Design: derive the CLI version from package metadata

Phase 2 of 3 (bugfix → design → tasks).

Approach

Replace the hardcoded __version__ literal with a value read from the installed distribution's metadata via the stdlib importlib.metadata (available on the CLI's requires-python = ">=3.9" floor, keeping the zero-runtime-dependency guarantee). The distribution name is the-loopy-one (import package the_loop, decision-019).

from importlib.metadata import PackageNotFoundError, version as _dist_version

try:
    __version__ = _dist_version("the-loopy-one")
except PackageNotFoundError:
    # Running from an uninstalled source tree (no package metadata).
    __version__ = "0.0.0+unknown"

Everything downstream already reads the_loop.__version__:

• cli/the_loop/cli.py builds --version as f"the-loop {__version__}" — unchanged.
• cli/the_loop/webhook/server.py had its own hardcoded "the-loop-gh-webhook/0.1.0"; it now imports __version__ and interpolates it into server_version, removing the second stale copy.

Why metadata, not a version_files entry

Adding __init__.py to .cz.toml version_files would fix the number but keep a duplicate that must stay in lockstep (guarded by scripts/check_version_lockstep.py). Deriving from metadata removes the duplicate: there is exactly one source of truth (cli/pyproject.toml [project] version, itself a version_files target bumped by commitizen), and the CLI reflects whatever is installed. Fewer moving parts, no new guard.

Data flow

flowchart LR
    A[".cz.toml version<br/>(canonical, cz bump)"] -->|version_files| B["cli/pyproject.toml<br/>[project] version"]
    B -->|build / install| C["installed package<br/>metadata"]
    C -->|importlib.metadata.version| D["the_loop.__version__"]
    D --> E["the-loop --version"]
    D --> F["webhook Server header"]

Failure modes

• Uninstalled source tree (e.g. running python cli/the_loop/... without an install): PackageNotFoundError → sentinel 0.0.0+unknown. Never raises at import time.

Testing strategy

Unit tests (cli/tests/test_cli.py):

• __version__ equals importlib.metadata.version("the-loopy-one") and is not "0.1.0".
• the-loop --version prints the-loop <__version__>.

The existing test_version_exits_zero continues to guard exit-code behaviour. The test suite runs under uv, which installs the package, so metadata resolves in CI.

Security design

No new trust boundary. importlib.metadata reads local install metadata only.