# Filesystem Process Safety

> Use when code mutates files, resolves paths, applies file protection, or controls child processes. Skip uploads, shell syntax, build graphs, services, and host administration.

- Skill: `machenjie/filesystem-process-safety` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds add machenjie/filesystem-process-safety`
- Raw SKILL.md: https://api.skillmd.com/api/skills/machenjie/filesystem-process-safety/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: machenjie (https://skillmd.com/u/machenjie)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/machenjie/filesystem-process-safety

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# filesystem-process-safety

## Registry Trigger

**Use when**

- Local create, temporary commit, replace, durability, cleanup, protection, ownership, path containment, link, or reparse behavior can change.
- Direct child-process executable, argv, environment, working directory, inherited-resource, stdio, exit, timeout, cancellation, descendant, cleanup, or unknown-result behavior can change.

**Do not use when**

- The decision concerns uploads or object storage, shell syntax, Linux host administration, build graphs or code generation, or service business logic.
- No task-local filesystem or child-process safety decision changes.

## Skill Role

Define portable application-runtime safety for local mutation and direct child processes from current platform, runtime, filesystem, trust, and consumer facts.

## Inputs

- supported platforms, filesystems, runtime APIs, path authority, who can write the path, whether any writer is less trusted, link policy, replacement, durability, protection, and cleanup owner
- executable identity, argv, environment, working directory, stdio, deadline, cancellation, descendants, exit meaning, and effect reconciliation

## High-Value Rules

- Define exclusive temporary creation in the destination directory, restrictive protection, documented same-filesystem commit, atomic visibility, and separate crash-durability proof.
- Classify path trust from writer identity, reachable impact, handle-relative confinement, and traversal exclusions; same-user writability or path difference alone does not establish a material boundary.
- Apply mode, ACL, ownership, and inheritance at creation where supported; verify final protection because replacement APIs preserve metadata differently.
- Execute a selected program directly with structured argv. Make lookup, environment, working directory, credential, and inherited-resource policy explicit; route shell semantics elsewhere.
- Define stdin closure, separate stdout/stderr, encoding, bounds, redaction, and concurrent draining before waiting.
- Distinguish spawn failure, exit, signal or forced termination, timeout, cancellation, partial output, and unknown effects. Start or termination request is not completion.
- Define timeout and cancellation with a deadline, graceful request, escalation, descendant policy, final wait/reap, reconciliation, and no blind retry after an unknown effect.
- Close handles, pipes, and temporary resources while preserving the primary failure; report cleanup failure and surviving or unknown state.

## Anti-Patterns

- Cross-volume replacement fails or degrades to copy/delete, exposing partial state.
- Check-then-open permits a link or reparse swap before mutation.
- Create-then-tighten protection briefly exposes bytes under default access.
- Treating every writable or replaceable path as attacker-controlled invents a trust boundary without writer evidence.
- Waiting before draining both pipes can deadlock parent and child.
- Killing only the direct child leaves descendants or effects running; timeout is not rollback.

## Stop Conditions

- Stop when the trusted base, target, executable, platform guarantee, effective protection, descendant scope, or reconciliation owner cannot be bounded.
- Reject atomicity, durability, containment, termination, or result claims based only on an API name.
- Route uploads, shell behavior, Linux host operations, build graphs, and service rules to their existing owners.

## Output Contract

- Return a Filesystem/Process Safety Record covering platform, path/link, commit, durability, protection, cleanup, executable, argv, environment, working-directory, inherited-resource, and stdio decisions.
- Include exit, timeout, cancellation, descendants, unknown results, evidence, proof limits, and residual owners.

## Targeted References

| Path | Type | Load when | Do not load when | Required by | Required output |
|---|---|---|---|---|---|
| [atomic filesystem commit and containment](references/atomic-filesystem-commit-and-containment.md) | targeted | Local creation, replacement, durability, containment, link, permission, ownership, or cleanup semantics remain open | No local filesystem mutation or path-authority decision changes | analysis-agent, task-agent, review-agent | boundary-decision, proof-limit, residual-risk |
| [child process invocation and completion](references/child-process-invocation-and-completion.md) | targeted | Executable selection, argv, environment, stdio, exit, timeout, cancellation, descendants, or result certainty remains open | No direct child-process execution contract changes | analysis-agent, task-agent, review-agent | boundary-decision, proof-limit, residual-risk |