FEATURE: CLI Errors

Field	Value
Version	20260812 V1
Description	Defines deterministic process failure behavior for the parser executable.
Depends On	FEATURE-CLI-ENTRYPOINT.md
Provides	parser error behavior
Consumes	parser executable

Operational Behavior

Operational failures produce a nonzero exit status. Diagnostics are written to standard error, and standard output remains empty when processing cannot complete. Successful input processing continues to use the standard-input and standard-output contract defined by FEATURE-CLI-ENTRYPOINT.md.

Programmatic Acceptance

=== AC cli-errors-success-contract ===
Intent: A successful invocation returns zero and keeps diagnostics off standard error.

import subprocess

result = subprocess.run( ["./cmark"], input="plain text\n", capture_output=True, text=True, encoding="utf-8", ) assert result.returncode == 0 assert result.stdout == "plain text\n" assert result.stderr == "" === END AC cli-errors-success-contract ===

=== AC cli-errors-stdout-integrity ===
Intent: The executable emits a complete HTML document result without diagnostic text in standard output.

import subprocess

result = subprocess.run( ["./cmark"], input="a\n\nb\n", capture_output=True, text=True, encoding="utf-8", ) assert result.returncode == 0 assert result.stdout == "a\nb\n" assert "error" not in result.stdout.lower() === END AC cli-errors-stdout-integrity ===

User Acceptance

None.

Guardrails

Failure diagnostics never replace rendered output on standard output.
Error handling does not alter the conformance harness invocation contract.
Acceptance does not depend on diagnostic wording.