Pick best available installer for generic Python project setup

[basnijholt]

Problem

ag dev new on a generic Python project (bare pyproject.toml or requirements.txt) hardcodes pip:

→ Running: pip install -e .
Warning: Setup failed: /bin/sh: pip: command not found

macOS commonly has no bare pip on PATH (Homebrew/Xcode Python only ship pip3), so worktree setup always failed on these projects.

Fix

Choose the installer at detection time, following the existing _unidep_cmd availability-check pattern:

1. uv (preferred): uv venv && uv pip install ... — uv venv creates ./.venv and uv pip install targets it from the working directory (docs). run_setup() already clears VIRTUAL_ENV from the subprocess env, so the caller's activated environment doesn't hijack the install (verified live).
2. pip: previous behavior.
3. pip3: macOS fallback.
4. None available: detection skips setup gracefully instead of failing.

Bonus: since uv creates ./.venv during setup, the subsequent direnv step now generates a source .venv/bin/activate .envrc for generic Python projects (it previously found no venv).

Tests

• Fallback tier tests with mocked shutil.which, with evidence docstrings per repo convention (uv docs + live verification with uv 0.9).
• Verified end-to-end: detect_project_type + run_setup on a temp pyproject project creates .venv and installs editable.
• Full suite: 1419 passed, 4 skipped.

[greptile-apps]

Greptile Summary

Replaces the hardcoded pip install commands for generic Python projects with a tiered installer-detection helper (uv → pip → pip3) chosen at detection time, matching the existing _unidep_cmd pattern. When no installer is found, detection returns None and setup is skipped gracefully instead of failing with a command-not-found error.

• _python_install_commands checks shutil.which for uv, pip, and pip3 in order; the uv path emits uv venv && uv pip install … so a .venv is created in the project directory, and run_setup's existing VIRTUAL_ENV clearing ensures uv pip targets that venv rather than the caller's activated environment.
• _detect_pip_install_project extracts the requirements.txt and generic pyproject.toml branches from detect_project_type, each delegating to the new helper, and returns None when no installer is available.
• Tests add shutil.which mocks to the two pre-existing detection tests (addressing prior environment-sensitivity feedback) and introduce five new focused tests covering all installer tiers and the no-installer case.

Confidence Score: 5/5

Safe to merge — the change is a targeted, well-tested fix with no regressions on existing project-type detection paths.

The new helper follows an already-established pattern (_unidep_cmd), every code path has a corresponding test with proper shutil.which mocking, run_setup's existing VIRTUAL_ENV clearing correctly handles the uv venv case, and the no-installer fallback (returning None) is the graceful behavior described in the PR and covered by a dedicated test.

No files require special attention.

Important Files Changed

Filename	Overview
agent_cli/dev/project.py	Adds _python_install_commands and _detect_pip_install_project helpers that detect the best available installer (uv → pip → pip3) at detection time; refactors the two hardcoded pip install branches out of detect_project_type. Logic is clean and mirrors the existing _unidep_cmd pattern.
tests/dev/test_project.py	Adds shutil.which mocks to the two pre-existing pip/generic tests (fixing the environment-sensitivity gap noted in a previous review) and adds five new installer-tier tests covering uv preference, pip/pip3 fallbacks, and the no-installer-available case. test_python_unidep_excludes_test_example_dirs also gains the mock to avoid a false-None from the new pip fallback path.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[detect_project_type] --> B{uv.lock or uv in pyproject.toml?}
    B -- Yes --> C[python-uv: uv sync]
    B -- No --> D{pixi.toml / pixi.lock?}
    D -- Yes --> E[pixi: pixi install]
    D -- No --> F{unidep project?}
    F -- Yes --> G[python-unidep / monorepo]
    F -- No --> H{poetry.lock?}
    H -- Yes --> I[python-poetry: poetry install]
    H -- No --> J[_detect_pip_install_project]

    J --> K{requirements.txt exists?}
    K -- Yes --> L[_python_install_commands]
    K -- No --> M{pyproject.toml exists?}
    L --> N{uv on PATH?}
    N -- Yes --> O[python-pip: uv venv + uv pip install]
    N -- No --> P{pip on PATH?}
    P -- Yes --> Q[python-pip: pip install]
    P -- No --> R{pip3 on PATH?}
    R -- Yes --> S[python-pip: pip3 install]
    R -- No --> M

    M -- Yes --> T[_python_install_commands]
    M -- No --> U[None — skip setup]
    T --> V{uv on PATH?}
    V -- Yes --> W[python: uv venv + uv pip install -e .]
    V -- No --> X{pip on PATH?}
    X -- Yes --> Y[python: pip install -e .]
    X -- No --> Z{pip3 on PATH?}
    Z -- Yes --> AA[python: pip3 install -e .]
    Z -- No --> U

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