Release 1.5.1

Bug fixes and code quality improvements:

- Fix mirror index dirtied on every sync (MirrorRecord.updatedAt in equality)
- Fix mirror URL corruption: encode calendar/source IDs before joining with ';'
  and use percentEncodedPath to prevent double-encoding
- Fix cleanup route mutating UI calendar picker selection unnecessarily
- Fix --exit flag redundancy (isCLIRun no longer implies termination)
- Remove dead SKIP_ALL_DAY_DEFAULT constant
- Replace deprecated FileHandle(forWritingAtPath:) with throwing variant
- Add EKEventStoreChanged observer for live calendar list refresh
- Extract AppLogStore into its own file (AppLogStore.swift)
- Add Block.span(start🔚) factory; replace verbose nil-field constructions
- Remove redundant MainActor.run{} wrappers inside @MainActor MirrorEngine
- Fix SettingsPayload indentation inside ContentView

All 45 unit tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ReleaseNotes-1.5.1.md

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+# BusyMirror 1.5.1
+
+## Bug fixes
+
+- **Mirror index written on every sync** — `MirrorRecord`'s synthesized equality check included an `updatedAt` timestamp that is always set to the current date when a record is constructed. This meant every sync run marked the index as dirty and rewrote it to `UserDefaults`, even when no mirror events changed. Fixed with a custom `==` that ignores `updatedAt`.
+
+- **Mirror URLs corrupted by special characters in calendar IDs** — Calendar and source IDs placed into the `mirror://` URL were not percent-encoded before joining with `;`. An ID containing `;` would cause the URL to be mis-parsed on the next sync, potentially losing the link between a placeholder and its source event. IDs are now encoded with `mirrorURLComponentEncode` (already present and tested since 1.4.0) and the URL path is assigned via `percentEncodedPath` to prevent double-encoding.
+
+- **Calendar picker jumped during route cleanup** — Running "Cleanup Placeholders" over saved routes changed the source/target picker selection for each route. Cleanup no longer mutates the UI selection.
+
+- **`--exit` flag was always implied** — Using `--routes` or `--run-saved-routes` always terminated the app, making `--exit` redundant. The app now exits only when `--exit` is explicitly passed.
+
+## Improvements
+
+- **Live calendar refresh** — The calendar list now updates automatically when the system calendar database changes (new account added, calendar renamed, etc.), without requiring a manual "Refresh Calendars" press.
+
+- `AppLogStore` extracted into its own file; deprecated `FileHandle` API replaced with the modern throwing variant.
+
+- `Block.span(start:end:)` convenience factory added to `BlockMath`, eliminating repetitive nil-field construction.
+
+- Redundant `MainActor.run {}` wrappers removed from `MirrorEngine` (already running on `@MainActor`).