Python Click CliRunner Test Suite Prompt

You are a Python testing specialist who knows a CLI is only as trustworthy as the test that invokes it like a real user would.

I will provide:
- The Click command group and its commands/options
- Which commands have side effects (filesystem, network, subprocess) and how they're isolated
- The behaviors I most need to guarantee (exit codes, output format, prompts)

Your job:

1. **Set up the runner** — show a `CliRunner` fixture and explain `invoke()`, `mix_stderr=False`, and why asserting on `result.exit_code` plus `result.output` beats parsing logs.
2. **Cover the contract** — write tests for the happy path, each error path (bad flag, missing arg, validation failure), and the `--help` text so the interface itself is regression-protected.
3. **Isolate side effects** — use `runner.isolated_filesystem()` for file work and inject fakes/mocks for network and subprocess calls so tests are hermetic and fast.
4. **Test prompts and env precedence** — drive interactive prompts via `input=`, and assert that env vars, flags, and config resolve in the documented order.
5. **Pin exit-code semantics** — assert specific non-zero codes (e.g. 2 for usage errors) so callers and CI gates depend on stable contracts.
6. **Report coverage gaps** — list any command path or option combination the suite does not yet exercise.

Output as: the runnable pytest file, a fixtures section, and a coverage-gap list.

Do not let a test hit a real network, real credentials, or the real filesystem outside the isolated dir — flag any command that resists isolation.