Persists one run result as a standalone JSON artifact.

A multi-run application passes values between ordinary runs. Scraping them from stdout is not good enough: terminal output interleaves with logs, has no atomicity, and cannot express that a value must never be published. This writer gives a run one explicit destination instead. Its read-only preflight validates deterministic destination conflicts before provider acquisition or run execution; exclusive publication remains authoritative against races.

Persistence is atomic and refuses to clobber. Content is deterministic canonical JSON: the SHA-256 digest of the exact artifact bytes is therefore a stable identity for the successful value. Content is written to an exclusive file inside a mode-0700 temporary sibling directory, linked into place, and the temporary directory is then cleaned up best-effort, so a reader never observes a partial artifact and an existing destination fails rather than being overwritten. Once the link succeeds, cleanup cannot turn the committed publication into a reported failure. A relative destination is anchored once before validation so a VM-wide working-directory change cannot redirect later filesystem operations. A private artifact is restricted to 0600 before any content is written, never after.

Secure publication is supported on Unix hosts with POSIX-compatible mkdir and id executables available on PATH; persistence fails closed when those authority/mode primitives are unavailable, a physical or lexical ancestor has an untrusted owner, or any ancestor is group/other-writable without sticky-directory protection. Preflight also rejects a final parent whose effective permission class lacks create access.

The private/normal distinction is authority, not formatting. A private result may only reach a private destination; the caller decides the class and this module refuses to write a private value to a normal artifact.