fix(macos-app): disable URL response caching for cluster-state polling

[ecohash-co]

Fixes #2004.

ClusterStateService polls /state at 2 Hz via URLSession.shared, which keeps an on-disk URLCache attached by default. Every polled response body gets persisted under ~/Library/Caches/exolabs.EXO/, sustaining ~500–620 KB/sec of file-backed memory dirtied — far above macOS's ~25 KB/sec per-process daily-average baseline. Six microstackshot reports observed on a single Mac Studio M3 Ultra over eight days, with one 15-hour run accumulating 34.36 GB of cache writes.

Heaviest stack on every diagnostic report (96–98% of samples):

_dispatch_workloop_worker_thread → _dispatch_block_async_invoke2 →
  __CFURLCache::CreateAndStoreCacheNode → write

Full diagnostic data and analysis in #2004.

What changed

ClusterStateService now defaults to an ephemeral, non-caching URLSession instead of URLSession.shared. Cluster-state responses are time-sensitive and small; nothing benefits from being cached on disk.

private static func makeNonCachingSession() -> URLSession {
    let config = URLSessionConfiguration.ephemeral
    config.urlCache = nil
    config.requestCachePolicy = .reloadIgnoringLocalCacheData
    return URLSession(configuration: config)
}

The existing per-request request.cachePolicy = .reloadIgnoringLocalCacheData calls are kept as defense in depth — they only affect read behavior, but harmless to leave alongside the session-level config.

Scope

• Behavioral: none. Polled requests still go out at the same cadence; responses still parse the same; no semantic change to any API surface.
• Test injection: the session: parameter remains in init, so tests can still inject a custom mock session unchanged.
• BugReportService and other URLSession.shared callers: untouched. If maintainers prefer an app-wide URLCache disable instead, happy to switch the approach (issue body has the alternative spelled out).

Verification

Verified locally that compiling EXO with this change produces a working menubar app and ClusterStateService continues to fetch state correctly. After ~30 min of idle polling, no new entries in /Library/Logs/DiagnosticReports/EXO_*.diag and no growth in ~/Library/Caches/exolabs.EXO/.

Test plan

• Build EXO from this branch on macOS 26.4
• Launch, let cluster state polling run for 30+ min
• Confirm no new microstackshot diagnostic reports
• Confirm ~/Library/Caches/exolabs.EXO/Cache.db* does not grow

🤖 Generated with Claude Code

[AlexCheema]

great, thank you