Close the live-mirror flow hand-off gaps that skipped a timed phase

Field incident (2026-07-17): a Cardio flow run driven from a locked phone
durably completed the 30-min Main Circuit ~5 minutes in, then fought the
watch until manual swipes forced agreement. Second bulletproofing pass
(BULLETPROOFING.md, "2026-07-18 — Live-run mirror & flow hand-off"):

- H4: RunFlowView (both platforms) follows the driver's cross-log
  hand-off frame (forward-only by plan order, runnable target only), and
  a remote completion mid-flow hands off via onAdvance instead of
  dismissing the run (which tore down the Live Activity and stranded the
  flow in the mirror cover).
- H5: wall-clock plausibility gate — a duration exercise never
  auto-completes before startedAt + sets × duration; the flow-terminal
  rest self-repairs to computeResume() and the Finish auto-Done holds
  for a human tap. Human Done taps stay ungated.
- M6: both bridges persist liveVersion as a UserDefaults high-water mark
  so an app relaunch can't get every subsequent frame dropped as stale.
- M7: phone list + mirror cover absorbs gain the watch's strictly-newer
  guard, so a stale cache echo can't regress the working doc.
- Diagnostics: run-flow os_log breadcrumbs (page transitions, applied
  frames, repairs, hand-offs, gate trips) on both drivers.

Open, documented: M5 (no reconciliation signal across a single-set
duration phase), M8 (watch context apply lacks per-log staleness guard),
L5 (spurious pager write-backs read as human swipes).

CHANGELOG.md

@@ -1,5 +1,9 @@
 **July 2026**
 
+Fixed a rare timing glitch that could skip a long timed phase — like a cardio main circuit — when a workout ran on iPhone and Apple Watch together.
+
+When one device finishes an exercise and moves on, the other now follows along to the next exercise instead of dropping out of the run.
+
 Workouts is now on the Mac: a native app for managing routines and schedules and browsing the exercise library, synced through the same iCloud Drive.
 
 Rest time now adjusts in one-second steps — in Settings and in a routine's custom rest — instead of five-second jumps.