Mirror global system-Python cache into workspaceState to survive cold globalState on remotes

[Copilot]

context.globalState is scoped per-remote, so the cross-session cache for the discovered global system Python (PR #1455) starts cold on every fresh SSH host, WSL distro, dev container, or codespace — and on local profile resets. Every cold start falls through to a full PET refresh on the foreground env-selection path, which is the dominant remaining Linux hang.

Changes

src/managers/builtin/cache.ts — promote workspaceState to a primary layer for SYSTEM_GLOBAL_KEY, keep globalState as fallback:

• getSystemEnvForGlobal() — read workspaceState[SYSTEM_GLOBAL_KEY] first, fall back to globalState[SYSTEM_GLOBAL_KEY].
• setSystemEnvForGlobal() — write (and undefined-invalidate) to both layers in parallel.
• clearSystemEnvCache() — also clear the mirrored SYSTEM_GLOBAL_KEY from workspaceState.

export async function getSystemEnvForGlobal(): Promise<string | undefined> {
    const workspaceState = await getWorkspacePersistentState();
    const workspaceValue = await workspaceState.get<string>(SYSTEM_GLOBAL_KEY);
    if (workspaceValue) {
        return workspaceValue;
    }
    const globalState = await getGlobalPersistentState();
    return await globalState.get<string>(SYSTEM_GLOBAL_KEY);
}

No call-site changes. The fastPath contract is preserved (single string | undefined), so global_env.cache telemetry (hit / miss / stale) and the workspace-scoped path (SYSTEM_WORKSPACE_KEY) are unaffected.

Tests

New src/test/managers/builtin/cache.systemEnvGlobal.unit.test.ts (10 cases): workspaceState-primary lookup, globalState fallback (incl. empty-string), dual-write of values and undefined, set→get round-trip, and full invalidation through both layers via clearSystemEnvCache.

Acceptance criteria mapping

• Same remote, same workspace, fresh session → cache hit, no PET refresh ✅ (workspaceState mirror).
• Same remote, brand-new workspace folder → unchanged (cache miss → PET) ✅ (workspaceState mirror is per-folder; globalState fallback only primes after first-time global resolution on that remote).
• Brand-new remote + brand-new workspace → unchanged ✅ (out of scope for this option).
• Telemetry hit / miss / stale unchanged ✅.
• Workspace-scoped fast path unchanged ✅.

[Copilot]

Pull request overview

This PR improves startup/performance for global system Python discovery on remote scenarios by mirroring the cross-session system-Python cache into workspaceState, using globalState as a fallback. This helps avoid foreground PET refreshes when context.globalState is effectively “cold” per-remote.

Changes:

• Update system-Python global cache read/write logic to be workspaceState-primary with globalState fallback, and clear both layers during cache clears.
• Add a new unit test suite covering the two-tier lookup behavior, dual writes, and full invalidation.
• Regenerate package-lock.json metadata (removing several "peer": true entries).

Show a summary per file

File	Description
src/managers/builtin/cache.ts	Mirrors SYSTEM_GLOBAL_KEY into workspaceState, adds fallback read, and clears both layers.
src/test/managers/builtin/cache.systemEnvGlobal.unit.test.ts	Adds unit tests validating workspaceState-primary + globalState fallback behavior and clearing semantics.
package-lock.json	Lockfile metadata normalization (no functional code impact).

Copilot's findings

• Files reviewed: 2/3 changed files
• Comments generated: 1