Day 64 — Persistence & Storage: PathStorage, the Complete Crash-Safe Workspace

This workspace delivers PathStorage, the atomic JSON persistence layer that every later module — FillAuditLog, SlippageMonitor, PositionReconciler — writes through instead of calling open() directly. It exists because a truncated state file after a crash is indistinguishable from “nothing happened yet,” and that ambiguity is what lets position drift go unreconciled.

What You’re Building

PathStorage wraps a base directory and exposes write_json, read_json, and resolve. Every write goes to a temp file, gets fsync‘d, then replaces the destination in one atomic OS call — so a crash mid-write never corrupts the live file. Every read either returns valid data or raises StorageCorruptionError, never an empty default. It plugs directly into Day 34’s PositionReconciler: instead of FillAuditLog calling open() itself, it calls storage.write_json("audit/AAPL.json", fills) and lets PathStorage own the crash-safety guarantees.