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

[Copilot]

The stopwatch is started after awaiting the persisted-path lookup, so the emitted <duration> excludes time spent reading the global cache (and will also be near-zero for miss). If the intent is to measure end-to-end global fast-path latency, start timing before the lookup (or rename/comment to clarify that the duration is resolve-only).

Suggested change

	// Look up the persisted path — either from workspace cache or global cache
	const persistedPath = isGlobalScope
	? await opts.getGlobalPersistedPath!()
	: await opts.getPersistedPath(opts.getProjectFsPath(opts.scope as Uri));
	// Track cross-session cache performance for global scope
	const cacheStopWatch = isGlobalScope ? new StopWatch() : undefined;
	// Track end-to-end cross-session cache performance for global scope, including persisted-path lookup.
	const cacheStopWatch = isGlobalScope ? new StopWatch() : undefined;
	// Look up the persisted path — either from workspace cache or global cache
	const persistedPath = isGlobalScope
	? await opts.getGlobalPersistedPath!()
	: await opts.getPersistedPath(opts.getProjectFsPath(opts.scope as Uri));

[Copilot]

Using non-null assertions (opts.getGlobalPersistedPath!() and opts.scope as Uri) makes control-flow assumptions less explicit. Consider branching on isGlobalScope and assigning strongly-typed locals (e.g., const getGlobalPersistedPath = opts.getGlobalPersistedPath; / const scope = opts.scope as Uri) to avoid repeated assertions and make the two code paths clearer.

Suggested change

	const persistedPath = isGlobalScope
	? await opts.getGlobalPersistedPath!()
	: await opts.getPersistedPath(opts.getProjectFsPath(opts.scope as Uri));
	// Track cross-session cache performance for global scope
	const cacheStopWatch = isGlobalScope ? new StopWatch() : undefined;
	if (persistedPath) {
	try {
	const resolved = await opts.resolve(persistedPath);
	if (resolved) {
	if (isGlobalScope) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch!.elapsedTime, {
	managerLabel: opts.label,
	result: 'hit',
	});
	}
	return { env: resolved };
	}
	// Cached path found but resolve returned undefined (e.g., Python was uninstalled)
	if (isGlobalScope) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch!.elapsedTime, {
	managerLabel: opts.label,
	result: 'stale',
	});
	}
	} catch (err) {
	if (isGlobalScope) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch!.elapsedTime, {
	managerLabel: opts.label,
	result: 'stale',
	});
	}
	traceWarn(
	`[${opts.label}] Fast path resolve failed for '${persistedPath}', falling back to full init:`,
	err,
	);
	}
	} else {
	if (isGlobalScope) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch!.elapsedTime, {
	managerLabel: opts.label,
	result: 'miss',
	});
	}
	traceVerbose(`[${opts.label}] Fast path: no persisted path, falling through to slow path`);
	if (isGlobalScope) {
	const getGlobalPersistedPath = opts.getGlobalPersistedPath;
	if (!getGlobalPersistedPath) {
	return undefined;
	}
	const cacheStopWatch = new StopWatch();
	const persistedPath = await getGlobalPersistedPath();
	if (persistedPath) {
	try {
	const resolved = await opts.resolve(persistedPath);
	if (resolved) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch.elapsedTime, {
	managerLabel: opts.label,
	result: 'hit',
	});
	return { env: resolved };
	}
	// Cached path found but resolve returned undefined (e.g., Python was uninstalled)
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch.elapsedTime, {
	managerLabel: opts.label,
	result: 'stale',
	});
	} catch (err) {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch.elapsedTime, {
	managerLabel: opts.label,
	result: 'stale',
	});
	traceWarn(
	`[${opts.label}] Fast path resolve failed for '${persistedPath}', falling back to full init:`,
	err,
	);
	}
	} else {
	sendTelemetryEvent(EventNames.GLOBAL_ENV_CACHE, cacheStopWatch.elapsedTime, {
	managerLabel: opts.label,
	result: 'miss',
	});
	traceVerbose(`[${opts.label}] Fast path: no persisted path, falling through to slow path`);
	}
	} else {
	const scope = opts.scope as Uri;
	const persistedPath = await opts.getPersistedPath(opts.getProjectFsPath(scope));
	if (persistedPath) {
	try {
	const resolved = await opts.resolve(persistedPath);
	if (resolved) {
	return { env: resolved };
	}
	} catch (err) {
	traceWarn(
	`[${opts.label}] Fast path resolve failed for '${persistedPath}', falling back to full init:`,
	err,
	);
	}
	} else {
	traceVerbose(`[${opts.label}] Fast path: no persisted path, falling through to slow path`);
	}