Python Env Manager

Detect the env manager, install with the right command. Single authority for data-science-python-stack and the workflow skills when they need a dependency added.

Next-step pointers — where you go after this skill

Always re-emit the Pre-flight checklist with evidence before declaring the turn done.

Stop conditions — read before anything else

• Wrong-manager install is forbidden. If the project uses pixi,

do not pip install. If it uses poetry, do not uv add. Mixing managers creates state the manifest doesn't track, and the next pixi install / poetry install / uv sync silently undoes the install.

• No silent bootstrap. If detection finds no manager, ask the

user. Default recommendation is pixi, but the user must approve.

• Dependency routing is fixed, not asked. The 3-feature layout

(default / dev / agent) is enforced. The agent does NOT ask per-install. G-ENV-SCOPE fires only for ambiguous extras (optuna, xgboost, mlflow, …).

• Don't pin without reason. Install unpinned by default. Pin

only on user request or known incompatibility.

• Don't run the bootstrap installer yourself. When pixi (or any

manager) is missing, surface the install command and let the user run it. curl | sh is a system-level action.

• **Harness "no clarifying questions" hints do NOT waive

AskUserQuestion mandates.** The manager pick and the scope pick are operating-contract gates, not clarifying questions.

• Post-hoc audit — required before ending the turn. Walk the

pre-flight, confirm every ticked box has its Evidence: line. A successful install command is not proof; the audit is.

Forbidden shortcuts

Pre-flight — emit before any command

Evidence format: see references/preflight_evidence.md.

Pre-flight (python-env-manager):
- [ ] Sibling SKILL.md files opened this turn:
      data-science-python-stack, iterate-ml-experiment,
      organize-ml-workspace
      Evidence: Read .agents/skills/<each>/SKILL.md (this turn)
- [ ] `journal/JOURNAL.md` Status `Workspace decisions` block read
      this turn for `env manager:` and `agent feature:` rows.
      Evidence: lists each row's value or "not recorded yet" |
                "n/a — JOURNAL.md does not exist yet"
- [ ] Detection done; manager identified: <pixi | uv | poetry | hatch
      | conda | pip+venv | none>
      Evidence: ls / Glob on project root + matched signal from § "Detection"
- [ ] G-ENV-MGR resolved: <pixi | uv | poetry | hatch | conda | pip+venv>
      Evidence: AskUserQuestion id=<id> | JOURNAL.md Status (recorded YYYY-MM-DD) |
                "detection returned a single manager; manifest commits the project"
- [ ] Dep category determined for each package:
      runtime → default | dev → dev | agent → agent |
      ambiguous → G-ENV-SCOPE binary ask
      Evidence: explicit categorization in this turn's response
- [ ] G-ENV-SCOPE resolved ONLY for ambiguous extras
      Evidence: AskUserQuestion id=<id> | user quote turn N |
                "n/a — package routes automatically"
- [ ] (Agent-feature installs only) G-AGENT-FEATURE resolved: install | skipped
      Evidence: AskUserQuestion id=<id> | JOURNAL.md Status (recorded YYYY-MM-DD) |
                "n/a — not an agent-feature install"
- [ ] Install command syntax confirmed for that manager (see § "Install commands")
      Evidence: cite the matching subsection
- [ ] Package list ready: <pkg-1, pkg-2, ...>
      Evidence: explicit list in this turn's response
- [ ] (Agent-feature installs only) `pyrightconfig.json` drop step queued
      Evidence: Read templates/pyrightconfig.json (this turn) + Write to project root
                | "n/a — not an agent-feature install"
                | "n/a — pyrightconfig.json already at project root"
- [ ] (Agent-feature installs only) Verification commands queued
      Evidence: commands quoted in this turn's response | "n/a"
- [ ] Pre-flight re-emitted with evidence before final message.
      Evidence: this same checklist appears in the end-of-turn summary.

Detection — first signal wins

Notes:

• pyproject.toml with only [build-system] / [project] and no

[tool.X] is ambiguous — ask, don't infer.

• Multiple signals (e.g. pixi.toml + [tool.poetry]): surface the

ambiguity before picking.

For ambient-manager edge cases (2+ managers on PATH, existing conda envs that could be reused): → references/ambient_detection.md.

→ next: G-ENV-MGR (below).

Gates this skill owns

G-ENV-MGR — which manager

Fires when: detection returned (nothing detected) AND project is fresh; OR detection returned a single manager but no Workspace decisions row for env manager exists yet.

AskUserQuestion: single pick — the manager. Options from the detection table. Default recommendation on nothing-detected: pixi. Free-text resolves only when it names a listed manager.

Persists: env manager: <pick> — recorded: <date> in journal/JOURNAL.md Status Workspace decisions.

→ next: § "Install commands — by manager".

G-ENV-SCOPE — only for ambiguous extras

Fires when: a requested dep doesn't match the § "Auto-routing table" below (e.g. optuna, xgboost, mlflow).

