Make base_cli tests valid for source checkouts and installed distributions

[codeforester]

Goal

Make the base_cli test suite valid and meaningful both in the monorepo checkout and against an installed distribution.

Background

The supplied review found checkout-only tests that calculate Path(__file__).resolve().parents[4] and then read STANDARDS.md, scan cli/python, or invoke shell scripts under lib/shell and lib/bash. The current source confirms this pattern in test_python_standards.py, test_public_command_lifecycle.py, test_exit_code_adoption.py, and two protocol tests; other tests also reference checkout paths. Those tests will fail or become misleading when the package is installed from a wheel.

Depends on #1742 for the package artifact contract.

Scope

• Audit all lib/python/base_cli/tests for parent-repository and shell-checkout assumptions, not only the five findings named in the review.
• Separate monorepo contract tests from package unit/integration tests.
• Move checkout-only tests to the top-level repository test suite, or skip them in an installed-package context with an explicit reason while keeping them active in checkout CI.
• Replace package tests' repository-root dependencies with package-local fixtures or stable subprocess fixtures.
• Ensure the installed wheel does not accidentally ship the monorepo-only test suite; if package tests remain supported, provide a package-level pytest configuration and documented invocation.
• Add a clean-environment wheel-install test so missing checkout assets cannot produce a false-green result.

Acceptance Criteria

• Running the supported installed-package test command in a clean temporary environment does not attempt to open STANDARDS.md, scan cli/python, or invoke unavailable repository shell scripts.
• Checkout-only standards/lifecycle/exit-code tests still run in repository CI and fail when their Base contracts regress.
• Protocol tests validate the Python implementation without requiring shell files that are not part of the distribution, or are clearly classified as checkout integration tests.
• Wheel contents and test discovery are covered by an automated assertion.
• The source-checkout suite and installed-wheel smoke suite both pass without inherited monorepo paths.

Validation

• Run the focused base_cli tests from the checkout.
• Build and install the wheel in a fresh virtual environment, then run the package-supported test/smoke command from outside the repository.
• Confirm the checkout-only tests remain included in the normal repository test gate.
• git diff --check.

Non-Goals

• Do not weaken checkout contract tests by making them silently pass when required source files are missing.
• Do not duplicate the full monorepo test suite inside the published wheel.
• Do not change packaging metadata or publication credentials in this issue.

Project Fields

• Priority: P1
• Size: M
• Area: Packaging
• Initiative: Adoption Polish

Agent Assignment

Human first; this defines the boundary between repository validation and package validation.