feat: add durable sync state transitions

Add state-transition methods to ActivityRepository for advancing activity
stages (mark_downloaded, mark_converted, mark_imported, mark_duplicate,
mark_failed) with proper retention of last_completed_stage on failure.
Add list_pending_for_user to filter activities for processing. Implement
SyncRunRepository for creating and finalizing sync runs with counts and
summary errors.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/db/test_sync_state.py

@@ -0,0 +1,132 @@
+from app.db.models import ActivityStatus, SyncRunStatus
+
+
+def test_failure_retains_last_completed_stage(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_downloaded(seeded_activity.id, "/data/activities/1/a/source.fit")
+    activity_repository.mark_failed(seeded_activity.id, "Garmin timeout", retryable=True)
+    activity = activity_repository.get(seeded_activity.id)
+
+    assert activity.status == ActivityStatus.FAILED
+    assert activity.last_completed_stage == ActivityStatus.DOWNLOADED
+    assert activity.retryable is True
+
+
+def test_converted_activity_is_pending_until_terminal(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_converted(seeded_activity.id, "/data/activities/1/a/converted.fit")
+    ids = [item.id for item in activity_repository.list_pending_for_user(seeded_activity.user_id)]
+    assert seeded_activity.id in ids
+
+
+def test_list_pending_excludes_imported(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_downloaded(seeded_activity.id, "/data/activities/1/a/source.fit")
+    activity_repository.mark_converted(seeded_activity.id, "/data/activities/1/a/converted.fit")
+    activity_repository.mark_imported(seeded_activity.id, "garmin-123")
+
+    ids = [item.id for item in activity_repository.list_pending_for_user(seeded_activity.user_id)]
+    assert seeded_activity.id not in ids
+
+
+def test_list_pending_excludes_duplicate(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_downloaded(seeded_activity.id, "/data/activities/1/a/source.fit")
+    activity_repository.mark_duplicate(seeded_activity.id)
+
+    ids = [item.id for item in activity_repository.list_pending_for_user(seeded_activity.user_id)]
+    assert seeded_activity.id not in ids
+
+
+def test_list_pending_excludes_non_retryable_failed(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_downloaded(seeded_activity.id, "/data/activities/1/a/source.fit")
+    activity_repository.mark_failed(seeded_activity.id, "Cannot retry", retryable=False)
+
+    ids = [item.id for item in activity_repository.list_pending_for_user(seeded_activity.user_id)]
+    assert seeded_activity.id not in ids
+
+
+def test_list_pending_includes_retryable_failed(activity_repository, seeded_activity) -> None:
+    activity_repository.mark_downloaded(seeded_activity.id, "/data/activities/1/a/source.fit")
+    activity_repository.mark_failed(seeded_activity.id, "Temporary error", retryable=True)
+
+    ids = [item.id for item in activity_repository.list_pending_for_user(seeded_activity.user_id)]
+    assert seeded_activity.id in ids
+
+
+def test_sync_run_start_and_finish(sync_run_repository, user_repository) -> None:
+    user = user_repository.create(
+        name="Test User",
+        enabled=True,
+        health_state="healthy",
+        mywhoosh_email_enc="test@example.com",
+        mywhoosh_password_enc="password",
+        garmin_email_enc="test@garmin.com",
+        garmin_password_enc="garmin_password",
+    )
+
+    sync_run = sync_run_repository.start(user.id)
+    assert sync_run.status == SyncRunStatus.RUNNING
+    assert sync_run.discovered_count == 0
+    assert sync_run.imported_count == 0
+    assert sync_run.skipped_count == 0
+    assert sync_run.failed_count == 0
+
+    finished = sync_run_repository.finish(
+        sync_run.id,
+        status=SyncRunStatus.SUCCESS,
+        discovered=5,
+        imported=3,
+        skipped=1,
+        failed=1,
+    )
+
+    assert finished.status == SyncRunStatus.SUCCESS
+    assert finished.discovered_count == 5
+    assert finished.imported_count == 3
+    assert finished.skipped_count == 1
+    assert finished.failed_count == 1
+    assert finished.finished_at is not None
+
+    # Reload from DB to verify persisted
+    reloaded = sync_run_repository.get(sync_run.id)
+    assert reloaded.status == SyncRunStatus.SUCCESS
+    assert reloaded.discovered_count == 5
+    assert reloaded.imported_count == 3
+
+
+def test_sync_run_finish_with_error(sync_run_repository, user_repository) -> None:
+    user = user_repository.create(
+        name="Test User",
+        enabled=True,
+        health_state="healthy",
+        mywhoosh_email_enc="test@example.com",
+        mywhoosh_password_enc="password",
+        garmin_email_enc="test@garmin.com",
+        garmin_password_enc="garmin_password",
+    )
+
+    sync_run = sync_run_repository.start(user.id)
+    error_msg = "Connection timeout"
+
+    finished = sync_run_repository.finish(
+        sync_run.id,
+        status=SyncRunStatus.FAILED,
+        discovered=0,
+        imported=0,
+        skipped=0,
+        failed=0,
+        summary_error=error_msg,
+    )
+
+    assert finished.summary_error == error_msg
+
+    # Verify truncation works
+    long_error = "x" * 5000
+    finished_long = sync_run_repository.finish(
+        sync_run.id,
+        status=SyncRunStatus.FAILED,
+        discovered=0,
+        imported=0,
+        skipped=0,
+        failed=0,
+        summary_error=long_error,
+    )
+    assert len(finished_long.summary_error) == 2000
+    assert finished_long.summary_error == long_error[:2000]