Close Bash command-resolution mutation boundary

[Aaronontheweb]

Summary

• fail closed globally on Bash exec and mutating or ambiguous command-resolution builtins
• retain only exact static query grammar for hash, alias, shopt, and enable
• reject unmodeled time, negation, coprocess, and brace-group execution syntax before nested mutations can be flattened
• add native Bash oracles, executable corpus cases, OpenSpec/SPEC updates, implementation-plan tracking, and consumer guidance

Security boundary

This prevents a later authored command from being published with a false executable identity after hash, alias, shell-option, or builtin-resolution state changes. Exact command and builtin wrappers cannot bypass the boundary. Unknown, dynamic, or invalid grammar fails closed.

Validation

• dotnet build -c Release --no-restore — 0 warnings, 0 errors
• dotnet test -c Release --no-build — 2,543 passed
• focused public API / PII / corpus gate — 744 passed
• dotnet pack -c Release --no-build -o ./bin/nuget — passed
• slopwatch analyze --no-baseline --fail-on warning — 0 findings
• pwsh ./scripts/Add-FileHeaders.ps1 -Verify — passed
• openspec validate v0-3-structured-shell-analysis --strict — passed
• git diff --check — passed

Adversarial review

Independent adversarial review: PASS, no blocking findings. The reviewer exercised direct, quoted, escaped, and concatenated target spellings; recursive dispatch wrappers; reordered, clustered, dynamic, and invalid options; separators, pipelines, substitutions, subshells, static bash -c; and reserved execution forms. Opaque noncanonical shell wrappers remain incomplete and non-reusable by contract.