* fix(metrics): host memory usage excludes reclaimable page cache
Host RAM was computed as mem.used / mem.total via systeminformation, but mem.used counts
reclaimable buffers/cache as used, so a busy Linux host read ~99%. Switch the dashboard stats,
the fleet node self-report, and the host-RAM alert threshold to mem.active / mem.total
(cache-excluded), and report used: mem.active and free: mem.available so the byte readout stays
consistent with the percentage. Add regression tests for a cache-heavy host (no false alert) and
a genuinely busy host (alert still fires).
* test(metrics): assert system stats memory excludes reclaimable cache
The cached /api/system/stats test mocked si.mem() without active/available, so after
the route switched to the cache-excluded fields it produced a NaN percentage that the
shape-only assertions did not catch. Fill the mock with a realistic shape and assert the
route reports the active working set, not the cache-inclusive used/free.
Replaces five ad-hoc in-process caches (project name map, templates, latest
version, fleet update status, remote node meta) with a single internal
CacheService that provides TTL, inflight-promise deduplication to protect
against thundering herd, stale-on-error fallback, and per-namespace
hit/miss/stale/size counters for observability.
Wraps the hot-path dashboard endpoints in the cache with write-path
invalidation: /api/stats (2s), /api/system/stats (3s), and
/api/stacks/statuses (3s). Keys are namespaced by nodeId so switching nodes
never serves another node's data. Every route that mutates container or
stack state calls invalidateNodeCaches(nodeId), which also drops the global
project-name-map, so user actions stay instantly reflected in the UI.
For /api/system/stats the cheap per-request network rx/tx block is kept
outside the cache so live-updating charts stay smooth while the expensive
systeminformation.currentLoad() CPU sample (~200ms) is reused across the
TTL.
Adds admin-only GET /api/system/cache-stats returning per-namespace
counters for operators who want to observe cache effectiveness.
Enables the compression middleware site-wide for JSON responses. Large
payloads like /api/templates shrink roughly 5x on the wire. SSE endpoints
are explicitly excluded via a Content-Type filter so live log tails and
metric streams are not buffered.
Bumps vitest hookTimeout to match testTimeout (15s) so parallel fork
workers do not hit the default 10s hook limit under CPU contention.
Adds 35 new tests (26 unit for CacheService, 9 integration for cached
endpoints) covering TTL expiry, inflight dedup, stale-on-error,
namespace invalidation, entry-cap safety guard, and write-path
invalidation end-to-end through Express routes.
Anso