Engineering portfolio and notebook of Keshav: production backend work on GST compliance, document AI and real-time infrastructure, plus personal systems and AI projects.http://amkeshav.me/enhttp://amkeshav.me/writing/durable-sse-notifications/http://amkeshav.me/writing/durable-sse-notifications/Replacing several ephemeral SSE channels with one table-backed notification stream — 25-second heartbeats, Last-Event-ID replay and runId correlation across async workflows. A walkthrough from the wire up.Fri, 25 Sep 2026 00:00:00 GMTReal-TimeBackendNestJSDistributed Systemshttp://amkeshav.me/writing/gst-returns-read-model/http://amkeshav.me/writing/gst-returns-read-model/GST return status queries went from 3,000ms+ to sub-15ms at peak load by reading a precomputed projection that filing writers keep fresh through domain events. Requirements, options and the update path.Fri, 25 Sep 2026 00:00:00 GMTPerformanceBackendPostgreSQLGSThttp://amkeshav.me/writing/http-200-integration-failure/http://amkeshav.me/writing/http-200-integration-failure/Four ways a GST portal integration lost or corrupted data while every request succeeded — a case-sensitive parameter, an unechoed field, a delegated rule and an over-broad sum — and how each was closed.Fri, 25 Sep 2026 00:00:00 GMTIntegrationBackendGSThttp://amkeshav.me/writing/pr-reviewer-cannot-modify-main/http://amkeshav.me/writing/pr-reviewer-cannot-modify-main/A threat model for Antigravity, an unattended PR reviewer — per-PR worktrees, an AST-level ban on mutation paths, an evidence gate, and the risk a worktree does not remove.Fri, 25 Sep 2026 00:00:00 GMTRustDeveloper InfrastructureSecurityhttp://amkeshav.me/writing/rag-retrieval-gating/http://amkeshav.me/writing/rag-retrieval-gating/In BARA, retrieval is three separate decisions — whether, from where and how much, then which chunks — made by deterministic rules before a vector is ever compared. A research note with the code.Fri, 25 Sep 2026 00:00:00 GMTAIRAGLLMSystemshttp://amkeshav.me/writing/redis-bullmq-namespace-bug/http://amkeshav.me/writing/redis-bullmq-namespace-bug/Two services used the same BullMQ queue name under different Redis key prefixes, so every OCR extraction result was enqueued where nothing would ever read it. An incident write-up.Fri, 25 Sep 2026 00:00:00 GMTDistributed SystemsRedisDocument AI