uv-worktree-venv-fallthrough

uv run pytest fails in a fresh git worktree because the virtual environment is empty, causing uv to fall through to the system PATH and resolve the wrong Python interpreter. Running uv sync first restores the local .venv with pinned dependencies to fix the phantom failures.

To fix uv run resolving the wrong Python interpreter in isolated worktrees, run uv sync with dev dependencies to populate the worktree's .venv. This ensures pytest, ruff, and mypy resolve from the local virtual environment instead of falling back to system PATH.

Yes, you need to run uv sync before executing pytest in a new git worktree. A completed uv sync populates the empty virtual environment with the project's pinned Python and dependencies, preventing uv run from falling through to the system PATH and causing phantom test failures.

Phantom Python test failures in parallel agent setups happen when fresh git worktrees have empty virtual environments, causing uv run to fall back to system-installed commands. This leads to import errors, version mismatches, and collection failures from resolving the wrong Python interpreter.

Yes, this approach fixes ruff and mypy resolution errors in uv-managed repositories. By running uv sync to populate the worktree's .venv, uv run resolves ruff and mypy from the local virtual environment with the project's pinned Python and dependencies instead of the system PATH.

The limitation of fixing uv worktree fallthrough is that it requires a completed uv sync in the worktree first. If the virtual environment is not fully populated with dev dependencies, uv run will continue falling through to the system PATH and resolving the wrong Python interpreter.