain.
+     */
+    use(middleware: McpMiddleware): this {
+        this.middlewares.push(middleware)
+        return this
+    }
+
+    /**
+     * Execute the pipeline, processing the context through all middlewares,
+     * and finally invoking the terminal handler.
+     */
+    async execute(
+        context: McpExecutionContext,
+        finalHandler: McpMiddlewareNext
+    ): Promise<McpToolResult> {
+        let index = -1
+
+        const dispatch = async (i: number): Promise<McpToolResult> => {
+            if (i <= index) {
+                throw new Error('next() called multiple times')
+            }
+            index = i
+
+            // If we reached the end of the middlewares, call the final handler
+            if (i === this.middlewares.length) {
+                return finalHandler(context)
+            }
+
+            const middleware = this.middlewares[i]
+            return middleware.execute(context, () => dispatch(i + 1))
+        }
+
+        return dispatch(0)
+    }
+}