[platform] Build a language-neutral black-box CLI conformance runner

[codeforester]

Goal

Prove CLI behavior by running real executables, regardless of their implementation language or parser.

Background

Issue #241 added golden JSON fixtures and a dependency-free Node reader. That proves the fixtures are portable, but not that a Python, Go, Rust, Node, JVM, or .NET executable actually follows help, stdout/stderr, exit, signal, configuration, destructive-action, and redaction rules.

Scope

• Build a black-box subprocess runner driven by the versioned platform contract/spec.
• Define progressive conformance levels:
  • L1: identity/version/help, stdout/stderr, basic structured output, portable exit codes.
  • L2: configuration precedence/provenance, platform/dependency diagnostics, signals/cancellation, offline behavior.
  • L3: destructive confirmation/dry-run, redaction, authentication/data-classification boundaries, audit evidence.
• Emit a stable machine-readable report plus actionable human diffs.
• Run only declared safe fixtures in isolated temporary environments.
• Publish adapters/examples for common CI systems without coupling the contract to one provider.

Acceptance Criteria

• The runner treats the CLI as an executable and requires no Python imports or source checkout.
• The same suite validates one base-cli consumer and at least one non-Python reference CLI.
• Assertions cover stdout and stderr bytes, exit status, signals/timeouts, files changed, environment/config precedence, and schema validation.
• Destructive cases use disposable fixtures and prove no mutation in dry-run/non-consented paths.
• Results name the contract version, capability level, artifact digest, implementation identity, and skipped capabilities.
• Failures are deterministic and suitable as required CI checks.
• Windows and POSIX process differences have explicit portable expectations.
• The runner itself has a versioning and backward-compatibility policy.

Validation

Exercise known-good and deliberately non-conforming Python and non-Python fixtures on Linux, macOS, and Windows.

Non-Goals

• Do not require all CLIs to use the same parser.
• Do not execute arbitrary repository code during discovery.
• Do not claim conformance from static schema validation alone.

Dependencies

• cli-platform/v1 behavioral contract
• portable CLI specification artifact
• [v1.0] Add golden cross-language contract fixtures and validators #241

Project Fields

• Status: Backlog
• Priority: P1
• Area: CI
• Initiative: v1.0 Readiness
• Size: L

Ownership

• Assignee: @codeforester