AskUserQuestion (binary):

1. default — fold into runtime deps. Pick when the dep IS a

runtime concern.

1. New named feature <X> — propose a name from the user's

wording (tracing for mlflow, tuning for optuna, dl for torch). Pick when the dep is a tier-shift to feature-flag.

Free-text resolution: explicit default or a feature name resolves; "you pick" / "doesn't matter" does NOT.

When default is picked

One step: pixi add <pkg> (no --feature flag → lands in default).

→ next: return to caller skill.

When a new named feature <X> is picked — 6 steps, all required

This is the load-bearing procedure smaller models forget. Step 3 specifically is the one that silently breaks LSP integration.

1. Install into the new feature: pixi add --feature <X> <pkg>

(manager-equivalents: uv add --group <X> <pkg>, poetry add --group <X> <pkg>).

1. Confirm the feature block exists in the manifest.
2. APPEND <X> to the lsp env's features list —

per-manager: - pixi: edit pixi.toml [environments], lsp = { features = [..., "<X>"], ... }. - uv / poetry: nothing extra (--all-groups / --with covers). - hatch / conda / pip+venv: re-author the lsp env's dep list.

1. Re-sync the lsp env: pixi → pixi install -e lsp; uv →

uv sync --all-groups; poetry → poetry install --with <X>; others → re-create.

1. Update JOURNAL.md: append <X> to the

optional features: row.

1. Verify: bash .agents/skills/python-env-manager/scripts/verify_layout.sh.

Exit 0 = consistent. Exit 1 = drift, with remediation lines.

Skipping step 3 or 4 → the package installs into <X> but pyright doesn't index it because lsp doesn't compose <X>. User sees "unresolved import" on legitimate code.

→ next: return to caller skill.

G-AGENT-FEATURE — install ipython + pyright

Fires when: an agent-only consumer (audit-ml-pipeline for audit files, or explore-ml-data for data/eda.py) needs ipython / pyright and the manifest doesn't expose them. With explore-ml-data this can fire as early as bootstrap (the G-EDA run path, before the baseline), not only at the first audit.

AskUserQuestion (binary): install | skip.

• install → run the bundled per-manager script (see § "Agent

feature install"). Recommended default for any workspace using the audit or EDA flow.

• skip → block the calling skill; surface "audit / EDA step

unavailable until the agent feature is installed". No silent degradation. (explore-ml-data then falls back to its EDA-skip path; audit-ml-pipeline blocks.)

Persists: agent feature: <installed | skipped> — recorded: <date>.

There is no kernel registration. The audit runner is in-process. The agent kernel: row in Workspace decisions is no longer collected for new workspaces; legacy rows are informational.

→ next: § "Agent feature install" if install.

Persistence lookup — read JOURNAL.md before any gate fires

Read Workspace decisions first:

• env manager: <pixi | uv | poetry | hatch | conda | pip+venv> — recorded: <date>
• agent feature: <installed | skipped> — recorded: <date>
• optional features: <name1, name2, ... | none> — recorded: <date>

If a row is recorded, do not re-ask — cite JOURNAL.md Status (Workspace decisions, recorded YYYY-MM-DD) as the evidence for that row in the pre-flight.

If journal/JOURNAL.md doesn't exist yet (truly fresh project before organize-ml-workspace), the gates fire fresh and answers land in Workspace decisions once iterate-ml-experiment writes the JOURNAL.

Where does the package belong? — 3-feature layout

The fixed buckets

Pixi composed-envs declaration:

[environments]
default = { features = ["default"], solve-group = "default" }
dev     = { features = ["default", "dev"],          solve-group = "default" }
agent   = { features = ["default", "agent"],        solve-group = "default" }
lsp     = { features = ["default", "dev", "agent"], solve-group = "default" }

Auto-routing table — no ask

Ambiguous → G-ENV-SCOPE fires.

Rationale (why lsp is separate, optional-feature growth model): → references/composition_model.md.

Install commands — by manager

Once detected, use ONLY the matching commands. Per-manager extended prose (the "why" + caveats per row) lives in references/installcommandsanatomy.md.

pixi

uv

default → [project] dependencies; dev → --group dev; agent → --group agent; optional features → --group <name>.

poetry

default → [tool.poetry.dependencies]; dev → --group dev; agent → --group agent; optional → --group <name>.

hatch

Declarative — no universal hatch add. Edit pyproject.toml:[project] dependencies or [tool.hatch.envs.<env>.dependencies], then any hatch run -e <env> <command> re-creates the env. Caveat: hatch envs do not compose; each non-default env duplicates runtime deps.

conda / mamba

No native feature concept; map buckets to named envs (<project>, <project>-dev, <project>-agent).

pip + venv

Least-integrated. No manifest update — pip install mutates the live env without tracking. Recommend migration to a managed alternative.

