Consolidate duplicated workspace CLI test invocation harnesses

[codeforester]

Goal

Create a package-local test invocation helper/fixture and migrate the identical clone/configure/pull harnesses first. Support explicit stream and environment overrides for related variants without hiding test setup.

Background

Repository-wide duplication review against f9c18f3294873cbbcda9acc7af7f1bc6b17eed45 (2026-09-17).

Three invoke_engine bodies are AST-identical and duplicate HOME/Base environment setup, optional user-config writing, output capture and engine invocation. Additional workspace suites repeat closely related TTY and project-context variants. This is test infrastructure duplication, separate from independently valuable scenario assertions.

Verified source locations:

• cli/python/base_projects/tests/test_workspace_clone.py:59-80
• cli/python/base_projects/tests/test_workspace_configure.py:65-86
• cli/python/base_projects/tests/test_workspace_pull.py:28-49
• cli/python/base_projects/tests/test_workspace_onboarding.py:80-92

Closed #1912 introduced root ManifestFactory fixtures and #1075 addressed older test-suite helpers. This issue concerns remaining CLI invocation harnesses, not re-creating those completed manifest fixtures.

This is a maintainability refactor. Similarity alone is not evidence of a production failure; any demonstrated differences are called out above.

Scope

Create a package-local test invocation helper/fixture and migrate the identical clone/configure/pull harnesses first. Support explicit stream and environment overrides for related variants without hiding test setup.

Acceptance Criteria

• The three identical harnesses use one helper.
• Tests retain explicit args, HOME/Base paths, optional config and environment overrides.
• Preserve TTY simulation and restoration of process environment/stdout/stderr.
• Keep scenario-specific fake commands and assertions local; do not create a production dependency on test code.

Validation

Run the affected workspace test modules, then all base_projects tests. Verify ordinary and TTY output capture and environment restoration on success and exception.

Run focused checks first, then the repository-required broader checks for the actual implementation. Preserve public command contracts and review .ai-context/ impact in the PR.

Non-Goals

No wholesale fixture rewrite, test-case merger, reduced assertions or migration of every test to one framework.

Project Fields

• Status: Ready
• Priority: P3
• Area: Python
• Initiative: Contract Hardening
• Size: S
• Milestone: Unscheduled; no release commitment is implied by this audit.

Agent Assignment

Implementation-ready scoped follow-up, assigned to codeforester. Follow AGENTS.md and docs/github-workflow.md: start through basectl gh issue start, use the canonical issue worktree, characterize current behavior before extraction, and open an issue-linked PR. Keep each refactor independently reviewable.