fix(WhereUI): Make transient Locations loading diagnosable

[kyleve]

Posted by an AI agent on kve's behalf.

Summary

• record each foreground entry with the scene callback and the lifecycle runner's pre-promotion reason and phase
• record each year-report activation with its trigger, whether it is the model's first activation, and whether a report was already present
• keep report loading scene-scoped and preserve the existing headless-launch and warm-refresh behavior
• pin the structured payloads and the ready-headless / fresh-versus-retained classifications with Swift Testing

Why

The Locations screen can briefly reveal its loading state when launch reaches ready before the scene-scoped year report finishes its first pull. Existing spans measured the work but could not distinguish a fresh scene model from an ordinary foreground refresh or say whether a headless drive had already completed. These events capture those facts before promotion or refresh changes them.

Interpretation:

• foregroundEntered(... previous phase: ready) means the launch trunk had completed before the scene entered the foreground.
• activationStarted(... first: true, had report: false) identifies a fresh report model that can show initial loading.
• activationStarted(... first: false, had report: true) identifies a retained report performing a warm refresh without replacing the cards.

Review focus

• the diagnostic event values are captured before the relevant await, while emission remains on the existing typed Where log tree
• this does not work around Periscope's known pre-sink window: a very early cold-launch foreground event may remain OSLog-only until the scope's durable sink attaches
• no rendered UI or report-loading policy changes

Testing

• python3 -m unittest discover -s Tools/Tests -p 'test_snapshot_shards.py' (10 tests passed)
• ./snapshot-shards check (42 suites assigned)
• ./swiftformat --lint
• ./test (7 backup-upgrader tests, 471 unit/integration tests, and 39 snapshot tests passed)