atomic-ipc-fileslisted

# Atomic IPC File Guidelines The host and the editor exchange state through polled files. A plain write lets the poller observe a half-written file (truncated JSON) or hit a Windows sharing violation mid-write; a naive reader can then *consume* the torn file and lose the response forever. Atomicity here is a **writer+reader co-design** — fixing only one side still loses data under version skew, because old writers and new readers (and vice versa) coexist across package releases. --- ## 1. Writers Publish Atomically - Write to a temp file **in the same directory**, then rename over the destination: Python `server_core.write_json` (temp + `os.replace`), C# `XUUnityLightMcpAtomicFileWriter` (temp + `File.Replace`/`File.Move`). - The temp name must not match any reader's scan glob: `<name>.<uuid>.tmp` never matches `*.json`, so the editor request pump and result scanners cannot pick up a partial file. - C# side: `File.WriteAllText` is allowed **only inside** `XUUnityLightMcpAtomicFileWriter` — `tests/test_atomic_ipc_contract.py` enforces the single-call-site invariant over the whole `Editor/` tree. Route new polled-file writers through it; do not add direct writes. ## 2. Contention Handling Depends on the Writer's Thread - On Windows, `os.replace`/`File.Replace` can fail transiently while a poller briefly holds the destination open (readers poll `bridge_state.json` at up to 5 Hz during active operations). - **Host process (Python):** bounded sleep-retry is fine (`write_json