feat: TypeScript rewrite with zero dependencies, interface-based DI, and comprehensive tests

.claude/tasks/context_session_a9973aa3-2e87-420a-9c57-c48fd5f3a2d4.md

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+# Session Context: TypeScript Rewrite Plan
+
+## Session ID
+a9973aa3-2e87-420a-9c57-c48fd5f3a2d4
+
+## Goal
+Create a comprehensive implementation plan to rewrite the ABSmartly JavaScript SDK in TypeScript from scratch.
+
+## What Was Done
+1. Created git worktree `worktree-typescript-rewrite` based on `main`
+2. Thoroughly explored the entire codebase (43 source files, 34 test files, all config)
+3. Read every source file, understanding all types, APIs, and algorithms
+4. Read all 20 JsonExpr operators
+5. Read all 14 test files to understand test patterns and fixture data
+6. Wrote comprehensive 17-task implementation plan
+
+## Plan Location
+`docs/superpowers/plans/2026-03-28-typescript-rewrite.md`
+
+## Key Decisions
+- **Drop legacy support**: Node 18+ / modern browsers only (was Node 6+ / IE 10+)
+- **Drop dependencies**: node-fetch, rfdc, core-js (use native fetch, structuredClone)
+- **Drop polyfills**: fetch-shim, abort-controller-shim, platform detection wrappers
+- **Drop Babel**: Use tsup (esbuild-based) for bundling ESM + CJS + browser IIFE
+- **Test framework**: Vitest instead of Jest
+- **Keep identical**: Public API, hashing algorithms, variant assignment, client retry logic
+
+## Task Breakdown (17 tasks)
+1. Project scaffolding & build system (package.json, tsconfig, tsup, vitest)
+2. Types & errors
+3. Murmur3 hash
+4. MD5 hash
+5. Hashing utilities
+6. Core utilities (isObject, isEqualsDeep, etc.)
+7. Variant assigner
+8. JsonExpr evaluator
+9. JsonExpr operators (all 20 in one file)
+10. JsonExpr facade & AudienceMatcher
+11. HTTP client with retry
+12. Provider & publisher
+13. Context class (largest module)
+14. SDK class
+15. Config merge utility
+16. Public API & index exports
+17. Full integration & cleanup