Cross-session cache for discovered system Python path

[eleanorjboyd]

Persist the discovered system Python path (e.g., /usr/bin/python3 or C:\Python312\python.exe) to globalState. On next startup, use the cached path immediately and verify it's still valid in the background.

Potential risk: The cache could become stale if the user uninstalls/upgrades Python. Background verification mitigates this — the cached env is used immediately, and if verification fails, a re-scan is triggered. The user would see a brief env switch in the rare case the cache is wrong.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR adds a cross-session “fast path” for resolving the system Python by persisting the discovered global Python path and using it immediately on next startup, while verifying validity in the background.

Changes:

• Add optional global-scope persisted-path support to tryFastPathGet() and emit telemetry for global cache hit/miss/stale.
• Update system Python manager/cache to read/write the global persisted path via global persistent state.
• Extend unit tests to cover global-scope fast-path behavior and telemetry emission.

Show a summary per file

File	Description
src/test/managers/fastPath.get.unit.test.ts	Stubs global cache getter to avoid test behavior changes with new global fast-path support.
src/test/managers/common/fastPath.unit.test.ts	Adds test coverage for global persisted-path behavior and verifies telemetry results.
src/managers/common/fastPath.ts	Implements optional global persisted-path lookup and emits global cache telemetry.
src/managers/builtin/sysPythonManager.ts	Wires system manager into new global persisted-path fast-path option.
src/managers/builtin/cache.ts	Moves global key storage to global persistent state and clears workspace/global keys in their respective stores.
src/common/telemetry/constants.ts	Adds GLOBAL_ENV_CACHE event and GDPR property mapping for the new telemetry.

Copilot's findings

• Files reviewed: 6/6 changed files
• Comments generated: 2

[eleanorjboyd]

@copilot resolve the merge conflicts in this pull request