[UtkuDenizAltiok]

What this PR does

iOS measures every app on the phone and will hand an app its own numbers through MetricKit: about once a day, what it used the day before (foreground and background time, CPU, peak memory, disk writes, hangs, and why it exited — normally, at the CPU or memory limit, by the watchdog, by a crash), and after a crash, a hang, a CPU or disk-write exception or a slow launch, a report about it. NOOP did not subscribe.

MetricKitLog registers once at launch and writes one line per report into the strap log (MetricKitLine), for example:

MetricKit day 2026-09-22 00:00 → 2026-09-23 00:00 (NOOP 11.8.0): foreground 1h 12m, background 9h 40m, CPU 6m 12s, peak memory 180 MB, disk writes 1.5 GB, hangs 3, exits: normal 4, CPU limit 1
MetricKit CPU exception (NOOP 11.8.0, reported 2026-09-22 20:42): 48s of CPU in 1m 0s

Nothing is sent anywhere. iOS gathers the numbers on the phone and delivers them to the app; the lines go only into the strap log a person exports by hand — no telemetry, no network, no file of its own, no timer. Between reports it costs nothing.

Why: on 22 Sep iOS closed NOOP four times during a session for background CPU (cpu_resource_fatal), and the only evidence was crash reports the tester had to find by hand in Settings → Privacy → Analytics Data. The same facts now arrive in the file testers already send, and the daily line gives battery questions a measured answer.

A line says only what iOS reported: a field MetricKit left out is left out of the line, not printed as a zero. Android has no equivalent API, so this is iOS-only.

Type of change

• New feature (local diagnostics)

How it was tested

• MetricKitLineTests (StrandTests), 4 tests: a full day, a day with nothing reported, a diagnostic line, durations and sizes. With a missing value printed as zero, the "not reported" test fails, and the file restored byte-identical (sha256).
• Full local run on the change (6721e3b2; the head is the same diff rebased onto 8f064df7, whose newer commits touch none of these files), every step passed: WhoopStore 611 · StrandAnalytics 2048 · StrandImport 327 · doc lint · i18n · parity ledger, ratchet, governance (124) · macOS StrandTests 2,121 (only the two locale-dependent TodayCarryOverTests) · iOS build, no warnings in the new files.
• MetricKit payloads cannot be constructed in a test and arrive only on a device about once a day, so the subscriber's mapping is covered by the build and review; the first real line will be checked in a tester's strap log.

Checklist

• No UI change
• Follows the conventions in docs/CONTRIBUTING.md — no data leaves the device
• I did not commit generated output (Strand.xcodeproj/) or any secrets/keystores

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