I scale C++ network gateways, build high-volume mail infrastructure, and write the systems plumbing under AI products. Backend and systems engineer in Karachi (UTC+5), about three years in.

Open to work. Fully remote, working Gulf (GMT+4) and European hours, via EOR or contractor. Also open to relocating where the employer sponsors the visa. Website · Resume (PDF) · LinkedIn · sarbzga@gmail.com

• A C++ TLS WebSocket gateway taken from 200 to 5,000 concurrent clients at Ebryx, by replacing blocking polling, pooling connections, batching Arena requests, and initializing Arena memory up front. Stress-tested past normal traffic and fixed the failure paths that only showed up there, including a log-rotation race that crashed a worker thread.
• Enterprise email infrastructure sending 200K+ emails a day across 1,000+ domains at Softaims: a multi-channel campaign engine over KumoMTA and Amazon SES edge nodes, automated SPF/DKIM/DMARC lifecycle, Redis-locked graduated warmup, blacklist monitoring, and bi-directional Salesforce sync. Built solo.
• Colloid Swarm, a portable multi-agent engineering harness adopted company-wide by roughly 50 engineers. Seven delegating personas route work across three cost tiers, with hostile review run as an independent gate rather than self-assessment. One engine-neutral layer, thin adapters for Claude Code, Codex, Kimi, and Copilot.

Hardest and lowest-level first:

• colloid-swarm. The harness above. Canonical instructions, skills, hook policies, and the MCP server registry live in one layer; an exporter transplants the scaffold into a target repository at a pinned commit.
• WARPO. WhatsApp backup decryption and export for Android (crypt12/14/15) and iOS. Parses the binary formats and handles key extraction. Hard to fake, which is the point.
• npi-discovery-service. Bulk export of US healthcare providers from the NPPES registry. A partition-aware collector splits by provider type and narrows by postal prefix until each query fits the upstream limit, and reports incomplete partitions instead of silently truncating. Redis caching, WebSocket progress streaming across API instances, correlation-ID tracing, Terraform deploys.
• balloon-game-8086. DOS text-mode animation in 8086 assembly. Writes straight to the CGA buffer at 0xB800, hooks the IRQ 0 timer through the interrupt vector table, no BIOS or DOS print calls.
• EmotionRecognitionModel. My final-year project at FAST NUCES: a CNN trained from scratch on FER2013 (28,709 training images, 7 classes), real-time OpenCV inference loop with Haar-cascade detection, exported to ONNX for on-device inference inside a Unity game.
• music-tools. A Discord bot streaming a GitHub-backed music library with no local storage, transcoding to 16-bit PCM at 48 kHz through ffmpeg and preloading the next track to avoid dropouts.

• Systems and networking. The gateway scale-up above, plus an auto-update migration system for a multi-tenancy move, a ZTNA gateway component ported from x86-64 to ARM (Raspberry Pi) for on-prem deployment, and a device profiler packaged as a standalone Ubuntu Server binary with Cython.
• Event-driven and data-intensive backends. Policy evaluation re-architected from cron to event-driven, cutting redundant database load 29% on cProfile benchmarks. A Kafka pipeline scoring network-agent risk for both ML training and live inference. MySQL pooling rewritten with RAII to stop pool exhaustion.
• The plumbing under AI products. A voice onboarding agent on ElevenLabs Conversational AI whose backend keeps conversation state in a slot-walk, so the whole interview script replays offline without a live call, with scoped tool tokens, signed webhooks, and exactly-once writes keyed on session, tool-call ID, and body hash. Also a LangChain deep-research agent framework, a RAG recommendation system on OpenAI embeddings, and Playwright scraping infrastructure collecting 10,000+ records a day from 50+ sources.

Plus the parts without a logo: networking and concurrency, event-driven architecture, SMTP/MTA and deliverability infrastructure, LangChain and LangGraph, MCP, NumPy, Pandas, OpenCV, Cython, Playwright, SonarQube, cProfile.

Learning Rust by building a terminal music player. Drawn to computer vision, robotics, and autonomy, specifically the backend and infrastructure side of hard-tech. Writing occasionally at abdulrafayzahid.dev.