Moves direct psutil.* calls behind a MetricsProvider Protocol so the
codebase no longer needs ad-hoc `if psutil is not None` guards at every
call site. Each provider lives in its own module under
utils/metrics/: PsutilMetricsProvider for desktop, NullMetricsProvider
as a zeroed fallback, AndroidMetricsProvider that reads /proc/stat,
/proc/meminfo, /proc/self/stat, and /proc/self/status directly (psutil
isn't available under Chaquopy). The Android provider tracks the
previous CPU sample so cpu_percent() returns delta-based percentages
matching psutil's interval=None semantics, and degrades to zeros when
any /proc file is unreadable instead of crashing the dashboard.
Factory get_metrics_provider() in utils/metrics/__init__.py picks
Android > psutil > Null. api/routes/system.py and
core/processing/metrics_history.py now go through the factory; psutil
import is confined to one place. 12 new unit tests cover paren-in-comm
parsing of /proc/self/stat, delta CPU%, missing-file resilience, and
factory selection order. Full suite: 727 passing.
alexei.dolgolyov
546b24d015