fix: defer install prompt until after manager timeout to prevent false positives

[edvilme]

Fix: Only show install prompt after manager timeout, not during startup

Fixes #1465

Problem

Users consistently see a false "Do you want to install extension ms-python.python to enable ms-python.python:venv support" prompt despite having the extension installed. This happens across Windows/Linux, persists despite reinstalls, and is a race condition during startup.

Root Cause

The race condition:

• A) The extension host is loading all extensions (takes variable time)
• B) Our code calls checkExtension() which queries getExtension() after just 1 tick (setImmediate)

B can execute BEFORE A finishes — getExtension() returns undefined even though the extension IS installed, triggering a false install prompt.

The Fix

Separate the two concerns:

1. checkExtension() — fires early, but only does activation (harmless if it sees stale state — worst case it's a no-op). Never prompts to install.
2. promptInstallExtensionIfMissing() — fires ONLY after the 30s timeout in withManagerTimeout(), when getExtension() is guaranteed to be reliable.

The install prompt can no longer race against extension host initialization because it's gated behind the same 30s timeout that already exists for "manager didn't register."

Flow (annotated)

// BEFORE (broken):
waitForEnvManagerId(["ms-python.python:venv"])
  ├─ checkExtension()
  │     └─ setImmediate (1ms) → getExtension() → undefined (host still loading!)
  │           └─ ❌ showErrorMessage("Do you want to install...?")  // FALSE PROMPT
  └─ setTimeout(30s) → ...

// AFTER (fixed):
waitForEnvManagerId(["ms-python.python:venv"])
  ├─ checkExtension()
  │     └─ setImmediate (1ms) → getExtension()
  │           └─ ✅ Only activates if found inactive. Never prompts.
  └─ withManagerTimeout(30s)
        ├─ Manager registers at ~200ms → deferred resolves → timer cleared → done ✅
        └─ 30s expire → promptInstallExtensionIfMissing()
              ├─ getExtension() → found? → log warning, NO prompt ✅
              └─ getExtension() → not found? → show install prompt ✅ (genuinely missing)

Changes

• withManagerTimeout: Now calls promptInstallExtensionIfMissing() on timeout expiry
• promptInstallExtensionIfMissing (new): Checks getExtension() after 30s; only prompts if extension truly missing; logs warning if installed but manager never registered
• checkExtension: Simplified to only attempt activation — no install prompts
• Added 5 regression tests covering: timeout with/without extension installed, manager registering before timeout, pre-registered managers, package manager wait

[Copilot]

Pull request overview

This PR addresses a startup race where getExtension() can temporarily return undefined while the VS Code extension host is still initializing, causing a false “install ms-python.python” prompt even when the extension is installed.

Changes:

• Defers the install prompt until the manager registration timeout expires, preventing false positives during startup.
• Refactors checkExtension() to only perform best-effort activation (no prompting).
• Adds regression unit tests covering timeout vs. successful registration scenarios for both env and package managers.

Show a summary per file

File	Description
src/features/common/managerReady.ts	Moves install prompting behind the manager timeout and simplifies early extension checks to activation-only.
src/test/features/common/managerReady.unit.test.ts	Adds unit tests validating the deferred prompt behavior and race-condition scenarios.

Copilot's findings

• Files reviewed: 2/2 changed files
• Comments generated: 4

[edvilme]

All 4 review comments addressed in commit 2151164:

1. Unhandled promise rejection - Wrapped with void ... .catch(traceError)
2. Activate inactive extension post-timeout - Now attempts ext.activate() when installed but inactive
3. Punctuation - Changed period to question mark
4. Deduplicate install prompts - Added module-level prompted Set keyed by extId