[Siddharth S Shah (SIDLAD)]

Written with Claude Code (AI-assisted) and reviewed by me.

Fixes #1997.

Problem

Startup selection (applyInitialEnvironmentSelection) doesn't wait for environment managers contributed by other extensions. When python-envs.defaultEnvManager or a pythonProjects[] entry names such a manager (Pixi, Hatch, …) and it registers after the priority chain ran, selection falls back to another environment and is never corrected. #1533 suppressed the warning for this case, but the selection stays on the fallback.

Change

• After each workspace folder is selected, applyInitialEnvironmentSelection records whether it fell back because a manager named by pythonProjects[] / defaultEnvManager wasn't registered (fallbackSelections, built from the existing managerNotRegistered errors).
• New registerLateManagerRegistrationListener subscribes to envManagers.onDidChangeEnvironmentManager. When a manager registers, it re-selects only the folders that fell back for that manager, using the same priority chain:
  • other folders and the global scope are left alone,
  • corrections only apply within MANAGER_READY_TIMEOUT_MS (30s, the window managerReady already uses) of the fallback, so a manager that shows up much later (e.g. an extension installed mid-session) doesn't switch the interpreter under a running session,
  • registrations of managers no folder is waiting for are ignored.
• Selection runs (startup, settings changes, late re-selection) are serialized through a promise queue. Without it, a re-selection triggered mid-startup can be overwritten by the still-running startup selection. The logs in the issue show exactly that overwrite.
• In extension.ts the listener is registered before startup selection, so a manager that registers while selection is still running is picked up too (the queued re-selection runs after startup has recorded which folders fell back).

This doesn't add any waiting or deadline to startup, and a genuinely misconfigured manager id still warns immediately, which addresses the concerns in the #1533 description.

Tests

New suite Interpreter Selection - late manager registration:

• re-applies selection when the configured manager registers after startup selection,
• picks up a manager that registers while startup selection is still running (the queued re-run wins),
• ignores registrations of managers no setting is waiting for,
• does not switch the environment when the manager registers after the timeout,
• only re-selects the workspace folders that fell back for the registered manager (and not the global scope).

I checked that each test catches the behaviour it covers: with the listener disabled, tests 1, 2 and 5 fail; with the time check removed, test 4 fails; with the queue removed, test 2 fails.

• npm run unittest: 3527 passing, 9 pending (Node 22.21.1, per .nvmrc).
• npm run lint clean, npm run compile succeeds.

Manual verification

Windows 11, Pixi Code 0.2.0, defaultEnvManager set to renan-r-santos.pixi-code:pixi, running the first iteration of this branch via F5. That iteration re-ran full selection; the second commit narrows it to the fallen-back folders and adds the time window, and is covered by the unit tests above.

12:32:46.894 [warning] [priorityChain] d:\Projects\LearningMLDL defaultEnvManager 'renan-r-santos.pixi-code:pixi' not found, trying next priority
12:32:46.894 [interpreterSelection] Configured manager 'renan-r-santos.pixi-code:pixi' registered after it was skipped, re-applying environment selection
12:32:57.167 [interpreterSelection] LearningMLDL: base (3.13.5) (source: defaultInterpreterPath)
12:32:57.172 [interpreterSelection] Applying initial environment selection for 1 workspace folder(s)
12:32:57.203 [interpreterSelection] LearningMLDL: LearningMLDL:default (3.15.2) (source: defaultEnvManager)

The workspace ends on the Pixi environment after a reload, with no user action.

Open question for reviewers

Within the 30s window, if the user manually picks an interpreter for a fallen-back folder before the configured manager registers, the re-selection replaces that pick with the configured manager's environment. That matches how the settings-change listener already behaves (settings win), but I'm happy to skip folders with a user-made selection if you'd prefer. That would need a small accessor on EnvironmentManagers for the existing userSelected flag, which I didn't want to add without asking.

Notes

• The global scope isn't re-selected; files outside workspace folders keep the fallback for the session.
• Prettier reports existing style differences in the touched files on main. I left those untouched to keep the diff focused. The new lines are Prettier-formatted.

🤖 Generated with Claude Code

[Siddharth S Shah (SIDLAD)]

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