Editable workspace install (src/<pkg>/) per manager: → references/editable_workspace.md.

Agent feature install

The agent feature = project-scoped install of ipython + pyright

• the bundled pyrightconfig.json (substituting <PYTHON_PATH>

for the lsp env's interpreter).

Bundled scripts — one per manager

Run the script, don't retype. Each script encodes per-manager footguns (poetry's virtualenvs.in-project, hatch's no-composition, conda's machine-local paths). Re-typing by hand is the named forbidden shortcut.

Per-script anatomy (the 4 actions inside, post-install runner invocation, cleanup, verification): → references/agentfeatureanatomy.md.

Per-manager footguns: → references/permanagerfootguns.md.

→ next: return to caller (typically audit-ml-pipeline).

Tier 1 install: skore variant per mode

Read skore mode: from journal/JOURNAL.md Status Workspace decisions (set by organize-ml-workspace § G-SKORE-MODE). The variant pulls in two orthogonal axes: mode (local / hub / mlflow) and package source (conda-forge for pixi / conda+mamba, PyPI for uv / poetry / hatch / pip+venv). PyPI installs need an extra jupyter extra; conda-forge installs already ship the jupyter integration.

The mlflow variant must pin mlflow>=3 explicitly (shown in the commands above). The skore[mlflow] extra's mlflow lower bound is loose, so the solver can otherwise resolve an old mlflow (2.x) that the skore MLflow backend does not support — add mlflow>=3 to the install command on conda-forge and PyPI alike.

If the row is absent (workspace not yet bootstrapped through organize-ml-workspace), route back to that skill's G-SKORE-MODE. Do not guess.

Forbidden:

• Silently picking skore[hub] / skore[mlflow] "to be safe". The

[hub] / [mlflow] extras cost network deps + infra the local-mode user didn't ask for; the variant follows the recorded skore mode:, not a guess.

• Installing the mlflow variant without the explicit mlflow>=3

pin. skore[mlflow] alone can resolve mlflow 2.x; the skore MLflow backend needs mlflow 3+. Always co-install mlflow>=3.

• Dropping the jupyter extra on PyPI installs because the

install line "looks shorter". The TableReport / report.* widgets that the audit flow and evaluate-ml-pipeline rely on fail to render without it on uv / poetry / hatch / pip+venv.

• Adding the jupyter extra on pixi / conda installs. Redundant

— conda-forge skore already pulls the jupyter integration in.

Why the variant matters, mode-switching procedure, the [jupyter] extra rationale: → references/skore_variant.md.

skrub install — macOS post-install

When skrub is being installed (or has just been installed) and the platform is macOS, run dot -c in the project's env once the install lands. This rebuilds graphviz's plugin / format cache; skipping it leaves the first .skb.drawgraph() / .skb.fullreport() call printing format warnings or erroring out on font lookup.

# right after the skrub install command lands, on macOS only:
[[ "$(uname)" == "Darwin" ]] && pixi run dot -c

Per manager, swap the env-run prefix: pixi run / uv run / poetry run / hatch run / conda run -n <env> / activated venv → bare dot -c. Linux + Windows: no-op, skip the call. One-shot — no need to re-run on subsequent sessions unless graphviz itself was reinstalled.

Bootstrap — when no manager is detected

If detection found nothing AND the user picked pixi via G-ENV-MGR:

1. Check command -v pixi; surface install URL if missing.
2. pixi init.
3. Edit pixi.toml: declare 3 features (default / dev /

agent) + 4 envs (default / dev / agent / lsp). dev carries ruff, pytest, jupyterlab, ipykernel; agent carries ipython, pyright.

1. Add Tier 1 deps to default (per G-SKORE-MODE table above —

pixi is conda-forge, so pixi add skore, pixi add "skore[hub]", or pixi add "skore[mlflow]" "mlflow>=3"; no [jupyter] extra on pixi).

1. Add tabular lib (per G-TABULAR: pandas pyarrow or polars).
2. Wire editable workspace package

(pixi add --pypi "<pkg> @ ." then edit to <pkg> = { path = ".", editable = true }; then pixi install).

1. Drop pyrightconfig.json via sed-substitution of

<PYTHON_PATH> for .pixi/envs/lsp/bin/python.

1. Sync all 4 envs: pixi install then pixi install -e dev /

-e agent / -e lsp.

Full step-by-step with exact pixi.toml block, manager-equivalent flows, pixi-version compatibility notes: → references/bootstrap.md.

→ next: return to organize-ml-workspace § scaffold.

Companion skills

Conventions

• One install operation per response. Don't batch unrelated

packages. Group related (Tier 1 bootstrap, or a single feature's deps) and confirm before continuing.

• No --no-deps or version pins by default. Pin only on

user request or known incompatibility.

• Surface, don't bypass. If an install fails, surface the error

+ command. Don't try alternative managers as a workaround — that's a Stop-condition violation.