The two Defenseurs mounts are now read-only in the container, so a write
added one day under REPORTS_DIR or /data/defenseurs would fail in
production as a 500 (EROFS) while every other test stays green: their
fixtures are writable temp dirs, and CI runs as root.
writes.test.js spies every node:fs write API (callback, Sync and
fs.promises forms) before a fresh require, after purging all runtime
modules from the require cache, and records the calls whose stack goes
through a runtime file. It covers boot (the temp-file sweep), the six GET
routes (no write at all, one macrotask after the response included) and
POST /hosts/<id> (writes only under HOSTS_DIR). Each case proves its own
spies are live, and the require.main block is pinned since it never runs
in-process.
Mutation proofs: a write at module load, in the scan collector, through an
fs function not imported today, in the ingest rename or in metrics.js, a
dead spy, and a new call in the main block each turn the expected case
red. With the cache purge narrowed to index.js, the metrics.js write stays
green.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
