[telemetry] Detect Python package manager(s) at project setup

[rugpanov]

Changes

Measurement-only telemetry to learn which Python package manager(s) our users' projects actually use (pip / conda / uv / poetry), so the VPEX setup-flow investment can be prioritized from first-party data instead of public-survey estimates. No setup behavior changes — this is detection only.

The work splits cleanly into three layers so each is independently testable and the dependency direction stays correct (high-level → low-level):

• Pure classifier (packageManagerDetection.ts): given a set of already-collected signals, reports every applicable manager, a best-guess primary (priority uv > poetry > conda > pip), the firing signals, hasLockfile, and interpreter source. Side-effect free and total.
• Emit (telemetry/packageManagerExtensions.ts): adds recordPackageManagerDetection to the existing Telemetry class via the same declare module pattern as commandExtensions.ts. Keeps disk/Python-extension dependencies out of the telemetry client.
• Collection (PackageManagerTelemetry.ts): a best-effort, non-blocking collector that reads disk and already-resolved interpreter metadata, runs the pure classifier, and calls the emit method. Deduplicated per session on (trigger, projectRoot); any failure degrades to unknown and is swallowed so it never disrupts setup.

Emission is wired into three setup touchpoints: project-open environment check (auto_open), the set-up-environment command (explicit_command), and first Run/Debug with Databricks Connect (run/debug).

A new Events.PYTHON_ENV_SETUP_DETECTED event carries a typed, documented schema (reuses the existing telemetry transport; opt-out honored; categorical data only — no paths, package names, or cluster names). A handoff note for the analytics/dashboard owner is included at src/telemetry/PACKAGE_MANAGER_DETECTION.md.

Detection correctness (the parts most worth reviewing):

• interpreterSource is derived from the active interpreter alone, never from project files. A uv.lock project running a conda/venv/system interpreter reports that interpreter's real source, keeping the "uv project, interpreter not uv-managed yet" setup-flow gap visible. A genuinely uv-provisioned venv is identified by the uv = marker in pyvenv.cfg, not by uv.lock.
• conda is attributed only when the active interpreter resides under CONDA_PREFIX (path-boundary checked), not on the bare env var — which is session-global in the extension host (launching VS Code from an activated conda shell) and would otherwise over-count conda for uv/poetry/pip projects.
• pyproject [tool.uv]/[tool.poetry] detection uses a bounded table-header scan, not substring matching: ignores comments and in-value mentions, rejects prefix collisions (e.g. tool.uvicorn), and matches subtable and array-of-table headers ([tool.uv.sources], [[tool.poetry.source]]).
• No external executable is run for telemetry: the uv-on-PATH probe was removed (it spawned a PATH-resolved uv for a weak, non-attributing signal). Detection reads only disk and already-resolved interpreter metadata.

Scope / privacy: measurement only — no changes to setup behavior (the VPEX flows are a separate effort). Only enum/categorical data and a closed set of signal identifiers are emitted; the existing telemetry opt-out (telemetry.telemetryLevel) is respected by the transport.

Tests

• yarn run test:unit: 202 passing, 0 failing — includes the pure classifier (each manager, interpreter sources, overlaps like uv+pip / conda+pip / poetry+uv, weak signals, none) and pure helpers (pyprojectHasToolSection, pyvenvCfgMarksUv, interpreterUnderCondaPrefix), covering the conda-prefix boundary and shell-global false-positive cases.
• yarn run build (typecheck) passes.
• eslint clean; prettier formatted.

Reviewer can validate with:

cd packages/databricks-vscode
yarn run build
yarn run test:unit
npx eslint src --ext ts && npx prettier . -c

[github-actions]

If integration tests don't run automatically, an authorized user can run them manually by following the instructions below:

Trigger:
go/deco-tests-run/vscode

Inputs:

• PR number: 1918
• Commit SHA: be9f1746227ce20e8261ed183a86775c0b99da9e

Checks will be approved automatically on success.