Plan 02: Dashboard Schedule Refactor with AR Scopes and Per-Bucket Pagination

Goal

Replace the in-memory grouping in UpcomingFetchSchedule with ActiveRecord scope-based bucket queries. Add per-bucket pagination using the existing Paginator (using has_next_page/has_previous_page -- not total_count, which is plan 01's work). Wrap each bucket in a Turbo Frame for independent pagination.

Task 1: Refactor UpcomingFetchSchedule to use AR scopes

What: Replace the current approach (load ALL active sources, iterate in Ruby to assign to groups) with per-bucket AR queries using WHERE next_fetch_at range conditions.

Files to modify:

• lib/source_monitor/dashboard/upcoming_fetch_schedule.rb

Implementation details:

• Keep INTERVAL_DEFINITIONS and Group struct (add page, has_next_page, has_previous_page fields to Group)
• Remove build_groups, scheduled_sources, unscheduled_sources, definition_for, minutes_until, sort_sources methods
• Replace with build_groups that iterates INTERVAL_DEFINITIONS, builds an AR scope per bucket, paginates each:
  • Bucket "0-30": scope.where(next_fetch_at: reference_time..(reference_time + 30.minutes))
  • Bucket "30-60": scope.where(next_fetch_at: (reference_time + 30.minutes)..(reference_time + 60.minutes))
  • etc.
  • Bucket "240+": scope.where(next_fetch_at: (reference_time + 240.minutes)..) + scope.where(next_fetch_at: nil) combined via .or()
• Accept pages parameter (hash of { bucket_key => page_number }) in initializer, default {}
• Per bucket, use Paginator.new(scope: bucket_scope.order(:next_fetch_at, :name), page: pages[key] || 1, per_page: per_page) where per_page defaults to 10
• Store pagination results in Group struct: sources, page, has_next_page, has_previous_page
• Hide empty buckets: only return groups where the bucket scope has at least one record (use .exists? to avoid loading data for empty buckets)

Acceptance criteria:

• No full-table load -- each bucket does its own scoped query
• Empty buckets are excluded from the groups array
• Each group has page, has_next_page, has_previous_page fields
• groups method returns only non-empty groups

Task 2: Update DashboardController to pass bucket page params

What: Modify the dashboard controller to extract per-bucket page params from the request and pass them to UpcomingFetchSchedule.

Files to modify:

• app/controllers/source_monitor/dashboard_controller.rb

Implementation details:

• Extract schedule_pages from params: params.fetch(:schedule_pages, {}).permit!.to_h
• Pass to UpcomingFetchSchedule.new(scope: ..., pages: schedule_pages)
• Pass schedule_pages to the view as @schedule_pages so the partial can build links

Acceptance criteria:

• Controller passes page params per bucket
• Default behavior (no params) shows page 1 for all buckets

Task 3: Update fetch_schedule partial with Turbo Frames and pagination

What: Wrap each schedule bucket in a Turbo Frame with a unique ID. Add prev/next pagination controls per bucket. Build inline pagination (simpler than the shared partial since we use has_next/previous without total count).

Files to modify:

• app/views/source_monitor/dashboard/_fetch_schedule.html.erb

Implementation details:

• Wrap each group in turbo_frame_tag "source_monitor_schedule_#{group.key}"
• After the source table, render pagination controls (Previous/Next) if group has more than one page
• Pagination links target the dashboard path with schedule_pages[bucket_key]=N param
• Each link sets data-turbo-frame to the bucket's frame ID so only that section reloads
• Update the group header badge to show page info: "X sources" (count badge stays, since we don't have total without plan 01)
• When a bucket is empty (0 sources), it's already excluded from groups by Task 1
• The overall schedule header ("Upcoming Fetch Schedule") stays outside all frames so it never disappears

Acceptance criteria:

• Each bucket is independently scrollable via Turbo Frames
• Navigating one bucket doesn't affect other buckets or the rest of the dashboard
• Pagination controls only show when the bucket has multiple pages
• Empty buckets don't render at all

Task 4: Update Dashboard::Queries to pass pages param through

What: Modify Queries#upcoming_fetch_schedule to accept and forward the pages parameter.

Files to modify:

• lib/source_monitor/dashboard/queries.rb

Implementation details:

• Change upcoming_fetch_schedule to accept pages: {} keyword argument
• Forward to UpcomingFetchSchedule.new(scope: ..., pages: pages)
• Update the cache key to include pages so different page views don't return stale cached data: [:upcoming_fetch_schedule, pages]

Acceptance criteria:

• Different page params produce different cache entries
• Default (no pages) still works as before

Task 5: Write tests for refactored UpcomingFetchSchedule

What: Add/update tests for the scope-based schedule with pagination.

Files to create:

• test/lib/source_monitor/dashboard/upcoming_fetch_schedule_test.rb

Test cases:

• test "groups sources into correct time buckets using AR scopes" -- Create sources with different next_fetch_at values, verify they land in correct buckets
• test "hides empty buckets" -- Create sources only in one bucket, verify other buckets are absent from groups
• test "paginates within a bucket" -- Create 15 sources in one bucket (per_page 10), verify page 1 has 10, page 2 has 5
• test "includes unscheduled sources in the 240+ bucket" -- Source with nil next_fetch_at lands in last bucket
• test "respects per-bucket page params" -- Pass pages: { "0-30" => 2 }, verify second page loads

Acceptance criteria:

• All tests pass with thread-based parallelism
• Tests create their own scoped data to avoid cross-test contamination

File Disjointness (Wave 1)

This plan modifies:

• lib/source_monitor/dashboard/upcoming_fetch_schedule.rb
• lib/source_monitor/dashboard/queries.rb
• app/controllers/source_monitor/dashboard_controller.rb
• app/views/source_monitor/dashboard/_fetch_schedule.html.erb
• test/lib/source_monitor/dashboard/upcoming_fetch_schedule_test.rb (NEW)

No overlap with Plan 01 (paginator lib, shared partial, application_helper) or Plan 04 (stats query, stats partial).